Re: Low drift OP amp for photodiode circuit

Phil Hobbs wrote:

It's worse than that though--don't forget the big noise peak caused by
the input capacitance and the amplifier's input noise--with a 500G
resistor and a 3 pF input capacitance, the noise starts to rise linearly
at 1 Hz!

Yeah, that's a problem. Then there's the e_n/I_leak tradeoff with JFET
inputs. I haven't looked into CMOS amps in the past 10 years; have they
improved significantly noise-wise?

If you use a capacitor across Rf to
reduce the bandwidth to the same value you'd get by charge dispensing,
you basically wind up with an integrator with a continuous resistive
reset as opposed to a switched one.

I wonder if the switched-integrator method could be beneficial in an
all-analog signal chain; i.e., if the sawtooth output could be
differentiated back into a voltage so that the overall noise/bandwidth
performance would be superior to what could be practically achieved with a
transimpedance amp.

robert
.

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