Marc, Yuhang

Today we pursued the investigation of this photodiode. Especially, we investigated if there is some offset present that could saturate the mixer used for the demodulation.

First (with high resistors of previous entry) we measured an offset of -1.68V.

Adding a DC block reduces it below 2mV.

Then, we replaced the resistors (low in previous entry) :

We measured an offset with mean value -90mV and also a clear frequency modulation around 180MHz and peak to peak around 148 mV (Fig 1)

Adding a DC block reduced the offset mean value to -2mV but the signal around 160MHz had an increased peak to peak amplitude around 360mV (Fig 2)

As there is a 20dBm amplification after the mixer, this high frequency signal is larger than the 14MHz one (at -10dBm) and is close to saturation of the mixer.

We'll try to compare this result with simulation (performed up to 100 MHz for now)