Other Parts Discussed in Thread: LM7171, , LMH6622, OPA838
Hi
I have designed a TIA with a gain of 500k at a frequency of 451Khz using OPA657. I have connected a voltage amplifier stage using LM7171 to further increase a gain of 10. I wanted to analyze the noise power spectral density of the whole circuit. But my TINA simulation power spectral density and the results obtained through PCB are not matched. In my simulation the power spectral density increases upto 731Khz and after that it begins to fall. But for my PCB when I took my data using an oscilloscope I found the power spectral density increases only upto 200KHz after that it begins to fall. I have decreased my feedback resistor from 500k to 100k of TIA but the power spectral density in the PCB is still the same.
I have used Judson Photo diode having 1.2nV terminal capacitance. I have taken my PCB observation by placing the photo diode in a closed box where no light falls on it.
Please help me to solve this problem.
I have attached my Tina file and measured results that I have processed in Excel.