Photodiode transimpedance amplfier

[santais]

Hi all.

I've been struggling with my Photodiode Transimpedance Amplifier for some time now and was hoping some of you could help me make this a bit more clear.

So far I've tried to measure the output voltage in different light conditions, which gives a reasonable output. Using the -Id * Rf = Vout and calculating a output of 5V (Vmin = GND Vdd = 5V), got me to a resistor of approximately 400 KΩ. When i measure the Vout of my operational amplifier relative to ground, there's basically no output signal. If I measure the voltage across the resistor, I can measure the desired output, which also makes sense.

My question is: When I measure the Vout of the amplifier relative to ground, isn't that my actual amplfication, which is lead further on into the circuit. This output is supposed to be fed into an ADC converter.

OP Amp: LM358N
Rf = 400KΩ
Cf = 5.7p pF

 

[D.A.(Tony)Stewart]

Depends on reference voltage , feedback , input polarity and offset

OA inputs will always be 0V differential in linear mode. So choose a common mode voltage ref. that works with input stage.

Since OTA basic design is inverting , you need a negative supply if not using mid-Vcc bias.

 

[KlausST]

Hi,

pleas show us your circuit.

for your application the voltage across the resistor shouldbe the same as the output voltage ( because OPAMP IN+ sould be 0V)

Sometimes one uses a bias voltage. This voltage is applied to IN+ and causes the diode to be biased with this voltage, because the anode of your photodiode should be connected to 0V also.

But there are many circuits. Pleas show us yours.

Klaus