Browse Prior Art Database

Digital Directional Coupling Circuit

IP.com Disclosure Number: IPCOM000086800D
Original Publication Date: 1976-Oct-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 4 page(s) / 95K

Publishing Venue

IBM

Related People

Stuckert, PE: AUTHOR

Abstract

Narrow-band directional couplers have responses of the general form shown by curve A of Fig. 1. Typically, they are linear, bilateral and passive devices which are suitable for use only with modulated digital signals because their response does not extend to DC. They are costly, and they are physically large.

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

Digital Directional Coupling Circuit

Narrow-band directional couplers have responses of the general form shown by curve A of Fig. 1. Typically, they are linear, bilateral and passive devices which are suitable for use only with modulated digital signals because their response does not extend to DC. They are costly, and they are physically large.

A form of broad-band directional-coupling circuit, known in the art, has a response of the general form shown by curve B of Fig. 1. Since the response of this circuit is flat to DC it can be used with conventional (i.e., unmodulated) digital signals and analog signals. Moreover, this circuit substantially overcomes the other disadvantages of narrow-band directional couplers. In digital applications, however, such a circuit has two disadvantages: 1. It requires analog differential amplifiers.

2. It introduces attenuation in the main signal line.

A digital directional coupler will now be described which eliminates disadvantages 1 and 2, above, and which is built entirely with digital circuit components. This circuit takes advantage of the following characteristics of digital signals: 1. Signal Magnitudes are constrained in range and, except for transitions, have two nominal magnitudes. 2. The signal patterns which represent "0" and "1" are constrained to a fixed predetermined temporal format.

Throughout the following, the symbols in Fig. 2a will be used to represent the circuit in Fig. 2b, all of whose parts may or may not be present. In Fig. 2b, (a) the clipper may or may not be present depending on the nature of the logic circuit which is driven by the transmission line, the speed of operation, and whether the delay is active or passive circuitry, (b) the isolator may be a one-legged OR circuit which has a high input impedance relative to the characteristic impedance of the transmission line and a low output impedance, and (c) the delay may be provided by active circuits or by a physical delay line.

Using the symbols described above, the basic digital directional coupler is shown in Fig. 3, wherein: - E and W represent pulse sources which drive and terminate the transmission line which has a characteristic impedance of Z(o). - T(D)* is a physical delay line of characteristic impedance Z(o) whose delay equals the T(D) of Fig. 2.

The blocks marked "A" are logical AND circuits.

Operation of the circuit of Fig. 3 is illustrated in Fig. 4, assuming a bidirectional transmission path wherein each source of signals (E and W) has a minimum pulse repetition period T, a maximum pulse duration T/2, and in which "1" is the presence of a...