On the design of RC-active highpass filters using 2-OA GIC

The design philosophy for RC-active highpass filters has not received as much consideration as lowpass and bandpass structures. The highpass filter (HPF) has a reasonable passband behaviour at high frequencies, at least up to 10 times the corner frequency. This is difficult to achieve due to the deteriorating behaviour of the practical operational amplifier (OA). In high order ladder structures, widely used because of their low sensitivity, improving the HPF behaviour is equivalent to designing a high quality grounded inductor at high frequencies. This evolves a procedure for the appropriate design of 2-OA GIC (generalized impedance converter) simulated inductances, suitably compensated for the nonideal aspects of the OA such as finite bandwidth, signal handling capability, output resistance, etc. Experimental results for 0.1 dB 7th order Cauer-Chebyshev highpass filters with corner frequencies at 10 KHz and 30 KHz are presented to evaluate the procedure. The two filters are studied at different signal levels using two types of OAs with gain-bandwidth products of 3 and 4.5 MHz.