- Joined Jan 23, 2018
K.I.SS. is totally correct about the input return current connection being a potential issue. I can tell you that it can be a very real issue as an input without any ground reference will drift around until one input reaches saturation So rather than a direct ground, a 1Megohm resistor from each input side to the analog ground buss should solve your problems completely.A couple of comments:
1. You always need a place for Ib to go
2. Vref most of the time has to be supplied by a low Z source
3. Vref is many times Vcc/2; Note Vcc/2 is not 2.5 V if the supply is 5V. This is called a ratiometric measurement.
If Vref was 2.5V then that's an absolute measurement.
4. Sensors, especially Automotive use the Vcc/2. The sensors can't output 0V, nor can output the supply voltage. They get close.
5. OP amps may blow up if the input current is higher that allowed. When the supply is 0V, you effectively are operating into max of +-0.3V diode that needs to be current limited. This depends on the OP amp. Analog Devices/Linear Technology has some "Over the Top" op amps which allow the inputs to exceed the supply.
6. The output of an IA direclty into another OP-amp without a resistor will cause you undue grief, if you don;t know what's going on.
7. Bypass caps are often neglected. Use manufacturer's recommendation.