Low Noise Pre-amplifier (Frascati)

I have done some measure about low noise pre-amplifier built in Frascati.

I have measured the transfer function



and the Noise (AC coupling) refered to the output of the pre-amplifier.
The Theoretical Gain of this pre-amplifier is 100. The Measured Gain is around 110
and the noise measured at 1kHz is 0.9 nV/sqrt(hz).




After i have measured the noise refered to the output of the pre-amplifier in DC coupling.



In this case the noise is more bigger that noise in ac coupling.

Today i would try measure the noise with a power supply and don't use the batteries.

Very well Maurizio. It seems the new pre amp is working fine (looking at graph 2). If I look at graph 3, I think there is a problem with the measurement, but it is not important. I have a question: what is the DC output of the pre? It should be around zero.

Another question: it seems that the gain is constant at all frequencies, why do you say it is 100 and 110 at 1kHz?

I would not loose to much time on chaging the pre to use a power supply, I would immediately measure the dark noise of PD12595 and, if the measurement is good, imtegrate it in the closed loop measurement setup.

The DC output of the pre-amp is around -1 V.

I have tried to measure the noise of the pre-amp when it is into the lab laser. The data are very strange, in particular the noise is very high...around 10 nV. I dont't report the graphs and tomorrow i will try to measure the noise and in particular to measure the 12595 PD noise.

Today i have had some difficulty into measures and i have observed that the voltage of the batterie is 8 V. I have observed things strange in the spectrum and to the end i have changed the battery with the power supply. The voltage of the battery was 8 V. I think that if the voltage is 8 V the polarization of the JFET change and can change the characteristics of the pre-amp.

I have used the power supply and in the following graph the comparison of the noise of the pre-amp with battery and power supply...so, more o less is the same but the life of the battery is very short.



After i have measured the noise of the PD 12595. I report the graphs V/sqrt(hz) vs Frequency (hz).



Now i would measure the noise of the laser with PD 12595. After to start with measure of loop.

Last thing, The DC output of the pre-amp isn't 0 but is -1 V...For decreasing this value the voltage of the power supply must be increased.