Voltage Controlled Butterworth Hi-Pass Filter using a Transconductance Op Amp?
You can use filters subtractively....

Take your original signal and produce the low pass output version using the circuit in your question. Then, take your original signal and subtract the low pass output from it. What you are left with (as a new signal) is the high pass version.

So what you get is two outputs; one is low-pass with a cut-off frequency at (say) 1kHz and the other is a high pass with cut-off frequency also locked-in to 1kHz - if you lower the cut-off frequency of the LP filter then the HP also lowers its cut-off.







simulate this circuit &ndash; Schematic created using CircuitLab