0195136047.pdf

PROBLEMS 265

*5.4.7In the noninverting summing amplifier of Figure

5.4.4, letRd=1kandM=6. FindRfso that

vo=

∑ 6
m= 1 vim.
5.4.8An inverting amplifier is designed with three in-
puts,v 1 ,v 2 , andv 3 , as shown in Figure P5.4.8. De-
termine the output voltage. Then indicate how the
circuit may be modified to perform as a summer.
5.4.9A negative impedance converter is used, as shown
in Figure P5.4.9. Show that the load currentiL
is given byvin/R, which is independent ofZL.
Note that since the load sees a current source, the
network is avoltage-to-current converter.
5.4.10Determine how Equation (5.4.31) will be affected
if the op amp of the negative impedance converter
(Figure 5.4.8) has a finite gainA 0 but is otherwise
ideal.
5.4.11Find the input impedanceZinfor thegeneral-
ized impedance convertercircuit shown in Figure
P5.4.11 if the op amps are ideal.
*5.4.12Consider Figure 5.4.9 of the weighted differencing
amplifier. LetR 3 =R 1 andR 4 =R 2. Determine the

input resistance between terminalsaandbof the

circuit.

5.4.13In the circuit shown in Figure P5.4.13 with an ideal

op amp, findvoas a function ofvaandvb.

5.4.14For the low-pass filter configuration of Figure

5.4.13, withRi=Rf=1M, calculateCfsuch

that the 3-dB point is at 1 kHz.

5.4.15For the high-pass filter configuration of Figure

5.4.13, withvo/vi=2.5 at 10 MHz andCi= 100

pF, determineRiandRfto yield a 3-dB point at 1

MHz.

5.4.16Comment on the behavior of the circuit of Figure

P5.4.16 at low and high frequencies.

*5.4.17The input resistance of an ideal op amp with no

feedback is infinite. Investigate the input resis-

tance of an op amp with a feedback resistanceRF:

(a) When there is no resistance placed in the−

input line.

(b) When a resistanceR 1 is placed in the−input

line.

−

+

vo

v 2 R 2

X

v 1 R 1

v 3 R 3

RF

R

Figure P5.4.8

−

+

Ideal

op amp

R 1

vin

R R

R 1

ZL

iL

Figure P5.4.9

i 2

i 3 i 4

Op amp

1

Op amp

2

v 1 v 2 v 3 v 4

+−

−+

i 5

i 1

vin

Zin

Z 1 Z 2

Z 5

Z 3 Z 4

Figure P5.4.11