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Log amps? for dB metering.

Eeyore said:
Reliably over 10 decades ?

Two stages of AGC amp, then, each spanning five decades (the
logarithm function is accurate to 6 decades in most transistors,
and to eight decades in low-noise types). You cascade two
stages and there's your AGC module.

Yes, of course it's reliable.

As for temperature effects, these aren't power-hungry, you just monitor
the
temperature and correct (there was a microprocessor involved), or even
thermostat-stabilize it.
 
J

joseph2k

Jan 1, 1970
0
Bob said:
So, in your mind that is simpler than a switched gain, op-amp based front
end using a few resistors, a FET switch, an op-amp and an 8 bit processor?
How about cost, temperature stability, drift, offset and all of the other
problems of using p-n junctions as circuit elements? Thanks, but I would
stay away from analog p-n juction based designs and go as digital as
possible if I were doing it.

That is certainly a valid design choice, but 20-bit 1-MSPS ADCs are
definitely not jellybean parts, nor could the PIC eat the data, let alone
process it fast enough.
 
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