High CMRR

142

02:22:17

Two long-tailed pairs with FETs instead of BJTs because I learned how to make long-tailed pairs work with FETs first. 

CMRR = common-mode rejection ratio, meaning the ratio with which it rejects noise which appears equally on both inputs. In this case, there is 1kHz common-mode noise at 2Vp-p, and 2kHz signal at 0.4Vp-p. I think the two long-tailed pairs do a good job!

Keeping the FETs in their linear region seems to be a bit tricky. I think it's enough to make sure the output voltage never drops below the input.

Change all 3 resistors of a FET long-tailed pair to change the amplification. 

I didn't experiment with mis-matched transistors. I suppose it matters, so I guess I'd do this IRL with matched pairs.

published 8 years ago

eekee

8 years ago

Later, I learned that a single long-tailed pair using a constant current sink in place of the common resistor makes the CMRR much higher than these two together.

add comment in editor

EveryCircuit is an easy to use, highly interactive circuit simulator and schematic capture tool. Real-time circuit simulation, interactivity, and dynamic visualization make it a must have application for professionals and academia. EveryCircuit user community has collaboratively created the largest searchable library of circuit designs. EveryCircuit app runs online in popular browsers and on mobile phones and tablets, enabling you to capture design ideas and learn electronics on the go.