The LT®1190 is the ideal candidate for this application,
with a high 400V/μs slew rate, large 50mA output
current, and a wide 70 degree phase margin. The
closed-loop peak detector circuit of Figure 1 uses a
Schottky diode inside the feedback loop to obtain good
accuracy. The 20Ω resistor RO isolates the 0.01μF load
and prevents oscillation. The DC error with a sine wave
input is plotted in Figure 2 for various input amplitudes.
The DC value is read with a DVM. At low frequency, the
error is small and dominated by decay of the detector
capacitor between cycles. As frequency rises the error
increases because capacitor charging time decreases.
During this time the overdrive becomes a very small
portion of a sine wave cycle. Finally at approximately
4MHz the error rises rapidly due to the slew rate limitation
of the op amp. For comparison purposes the error
of an LM118 is also plotted for VIN = 2VP-P.