High-speed CMOS continuous-time complex graphic equalizer for magnetic recording

A high-speed continuous-time CMOS analog adaptive equalizer for use in magnetic recording read channels is presented. The equalizer is implemented as the summation of several bandpass filters covering different frequency bands as in a graphic equalizer. The outputs from each filter are weighted by a complex coefficient and summed, which results in a linear combiner structure guaranteed to converge under least mean square (LMS) adaptation. System-level simulations of our “complex graphic equalizer (CGE)” show that its performance is comparable to that of a ten-tap finite impulse response (FIR) equalizer following a fourth-order low-pass filter when tested with two different sequence detectors: EPR4-MLSD and fixed delay tree search with decision feedback (FDTS/DF). A five-band tunable CGE has been fabricated using a 0.8-μm CMOS technology. The highest band of the fabricated CGE was centered at 80 MHz (corresponding to channel data rate of about 200 Msymbols/s). Measured dynamic range was 68 dB, and measured total harmonic distortion was only -75 dB while consuming 97 mW at 3.3 V. The measured CGE performance agreed within 0.2 dB with the simulation results for an FDTS/DF system with an ideal CGE operating at 2.5 user bits/PW50