I would like to design a device with opamp LM324 operating at roughly >5V. The device has to manipulate a signal on +/2.5V (Vpp:5V, DC balanced).
If I want it to work without a split supply, can I use a 2.5V offset to bias the signal? (I understand that the Vdd of opamp should be at least 7V for fear of saturation).
Furthermore, is the diode necessary? In previous trials I found that when LM324 sinks current, output goes to saturation. Or did I just do something wrong?
ps forget about the pinouts number. I just randomly pick a opamp symbol.
Best Answer
If what happens when the input is open is important, then you can follow the answer from WhatRoughBeast (also see comment below). If not, you can simplify things a bit:
Get rid of D1, R1, R2 Change R3 to 20K and connect to the +5V reference voltage Change R5 to 20K
That will have an output of 0V with an input of -2.5V and +5V with an input of 2.5V.
The difference is the the output voltage with the input disconnected will be about 7.5V vs. 5.0V with WRB's circuit.
If that's important, you can still simplify it a bit:
Get rid of D1, replace R3 with a short and increase R1, R2 to 20K each. Leave R5 and R6 at 10K. This will be equivalent (0V out for -2.5V in, 5V out for 2.5V in, 5V out for input open), but will draw less current from the reference input (and have one fewer component).