Multiplex communications – Phantom
Reexamination Certificate
2000-05-11
2002-11-19
Ton, Dang (Department: 2661)
Multiplex communications
Phantom
C375S258000
Reexamination Certificate
active
06483802
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the use of twisted pair connections as communication links driven by transformer couplings, and particularly to the use of phantom circuits formed by pairs of transformers driving pairs of twisted pairs.
BACKGROUND TO THE INVENTION
A phantom circuit is formed by connections to the centre taps of a pair of transformers at a transmit end, which pair of transformers are linked by respective communication links to a pair of transformers at a receive end, connections to the centre taps of the transformers at the receive end forming the other end of the phantom circuit. The communication links between the two transformers of the transmit end and the two transformers of the receive end form two high speed communication links and the phantom circuit provides a further low speed communication link. Thus advantageously phantom circuits provide an additional communications link without the provision of additional communications link circuitry.
Typically the communication links formed by the respective pairs of transformers will transmit high speed data, typically between computers. The phantom circuit cannot support high speed communication such as that between computers, but can advantageously be used in accordance with the present invention to distribute power from a transmit end to a receive end; the phantom circuit being used to supply power to devices to which the high speed communication links are connected.
Thus according to the present invention there is provided a communication system comprising:
a first high speed link having a first transformer interface at a transmit end and a second transformer interface at a receive end;
a second high speed link having a third transformer interface at a transmit end and a fourth transformer interface at a receive end;
a low speed link comprising a phantom circuit formed by the first to fourth transformers, the transmit end of the low speed link being formed by connections to the centre taps of the first and third transformers and the receive end of the low speed link being formed by connections to the centre taps of the second and fourth transformers;
wherein the transmit end of the low speed link is connected to a power supply and at least one of the high speed links is connected to a device at the receive end for receiving signals from the respective high speed link, the receive end of the low speed link providing power to the device from the power supply.
Preferably one of the high speed links transmits a serial data signal, and the other high speed link transmits a strobe signal having transitions only at bit boundaries of the data signal where there are no transitions, thus forming a data-strobe communication link as disclosed in earlier European Patent Application Publication No. 0458648.
In addition to the distribution of power, the phantom circuit may be used to transmit low speed signals. The phantom circuit may also be used to distribute a global signalling clock. The global signalling clock may be implemented by providing a switch on the transmit side of the phantom circuit which switches the power supply for transmission in and out of the phantom circuit.
The phantom circuits may also be used to distribute power to remote destinations where there are no devices for receiving high speed communication signals.
The present invention also relates to a communication system in which a variable frequency clock is used in the transmission circuit. The invention is particularly, but not exclusively, concerned with the use of spread spectrum clocks in the transmission circuits of communications systems.
For communication networks, particularly those implemented in the home, there is a need to minimise electromagnetic radiation. The use of spread spectrum clocks reduces the peaks of electromagnetic radiation at harmonics of the clock frequency, and thus it would be advantageous to employ a variable frequency clock such as a spread spectrum clock in any communication system utilising a high speed network, particularly in the home.
SUMMARY OF THE INVENTION
Thus according to the present invention there is provided a communications interface comprising output circuitry for providing a data signal to be transmitted under the control of a transmit clock signal, the frequency of the transmit clock signal being continuously variable.
The data-strobe link can cope very well with changing clock frequency, whereas typical PLL clock recovery circuits may have more difficulty in tracking the viable frequency clock.
When using a variable frequency clock in a transmission circuit, further problems arise in attempting to recover the clock at the receive end. European Patent Application Publication No. 0458648 describes an encoding scheme where data is transmitted on one serial link, and on a parallel serial link a strobe signal is transmitted which has transitions only at bit boundaries of the data signal where there is no transition. Such an encoding scheme advantageously allows the transmit clock to be simply recovered at the receive end, and therefore such a communication system can be advantageously used with the variable clock.
Thus according to the present invention there is additionally provided a communications interface comprising:
output circuitry for providing two parallel outputs, one in the form of a data signal and one in the form of a strobe signal and including strobe generation circuitry, wherein the data signal comprises a serial bit pattern and the strobe generation circuitry generates the strobe signal such that the strobe signal has signal transitions only at bit boundaries where there is no transition on the data signal, the strobe generation circuitry being controlled by a clock signal such that for each clock pulse where there is no signal transition in the data signal a signal transition is generated in the strobe signal, the frequency of the clock signal being continuously variable; and
input circuitry having two inputs for receiving data and strobe signals, and including an exclusive-or circuit for receiving the data and strobe signals and generating a receive clock on the output thereof, the receive clock being generated with clock signal transitions having a timing matching that at which the strobe and data signals were transmitted.
The present invention also relates to receive circuitry for use in a communications system utilising data-strobe encoding in which the receiver is insensitive to which of the parallel signal lines the data signal is on. Data strobe encoding is described in earlier European Patent Application Publication No. 0458648.
In the data strobe encoding scheme, a data signal is transmitted on a serial data line, and a strobe signal transmitted on a serial strobe line parallel to the data line, the strobe signal having transitions only at bit boundaries of the data signal where there are no transitions. On the receive side, the transmit clock can be readily recovered by exclusive-ORing both the data and strobe signals.
According to the present invention there is provided data receiving circuitry comprising:
input circuitry having two inputs, one input for receiving a data signal and the other input for receiving a strobe signal, the strobe signal being parallel to the data signal and having signal transitions only at bit boundaries where there is no transition on the data signal;
an exclusive-or gate, having inputs connected to the two inputs, and generating a receive clock on the output thereof;
detection circuitry having two inputs coupled to the respective two inputs of the input circuitry and for detecting an expected bit sequence associated with the data signal on one of said two inputs;
output circuitry for outputting the data signal under the control of the receive clock; and
selection circuitry for connecting the one of said inputs on which said sequence is detected to the output circuit.
The present invention further relates to a communications system code which utilises transformer couplings to communication links, and particularly to such a c
Cook Barry Michael
Walker Christopher Paul Hulme
4Links Ltd.
Darby & Darby
Nguyen Brian
Ton Dang
LandOfFree
Communication system for driving pairs of twisted pair links does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Communication system for driving pairs of twisted pair links, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Communication system for driving pairs of twisted pair links will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2943772