Hello NG I'd like to amplify the signal of a photodiode to read it with a ad- converter.
Signal photodiode: 0-50mV Voltage range adc: 0-5V
I tried to use two types of amplyfiers, AD623 and INA126u. But in the tests some very strange clipping happened. (See below.) I think there's something basic about single supply amplifiers which I understand wrong.
Could you please tell me where the mistake is with my wiring or make a better proposal. If possible I want to use one of these amplifiers since they are lying right on my desk...
Thank you
Test1 with AD623 Pin1 -RG is connected to Pin8 +RG by a 1kOhm resistor (Gain = 100) Pin2 -IN is connected to GND Pin4 -VS is connected to GND Pin5 REF is connected to GND Pin7 +VS in connected to +5V or +10V (The result doesn't depend on this. - Capacitors to GND are applied...)
Test results: Pin3 +IN Pin6 OUT
0mV 0V
10mV 1V
20mV 1.2V
30mV 1.3V
40mV 1.5V
50mV 1.7V
Test2 with INA127u Pin1 RG is NC (Gain = 5 for testing purpous) Pin2 V-IN is connected to GND Pin4 V- is connected to GND Pin5 REF is connected to GND Pin7 V+ in connected to +5V Pin8 RG is NC
Test results: Pin3 V+IN Pin6 VO
0V 3.6V
1V 3.6V
2V 3.6V
3V 3.6V
3.6V 3.6V
3.7V 4.1V
3.8V 4.6V
3.9V 4.6V