Post History
synopsis Achievable by using a rail-to-rail op-amp. A small bias on the non-inverting input improves the transient response of the op-amp. That’s the second circuit in the O.P. I use such top...
Answer
#2: Post edited
by
Nick Alexeev
·
2024-11-24T01:26:56Z (1 day ago)
added schematic snippet
- <h3>synopsis</h3>
Achievable by using a rail-to-rail op-amp. A small bias on the non-inverting input improves the transient response of the op-amp. That’s the second circuit in the O.P.I use such topology myself for sensing flashing light, as well as steady ambient light.[Schematic snippet forthcoming. It’s on my other computer.]- <h3>rationale</h3>
- An op-amp may have a worse transient response when the output is at the rail. If you bias the non-inverting input to a modest voltage V_bias (0.1 to 0.3 mV) then the output of the TIA will never go below V_bias and never reach the lower rail.
- Such op-amp bias also reverse-biases the photodiode with the same V_bias, as a side effect. What are the consequences of the photodiode reverse bias? The dark current increases, the noise increases, the response time decreases. Check experimentally.
- If the ambient light is relatively stable [if the ambient light is DC] then the transient response may be less of a concern. My suggestion would be to design the circuit with the voltage divider for bias. If bias isn’t wanted, then leave out the upper resistor.
- <h3>synopsis</h3>
- Achievable by using a rail-to-rail op-amp. A small bias on the non-inverting input improves the transient response of the op-amp. That’s the second circuit in the O.P. I use such topology myself for sensing flashing light, as well as steady ambient light.
- 
- <h3>rationale</h3>
- An op-amp may have a worse transient response when the output is at the rail. If you bias the non-inverting input to a modest voltage V_bias (0.1 to 0.3 mV) then the output of the TIA will never go below V_bias and never reach the lower rail.
- Such op-amp bias also reverse-biases the photodiode with the same V_bias, as a side effect. What are the consequences of the photodiode reverse bias? The dark current increases, the noise increases, the response time decreases. Check experimentally.
- If the ambient light is relatively stable [if the ambient light is DC] then the transient response may be less of a concern. My suggestion would be to design the circuit with the voltage divider for bias. If bias isn’t wanted, then leave out the upper resistor.
#1: Initial revision
by
Nick Alexeev
·
2024-11-23T18:58:13Z (1 day ago)
<h3>synopsis</h3> Achievable by using a rail-to-rail op-amp. A small bias on the non-inverting input improves the transient response of the op-amp. That’s the second circuit in the O.P.  I use such topology myself for sensing flashing light, as well as steady ambient light. [Schematic snippet forthcoming. It’s on my other computer.] <h3>rationale</h3> An op-amp may have a worse transient response when the output is at the rail. If you bias the non-inverting input to a modest voltage V_bias (0.1 to 0.3 mV) then the output of the TIA will never go below V_bias and never reach the lower rail. Such op-amp bias also reverse-biases the photodiode with the same V_bias, as a side effect. What are the consequences of the photodiode reverse bias? The dark current increases, the noise increases, the response time decreases. Check experimentally. If the ambient light is relatively stable [if the ambient light is DC] then the transient response may be less of a concern. My suggestion would be to design the circuit with the voltage divider for bias. If bias isn’t wanted, then leave out the upper resistor.