I've come up with this simple circuit as an amplifier before an 8bit ADC which receives audio signals. R2 is actually a variable resistor (pot.) of 100k. The circuit also biases the signal to VCC/2 and uses large resistors to set the input impedance is pretty high all over the working audio frequency range. This works well for my application, however I would like to add a single low pass filter stage to this amplifier so I can remove some high freq. content that I would not be able to sample. How to approach this without having to use another op-amp and without changing the characteristics of the circuit in the spectrum I would like to pass?
Electronic – How to add a low pass filter to this non-inverting amplifier circuit
filterlow passnon-invertingoperational-amplifier
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Best Answer
The correct approach is to choose a LPF and sampling frequency such that the maximum signal at fs/2 is less than your ADC resolution. This means you need a brick wall filter at 3x your -3dB BW or 128 x faster sampling rate than your signal -3dB BW for a 20dB decade filter for an 8bit ADC... not 2x faster with a 1st order filter.