Different Resistor Values in RC Filters

Experimenting with different resistor value combinations in an RC bandpass filter network. Having high resistance values for the filter has the benefit of reducing signal drop from the input impedance (10K here) as it forms a voltage divider with the filter. Having a high value resistor at the start and low value at the end of the filter network seems to have a huge negative impact and flatten everything out. All these individual RC combinations have a cutoff frequency of 1.6kHz but having a low value resistor at the front of the filter seems to decrease the effective target frequency. I also have a current source at the top that controls transistors in each of the example circuits. This is because I was messing around with IR photo transistors at the time and wanted to filter the output from some pulsing light source. Increasing the current source at the top creates a negative offset in all the signals and at just 10uA the signals become visibly distorted and different from a pure sine wave because of the transistors entering saturation.

published 4 years ago