Is anybody aware of the transimpedance amplifier circuit shown below? I found it in an old textbook but unfortunately without further explanations. R1 and R2 seem to form a non-inverting amp, but I am not sure about the function of R3. And the non-inverting circuit is normally not used with transimpedance amplifiers. Has anybody seem this circuit elsewhere?
Hi Frank,
A similar TIA circuit is shown on "Photodiode Amplifiers" by Jerald Graeme on p.154, where the photodiode is connected across the inputs of the amplifier.
This circuit is useful for high-gain photodiode amplifiers. In the standard transimpedance amplifier (TIA), making the feedback resistance large produces high gain, but using very high resistances often introduces performance limitations, sensitivities to stray capacitances, and a reduction of bandwidth.
This circuit adds voltage gain (1+R2/R1) in a single stage TIA topology while allowing the use a smaller RF resistor. Essentially, in this transimpedance circuit, the current of the photodiode will flow through RF as shown below. The effective transimpedance gain is given by:
RT= RF*(1+R2/R1)
The resistances of R2 and R1 of the feedback network are kept relatively low compared to RF. Connecting the photodiode across the amplifier's input terminals bootstraps the diode, where the voltage across the photodiode is kept near ~0V, where the diode bias voltage does not see the voltage swing RF*Idiode, providing a linear response.
Thank you and Kind Regards,
Luis
Hi Frank,
a disadvantage of this circuit that it can generate considerably more noise:
By the way, exactly spoken the transimpedance is
(1 + R2 / R1) x RF + R2
But the last summand "R2" can be neglected in most cases.
Kai
