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Degating Noise from NRZI Data

IP.com Disclosure Number: IPCOM000076104D
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

Fiorino, BC: AUTHOR

Abstract

Shown in block diagram, is a detection circuit for degating noise from NRZI (nonreturn to zero) data by using the noise itself to perform the degating function.

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Degating Noise from NRZI Data

Shown in block diagram, is a detection circuit for degating noise from NRZI (nonreturn to zero) data by using the noise itself to perform the degating function.

In Fig. 1, both the positive and negative phases of the NRZI data are applied to low-pass filter 10 and high-pass filter 12. The output of the filters are summed by summing network 14 and applied to amplifier/ rectifier circuit 16. The output of circuit 16 is essentially a voltage level; however, the response of circuit 16 is rapid enough that this voltage level will track the variations in the amplitude of the signals of interest.

The voltage level out of rectifier circuit 16 is compared by voltage comparator 17 against the amplitude of the positive and negative phases of the NRZI waveform. The output of the comparator 17 is a plus-phase gate or a negative- phase gate, depending upon whether the plus phase of the NRZI or the negative phase of the NRZI exceed the threshold from the circuit 16, respectively. The plus-phase gate and negative-phase gate are used to gate transitions through one's gate 18 -- transitions in NRZI code representing binary 1.

The output of the amplifier limiter 20 is the NRZI data waveform, both positive and negative phases. The waveform is squared up by the amplifier limiter 20. In order that the transitions in the NRZI waveform from amplifier limiter 20 be positioned at the center of the positive or negative-phase gate signals, the positive and negative NRZI signal into amplifier limiter 20 is shifted 90 degrees by the high-pass filter 12. This is due to the fact that the high-pass filter is a differentiating circuit and causes a 90 degrees phase shift in the frequency components of the NRZI waveform. Thus, the one's gate 18 will have an output one pulse, whenever there is a plus-gate signal an...