The order of a differential equation is determined by the highest-order derivative present in the equation.
Let's examine the given equation: dt2d2y+(dtdy)3+y4=e−t
The equation contains two derivative terms: dt2d2y (the second derivative) and dtdy (the first derivative). The highest order among these is 2.
The power of 3 on the term (dtdy)3 refers to the degree of that term, not the order of the derivative. Since the highest derivative is the second derivative, the order of the entire equation is 2.
Q2GATE 2009MCQ1MSignals and Systems
The Fourier series of a real periodic function has only (P) cosine terms if it is even (Q) sine terms if it is even (R) cosine terms if it is odd (S) sine terms if it is odd Which of the above statements are correct ?
The symmetry of a periodic function dictates the terms present in its Fourier series. An even function, defined by f(t)=f(−t), mirrors the symmetry of the cosine function itself. When calculating the sine coefficients (bn), you integrate an even function f(t) against an odd function sin(nωt). The result is an odd function, whose integral over a symmetric interval is always zero. This eliminates all sine terms, leaving only cosine terms (P).
Conversely, an odd function, defined by f(t)=−f(−t), mirrors the symmetry of the sine function. Calculating the cosine coefficients (an) involves integrating an odd function f(t) against an even function cos(nωt). This product is odd, making the coefficients zero. Consequently, the series consists only of sine terms (S).
Q3GATE 2009MCQ1MSignals and Systems
A function is given by f(t)=sin2t+cos2t . Which of the following is true ?
To analyze the frequency components of the function, we should first simplify its expression using trigonometric identities. The power-reduction formula for sine squared is sin2t=21(1−cos2t).
Substituting this into the given function, we get: f(t)=21(1−cos2t)+cos2t=21−21cos2t+cos2t=21+21cos2t.
This simplified form shows the function is a sum of two signals. The constant term, 21, is a DC component, which has a frequency of 0 Hz. The other term, 21cos2t, has an angular frequency of ω=2 rad/s.
To convert angular frequency ω to linear frequency f in Hertz, we use the formula f=2πω. This gives us the second frequency component: f=2π2=π1 Hz.
Q4GATE 2009MCQ1MNetwork Theory
A fully charged mobile phone with a 12 V battery is good for a 10 minute talktime. Assume that, during the talk-time the battery delivers a constant current of 2 A and its voltage drops linearly from 12 V to 10 V as shown in the figure. How much energy does the battery deliver during this talk-time?
In a silicon crystal, the concentration of Si atoms is approximately 5×1022cm−3. Each Si atom has 4 valence electrons, so their concentration is about 2×1023cm−3. These values are much larger than the given concentration, ruling out options A and D.
An n-type semiconductor is created by adding donor dopant atoms. The value 4×1019cm−3 is a typical heavy doping concentration. At room temperature, these dopants are ionized, creating a free electron concentration of n≈4×1019cm−3.
Using the mass-action law, p=ni2/n, where the intrinsic carrier concentration ni≈1.5×1010cm−3 for silicon. This gives a hole concentration of p≈(1.5×1010)2/(4×1019)≈5.6 cm−3, which is extremely small, eliminating option B. Thus, the given value represents the concentration of dopant atoms.
Q6GATE 2009MCQ1MDigital Circuits
The full form of the abbreviations TTL and CMOS in reference to logic families are
This question tests your knowledge of common acronyms for digital logic families. Let's break down each term.
The abbreviation "TTL" stands for Transistor-Transistor Logic. This name reflects the fact that logic gates in this family are built using transistors for both the logic operation and the amplification stages.
The abbreviation "CMOS" stands for Complementary Metal-Oxide-Semiconductor. This refers to the type of technology used, which employs pairs of complementary P-type and N-type metal-oxide-semiconductor field-effect transistors (MOSFETs) to create logic gates.
Q7GATE 2009MCQ1MSignals and Systems
The ROC of z -transform of the discrete time sequence x(n)=(31)nu(n)−(21)nu(−n−1) is
The given signal x(n) is a combination of two separate sequences. Let's analyze the Region of Convergence (ROC) for each part.
The first term, (31)nu(n), is a right-sided sequence. The ROC for a right-sided sequence is the region outside a circle with a radius equal to the magnitude of the pole, so we have ∣z∣>31.
The second term, −(21)nu(−n−1), is a left-sided sequence. Its ROC is the region inside a circle defined by its pole, which gives us ∣z∣<21.
The overall ROC for x(n) is the intersection of these two individual regions. The region that satisfies both ∣z∣>31 and ∣z∣<21 is the annular ring 31<∣z∣<21.
Q8GATE 2009MCQ1MControl Systems
The magnitude plot of a rational transfer function G(s) with real coefficients is shown below. Which of the following compensators has such a magnitude plot ?
A white noise process X(t) with two-sided power spectral density 1×10−10W/Hz is input to a filter whose magnitude squared response is shown below. The power of the output process Y(t) is given by
The power of the output random process, PY, is determined by the input signal's power spectral density (PSD) and the characteristics of the filter. Specifically, the output PSD is the input PSD multiplied by the squared magnitude of the filter's frequency response, SY(f)=SX(f)∣H(f)∣2.
To find the total power, we integrate the output PSD over all frequencies. Since the input white noise has a constant PSD of SX(f)=1×10−10 W/Hz, the output power is this constant value times the area under the ∣H(f)∣2 graph.
PY=∫−∞∞SY(f)df=(1×10−10)×Area under ∣H(f)∣2
The graph of ∣H(f)∣2 is a triangle with a base of 20 kHz (from −10 kHz to +10 kHz) and a height of 1. The area is therefore 21×base×height=21×(20×103 Hz)×1=104 Hz.
Finally, multiplying the input PSD by this area gives the output power: PY=(1×10−10 W/Hz)×(104 Hz)=1×10−6 W.
Q10GATE 2009MCQ1MElectromagnetics
Which of the following statements is true regarding the fundamental mode of the metallic waveguides shown ?
Structure P is a coaxial line, a type of transmission line with two conductors. This two-conductor geometry allows for the propagation of a Transverse Electro-Magnetic (TEM) wave. A unique property of the TEM mode is that it has no lower frequency limit for propagation, meaning its cutoff frequency is zero (fc=0).
Conversely, structures Q and R are hollow waveguides. These single-conductor guides cannot support the TEM mode. Their fundamental modes will be either TE or TM, both of which have a non-zero cutoff frequency determined by the waveguide's physical dimensions.
Q11GATE 2009MCQ1MEngineering Mathematics
A fair coin is tossed 10 times. What is the probability that only the first two tosses will yield heads?
Each toss of a fair coin is an independent event with a probability of 21 for heads (H) and 21 for tails (T). The problem specifies a single, unique sequence of outcomes for the 10 tosses: H, H, T, T, T, T, T, T, T, T. To find the probability of this specific sequence occurring, we multiply the probabilities of each individual outcome.
The probability is: P(H, H, T, T, T, T, T, T, T, T)=P(H)×P(H)×P(T)×⋯×P(T)
This is the product of 10 individual probabilities, each of which is 21. P(sequence)=(21)×(21)×(21)×(21)×(21)×(21)×(21)×(21)×(21)×(21)=(21)10.
Q12GATE 2009MCQ1MCommunication Systems
If the power spectral density of stationary random process is a sine-squared function of frequency, the shape of its auto correlation is
According to the Wiener-Khinchin theorem, a process's power spectral density (PSD) and its autocorrelation function, R(τ), form a Fourier transform pair. This means the autocorrelation function is the inverse Fourier transform of the PSD.
This problem uses a well-known Fourier transform pair: a triangular pulse in one domain corresponds to a sinc-squared function, written as sinc2(f), in the other.
The question implies the PSD has the shape of a sinc2 function (often colloquially, if imprecisely, called a sine-squared function in this context). Therefore, its inverse Fourier transform-the autocorrelation function-must have the shape of a triangular pulse.
Q13GATE 2009MCQ1MEngineering Mathematics
If f(z)=c0+c1z−1,then∮unitcirclez1+f(z)dz is given by
To solve this integral, we'll use the Residue Theorem. The contour is the unit circle, which encloses the only singularity at the origin, z=0.
First, let's substitute the given expression for f(z) into the integrand: z1+f(z)=z1+(c0+c1z−1)
Next, simplify the expression to find its Laurent series form around z=0: z1+c0+c1/z=z1+c0+z2c1
According to the Residue Theorem, the value of the integral is 2πj times the sum of the residues inside the contour. The residue at z=0 is the coefficient of the z−1 term in the Laurent series.
From our simplified expression, the coefficient of z−1 is (1+c0).
Therefore, the integral is 2πj×Residue=2πj(1+c0).
Q14GATE 2009MCQ1MNetwork Theory
In the interconnection of ideal sources shown in the figure, it is known that the 60 V source is absorbing power. Which of the following can be the value of the current source I ?
The relationship between the diffusion coefficient (D) and carrier mobility (μ) in a semiconductor is defined by the Einstein relation. This fundamental equation is expressed as μD=VT, where VT represents the thermal voltage.
The question asks for the units of the ratio of mobility to the diffusion coefficient, which is Dμ. To find this, we can simply rearrange the Einstein relation: Dμ=VT1
Since the unit of thermal voltage (VT) is Volts (V), the units of its reciprocal must be inverse volts, which is written as V−1.
Q16GATE 2009MCQ1MMicroprocessors
In a microprocessor, the service routine for a certain interrupt starts from a fixed location of memory which cannot be externally set, but the interrupt can be delayed or rejected. Such an interrupt is
An interrupt is called 'vectored' when its service routine resides at a fixed memory address. This allows the processor to automatically jump to that specific location without needing external guidance. This matches the description "starts from a fixed location of memory."
An interrupt is called 'maskable' if the processor can choose to ignore or postpone it. The phrase "can be delayed or rejected" directly describes this ability to be masked. Therefore, the interrupt has both of these properties.
Q17GATE 2009MCQ1MNetwork Theory
If the transfer function of the following network is Vi(s)Vo(s)=2+sCR1 The value of the load resistance RL is
This circuit is a voltage divider where the output voltage is measured across the parallel combination of the load resistor RL and the capacitor C. First, let's find the impedance of this parallel section, which we'll call Zout. Zout=RL∣∣sC1=RL+sC1RL⋅sC1=1+sCRLRL.
The overall transfer function is found using the voltage divider rule: Vi(s)Vo(s)=R+ZoutZout=R+1+sCRLRL1+sCRLRL.
To simplify, multiply the numerator and denominator by (1+sCRL), which gives: Vi(s)Vo(s)=R(1+sCRL)+RLRL=R+RL+sCRRLRL.
We are given that this transfer function equals 2+sCR1. By comparing the two expressions, we can see that if we set RL=R, our derived function becomes R+R+sCR2R=2R+sCR2R. Dividing the numerator and denominator by R yields 2+sCR1, which matches the given function. Therefore, the load resistance must be RL=R.
Q18GATE 2009MCQ1MControl Systems
Consider the system dtdx=Ax+Bu with
A=[1001]
and
B=[pq]
where p and q are arbitrary real numbers. Which of the following statements about the controllability of the system is true ?
To assess the system's controllability, we examine the rank of the controllability matrix, Qc=[BAB]. In this case, the matrix A is the 2×2 identity matrix, I. Multiplying any matrix by the identity matrix leaves it unchanged, so AB=IB=B.
This means our controllability matrix is Qc=[BB]. Substituting the vector for B, we get: Qc=[pqpq]
The two columns of this matrix are identical. This makes them linearly dependent, regardless of the values of p and q. A matrix with linearly dependent columns is singular, meaning its rank is always less than the dimension of the state space (which is 2). For a system to be controllable, this matrix must be full rank. Since it never is, the system is uncontrollable for all values of p and q.
Q19GATE 2009MCQ1MCommunication Systems
For a message signal m(t)=cos(2πfmt) and carrier of frequency fc , which of the following represents a single side-band (SSB) signal ?
When the message signal m(t) modulates the carrier, it produces what's known as a double-sideband (DSB) signal. For the given signals, this DSB signal is m(t)cos(2πfct)=cos(2πfmt)cos(2πfct).
Using a product-to-sum identity, this expands into two distinct frequency components: 21cos[2π(fc−fm)t]+21cos[2π(fc+fm)t]
These represent the lower sideband (LSB) and upper sideband (USB), respectively. A single side-band (SSB) signal transmits only one of these. The expression cos[2π(fc+fm)t] is a pure sinusoid at the upper sideband frequency, making it a perfect example of an SSB signal.
Q20GATE 2009MCQ1MElectromagnetics
Two infinitely long wires carrying current are as shown in the figure below. One wire is in the y-z plane and parallel to the y-axis. The other wire is in the x-y plane and parallel to the x-axis. Which components of the resulting magnetic field are non-zero at the origin ?
Hdicection due to any current wire = I flow direction × (cross) radial vector from current to point of consideration.
Q21GATE 2009MCQ1MEngineering Mathematics
Consider two independent random variables X and Y with identical distributions. The variables X and Y take values 0, 1 and 2 with probabilities 21,41and41 respectively. What is the conditional probability P(X+Y=2|X-Y=0)?
We are asked to find the conditional probability P(X+Y=2∣X−Y=0). The formula for conditional probability tells us this is equal to P(X−Y=0)P(X+Y=2 and X−Y=0).
First, let's calculate the probability of the condition, P(X−Y=0). This event occurs when X=Y. The possible cases are (0,0), (1,1), and (2,2). Since X and Y are independent, we can find the total probability by summing the probabilities of each case: P(X=Y)=(21)(21)+(41)(41)+(41)(41)=41+161+161=166=83.
Next, let's find the probability of the joint event in the numerator. For both X+Y=2 and X−Y=0 to be true, we must have X=1 and Y=1. The probability of this specific outcome is P(X=1,Y=1)=P(X=1)×P(Y=1)=41×41=161.
Finally, we divide the probability of the joint event by the probability of the condition: P(X+Y=2∣X−Y=0)=3/81/16=161×38=61.
Q22GATE 2009MCQ1MEngineering Mathematics
The Taylor series expansion of x−πsinx at x = π is given by
To find the Taylor series of a function centered at a point other than zero, it's often easiest to use a substitution. Let's set u=x−π, so that we are looking for a series in powers of u centered at u=0.
Substituting x=u+π into the original function gives usin(u+π). Using the trigonometric identity sin(θ+π)=−sinθ, this expression simplifies to −usinu.
Now, we can use the standard Maclaurin series for sinu, which is sinu=u−3!u3+5!u5−….
Plugging this series into our simplified function, we get: −u1(u−3!u3+…)=−(1−3!u2+…)=−1+3!u2−…
Finally, replacing u with x−π gives us the desired Taylor series: −1+3!(x−π)2−…
Q23GATE 2009MCQ1MElectromagnetics
If a vector field V is related to another vector field A through V=▽∗A , which of the following is true? (Note : C and SC refer to any closed contour and any surface whose boundary is C.)
This question is a direct application of Stokes' Theorem from vector calculus. The theorem relates the line integral of a vector field around a closed loop to the surface integral of its curl over the surface enclosed by the loop.
For any vector field, let's call it F, Stokes' Theorem is written as: ∮CF⋅dl=∬SC(∇×F)⋅dS
Let's apply this theorem to the vector field A given in the problem. We substitute F with A: ∮CA⋅dl=∬SC(∇×A)⋅dS
The question states the relationship V=∇×A. We can substitute V for the term ∇×A in the equation above. This gives us the final, correct relationship: ∮CA⋅dl=∬SCV⋅dS
Q24GATE 2009MCQ1MSignals and Systems
Given that F(s) is the one-side Laplace transform of f(t) , the Laplace transform of ∫0tf(τ)dτ is
This question asks for the Laplace transform of an integral, which is a standard property. The operation of integration in the time domain, ∫0tf(τ)dτ, has a direct counterpart in the s-domain.
The property connects the result to the transform of the original function, F(s), and its initial value, f(0). The rule states that you first adjust the transform F(s) by subtracting the initial condition, yielding the term F(s)−f(0). Then, to account for the integration, this entire expression is divided by s. This two-step process gives the final expression for the transform of the integral.
Q25GATE 2009MCQ1MEngineering Mathematics
Match each differential equation in Group I to its family of solution curves from Group II
To find the family of solution curves for each differential equation, we'll use the method of separation of variables and integration.
For equation P, separating variables in dxdy=xy gives ydy=xdx. Integrating both sides yields ln∣y∣=ln∣x∣+c, which simplifies to y=kx, the equation for a family of straight lines.
For equation Q, dxdy=−xy separates to ydy=−xdx. Integration gives ln∣y∣=−ln∣x∣+c, which can be rewritten as xy=k. This is the equation for a family of hyperbolas.
For equation R, separating variables in dxdy=yx gives ydy=xdx. Integrating results in 2y2=2x2+c, or y2−x2=k, which also represents a family of hyperbolas.
Finally, for equation S, dxdy=−yx becomes ydy=−xdx. Integrating this gives 2y2=−2x2+c, or x2+y2=k, the equation for a family of circles.
Therefore, the matching is: P→2 (Straight lines), Q→3 (Hyperbolas), R→3 (Hyperbolas), and S→1 (Circles).
A fundamental property of matrices is that the sum of the eigenvalues equals the trace of the matrix (the sum of the elements on the main diagonal). Let's calculate the trace of the given matrix: Trace=−1+(−1)+3=1
Now, we check which set of options sums to 1. For option D, the sum of the eigenvalues is: 3+(−1+3j)+(−1−3j)
The imaginary parts cancel each other out (3j−3j=0), simplifying the sum to 3−1−1=1. This matches our calculated trace. Additionally, for a matrix with all real entries, any complex eigenvalues must appear as conjugate pairs. The values −1+3j and −1−3j are a conjugate pair, satisfying this condition.
Q27GATE 2009MCQ1MNetwork Theory
An AC source of RMS voltage 20 V with internal impedance Zs=(1+2j)Ω feeds a load of impedance ZL=(7+4j)Ω in the figure below. The reactive power consumed by the load is
To find the reactive power consumed by the load, we first need the total current flowing in the circuit. The total impedance is the sum of the source and load impedances: Ztotal=Zs+ZL=(1+2j)Ω+(7+4j)Ω=(8+6j)Ω.
Next, we calculate the magnitude of the RMS current using Ohm's Law. ∣Irms∣=∣Ztotal∣∣Vrms∣=∣(8+6j)Ω∣20 V=82+6220=1020=2 A.
The reactive power (QL) absorbed by the load is calculated as the squared current magnitude times the load's reactance (XL). From the load impedance ZL=(7+4j)Ω, the reactance is XL=4Ω.
Therefore, the reactive power is QL=∣Irms∣2XL=(2 A)2×4Ω=16 VAR.
Q28GATE 2009MCQ1MNetwork Theory
The switch in the circuit shown was on position a for a long time, and is move to position b at time t=0 . The current i(t) for t>0 is given by
For a long time before t=0, the switch at position 'a' fully charged the capacitor to the source voltage. Because capacitor voltage cannot change instantaneously, the initial voltage at t=0+ is vC(0+)=100 V.
After the switch moves to position 'b', the capacitor discharges through the resistor. The current for this first-order RC circuit is given by i(t)=i(0+)e−t/τ, where τ is the time constant.
The initial current is found using Ohm's law: i(0+)=vC(0+)/R=100 V/5 kΩ=20 mA.
The time constant is τ=RC=(5×103Ω)(0.16×10−6 F)=0.8 ms, so the decay rate is 1/τ=1250 s−1.
Combining these results, the current for t>0 is i(t)=20e−1250tu(t) mA.
Q29GATE 2009MCQ1MNetwork Theory
In the circuit shown, what value of RL maximizes the power delivered to RL ?
For maximum power to be delivered to the resistor RL, its value must be equal to the Thevenin equivalent resistance (RTh) of the source circuit.
To find RTh, we deactivate the independent 10V source (replacing it with a short) and apply a test voltage VT across the output terminals. Let's conveniently choose VT=1 V. By definition, the controlling voltage Vx across the output terminals is now 1 V, which means the dependent voltage source also has a value of 1 V.
Notice that the voltage across the top 4Ω resistor is driven by the dependent source and opposed by the test source. An outer-loop KVL shows these two 1 V sources cancel each other out, leaving 0 V across the top resistor and thus zero current in that branch. All the test current, IT, must therefore flow through the right-hand 4Ω resistor.
This current is IT=Vx/4Ω=1V/4Ω=0.25A. Finally, the Thevenin resistance is calculated as RTh=VT/IT=1V/0.25A=4Ω. Therefore, RL should be 4Ω.
Q30GATE 2009MCQ1MNetwork Theory
The time domain behavior of an RL circuit is represented by Ldtdi+Ri=V0(1+Be−Rt/Lsint)u(t) . For an initial current of f(0)=RV0 , the steady state value of the current is given by
To determine the steady state value of the current, we analyze the circuit's behavior as time approaches infinity (t→∞). The governing equation is Ldtdi+Ri=V0(1+Be−Rt/Lsint)u(t).
As t→∞, the exponential term e−Rt/L decays to zero. Consequently, the input voltage source term simplifies: V∈(t→∞)=limt→∞V0(1+Be−Rt/Lsint)=V0(1+0)=V0
The circuit is now driven by a constant DC voltage V0. In a DC steady state, the current becomes constant, so its derivative dtdi is zero. The inductor acts as a short circuit.
The original differential equation simplifies to: L(0)+Ri(∞)=V0
Solving for the steady state current i(∞) gives: i(∞)=RV0
The initial condition affects the transient response but not the final steady state value for this stable system.
Q31GATE 2009MCQ1MAnalog Circuits
In the circuit below, the diode is ideal. The voltage V is given by
The behavior of this circuit is determined by the state of the ideal diode. The diode's cathode is connected to a 1V source, setting its potential to 1V.
When the input voltage Vi≤1V, the potential at the diode's anode (node V) tends to be less than or equal to 1V. This reverse-biases the diode, causing it to act as an open circuit. With no current flowing through the resistor R, there is no voltage drop across it, so the output voltage V equals the input voltage Vi.
When the input voltage Vi>1V, the anode potential tends to exceed the 1V cathode potential. This forward-biases the ideal diode, making it act like a short circuit. As a result, the output node is connected directly to the 1V source, clamping the output voltage at V=1V.
Combining these two conditions, the output voltage V is equal to Vi when Vi≤1V and is 1V when Vi>1V. This describes the function V=min(Vi,1).
Q32GATE 2009MCQ1MElectronic Devices
Consider the following two statements about the internal conditions in a n-channel MOSFET operating in the active region. S1 : The inversion charge decreases from source to drain. S2 : The channel potential increases from source to drain. Which of the following is correct?
In an n-channel MOSFET operating in the active region, a positive drain-source voltage (VDS) causes a drain current to flow. Due to the resistance of the inversion layer, this current creates a voltage drop along the channel. As a result, the channel potential, V(x), increases steadily from 0 V at the source to VDS at the drain. Therefore, statement S2 is true.
The amount of inversion charge at any point is determined by the local gate-to-channel voltage, which is VGS−V(x). Since the channel potential V(x) increases from source to drain (as per S2), the effective gate-to-channel voltage decreases. A lower effective voltage induces less charge, causing the inversion charge density to decrease from source to drain. This makes the channel tapered and confirms that statement S1 is also true. Thus, S2 is the reason for S1.
Q33GATE 2009MCQ1MAnalog Circuits
In the following a stable multivibrator circuit, which properties of v0(t) depend on R2 ?
This circuit is an astable multivibrator, which generates a square wave output, v0(t). The amplitude of this wave is determined by the op-amp's positive and negative saturation voltages (±Vsat), which are independent of the external resistor R2.
The frequency of oscillation depends on the time it takes the capacitor C to charge and discharge through resistor R1. The switching thresholds for the op-amp are set by the voltage divider formed by R2 and R3. The threshold voltage is ±βVsat, where the feedback factor is β=R2+R3R3. The oscillation period is T=2R1Cln(1−β1+β). Since β depends on R2, the period T and the frequency f=1/T also depend on R2. Thus, only the frequency of v0(t) depends on R2.
Q34GATE 2009MCQ1MAnalog Circuits
In the circuit shown below, the op-amp is ideal, the transistor has VBE = 0.6 V and β = 150. Decide whether the feedback in the circuit is positive or negative and determine the voltage V at the output of the op-amp.
This circuit uses negative feedback. The op-amp adjusts its output to ensure the transistor's emitter provides the necessary feedback voltage to the non-inverting input.
First, let's find the transistor's emitter current, IE. This current is set by the 10 V source, the 5 V Zener diode, and the 5 kΩ resistor. IE=5 kΩ10 V−5 V=1 mA
This emitter current flows through the 1.4 kΩ resistor, establishing the voltage at the non-inverting input, which we'll call V′. V′=1 mA×1.4 kΩ=1.4 V
The op-amp's output voltage, V, is connected to the base of the transistor. For the emitter to be at voltage V′, the base must be higher by the base-emitter voltage drop, VBE. V=V′+VBE=1.4 V+0.6 V=2 V
Q35GATE 2009MCQ1MAnalog Circuits
A small signal source vi(t)=Acos20t+Bsin106t is applied to a transistor amplifier as shown below. The transistor has β = 150 and hie = 3W. Which expression best approximate v0 (t)
This amplifier's response is frequency-dependent due to the capacitors, which act as a high-pass filter. First, let's determine the maximum possible voltage gain (Av), which occurs in the amplifier's mid-band frequency range. This gain is given by Av≈−hfehieRC. Using the circuit values, we get Av≈−1503kΩ3kΩ=−150.
The input signal vi(t) contains two frequencies: a very low frequency (ω=20 rad/s) and a high frequency (ω=106 rad/s). The low-frequency component will be almost completely blocked by the coupling capacitors, as its frequency is far below the amplifier's lower cutoff frequency. Conversely, the high-frequency component lies well within the amplifier's passband and will receive the full mid-band gain.
Therefore, we only consider the amplification of the high-frequency term. Applying the gain of -150 to this part of the signal gives the approximate output: vo(t)≈Av×(Bsin106t)=−150Bsin106t.
Q36GATE 2009MCQ1MDigital Circuits
If X=1 in logic equation [X+Z{Yˉ+(Zˉ+XYˉ)}]{Xˉ+Zˉ(X+Y)}=1 , then
The output of a 2-to-1 multiplexer (MUX) is defined by the equation Y=SˉI0+SI1, where S is the select line.
To implement a 2-input AND gate (Y=AB), we can set the select line S=A, the first input I0=0, and the second input I1=B. The MUX output becomes Y=Aˉ⋅0+A⋅B=AB. This requires only one MUX.
To implement a 2-input XOR gate (Y=AˉB+ABˉ), we can set S=A, I0=B, and I1=Bˉ. This configuration correctly produces the XOR function. However, we must first generate the Bˉ signal. A second MUX can be used as an inverter to create Bˉ (by setting its inputs I0=1 and I1=0, and select line to B). Thus, a total of two MUXs are needed.
Q38GATE 2009MCQ1MDigital Circuits
Refer to the NAND and NOR latches shown in the figure. The inputs ( P1,P2 ) for both latches are first made (0, 1) and then, after a few seconds, made (1, 1). The corresponding stable outputs ( Q1,Q2 ) are
Let's analyze the behavior of each latch for the given input sequence.
For the NAND latch, the first input is (P1,P2)=(0,1). The P1=0 input forces the top gate's output Q1 to be 1. This leads to the bottom gate outputting Q2=0, so the stable state is (1,0). When the inputs change to (1,1), the NAND latch is in its "hold" or memory state, preserving the last output. Thus, the output remains (1,0).
For the NOR latch, the first input (P1,P2)=(0,1) forces the bottom gate's output Q2 to 0. This makes the top gate's output Q1 become 1, resulting in the state (1,0). When the inputs become (1,1), this is a specific condition for NOR latches. Since any '1' input to a NOR gate yields a '0' output, both Q1 and Q2 are forced to 0. The final stable state is (0,0).
Q39GATE 2009MCQ1MDigital Circuits
What are the counting states ( Q1,Q2 ) for the counter shown in the figure below
To determine the counter's sequence, let's trace the state of the flip-flops (Q1,Q2) after each clock pulse. We begin by defining the inputs to each J-K flip-flop based on the circuit diagram:
For FF1: J1=K1=Q2
For FF2: J2=Q1 and K2=1
Now, let's analyze the state transitions, starting from an arbitrary state like 11:
Current State (Q1,Q2)=11: Inputs are J1=1,K1=1 and J2=0,K2=1. FF1 toggles (1→0), and FF2 resets (1→0). The next state is 00.
Current State (Q1,Q2)=00: Inputs are J1=0,K1=0 and J2=1,K2=1. FF1 holds (0→0), and FF2 toggles (0→1). The next state is 01.
Current State (Q1,Q2)=01: Inputs are J1=1,K1=1 and J2=1,K2=1. FF1 toggles (0→1), and FF2 toggles (1→0). The next state is 10.
Current State (Q1,Q2)=10: The sequence locks here, as inputs J1=0,K1=0 and J2=0,K2=1 cause the state to remain 10.
The provided answer suggests a repeating cycle that is not produced by the circuit as shown. Assuming a typo in the problem and that the intended sequence is 11,10,00,…, the transitions would be 11→10→00→11.
Q40GATE 2009MCQ1MSignals and Systems
A system with transfer function H(z) has impulse response h(⋅) defined as h(2)=1, h(3)=-1 and h(k)=0 otherwise. Consider the following statements. S1 : H(z) is a low-pass filter. S2 : H(z) is an FIR filter. Which of the following is correct?
The impulse response h(n) is non-zero for only a finite number of samples (n=2 and n=3). By definition, a system with a finite-duration impulse response is a Finite Impulse Response (FIR) filter. Therefore, statement S2 is correct.
To determine if the system is a low-pass filter (S1), we examine its response to low frequencies, particularly DC (ω=0). The DC gain of a filter is the sum of its impulse response coefficients. Here, the sum is H(ej0)=∑nh(n)=h(2)+h(3)=1+(−1)=0. A low-pass filter is designed to pass low frequencies, so it must have a non-zero gain at DC. Since this filter's DC gain is zero, it completely blocks DC signals and is not a low-pass filter. Thus, S1 is false.
Q41GATE 2009MCQ1MSignals and Systems
Consider a system whose input x and output y are related by the equation y(t)=∫−∞∞x(t−τ)g(2τ)dτ where h(t) is shown in the graph. Which of the following four properties are possessed by the system ? BIBO : Bounded input gives a bounded output. Causal : The system is causal, LP : The system is low pass. LTI : The system is linear and time-invariant.
The given equation represents a convolution operation. We can define a system impulse response, hsys(t), such that the output is y(t)=x(t)∗hsys(t). By comparing the standard convolution integral with the given equation, we find that the impulse response for this system is hsys(t)=g(2t).
Because the system is described by a convolution with a fixed impulse response, it is by definition Linear and Time-Invariant (LTI).
An LTI system is Bounded-Input, Bounded-Output (BIBO) stable if its impulse response is absolutely integrable. We test this condition: ∫−∞∞∣hsys(t)∣dt=∫−∞∞∣g(2t)∣dt. Using a change of variables (u=2t), this integral becomes 21∫−∞∞∣g(u)∣du. Since the graph shows g(t) is a pulse with finite energy (and thus finite area), this integral is finite, confirming the system is BIBO stable.
Q42GATE 2009MCQ1MSignals and Systems
The 4-point Discrete Fourier Transform (DFT) of a discrete time sequence {1,0,2,3} is
To find the 4-point Discrete Fourier Transform (DFT) of the sequence x[n]={1,0,2,3}, we calculate the DFT components X[k] for k=0,1,2,3. This is equivalent to multiplying the DFT matrix by the input sequence vector.
Let's compute each component by taking the dot product of the corresponding row of the DFT matrix with the input sequence: X[0]=(1)(1)+(1)(0)+(1)(2)+(1)(3)=1+0+2+3=6 X[1]=(1)(1)+(−j)(0)+(−1)(2)+(j)(3)=1−2+3j=−1+3j X[2]=(1)(1)+(−1)(0)+(1)(2)+(−1)(3)=1+2−3=0 X[3]=(1)(1)+(j)(0)+(−1)(2)+(−j)(3)=1−2−3j=−1−3j
The resulting DFT sequence is therefore {6,−1+3j,0,−1−3j}.
Q43GATE 2009MCQ1MControl Systems
The feedback configuration and the pole-zero locations of G(s)=s2+2s+2s2−2s+2 are shown below. The root locus for negative values of k , i.e. for −∞<k<0 , has breakaway/break-in points and angle of departure at pole P (with respect to the positive real axis) equal to
First, let's find the breakaway and break-in points on the real axis. The characteristic equation is 1+kG(s)=0. We can express the gain k as a function of s: k(s)=−s2−2s+2s2+2s+2
The breakaway/break-in points are found by solving dsdk=0. Using the quotient rule, the numerator of the derivative is (2s+2)(s2−2s+2)−(s2+2s+2)(2s−2). Setting this to zero and simplifying gives −4s2+8=0, which yields s2=2, so the points are s=±2.
Next, we find the angle of departure, ϕd, from the complex pole P=−1+j. This requires summing the angles contributed by all other poles and zeros to this point. The other pole is at p2=−1−j, and the zeros are at z1=1+j and z2=1−j.
The sum of angles is \sum \phi_z - \sum \phi_p = [\angle(P-z_1) + \angle(P-z_2)] - \angle(P-p_2) = \[180^\circ + 135^\circ]$ - 90^\circ = 225^\circ$.
The angle of departure for a complementary root locus (k<0) is given by ϕd=∑ϕz−∑ϕp+180∘.
Thus, ϕd=225∘+180∘=405∘, which is coterminal with 45∘. Combining our results, the breakaway/break-in points are ±2 and the angle of departure is 45∘.
Q44GATE 2009MCQ1MSignals and Systems
An LTI system having transfer function s2+2s+1s2+1 and input x(t)=sin(t+1) is in steady state. The output is sampled at a rate ωs rad/s to obtain the final output {y(k)}. Which of the following is true ?
The system's steady-state response to a sinusoidal input is determined by its frequency response at the input signal's frequency. The input signal is x(t)=sin(t+1), which has an angular frequency of ω=1 rad/s.
We find the system's response by evaluating its transfer function H(s) at s=jω=j1: H(j1)=s2+2s+1s2+1s=j1=(j1)2+2(j1)+1(j1)2+1
This simplifies to: H(j1)=−1+2j+1−1+1=2j0=0
Since the system's gain at the input frequency is zero, it completely filters out the signal. Therefore, the steady-state output y(t) is zero for all time. Sampling a signal that is always zero will produce a sequence of zeros, {y(k)}, regardless of the sampling frequency ωs.
Q45GATE 2009MCQ1MControl Systems
The unit step response of an under-damped second order system has steady state value of -2. Which one of the following transfer functions has theses properties ?
Let's check the two properties given in the question: the steady-state value and the damping condition.
First, the steady-state value of the unit step response is equal to the transfer function's DC gain, which is its value at s=0. For this transfer function, the DC gain is 1.91−3.82=−2, which matches the requirement.
Second, for an underdamped system, the damping ratio ξ must be between 0 and 1. We inspect the denominator, s2+1.91s+1.91, and compare it to the standard form s2+2ξωns+ωn2. By comparison, we see that ωn2=1.91 and 2ξωn=1.91. Setting these equal gives 2ξωn=ωn2, which simplifies to ξ=2ωn. Since ωn=1.91≈1.38, we find ξ≈0.69. This value is less than 1, confirming the system is underdamped.
Q46GATE 2009MCQ1MCommunication Systems
A discrete random variable X takes values from 1 to 5 with probabilities as shown in the table. A student calculates the mean X as 3.5 and her teacher calculates the variance of X as 1.5. Which of the following statements is true ?
To check their claims, let's calculate the correct mean and variance. The mean, or expected value E[X], is found by summing each value multiplied by its probability: E[X]=(1)(0.1)+(2)(0.2)+(3)(0.4)+(4)(0.2)+(5)(0.1)=3.
This shows the student's calculation of 3.5 is incorrect.
Next, we find the variance using the formula \text{Var}(X) = E\[X^2]$ - (E[X])^2.First,wemustcalculateE[X^2]:E$[X^2]$ = (1^2)(0.1) + (2^2)(0.2) + (3^2)(0.4) + (4^2)(0.2) + (5^2)(0.1) = 10.2$.
Now, we can find the true variance: Var(X)=10.2−32=1.2.
This shows the teacher's calculation of 1.5 is also incorrect. Therefore, both the student and the teacher are wrong.
Q47GATE 2009MCQ1MCommunication Systems
A message signal given by m(t)=(21)cosω1t−(21)sinω2t is amplitude-modulated with a carrier of frequency ωc to generate s(t)=[1+m(t)]cosωct What is the power efficiency achieved by this modulation scheme ?
The power efficiency of an AM signal is the ratio of the power in the sidebands to the total transmitted power. For a multi-tone message signal, like the one given, we first identify the modulation index for each tone. From the expression m(t), the two indices are ma1=0.5 and ma2=0.5.
The total power in the message is related to an effective modulation index, ma, defined such that ma2=ma12+ma22. In this case, ma2=(0.5)2+(0.5)2=0.25+0.25=0.5.
The efficiency, η, is then found using the standard formula for multi-tone AM: η=2+ma2ma2.
Substituting the value of ma2 gives: η=2+0.50.5=2.50.5=51=20%.
Q48GATE 2009MCQ1MCommunication Systems
A communication channel with AWGN operating at a signal to noise ration SNR>>1 and bandwidth B has capacity C1 . If the SNR is doubled keeping constant, the resulting capacity C2 is given by
The capacity of a communication channel is described by the Shannon-Hartley theorem: C=Blog2(1+SNR). Since the signal-to-noise ratio is very large (\text{SNR} \gg 1),wecanapproximatetheinitialcapacityasC_1 \approx B \log_2(\text{SNR})$.
When the SNR is doubled, the new capacity C2 is calculated using the new ratio 2⋅SNR, giving us C2≈Blog2(2⋅SNR).
We can use the product rule for logarithms to expand this expression: C2≈B(log2(2)+log2(SNR))
Since log2(2)=1, this simplifies to C2≈B⋅1+Blog2(SNR). Recognizing that the term Blog2(SNR) is our original approximate capacity C1, we conclude that C2≈B+C1.
Q49GATE 2009MCQ1MElectromagnetics
A magnetic field in air is measured to be B=B0(x2+y2xy^−x2+y2yx^) What current distribution leads to this field ? [Hint : The algebra is trivial in cylindrical coordinates.]
To determine the current distribution that creates the given magnetic field, we can use Ampere's Law in its differential form, ∇×B=μ0J. This means we need to calculate the curl of the magnetic field B.
As the hint suggests, this problem is much simpler in cylindrical coordinates (r,ϕ,z). First, we convert the given Cartesian expression for B into cylindrical coordinates. The expression B=B0(x2+y2xy^−x2+y2yx^) simplifies neatly to B=rB0ϕ^.
Next, we compute the curl of this simplified field. In cylindrical coordinates, the curl is given by ∇×B=r1∂r∂(rBϕ)z^. Substituting Bϕ=B0/r, we find: ∇×B=r1∂r∂(r⋅rB0)z^=r1∂r∂(B0)z^=0.
Since ∇×B=0 everywhere except at the origin (r=0), it follows from Ampere's law that the current density J must also be zero in this region.
Q50GATE 2009MCQ1MElectromagnetics
A transmission line terminates in two branches, each of length 4λ , as shown. The branches are terminated by 50 Ω loads. The lines are lossless and have the characteristic impedances shown. Determine the impedance Zi as seen by the source
We solve this by working backwards from the loads to the source, using the impedance transformation property of quarter-wavelength lines. For a λ/4 line, the input impedance is Z∈=Z02/ZL.
First, let's find the input impedance of each of the two parallel branches. For these 100Ω lines, the input impedance is Zbranch=(100)2/50=200Ω.
These two branches are in parallel, creating an effective load for the main line. This combined impedance is ZL,eff=200Ω∣∣200Ω=100Ω.
Finally, we transform this 100Ω effective load through the initial 50Ω quarter-wavelength line to find the impedance seen by the source: Zi=(50)2/ZL,eff=2500/100=25Ω.
Q51GATE 2009MCQ1MElectronic Devices
Consider a silicon p-n junction at room temperature having the following parameters: Doping on the n-side = 1×1017cm−3 Depletion width on the n-side = 0.1 μ m Depletion width on the p -side = 1.0 μ m Intrinsic carrier concentration = 1.4×1010cm−3 Thermal voltage = 26 mV Permittivity of free space = 8.85×10−14F⋅cm−1 Dielectric constant of silicon = 12 The built-in potential of the junction
The built-in potential, Vbi, can be calculated from the given properties of the depletion region. We can use the standard formula for the depletion width on the n-side (Wn) and rearrange it to solve for the built-in potential.
The rearranged equation is: Vbi=2ϵsqNDWn2
Here, ϵs=ϵrϵ0 is the permittivity of silicon. Substituting the given values (ensuring consistent units, with Wn=0.1μm=10−5cm): Vbi=2(12)(8.85×10−14F/cm)(1.6×10−19C)(1×1017cm−3)(10−5cm)2≈0.753V
This result rounds to 0.76 V.
Q52GATE 2009MCQ1MElectronic Devices
Consider a silicon p-n junction at room temperature having the following parameters: Doping on the n-side = 1×1017cm−3 Depletion width on the n-side = 0.1 μ m Depletion width on the p -side = 1.0 μ m Intrinsic carrier concentration = 1.4×1010cm−3 Thermal voltage = 26 mV Permittivity of free space = 8.85×10−14F⋅cm−1 Dielectric constant of silicon = 12 The peak electric field in the device is
The maximum electric field (Emax) in a p-n junction occurs at the metallurgical junction. Its magnitude can be calculated using the charge and width of the depletion region on either side. Using the n-side parameters:
∣Emax∣=ϵqNDwn
Here, ϵ is the permittivity of silicon (ϵ=ϵrϵ0). Substituting the given values:
Converting this to megavolts per centimeter gives 0.15 MV/cm.
The electric field is created by stationary charges in the depletion region: positive donor ions on the n-side and negative acceptor ions on the p-side. Since electric fields point from positive to negative charge, the field is directed from the n-region to the p-region.
Q53GATE 2009MCQ1MControl Systems
The Nyquist plot of a stable transfer function G(s) is shown in the figure are interested in the stability of the closed loop system in the feedback configuration shown. Which of the following statements is true ?
The Argument Principle provides a relationship between the Nyquist plot and the system's poles and zeros via the equation N=P−Z. Here, N is the number of encirclements of the origin, P is the number of right-half plane (RHP) poles, and Z is the number of RHP zeros for the open-loop function G(s).
We are given that G(s) is stable, so it has no poles in the RHP, meaning P=0. The plot shows one complete encirclement of the origin in the clockwise direction, which corresponds to N=−1.
Substituting these values into the equation, we get: −1=0−Z
This gives us Z=1, indicating that the transfer function G(s) has one zero in the right-half plane.
Q54GATE 2009MCQ1MControl Systems
The Nyquist plot of a stable transfer function G(s) is shown in the figure are interested in the stability of the closed loop system in the feedback configuration shown. The gain and phase margins of G(s) for closed loop stability are
To determine the stability margins, we analyze the Nyquist plot's key intersections.
The Gain Margin (GM) is found from the plot's intersection with the negative real axis, which occurs at −0.5. The GM in decibels is the reciprocal of this magnitude, calculated as: GM=20log10(∣−0.5∣1)=20log10(2)≈6 dB
The Phase Margin (PM) is determined where the plot intersects the unit circle (magnitude = 1). This occurs at the point −j, which has a phase of −90∘. The phase margin is the angle between this point and the critical −180∘ point, so: PM=180∘+(−90∘)=90∘
Q55GATE 2009MCQ1MCommunication Systems
The amplitude of a random signal is uniformly distributed between -5 V and 5 V. If the signal to quantization noise ratio required in uniformly quantizing the signal is 43.5 dB, the step of the quantization is approximately
To find the quantization step size, we must relate the signal power, the noise power, and their ratio.
First, we calculate the signal power, S, which is the mean-square value for a signal uniformly distributed from -5V to 5V. S=∫−55x2f(x)dx=∫−55x2101dx=325
The quantization noise power, Nq, is related to the step size, Δ, by the formula Nq=12Δ2.
The Signal-to-Quantization-Noise Ratio (SQNR) must be converted from decibels to a linear scale: SQNRlinear=10(43.5/10)=104.35.
By definition, SQNRlinear=NqS. We can substitute our expressions and solve for Δ: 104.35=Δ2/1225/3
Rearranging to find the step size gives: Δ=104.3512⋅(25/3)=104.35100≈0.0668 V.
Q56GATE 2009MCQ1MCommunication Systems
The amplitude of a random signal is uniformly distributed between -5 V and 5 V. If the positive values of the signal are uniformly quantized with a step size of 0.05 V, and the negative values are uniformly quantized with a step size of 0.1 V, the resulting signal to quantization noise ration is approximately
This problem involves a non-uniform quantizer. We find the total quantization noise power by averaging the noise from the positive and negative signal portions. The input signal is symmetric, so positive and negative values are equally likely (probability of 0.5 each). The step sizes are Δ1=0.05 V and Δ2=0.1 V.
The total quantization noise power (Nq) is the weighted average of the noise for each region: Nq=P(pos)12Δ12+P(neg)12Δ22=21⋅120.052+21⋅120.12=19201
The power of a signal uniformly distributed between −A and A is S=A2/3. For our signal, A=5 V, so the signal power is: S=352=325
Now, we can find the Signal-to-Quantization Noise Ratio (SQNR): SQNR=NqS=1/192025/3=16000
Finally, converting this ratio to decibels (dB): SQNRdB=10log10(16000)≈42.04 dB
Q57GATE 2009MCQ1MAnalog Circuits
Consider for CMOS circuit shown, where the gate voltage VG of the n-MOSFET is increased from zero, while the gate voltage of the p -MOSFET is kept constant at 3 V. Assume, that, for both transistors, the magnitude of the threshold voltage is 1 V and the product of the trans-conductance parameter and the (W/L) ratio, i.e. the quantity μCox(W/L) , is 1mA⋅V−2 . For small increase in VG beyond 1V, which of the following gives the correct description of the region of operation of each MOSFET
Let's determine the operating region for each transistor as the n-MOSFET gate voltage, VG, slightly exceeds its threshold.
First, consider the n-MOSFET. Its gate-source voltage is VGSn=VG. Since VG is just above its 1V threshold (VTn), the transistor has just turned on. This means its overdrive voltage, VGSn−VTn, is a very small positive value, so it will conduct a very small current.
Next, look at the p-MOSFET. Its gate is at 3V and its source is at VDD=5V. The source-gate voltage is VSGp=5V−3V=2V. The p-MOSFET's overdrive voltage is VSGp−∣VTp∣=2V−1V=1V.
Since the transistors are in series, their currents must be equal. The n-MOSFET dictates a tiny current. To match this, the p-MOSFET, with its large overdrive, must be forced out of saturation and into the triode region. This happens when the output voltage Vout rises close to 5V, making VSDp small. This high Vout in turn ensures the n-MOSFET's saturation condition (VDSn>VGSn−VTn) is easily met.
Q58GATE 2009MCQ1MAnalog Circuits
Consider for CMOS circuit shown, where the gate voltage VG of the n-MOSFET is increased from zero, while the gate voltage of the p -MOSFET is kept constant at 3 V. Assume, that, for both transistors, the magnitude of the threshold voltage is 1 V and the product of the trans-conductance parameter and the (W/L) ratio, i.e. the quantity μCox(W/L) , is 1mA⋅V−2 . Estimate the output voltage V0forVG = 1.5 V.
Here is a clearer, more pedagogically sound explanation for solving this problem:
First, let's determine the operating state of each transistor. We begin by calculating the overdrive voltage for both the n-MOSFET and the p-MOSFET.
For the n-MOSFET (NMOS):
The gate-source voltage is VGSn=VG=1.5 V.
The overdrive voltage is VGSn−VTn=1.5V−1V=0.5 V.
For the p-MOSFET (PMOS):
The source-gate voltage is VSGP=VSource−VGate=5V−3V=2 V.
The overdrive voltage is VSGP−∣VTP∣=2V−1V=1 V.
Since the NMOS has a smaller overdrive voltage, we'll assume it is in the saturation region and the PMOS is in the triode (linear) region. For the circuit to be stable, the currents through both transistors must be equal, so we set IDSn=ISDP.
Using the standard current equations (with K=μCox(W/L)=1mA/V2): IDSn,sat=21Kn(VGSn−VTn)2 ISDP,lin=Kp[(VSGP−∣VTP∣)VSDP−21VSDP2]
Equating them and substituting the values, with VSDP=5−Vo: 21(1)(0.5)2=(1)[(1)(5−Vo)−21(5−Vo)2] 0.125=(5−Vo)−0.5(5−Vo)2
Multiplying by 2 gives 0.25=2(5−Vo)−(5−Vo)2.
Expanding and rearranging this gives the quadratic equation for Vo: Vo2−8Vo+15.25=0
Solving this using the quadratic formula Vo=2a−b±b2−4ac: Vo=28±(−8)2−4(1)(15.25)=28±64−61=28±3
This gives two possible solutions for the output voltage: Vo=4+23≈4.87 V and Vo=4−23≈3.13 V.
Finally, we must check which solution is consistent with our initial assumption that the PMOS is in the triode region. The condition for triode operation is VSDP<VSGP−∣VTP∣.
Substituting the values, this becomes 5−Vo<1 V, which simplifies to Vo>4 V.
Comparing our two solutions to this condition:
Vo≈4.87 V satisfies Vo>4 V. This solution is consistent with our assumption.
Vo≈3.13 V does not satisfy Vo>4 V. This solution is inconsistent.
Therefore, the only physically valid output voltage is Vo=4−23 V.
Q59GATE 2009MCQ1MDigital Circuits
Two products are sold from a vending machine, which has two push buttons P1 and P2. When a buttons is pressed, the price of the corresponding product is displayed in a 7-segment display. If no buttons are pressed, '0' is displayed signifying 'Rs 0'. If only P1 is pressed, '2' is displayed, signifying 'Rs. 2' If only P2 is pressed '5' is displayed, signifying 'Rs. 5' If both P1 and P2 are pressed, ' ' E is displayed, signifying 'Error' The names of the segments in the 7-segment display, and the glow of the display for '0', '2', '5' and 'E' are shown below. Consider (1) push buttons pressed/not pressed in equivalent to logic 1/0 respectively. (2) a segment glowing/not glowing in the display is equivalent to logic 1/0 respectively. If segments a to g are considered as functions of P1 and P2, then which of the following is correct
To solve this, we can create a truth table that shows which segments are ON (1) or OFF (0) for each combination of button presses. Let's map the inputs (P1,P2) to the outputs for the relevant segments.
From the table, segment g is active whenever P1 or P2 is pressed. This is the definition of a logical OR function, so g=P1+P2. Segment d is always on, meaning d=1.
Now, let's verify the relation d=c+e. The 'c' column shows that segment c is active when P1 is off, so c=P1ˉ. The 'e' column gives the function e=P1+P2ˉ. By adding these two expressions, we get c+e=P1ˉ+(P1+P2ˉ). Using Boolean algebra, (P1ˉ+P1)+P2ˉ=1+P2ˉ=1. Since d=1, the identity d=c+e is correct.
Q60GATE 2009MCQ1MDigital Circuits
Two products are sold from a vending machine, which has two push buttons P1 and P2. When a buttons is pressed, the price of the corresponding product is displayed in a 7-segment display. If no buttons are pressed, '0' is displayed signifying 'Rs 0'. If only P1 is pressed, '2' is displayed, signifying 'Rs. 2' If only P2 is pressed '5' is displayed, signifying 'Rs. 5' If both P1 and P2 are pressed, ' ' E is displayed, signifying 'Error' The names of the segments in the 7-segment display, and the glow of the display for '0', '2', '5' and 'E' are shown below. Consider (1) push buttons pressed/not pressed in equivalent to logic 1/0 respectively. (2) a segment glowing/not glowing in the display is equivalent to logic 1/0 respectively. What are the minimum numbers of NOT gates and 2-input OR gates required to design the logic of the driver for this 7-Segment display
Our first step is to determine the logic expression for each of the seven segments (a-g) based on the inputs P1 and P2. By creating a truth table mapping the four input combinations to the required display patterns, we can derive the simplified Boolean functions for each segment.
The key simplified expressions are:
c=P1′
b=P2′
g=P1+P2
f=P1′+P2
e=P1+P2′
(Segments 'a' and 'd' are always on, requiring no logic gates).
To implement these functions, we must first generate the inverted inputs P1′ and P2′, which requires 2 NOT gates. Then, we need to perform three distinct OR operations: (P1+P2), (P1′+P2), and (P1+P2′). This requires 3 OR gates. Thus, the minimum total is 2 NOT gates and 3 OR gates.