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need some information on transimpedance amplifier

qwert trewq
Intellectual 395 points
Other Parts Discussed in Thread: LMV794

Dear all


The attachment is the design of a photodiode preamplifier.

i used a capacitor to block the DC current from going through the opamp  and i connect a positive voltage bias on the cathode.

i used high gain at first stage of amplifier 


Can I design in this way?

because the application circuit in lmv794 does not have a AC coupling capacitor.


 Thanks in advance.

only preamplifier.pdf

pls tell the circuit design is correct or wrong and suggestion of using capacitor series with photodiode 

  • 0
    TI__Guru* 93105 points

    Hello qwert trewq,

    It appears you plan to use the photodiode in the photoconductive mode. However, you need to have a dc path for the photodiode current to flow. Adding the capacitor blocks the dc current path. It is normal for the dc current to flow into the operational amplifier summing node where it then flows through the feedback resistor to the output stage. The current then flows to the output stage where an output transistor that sinks the to the negative supply. See the following wiki page, figure 2, for more information about the photoconductive transimpedance amplifier connection:

    http://en.wikipedia.org/wiki/Transimpedance_amplifier

    The voltage divider connected to the non-inverting input establishes the operational amplifier's common-mode voltage, about 0.8 V using the selected resistors. The output will sit close to that level when the photodiode is not producing current. However, when light is present and the photodiode produces current that current will cause the operational amplifier's output to move towards the negative supply rail; 0 Vin your circuit. The total output swing will be limited to about 0.8 V. Keep that in mind and make sure that is enough. The divider voltage could be moved more positive to increase the output swing range.

    Regards, Thomas

    PA - Linear Applications Engineering