N
Nemo
- Jan 1, 1970
- 0
I'm embarrassed to ask this but -
I have a high gain (transconductance) amp with a photodiode, biased to
be a few hundred pF, on its input. I was tweaking it to optimise the
noise levels and found the noise of the amp was way less than the noise
of (the amp with the diode on the front). So I replaced the diode with a
simple capacitor... and I still get extra noise when I fit it. It does
not appear to be noise from the bias supply; the capacitance can be to
ground and I still see the extra noise appearing.
The texts I've read say there's noise generated by Cin, and it certainly
seems like there is. I can understand it acts as a potential divider on
the amp's gain and attenuates high frequency signals. What I don't get
is why it generates noise without a signal present? What is the physical
mechanism which creates this noise?
I have a high gain (transconductance) amp with a photodiode, biased to
be a few hundred pF, on its input. I was tweaking it to optimise the
noise levels and found the noise of the amp was way less than the noise
of (the amp with the diode on the front). So I replaced the diode with a
simple capacitor... and I still get extra noise when I fit it. It does
not appear to be noise from the bias supply; the capacitance can be to
ground and I still see the extra noise appearing.
The texts I've read say there's noise generated by Cin, and it certainly
seems like there is. I can understand it acts as a potential divider on
the amp's gain and attenuates high frequency signals. What I don't get
is why it generates noise without a signal present? What is the physical
mechanism which creates this noise?