QI wanted to know the PSRR of AD8304, but I cannot find it from the datasheet. I
can find this parameter from the differential amplifiers or instrumentation
amplifiers. Why Log detector does not have this parameter? Is it because the
log detector is more complicated than the generic amplifiers and we cannot just
test this parameter or it is not important to log detector?
AWe don’t specify PSRR for any of our log-amps like AD8304, due to the
logarithmic characteristics. We call these log-amps, but they really are
logarithmic converters, which convert the input current into logarithmic scale
on voltage output. Thus the definition of PSRR does not hold well when
characterizing such devices. Alternatively, customers can take a look at TPC 3
on page 4, AD8304 datasheet. It should give you some ideas how different power
supply results in errors on the output over the dynamic range.