Analog Electronics - Study Mode

[#196] Introducing a resistor in the emitter of a common emitter amplifier stabilizes the dc operating point against variation in
Correct Answer

(C) both temperature and β

[#197] g m of MOSFET is controlled by
Correct Answer

(A) gate-source voltage

Explanation

Solution: The correct answer is Option A: gate-source voltage . Let's break down why: gm (transconductance) of a MOSFET tells us how much the drain current (Id) changes for a small change in the gate-source voltage (Vgs). Think of it like this: If you slightly adjust the voltage on the gate (Vgs), how much does the current flowing through the MOSFET from drain to source (Id) change? Option A: gate-source voltage (Vgs) - This is the primary way to control gm. A higher Vgs generally leads to a higher gm. Option B: drain-source voltage (Vds) - While Vds *does* influence the drain current, and therefore indirectly *can* affect gm, it's not the primary control. gm is *defined* by the relationship between gate voltage and drain current. Vds mainly affects the *saturation* region of operation, but the *control* is still largely through the gate. Option C: drain current (Id) - gm and Id are related, but Id doesn't directly *control* gm. Instead, gm is a *property* that describes how Id responds to changes in Vgs. Option D: gate current (Ig) - In a MOSFET, the gate current is ideally very, very small (close to zero). Therefore, it does not control gm. The gate is insulated. In simpler terms: The gate-source voltage (Vgs) is like the accelerator pedal in a car . It directly controls how much current (Id) flows through the MOSFET. gm is a measure of how sensitive the current flow is to changes in the accelerator pedal.

[#198] A 741 OP-AMP has an open loop gain 200,000. The output offset voltage is 2 mV. If the input terminals are shorted, the output voltage is
Correct Answer

(A) 0 V

[#199] An amplifier without feedback has a voltage gain of 50, input resistance of 1 kΩ & Output resistance of 2.5 kΩ.The input resistance of the current shunt negative feedback amplifier using the above amplifier with a feedback factor of 0.2 is
Correct Answer

(A) $$frac{1}{{11}}{ ext{k}}Omega $$

Explanation

Solution: The correct answer is Option A: ( frac{1}{11} ) kΩ Explanation: The input resistance of a current shunt negative feedback amplifier is given by the formula: [
R_{in(f)} = frac{R_{in}}{1 + Ax08eta}
] where, ( R_{in} ) = Input resistance without feedback = 1 kΩ ( A ) = Open-loop voltage gain = 50 ( x08eta ) = Feedback factor = 0.2 Substituting the values: [
R_{in(f)} = frac{1}{1 + (50 imes 0.2)}
] [
R_{in(f)} = frac{1}{1 + 10} = frac{1}{11} ext{ kΩ}
] Thus, the input resistance of the current shunt negative feedback amplifier is ( frac{1}{11} ) kΩ , which corresponds to Option A .

[#200] The most commonly used amplifier in sample & hold circuits is
Correct Answer

(A) A unity gain non-inverting amplifier

Explanation

Solution: Option A: A unity gain non-inverting amplifier is correct because the most commonly used amplifier in sample & hold circuits is a unity gain non-inverting amplifier. This configuration provides a stable output with no amplification (gain = 1), which is ideal for sample & hold applications where the input signal is maintained without distortion. Option B: A unity gain inverting amplifier is incorrect because inverting amplifiers flip the signal, meaning the output is inverted with respect to the input. This is not typically desired in sample & hold circuits, where the signal should remain in phase with the input. Option C: An inverting amplifier with a gain of 10 is incorrect because amplifying the signal in this way would distort the original input, which is undesirable in sample & hold circuits where the purpose is to maintain the exact value of the sampled signal. Option D: An inverting amplifier with a gain of 100 is incorrect because, like Option C, amplifying the signal with a high gain (such as 100) would lead to a distorted output, which is not suitable for sample & hold circuits. Conclusion: The correct answer is Option A: A unity gain non-inverting amplifier because this configuration is commonly used in sample & hold circuits due to its ability to maintain the input signal without inversion or amplification.