Pierre and Yuhang

To investigate if SNR can be improved by an improved photo detector design, we conducted TAMA resonant PD simulation by using two simulation tools. One is a python code called 'zeros', the other is a Texas Instrument software 'TINA'.

The configuration is based on the scheme in this link. In the real case, we have modified this scheme, which results in two cases. One case is using the same op-amp with R1 10Ohm and R2 100Ohm. The other case is using op-amp LMH6624 with R1 1kOhm and R2 10kOhm.

To measure PD noise, we used a 32dB amplifier to make sure the PD noise is well above the instrument noise. The use of this amplifier has been considered also in the simulation software. In the first attached figure, there are electronic noise measurement and simulation results. We could see that python code simulates well the floor noise. However, the noise around 14MHz is better simulated by TINA.

We anticipated a signal of 0.11uA from CCFC field. To compare signal and noise, we divided the voltage noise from figure one by the PD gain. Then we get the current input noise as the attached figure 2. This DC value of signal is much higher than the noise level at 14MHz. From the python simulation, LMH6624 has better performance. However, simulation of TINA tells us that AD8057 has better performance.

To compare, we put here also a measurement of PD noise budget (figure 3). From this noise budget, TINA simulation is closer with the real measurement.

Figure 4 and 5 show the SNR of different PD configurations with TINA simulation