These are the dark noise spectrum that I measured on the 11MHz and 55MHz PD prototypes I modified.
The plots take into account the 50Ohm input impedance of the spectrum analyzer (that is, the nosie is divided by 2).
 
With an estimated transimpedance of about 300Ohm, I would expect to have 2-3nV/rtHz at all frequencies except for the resonant frequencies of each PD. At those resonances I would expect to have ~15nV/rtHz (cfr elog entry 2760).
Problems:
- For the 55MHz PD the resonance peak is too small
- In the 55 MHz: noise is present at about 7MHz
- In the 11MHz PD there's a lot of noise below 10 MHz.
I have to figure out what are the sources of such noises.
Suggestions? |