Of new, please everyone a great god, and the low pass filter circuit is a few order, and the C6 and C7, C20, C21 these four capacitance is what role, thank you

CodePudding user response:

The capacitance of a single can't direct analysis, for the above circuit configuration is Sallen - Key topology, a kind of active filter topology,

CodePudding user response:

The first op-amp follow, op-amp inverting the second, third, four op-amp is 2 order filtering, so should be a fourth order filter
Vout=- I_in * (1 + 2 CRS)/(2 C ^ 2 R ^ 2 s ^ 2 + 4 CRS + 1) * (1 + 2 CRS)/(2 C ^ 2 R ^ 2 s ^ 2 + 4 CRS + 1), where C=0.1 uf, R=820 k
C6 and C7, C20, C21 along with C18, C19 is adjusting the parameters of the filter, the R8, and R9, R10, R11 (820 k) is the same too