Active Filters: High Pass

Active 2nd Order Filters:

Basic Introduction to Filters: application notes on active, passive and switched capacitor filters, document in PDF format

Butterworth Filters:

Chebyshe Volt / Butterworth Filters:

Chebyshe Volt Bandpass Filter:

Highpass Filters use Modified Equalelement Design: 05/24/01 EDN-Design Ideas / PDF contains multiple circuits - scroll to find this circuit.