Page 315 - Op Amps Design, Applications, and Troubleshooting

Ideal Rectifier Circuits 293

The manufacturer's data sheet provides us with worst-case and typical val-
ues for the maximum output swing. The minimum output swing for loads of 2
kilohms or more is listed as ±10 volts with a typical swing listed as ±13 volts. The
typical value for loads of greater than 10 kilohms is ±14 volts. For our current
analysis, let us use ±13 volts as the maximum output swing with ±15 volts V cc.
The maximum amplitudes for v Oi and v 02, then, are computed as

V 0i = -13 V + 0.7 V = -12.3 V, and

v 02 = +13 V - 0.7 V = +12.3 V

Voltage Gain. The voltage gain on either half cycle is found using the basic
gain equation for inverting amplifiers, Equation (2.6). In our present case, both half
cycles will have the same gain because resistors R 2 and R 3 are the same value. We
will compute the voltage gain of the amplifier using R 2 as the feedback resistor.

For most applications, resistors R 2 and R 3 are equal, but this is not necessary if
unequal gains are desired.

Maximum Input without Distortion. We compute the highest input signal
that we can have without distorting the output by applying our basic amplifier
gain equation, Equation (2.1). As mentioned in the preceding section, both half
cycles have the same gain in this particular circuit. Let's compute the maximum
input by using the maximum positive output signal:

Highest Frequency of Operation. The amplifier, in this case, is basically
amplifying sinewaves. In fact, the actual output terminal of the op amp will have
a sinusoidal waveform present, but, of course, the circuit can be used with non-
sinusoidal inputs as well. The bandwidth considerations of the amplifier are iden-
tical to those discussed in Chapter 2. The upper frequency limit will be established
by the finite bandwidth of the op amp or by the limits imposed by the op amp
slew rate. Since the amplifier is configured for unity voltage gain, we can expect
the bandwidth limitation to be similar to the unity gain bandwidth of the op amp.
The manufacturer's data sheet lists this limit as 1.0 megahertz.
The stew rate will likely impose a lower limit unless we apply only very-
low-amplitude signals. Assuming that we intend to apply maximum-amplitude