Digital Demodulator for Quad-Burst Position Error Signal
Original Publication Date: 1989-Feb-01
Included in the Prior Art Database: 2005-Jan-27
In conventional disk files which use a quad-burst position error signal (PES), the analog PES from the servo head is demodulated by analog techniques. This article describes a technique which digitizes the PES before demodulation and replaces the analog demodulation hardware with digital hardware. The invention is a direct digital demodulator for quad-burst PES encodement. As shown in Fig. 1, it uses a high-speed flash analog-to-digital conversion (ADC) to convert the filtered high-level modulated signal to numeric data. This numeric data is then multiplied by the clocking signal (+1 or -1) and by the gating signal to compute the area under the waveform of the signal. The numeric result is the PES Primary (P), Quad (Q), and AGC feedback control. A typical PES from the servo head is approximately 3 MHz.