Fast peak detector requires a special amplifier features. The output stage must have high slew rate to follow the stages of the transition from the amplifier. This led to the overload or DC accuracy fault. Amplifier should send a current to the load of large capacitive detector to maintain the slew rate of output. Another problem that needs to be solved include preservation of accuracy voltage output and instability on the big capacitive loads. Here is the schematic diagram :
With a current output of 50mA, phase margin of 70 degrees and 450 v/ms slew rate, LT1190 suitable for this application. A 20W (R0) resistor isolate loads 10nF and prevent oscillations. Good accuracy obtained by using closed-loop on a peak detector circuit using Schottky Diode in the feedback loop. Amplitude error of the circuit would be under 10% to up to 300 kHz frequency input signal, and below 20% to 3MHz frequency.
source : Linear Technology Application Notes