Deck 14: Special-Purpose Integrated Circuits

Question 1

Assume there is a phase shift between two common- mode signals. This can

A)increase the common mode voltage
B)lower the overall gain
C)create a differential voltage
D)all of the above

Answer 1

C

Question 2

Figure 2 Assume the bias current is 125 µA and g_m = 16 µS/µA.
Refer to Figure 2. If the power supplies have a lower voltage, the gain is

A)higher
B)lower
C)unaffected

Answer 2

B

Question 3

Refer to Figure 5. To change this to an antilog amplifier,

A)exchange the diode and R1
B)reverse the inputs on the op- amp
C)reverse the diode (anode and cathode)and reduce the value of R1
D)reverse the diode (anode and cathode)

Answer 3

A

Question 4

An ISO124 isolation amplifier has an internal oscillator of 500 kHz. The oscillator signal

A)is on a separate output
B)is filtered from the output by the user
C)is filtered from the output by the manufacturer
D)is added to the output signal

Question 5

With logarithmic signal compression,

A)all amplitudes are reduced by the same percentage
B)large amplitudes are attenuated more than small amplitudes
C)all amplitudes are reduced to a fixed value
D)none of the above

Question 6

Refer to Figure 5. If the input is 3.0 V and IR = 50 nA, VOUT will be

A)-325 mV
B)-550 mV
C)-145 mV
D)none of the above

Question 7

To avoid very large capacitors in a capacitively coupled isolation amplifier, the amplifier can use

A)modulation/demodulation
B)signal compression
C)a differential amplifier
D)dc coupling

Question 8

Figure 6
Refer to Figure 6(a). Assume S was momentarily closed and Vin is connected to a +3.0 VDC source. The voltage at the inverting input is

A)3.7 V
B)2.3 V
C)-0.7 V
D)3.0 V

Question 9

Isolation amplifiers can isolate the input and output by

A)transformer coupling
B)grounding both input and output to a common ground
C)both A and B
D)none of the above

Question 10

Figure 2 Assume the bias current is 125 µA and g_m = 16 µS/µA.
Refer to Figure 2. The voltage gain is

A)8.2
B)16
C)30
D)1.9

Question 11

An OTA with a transconductance of 2000 µS has a load resistance of 5 k▲. If the input voltage is 300 mV, the output voltage is

A)1.5 V
B)5.0 V
C)7.5 V
D)3.0 V

Question 12

The bandwidth of a typical instrumentation amplifier is

A)depends on the input signal amplitude
B)set by an external resistor
C)independent of the gain
D)lower at high gain

Question 13

The amount of bias current for an OTA changes the

A)transconductance
B)output resistance
C)input resistance
D)all of the above

Question 14

A log amplifier is used for

A)linearization of certain signals
B)signal compression
C)certain analog arithmetic operations
D)all of the above

Question 15

Figure 3
Refer to Figure 3. This purpose of R3 is to adjust the

A)gain
B)bandwidth
C)linearity
D)all of the above

Question 16

Figure 1 A capacitively coupled isolation amplifier
Refer to Figure 1. The box with the ? represents a

A)sinusoidal oscillator
B)pulse generator
C)modulator
D)sawtooth generator

Question 17

Figure 4 The circuit is a modulator for an audio signal.
Refer to Figure 4. The input at Vin1 is the _ and the input to the input at Vin2 is the .

A)audio signal, high- frequency oscillator
B)high- frequency oscillator, audio signal
C)either A or B will work
D)none of the above

Question 18

Figure 6
Refer to Figure 6(b). A shorted load, RL, is likely to cause

A)excessive current in R2
B)the op- amp to fail
C)both of the above
D)none of the above

Question 19

Figure 6
Refer to Figure 6(a). The circuit is

A)a peak detector
B)an antilog amplifier
C)a clamping circuit
D)a current source

Question 20

Figure 6
Refer to Figure 6(b). The circuit is

A)a current source
B)an antilog amplifier
C)a clamping circuit
D)a peak detector

Question 21

An excellent way to reduce leakage current on the input lines is to

A)connect an inductor in parallel with the stray capacitance
B)ground the shield
C)connect the common- mode signal to the shield
D)connect the output signal to the shield

Question 22

An instrumentation amplifier should have high CMRR.

Question 23

Figure 6
Refer to Figure 6(b). The current in RL is

A)5.1 mA
B)9.9 mA
C)23 mA
D)2.6 mA

Question 24

The purpose of guarding with an instrumentation amplifier is to

A)reduce radiated signal loss
B)provide a path to shunt high frequency noise to ground
C)avoid a safety hazard with exposed wires
D)reduce the effects of distributed capacitance

Question 25

An OTA has

A)fixed gain
B)differential input terminals
C)low output resistance
D)all of the above

Question 26

The classic three- op- amp instrumentation amplifier will have a differential gain of 1 if RG is not connected.

Question 27

An OTA is a current- to- voltage amplifier.

Question 28

An isolation amplifier requires two separate power supplies.

Question 29

Figure 6
Refer to Figure 6(b). If the zener is open, the output current will be

A)7.5 mA
B)6.8 mA
C)15 mA
D)1.3 mA

Question 30

The output signal from an isolation amplifier is a

A)dc level representing the peak input signal
B)pulse- width modulated signal
C)replica of the input
D)an amplitude modulated signal

Question 31

A typical application for an instrumentation amplifier is

A)interfacing a transducer
B)impedance matching
C)wave- shaping
D)all of the above

Question 32

Audio power amplifiers typically have a bandwidth from 3 kHz to 30 kHz.

Question 33

An OTA is often used to isolate a sensitive input from high voltage.

Question 34

Some instrumentation amplifiers can set gain with a binary input.

Question 35

The logarithm of a number is the power to which a base is raised to obtain the number.