Switched-capacitor IC forms notch filter

摘要

You can use a switched-capacitor lowpass filter (LPF) to implement an inexpensive notch filter . The internal architecture of the IC includes summing nodes similar to those nodes that analog-signal-processing stages use for feedback-errorgeneration. The IC lowpass-filters the quantity V{sub}(IN) V{sub}(COM) and adds V{sub}(OS) at the output. In other words, V{sub{(OUT) = (V{sub}(IN) -V{sub}(COM)){sub}(LPF) +V{sub}(OS), where V{sub}(COM) typically equals V{sub}(DD)/2. Thus, the IC addscommon-mode voltage (COM) at the input, and an internal resistor divider biases this voltage at midsupply. For applications that require offset adjustment or dc-level-shifting, the IC adds an external bias voltage (OS) at the output.