Browse Prior Art Database

Excessive Phase Shift Detection

IP.com Disclosure Number: IPCOM000075789D
Original Publication Date: 1971-Nov-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Fiorino, BC: AUTHOR [+2]

Abstract

Phase-encoded readback signals in hard-limited form are supplied to VFGC at 1. VFGC is built in accordance with U. S. Patent 3,401,346. VFGC generates a GATE signal 2 which is a predetermined portion of the bit period P. The GATE signal is supplied to data gate 10 for gating selected transitions from signal 1 as output DATA signals, all in accordance with the referenced patent. Excessive phase shift, such as at 12, in the direction of the arrow, can cause detection errors.

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Excessive Phase Shift Detection

Phase-encoded readback signals in hard-limited form are supplied to VFGC at 1. VFGC is built in accordance with U. S. Patent 3,401,346. VFGC generates a GATE signal 2 which is a predetermined portion of the bit period P. The GATE signal is supplied to data gate 10 for gating selected transitions from signal 1 as output DATA signals, all in accordance with the referenced patent. Excessive phase shift, such as at 12, in the direction of the arrow, can cause detection errors.

According to this description, such excessive phase shift is detected by circuit
13. Data GATE signal 2 is supplied through bipolar amplifier 14 charging reference capacitor 15 in a constant-current manner. This action generates linear time-representing ramp 3 at the capacitor terminal. During the first portion T of the VFGC gate 2, signal 3 increases positively; during the negative portion, it goes negative. At the end of each bit period, a squelch pulse is supplied over line 16 activating squelch transistor 17 to rapidly discharge capacitor 15. This action resets circuit 13 for verifying proper phase relationships during the next succeeding bit period. However, at 12 because of excessive phase shift, the phase-shifted transition resets VFGC such that portion T becomes a major portion of the cycle; i.e., the clock cycle has now been shortened by excessive phase shift. Upon occurrence of long wavelength 18, circuit 13 causes capacitor 15 to charge negatively belo...