A 70 mW 7th-order filter with 7 to 50 MHz cutoff frequency, programmable boost, and group-delay equalization

This continuous time filter is for the read channel of a disk drive using PRML detection. Similar to channels using peak detection, the filter performs two tasks. First it band limits the signal spectrum to about 1/4 of the bit-rate. This rejects high-frequency noise, increasing the signal-to-noise ratio (SNR). Second it equalizes pulse shape to achieve, in conjunction with an adaptive FIR, the target channel response (EPR4). A seventh order phase-equiripple response is used for linear phase response over a wider frequency range than a Bessel response. The filter cutoff frequency is programmable from 7 to 50 MHz for channel rates to 200 Mb/s and a servo information frequency as low as 5 MHz. In addition, both the amount of high frequency boost and the group delay response can be digitally programmed via two 7 b DACs. The boost at cutoff frequency can be changed from 0 to 13 dB while group delay variation from low to high frequency can be varied by /spl plusmn/30%. The filter is implemented in 0.7 /spl mu/m BiCMOS technology.