Current-mode delay equalizer design using multiple output OTAs

Two new current-mode allpass sections based on dual-output OTAs (DO-OTAs) and triple-output OTAs (TO-OTAs) and grounded capacitors are described. Techniques to minimize the equalizer active device count and efficiently simulate grounded resistors are proposed. A fifth-order group delay equalizer based on the presented allpass sections is designed and simulated using multiple-output CMOS OTAs. Numerical optimization is used to determine the equalizer order and parameters. SPICE simulation results are given, demonstrating that the equalizer can effectively compensate the delay characteristic of a fourth-order 4 MHz lowpass Chebyshev filter to less than or equal to 8 ns ripple over 90% of the filter passband.