# Question 18.1: One application for Fig. 18-6 is in a squelch circuit. This ...

One application for Fig. 18-6 is in a squelch circuit. This kind of circuit is used in communication receivers to reduce listener fatigue by having a low voltage gain when no signal is being received. This way, the user does not have to listen to static when there is no communication signal. When a signal comes in, the voltage gain is switched to high.

If $R_1 = 100$ kΩ, $R_f = 100$ kΩ, and $R_2 = 1$ kΩ in Fig. 18-6, what is the voltage gain when the JFET is on? What is the voltage gain when the JFET is off? Explain how the circuit can be used as part of a squelch circuit.

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Question: 18.2

## When we need to vary the amplitude of an out-of-phase signal, we can use a circuit like the one in Fig. 18-10. If R1 = 1.2 kΩ and R2 = 91 kΩ, what are the values of the maximum and minimum voltage gain? ...

With the equation given in Fig. 18-10, the maximum...
Question: 18.3

## If R = 1.5 kΩ and nR = 7.5 kΩ in Fig. 18-12, what is the maximum positive voltage gain? What is the value of the other fixed resistance? ...

The value of n is: n=\frac{7.5 \ k\Omega }{...
Question: 18.4

## In Fig. 18-18, R1 = 1 kΩ, R2 = 100 kΩ, and R = 10 kΩ. What is the differential voltage gain of the instrumentation amplifier? What is the common-mode voltage gain if the resistor tolerances in the second stage are ±0.01 percent? If vin = 10 mV and vin(CM) = 10 V, ...

With the equations given in Fig. 18-18, the voltag...
Question: 18.10

## If rds varies from 50 Ω to 120 kΩ in Fig. 18-32, what is the maximum voltage gain? What is the minimum voltage gain? ...

Using the values and equations of Fig. 18-32, the ...
Question: 18.9

## The Howland current source of Fig. 18-31 has R = 15 kΩ, vin = 3 V, and VCC = 15 V. What is the output current? What is the largest load resistance that can be used with this circuit if the maximum input voltage is 9 V? ...

With the equations of Fig. 18-31: i_{out}=\...
Question: 18.8

## If the current source of Fig. 18-28 has R = 10 kΩ, vin = 1 V, and VCC = 15 V, what is the output current? What is the maximum load resistance that can be used with this circuit if vin can be as large as 10 V? ...

With the equations of Fig. 18-28, the output curre...
Question: 18.7

## In Fig. 18-27, R1 = 1 kΩ and R2 = 51 kΩ. If a 741C is used for the op amp, what is the voltage gain of the circuit? What is the closed-loop output impedance?What is the shorted-load current of the circuit if each transistor has a current gain of 125? ...

With the equations given in Fig. 18-26, the voltag...
Question: 18.6