I was having a little difficulty debugging a diff amp today thought maybe the forum could help.
I have a textbook diff amp with a gain of 7, based on an LM324D, configured as shown in the drawing.
The supplies are set to +12 and ground.
The input is a sense resistor that's carrying between 0 and 20 amps, or between 0 and 20 mV across it's terminals.
For debugging, I left out the source resistor, and connected the input voltages to a function generator set to 1kHz sine wave, 40 mVpp, and 20mV DC offset.
I wasn't able to get a scaled version of the input at the output of the diff amp. I just got some strange noisy signal.
I tried using a larger input signal, but this did not solve the issue. The datasheet for the TI lm324d says "Common-Mode Input Voltage Range
Includes Ground, Allowing Direct Sensing Near Ground."
The remaining opamps in the quad pack are used in following stages, or have their inputs properly terminated.
Any debugging ideas would be greatly appreciated!
Thanks
m121212
I have a textbook diff amp with a gain of 7, based on an LM324D, configured as shown in the drawing.
The supplies are set to +12 and ground.
The input is a sense resistor that's carrying between 0 and 20 amps, or between 0 and 20 mV across it's terminals.
For debugging, I left out the source resistor, and connected the input voltages to a function generator set to 1kHz sine wave, 40 mVpp, and 20mV DC offset.
I wasn't able to get a scaled version of the input at the output of the diff amp. I just got some strange noisy signal.
I tried using a larger input signal, but this did not solve the issue. The datasheet for the TI lm324d says "Common-Mode Input Voltage Range
Includes Ground, Allowing Direct Sensing Near Ground."
The remaining opamps in the quad pack are used in following stages, or have their inputs properly terminated.
Any debugging ideas would be greatly appreciated!
Thanks
m121212
Attachments
-
4.2 KB Views: 50