A 35 Mb/s mixed-signal decision-feedback equalizer for disk-drive applications

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

“…In a previous mixed-signal DFE implementation, a 10-b Up/Down (U/D) counter followed by a 6-b DAC was used to build each discrete-time integrator, as shown in Figure 3(a) [5]. The integer input is a binary signal with value ±1.…”

“…Currentoutput multipliers form the product of the coefficient c k and the delayed binary data â[n-k]. They are implemented using switched transconductors [5]. The resulting current is converted to a voltage by a transresistance (or i2v) stage.…”

“…Figure 8 shows a schematic of the transresistance stage which precedes the 2-b ADC in the DFE. It is similar to the one used in [5]. The transresistance is set by the two 600 Ohm polysilicon load resistors.…”

“…In this DFE, the ISI cancellation and the adaptive loops are realized with analog circuits. Conventional (or "linear") mixed-signal DFE's and a mixed-signal RAM-DFE have proven the feasibility and efficiency of mixed-signal implementations of DFE detectors [5][6][7]. These DFE's use digital integrators in the adaptive loops.…”

“…This paper describes an adaptive analog DFE for the disk-drive read channel. The key difference in this DFE is that each coefficient is adapted using a mixed-signal integrator that is much smaller than the integrator used in two previous mixed-signal DFEs [5,6].…”