W
Warren
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
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
