[SOLVED] Calculating noise for a sensing circuit

[blackdeath320]

Hey guys,

I was hoping someone could help me out with the noise analysis for a circuit. Basically the I'm using behavioural models to modulate a 2000Hz signal with a 90kHz carrier and the noise voltages at 90k for High power and low power amps 32.74nV and 68nV respectively from the simulations shown below. The first opamp is just used as a non-inverting amplifier and the second one is being used to demodulate the signal. Three more low power opamps form the anti-aliasing filter.
HP: https://i.imgur.com/pJBMQ.jpg
LP: https://i.imgur.com/QbTUN.jpg

Any help would be appreciated.

Regards

 

[FvM]

In a rough estimation the input amplifier will be the dominant source due to the involved gain. The input signal is demodulated with a square wave, so noise at the odd harmonics of the carrier also contribute to total noise. A noise optimal system woul place a low-pass before the demodulator that supresses signal components at the carrier harmonics.