I have been doing some noise simulations on this design trying to reduce the noise and there is is something I just dont quite understand.
Usually resistor noise goes UP when you increase the resistor value and DOWN when you reduce the resistor value.
But R8 and R5 in my current mirror does something I can not explain.
22R degeneration resistor gives me 12nV/Hz from each of those 2 resistors. Increasing them to 62R gives me 9nV/Hz, further increase to 120R gives 7nV/Hz, 240R gives 5.1nV/Hz, further increases gives slight improvements but amp distortion starts to suffer.
What gives? What am I overlooking?
Usually resistor noise goes UP when you increase the resistor value and DOWN when you reduce the resistor value.
But R8 and R5 in my current mirror does something I can not explain.
22R degeneration resistor gives me 12nV/Hz from each of those 2 resistors. Increasing them to 62R gives me 9nV/Hz, further increase to 120R gives 7nV/Hz, 240R gives 5.1nV/Hz, further increases gives slight improvements but amp distortion starts to suffer.
What gives? What am I overlooking?