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NRZI Detection Using Multiple Conditions for Bit Gating

IP.com Disclosure Number: IPCOM000076103D
Original Publication Date: 1972-Jan-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 41K

Publishing Venue

IBM

Related People

Coburn, RL: AUTHOR [+3]

Abstract

Shown in Fig. 1 is a nonreturn to zero (NRZI) data detection apparatus which will identify a 1-bit from NRZI code only if (1) the amplitude of the original data is above a predetermined threshold, (2) the peak detector has an output, and (3) the time separation between detected peaks is at least a predetermined interval.

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NRZI Detection Using Multiple Conditions for Bit Gating

Shown in Fig. 1 is a nonreturn to zero (NRZI) data detection apparatus which will identify a 1-bit from NRZI code only if (1) the amplitude of the original data is above a predetermined threshold, (2) the peak detector has an output, and (3) the time separation between detected peaks is at least a predetermined interval.

In Fig. 1, the NRZI signal is read by the read head 10 and amplified by amplifier 12. The amplified signal is passed through low-pass filter 14 and, thereafter, branches to a differentiator 16 and a threshold detector 18. The threshold detector monitors the read signal to determine when the signal exceeds a predetermined threshold, either above or below zero or no-signal level. Differentiator 16 in combination with amplifier limiter 20 operate to perform the peak detection function, whereby the output of the amplifier limiter 20 will be a binary waveform having a transition for each peak, positive or negative-going, in the data waveform.

Transition pulser 22 and delay 24 cooperate to provide the condition that the time between transitions in the peak detected waveform must be greater than a predetermined interval before there will be an output signal from the apparatus. The combination of all conditions is achieved by the AND gates 26 and 28 along with OR gate 30.

The operation of the apparatus in Fig. 1 may be better understood by reference to the waveforms in Fig. 2. The waveforms are identified by alphabetic characters. The same alphabetic characters indicate where the waveforms of Fig. 2 exist in Fig. 1.

Signal A-A' is the data signal picked up by the read head 10. Signal B is the output of the threshold detector 18. The predetermined threshold of the detector is shown in dashed lines about signal A-A'. Thus, the signal B indicates when the data signal is above the predetermined threshold and is one of the conditions applied to AND gates 26 and 28. The output of differentiator 16 is waveform C-C', which is further acted upon by the amplifier limiter 20 to produc...