An analog DFE for disk drives using a mixed-signal integrator

Intersymbol interference (ISI) limits the density in modern disk-drive systems. A forward equalizer (FE) used in conjunction with a decision-feedback equalizer (DFE) can effectively remove ISI. The functional blocks shown are: a low-noise preamp and automatic gain control (AGC), band-limiting low-pass filter (LPF), timing recovery, FE and DFE. The FE removes precursor ISI. The remaining postcursor ISI is removed by the DFE. Assuming the past decisions are correct, the DFE cancels ISI without noise enhancement. This paper describes an analog DFE. Area and power are saved by using analog rather a digital equalizers because a 6-b high-speed ADC is not required and a small analog FE can be used instead of a digital FE. The key component to realizing the analog DFE in a small area is a mixed-signal integrator.