Method and apparatus for implementing carrierless amplitude/phase encoding in a network

• US 5,812,594 A
• Filed: 10/14/1994
• Issued: 09/22/1998
• Est. Priority Date: 10/14/1994
• Status: Expired due to Fees

• Current Assignee: Selim Rakib
• Original Assignee: Selim Rakib
• Inventors: Rakib, Selim
• Primary Examiner(s): Bocure, Tesfaldet
• Application Number:
  US08/324,171
• Time in Patent Office: 1,439 Days
• Field of Search: 375/219, 375/222, 375/261, 375/298, 375/316, 375/295, 375/340, 375/345, 375/371, 375/376, 375/369, 375/231, 375/355, 375/358, 375/208, 375/205, 370/84, 370/85.3, 370/110.1, 370/110.4, 370/85.11, 370/286, 370/289, 330/154, 455/232.1, 455/234.1, 327/54, 379/410
• US Class Current: 375/219
• CPC Class Codes: H04L 25/4921 using quadrature encoding, e.g. carrierless amplitude-phase coding
• CPC Class Codes: H04L 27/34 Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
• CPC Class Codes: H04L 27/38 Demodulator circuits; Receiver circuits

Abstract

A method and apparatus for (1) transmitting large amounts of data between a least a first and second station over a single twisted pair, (2) reducing cross talk in a network using carrierless amplitude modulation and phase modulation encoding (CAP) with independent data clock source at each station, (3) providing a relatively simple and fast data detection apparatus, (4) maintaining synchronization between stations during idle periods while minimizing cross talk, (5) providing a technique to allow filters to be trained during idle periods, and (6) providing a technique which allows automatic gain control to be used with CAP. Particular signalling symbols are associated with each of the following conditions: (1) idle state, (2) preamble, (3) start of frame detection, (4) test condition, (5) each possible combination of five binary bits representing 32 different data symbols, and (6) jam condition. For example, a unique pair of the four inner most points on the CAP 36 constellation are used for indicating idle mode. All four inner most points are used for testing the link and training the filters in the receiver.

Claims

1. A transceiver for communicating data over a single twisted pair of metal conductors, including:

(a) an encoder for encoding information using carrierless amplitude and phase (CAP) such that the amplitude of an in-phase component at a carrier frequency in combination with the amplitude of a quadrature component at the carrier frequency defines a unique point within a CAP constellation; and

(b) a summing circuit, coupled to the encoder, for combining the inphase and quadrature components;

wherein the encoder generates a sequence of alternating first and second preamble symbols, each preamble symbol being in opposite quadrants of the CAP constellation;

wherein the encoder generates a start of frame detect symbol encoded to have in-phase and quadrature components with the amplitude of each component being in a range which defines a third and fourth CAP constellation point, the range of the third and fourth CAP constellation points including the maximum amplitude for both the in-phase and quadrature components, the start of frame detect symbol being generated in response to receipt in the encoder of a first bit of data.

2. The transceiver of claim 1, wherein the encoder selects the start of frame detect symbol to be encoded to have in-phase and quadrature components in the range of the third or the fourth CAP constellation symbol, depending upon whether the first bit of data received in encoder is a "1" or a "0".

3. A transceiver for communicating data over a single twisted pair of metal conductors:

(a) including an encoder for encoding information using carrierless amplitude and phase (CAP) such that the amplitude of an in-phase component in combination with the amplitude of a quadrature component defines a unique point within a CAP constellation; and

(b) a summing circuit, coupled to the encoder, for combining the inphase and quadrature components;

wherein the encoder generates a first JAM symbol which lies at an innermost point of a first quadrant of the CAP constellation and a second JAM symbol which lies at an outermost point of the CAP constellation within the first quadrant of the CAP constellation.

4. A transceiver for communicating data over a single twisted pair of metal conductors, including a receiver including a clock recovery circuit for generating a receive clock, including:

(a) a frequency controllable oscillator;

(b) a symbol detector, coupled to the frequency controllable oscillator, for generating a phase error signal which is derived from the difference between the amplitude of the in-phase and quadrature components of an ideal input signal and the amplitude of the in-phase and quadrature components of an actual received signal;

wherein the phase error output from the symbol detector controls the output of the frequency controllable oscillator, such that the output of the frequency controllable oscillator is phase corrected to the symbols received.

5. A transceiver for communicating data over a single twisted pair of metal conductor, including a receiver including a clock recovery circuit for generating a receive clock, including:

(a) a frequency controllable oscillator;

(b) a symbol detector, coupled to the frequency controllable oscillator, for generating a phase error signal which is derived from the difference between the amplitude of the in-phase and quadrature components of an ideal input signal and the amplitude of the in-phase and quadrature components of an actual received signal;

wherein the phase error output from the symbol detector controls the output of the frequency controllable oscillator, such that the output of the frequency controllable oscillator is phase corrected to the symbols received;

wherein the clock recovery circuit further includes;

a phase detector configured to be coupled to a reference signal;

a mode switch coupled to the output of the phase detector, the output of symbol detector, and the input of the frequency controllable oscillator, for selectively coupling either the phase detector or the symbol detector to the frequency controllable oscillator, the mode switch being responsive to the magnitude of the phase error signal generated by the symbol detector;

wherein the mode switch couples the phase detector to the frequency controllable oscillator when the phase error signal generated by the symbol detector is greater than a predetermined value and otherwise couples the symbol detector to the frequency controllable oscillator.

6. A transceiver for communicating data over a single twisted pair of metal conductors, including an automatic gain control device, operational in at least one of two modes, for adjusting gain applied to received signals, including:

(a) a variable gain amplifier for receiving, and applying gain to, received signals, and

(b) an automatic gain control circuit having at least two modes of operation, coupled to the variable gain amplifier, for controlling the gain applied to the received signals based upon the average peak amplitude of the received signals, such that more gain is applied to signals having relatively lower average peak amplitude than is applied to signals having relatively higher average peak amplitude;

wherein the automatic gain control circuit causes the variable gain amplifier to apply less gain to input signals of a particular average peak amplitude level when the automatic gain control device is operating in a first mode of operation, than is applied to input signals of the same average peak amplitude level when the automatic gain control circuit is operating in a second mode of operation.

7. A transceiver for communicating data over a single twisted pair of metal conductors, including an automatic gain control device, operational in at least one of two modes, for adjusting gain applied to received signals, including:

(a) a variable gain amplifier for receiving, and applying gain to, received signals, and

(b) an automatic gain control circuit having at least two modes of operation, coupled to the variable gain amplifier, for controlling the gain applied to the received signals based upon the average peak amplitude of the received signals, such that more gain is applied to signals having relatively lower average peak amplitude than is applied to signals having relatively higher average peak amplitude;

wherein the automatic gain control circuit causes the variable gain amplifier to apply less gain to input signals of a particular average peak amplitude level when the automatic gain control device is operating in a first mode of operation, than is applied to input signals of the same average peak amplitude level when the automatic gain control circuit is operating in a second mode of operation; and

wherein the first mode of operation is a non-data mode, and the second mode of operation is a data mode.

8. A transceiver for communicating data over a single twisted pair of metal conductors, including an automatic gain control device, operational in at least one of two modes, for adjusting gain applied to received data signals representing frames of data, including:

(a) a variable gain amplifier for receiving, and applying gain to, received signals;

(b) a peak detector, coupled to the output of the variable gain amplifier, for;

(1) detecting the peak value at the output of the variable gain amplifier, storing the detected peak value, allowing the stored peak value to decay at a predetermined rate, and reducing the stored value by an amount proportional to the difference between the stored value and the next peak value when a next peak value is less than the stored value, and replacing the stored value with the next peak value if the next peak value is greater than the stored value, when the automatic gain control device is in the first mode of operation;

(2) detecting and storing the first peak value output by the variable gain amplifier at the start of a frame of data, storing in place of the stored peak value, each next detected peak value output by the variable gain amplifier if the next peak value is greater than the stored peak value.