Browse Prior Art Database

Nr/Nrzi Data Modulation-Demodulation

IP.com Disclosure Number: IPCOM000036788D
Original Publication Date: 1989-Oct-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 4 page(s) / 100K

Publishing Venue

IBM

Related People

Graham, AD: AUTHOR [+5]

Abstract

This article describes a circuit arrangement which provides high performance data transmission over a local area network (LAN).

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 54% of the total text.

Page 1 of 4

Nr/Nrzi Data Modulation-Demodulation

This article describes a circuit arrangement which provides high performance data transmission over a local area network (LAN).

Non-return-to-zero level (NRZ-L) or non-return-to-zero mark (NRZ- M) and non-return-to-zero space (NRZ-S) or non-return-to-zero-inverted (NRZI) encoding and decoding schemes are commonly used in communications to send and to receive data serially from one station to another.

The NRZ is a coding scheme that pertains to a binary signal stream in which a signal parameter, such as current or voltage, represents a logic one by one signal level, and a logic zero by the other level. The NRZ-M is a coding scheme that pertains to a binary signal stream in which a signal parameter, such as current or voltage, undergoes a change in its condition or level every time that a logic one occurs, but when a logic zero occurs, it remains the same, that is, no transition occurs. The NRZI, on the other hand, undergoes a change in

(Image Omitted)

its condition or level every time that a logic zero occurs, but when a logic one occurs, it remains the same, that is, no transition occurs.

The level durations, say, "carrier frequencies", for data that either use the NRZ, the NRZ-M, or the NRZI coding scheme would vary in accordance with the data bit stream.

Using a pulse transformer as an isolation device for a circuit that transmits and receives NRZ, NRZ-M or NRZI coding data across voice-grade twisted pair wires presents a challenge for the designer. First, the impedance of the media, such as voice-grade twisted pairs (telephone wires), can vary based upon the carrier frequencies of the data to be transferred (Fig. 1). Second, the signal level (converted voltage to the reference point or reference ground) from the pulse transformer often varies in accordance with the changes in carrier frequencies of the data to be transferred. Therefore, when NRZ, NRZ- M, or NRZI coding is used in data transmission, for some data bit stream, it often results in greater signal distortion and higher error rate at the receiving end.

To overcome the problems described above, circuitry is disclosed herein which minimizes the signal distortion throughout the data transmission process. Fig. 2 shows the transmit circuit, and Fig. 3 shows the data receive circuit, both in block diagram.

A data-synchronized pulse train, known as transmit clock (TxC), is used in the circuit as the data carrier signal. The NRZI (NRZ) data, say, TxD, is synchronous with the TxC. In other words, the TxD will change the signal levels only at the rising or falling edge of the TxC and not anywhere else.

The TxD and the TxC are put into a mixer logic block that modu

(Image Omitted)

1

Page 2 of 4

lates the TxD into a pulse train. The mixer logic consists...