An asynchronous fully digital channel for magnetic recording

The asynchronous sampling, digital detection (ASDD) channel samples the analog waveform slightly above the timing frequency, with arbitrary phase. Both timing and detection functions are digital, unlike other hybrid channels with digital detection and analog timing. Software channels were written for both sampling detection and peak sensing, but the latter only was implemented in hardware. The digital peak sensing implementation requires second order differencing and nonlinear interpolation only when the sampling rate is below 1.25 times the clock rate, for an equalized (1-7) waveform. The timing function is a unique digital algorithm, analogous to a Type 2 PLO. The channel was implemented on a CMOS chip. Maximum sampling frequency is 90 MHz, power dissipation about 1 watt.