Other Parts Discussed in Thread: REF2030, LMP7721
Hi, I'm designing a current sensor for the photodiode.
The sensor input is a maximum of 20fA.
The target gain of the circuit is 260dB and the target bandwidth is 3kHz.
Because the application uses a 3.7V LiPo battery, I used a rail-to-rail OP amp(OPA2353).
I used a trans-impedance amplifier with a gain of 140dB and a three-stage AC coupled voltage amplifier with a gain of 60dB, 40dB, and 20dB
The schematic is shown below.
When I performed a transient simulation, the result showed a very noisy signal.
I changed the last stage gain to 10dB, then the result showed a very clean signal.
Here are my questions.
1. Why did this happen?
2. How can I fix it?
3. Can I replace the voltage amplifier stages with a better circuit design?
4. Can I use a voltage reference (like REF2030) to drive the four operational amplifiers? (The four amplifier need 1.5V bias at + input)