Peak detector circuit

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT Before proceeding into a detailed explanation of an illustrative embodiment of the invention, a brief digression to explain the nature of the recording and detection processes and the associated circuit design problems would be appropriate and helpful.
FIG.
1 shows a typical example of a double frequency recording of a 0110100 pattern of data bits and the corresponding waveforms at the recording head during the write operation and at the peak detector input during the read operation.
Line (A) shows the binary bit pattern to be recorded.
The encoded data is fed to the writing head which is driven by the recording current indicated in line (B).
Upon reading the recorded data from the surface of the magnetic medium, a voltage waveform such as that indicated at line (C) is typically obtained at the output of the read head amplifier.
The time scales of the waveforms on lines (B) and (C) are the same (although displaced from each other) and corresponding features are thus presented at the same horizontal position; several dashed vertical lines 12-18 have been drawn between the two waveforms to connect corresponding features thereon, in order to highlight the correspondences.
At the boundaries of the data "cells," where the magnetic flux changes polarity (or direction), the amplitude of the detected voltage is greatest.
This is illustrated, for example, at the points on curve (C) of FIG.
1 indicated by the lines 12 and 14.
Peak detecting will accurately recover the information as to the position of the cell boundaries, and this information is necessary in order to permit the proper recovery of timing information and of the recorded data.
Typical prior art peak detectors are illustrated generally in FIGS.
2A-2D.
The circuit in FIG.
2A uses a simple RC differentiator and a comparator to detect the peak through simple cross-over detection of the derivative of the input signal thereto.
A change of state of the comparator output indicates a peak.
Because of the inherent phase shift of the circuit, however the output of the comparator only approximately indicates the position of the peak of the input signal