Communication system interface circuit

• US 4,010,327 A
• Filed: 05/11/1976
• Issued: 03/01/1977
• Est. Priority Date: 05/11/1976
• Status: Expired due to Term

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Kobrinetz, Anthony
• Primary Examiner(s): Cooper, William C.
• Assistant Examiner(s): Brigance, Gerald L.
• Application Number:
  US05/685,223
• Time in Patent Office: 294 Days
• Field of Search: 179/41 A, 179/2.5 B, 179/170 D, 325/53, 325/54, 325/304, 325/67, 333/4, 333/5, 333/11, 333/25
• US Class Current: 455/561
• CPC Class Codes: H04B 7/022 Site diversity; Macro-diversity using two or more spaced independent antennas H04B7/04

Abstract

A communication system includes a mobile station, a plurality of base stations and a central terminal. Each base station converts RF signals from the mobile station to AF signals. The AF signals are carried over a balanced line to the central terminal. Each base station generates a DC voltage signal whose level is representative of the level of its received RF signal. The central terminal includes means to monitor DC current levels, from each base station, on the balanced line and select that base station producing the highest DC current.

The unique interface circuit senses the base station generated DC voltage, which is referenced to a fixed ground potential, and produces a corresponding current which is referenced to a floating ground potential. This current is then coupled to the balanced line for transmission to the central terminal. The interface circuitry includes a DC to AC converter which converts the DC signal voltage to an AC signal. This AC signal is capacitively coupled to an AC to DC converter which generates a corresponding DC voltage. The final stage is a transconductance circuit which produces an output current presenting the DC voltage level generated by the AC to DC converter. In this manner, a ground referenced voltage is transformed to a floating ground reference current suitable for transmission down a balanced line.

Claims

1. In a communication system having first and second stations, the first station generating a DC signal voltage referenced to a ground potential, the two stations being intercoupled by a balanced line which is isolated from the ground potential, the improvement comprising:

Dc-to-AC converter means for converting said DC signal voltage to a corresponding AC signal voltage;

Ac-to-DC converter means for converting AC signals, at its input, to corresponding DC signals, at its output;

Ac coupling means for AC coupling, but DC blocking, the AC signal voltage, from the DC-to-AC converter, to the input of the AC-to-DC converter; and

line coupling means for coupling the output of the AC-to-DC converter to the balanced line for transmission to the second station thereon.

2. The improvement of claim 1 wherein the DC-to-AC converter means comprises an astable multivibrator whose peak-to-peak output voltage is representative of the level of the DC signal voltage.

3. The improvement of claim 1 wherein the AC-to-DC converter comprises means for producing an output DC voltage whose magnitude is related to the peak-to-peak value of signals at its input.

4. The improvement of claim 2 wherein the AC-to-DC converting comprises means for producing an output DC voltage whose magnitude is related to the peak-to-peak value of signals at its input.

5. The improvement of claim 1 wherein the AC coupling means comprises a capacitor series connected from the DC-to-AC converter to the input of the AC-to-DC converter.

6. The improvement of claim 4 wherein the AC coupling means comprises a capacitor series connected from the DC-to-AC converter to the input of the AC-to-DC converter.

7. The improvement of claim 1 wherein the line coupling means comprises:

a transconductance circuit for converting the voltage output from the AC-to-DC converter to a corresponding current, which current originates from a source having a high impedance; and

means for coupling said current to the balanced line for transmission, to the second station, thereon.

8. The improvement of claim 6 wherein the line coupling means comprises:

a transconductance circuit for converting the voltage output from the AC-to-DC converter to a corresponding current, which current originates from a source having a high impedance; and

means for coupling said current to the balanced line for transmission, to the second station, thereon.

9. In a communication system having a mobile station, a plurality of base stations, and a central terminal, wherein each base station converts an RF transmission from a mobile station to an audio signal which is coupled via a two lead balanced line to the central terminal, and wherein each base station generates a DC signal voltage, referenced to a ground potential, representative of the magnitude of its received RF signal, an interface means for coupling the base station audio signal and the DC signal voltage to the balanced line for transmission to the central station comprising:

a transformer having a primary winding and first and second secondary windings, each secondary winding having first and second terminals;

a power supply means for producing a DC bias voltage referenced to a floating reference potential;

means for coupling the audio signal to the transformer primary for AC coupling the audio signal to each transformer secondary winding;

Dc-to-AC converter means for converting said DC signal voltage to a corresponding AC voltage;

Ac-to-DC converter means for converting AC signals, at its input, to corresponding DC signals, referenced to the floating reference potential, at its output,

Ac coupling means for AC coupling, but DC blocking, the AC signal voltage, from the DC-to-AC converter, to the input of the AC-to-DC converter;

a transconductance circuit for converting the DC signal output from the AC-to-DC converter to a corresponding current, which current is generated by a source having a high impedance;

means for connecting the DC bias from the power supply means to the second terminal of the first secondary winding;

means for connecting one lead of the balanced line to the first terminal of the first secondary winding, and for connecting the remaining lead of the balanced line to the second terminal of the second secondary winding; and

means for connecting the transconductance circuit to the first terminal of the second secondary winding,

whereby a current path is created from the power supply means through the first secondary winding, the central terminal, the second secondary winding and to the transconductance circuit for conduction of said transconductance current.

10. The interface means of claim 9 wherein the DC-to-AC converter means comprises an astable multivibrator whose peak-to-peak output voltage is representative of the level of the DC signal voltage.

11. The interface means of claim 9 wherein the AC-to-DC converter comprises means for producing an output DC voltage whose magnitude is related to the peak-to-peak value of signals at its input.

12. The interface means of claim 10 wherein the AC-to-DC converter comprises means for producing an output DC voltage whose magnitude is related to the peak-to-peak value of signals at its input.

13. The interface means of claim 9 wherein the AC coupling means comprises a capacitor series connected from the DC-to-AC converter to the input of the AC-to-DC converter.

14. The interface means of claim 12 wherein the AC coupling means comprises a capacitor series connected from the DC-to-AC converter to the input of the AC-to-DC converter.

15. The interface means of claim 9 further comprising a means for capacitively coupling the second terminal of the first secondary to the first terminal of the second secondary.