This is a homebrew pet project that I'm hoping there is a simple answer to.
I want to create a logarithmic opamp stage that operates _linear_ during the alternate (negative) half of the input wave.
Here is a textbook log amp with simple diode in the feedback loop (display in fixed font):
Diode +--------->|---+ | | | |\ | o-----R1----+---(-)\ | | \ | | >-----+---------o out | / ----(+)/ | |/ | _ V
The above suggests to me that the alternate half of the wave will be linear BUT with open loop gain. But I want to establish/lower the gain to be about 3 or so.
The obvious thing would seem to be to add a reverse biased diode in series with a resistor in the feedback path (the resistor to establish the gain). But this also suggests to me that I will still have a _log_ function but in the reverse. I'm trying to keep that linear.
I'm trying to avoid the need for precision rectifier(s).
Warren