peak detector in agc

[matin-kh]

Hi every one,
I want to design a peak detector in my AGC circuit which be compared with reference voltage and produce the control voltage of VGA.the peak detector should be linear with input magnitude I couldn't find any reasonable circuit to satisfy my idea.
could you please help me...
with best regards
matin

 

[D.A.(Tony)Stewart]

Peak detectors have low threshold, fast attack, slow decay and may be linear, quadratic or logarithmic.

The input may be an RF carrier or a nanosecond pulse. Each of these metrics must have a spec as each solution may be different. Some with perpetual S&H, others with decay on pulse etc.

Long long ago IBM invented a way of define problems called HIPO.

Hierarchical, Input, Process, Output

YOu may also have a process with just a simple proportional gain control with noise rejection that needs to be defined. You may also have an nonlinear response to big signals, dropouts and small signals. YOu may want to compress noise spikes.

INPUTS
Input range [V]
frequency range [Hz]
Rise time
Decay time

PROCESS

OUTPUT

Precision rectifiers for audio range use a diode feedback and Op AMps.
RF may use Pin diodes.