i understand we need the output 1k+2.2nf lowpass filter due to the sigma-delta converters. but how important are the input 1k+1nf lowpass filters?
i did see this thread, where frank mentions “rolling off the out-of-band high end a little prior to the ADC can only help”, which makes me think it's not too important.
http://www.spinsemi.com/forum/viewtopic.php?f=2&t=88
i’ve got an inverting opamp buffer before the fv1. so if it’s just to prevent the circuit from amplifying any up high frequency noise on the input, i’m thinking of using a filter in the feedback path of that buffer instead.
and while we're on the topic, i always thought the datasheet values of 1k and 1n resulted in a fairly high frequency lowpass. is there a reason that a slightly larger cap value wasn't recommended? 4.7nf seems like it'd keep the input signal even cleaner (~34kHz cutoff), while still being above the bandwidth of the fv1 when using the 32768Hz crystal.
any advice would be very much appreciated
fv1 input lowpass filter
Moderator: frank
fv1 input lowpass filter
Last edited by smear on Wed Sep 09, 2020 10:33 pm, edited 1 time in total.
Re: fv1 input lowpass filter
i'm dumb and didn't see this bit in the manual "The purpose of this input bypassing is to remove any high frequency noise from the input signals, and to provide a low impedance at very high frequencies."
so i'll take that as assurance enough and just use whichever similar cap values i have lying around
so i'll take that as assurance enough and just use whichever similar cap values i have lying around