Digital isolation system with data scrambling

• US 6,359,983 B1
• Filed: 03/04/1998
• Issued: 03/19/2002
• Est. Priority Date: 04/22/1997
• Status: Expired due to Fees

• Current Assignee: Silicon Laboratories Incorporated
• Original Assignee: Silicon Laboratories Incorporated
• Inventors: Scott, Jeffrey W., Krone, Andrew W., Welland, David R., Sooch, Navdeep S.
• Primary Examiner(s): Isen, Forester W.
• Assistant Examiner(s): SINGH, RAMNANDAN P
• Application Number:
  US09/034,687
• Time in Patent Office: 1,476 Days
• Field of Search: 379/106.01, 379/355, 379/58, 379/61, 379/376, 379/130, 379/412, 379/382, 379/416, 379/93.05, 379/399.01, 379/399.02, 455/3.1, 455/4.1, 455/38.1, 370/252, 370/331, 370/335, 370/342, 381/315, 381/94.2, 375/285
• US Class Current: 379/399.01
• CPC Class Codes: H04L 25/0266 Arrangements for providing Galvanic isolation, e.g. by means of magnetic or capacitive coupling
• CPC Class Codes: H04L 25/06 Dc level restoring means; Bias distortion correction ; Decision circuits providing symbol by symbol detection
• CPC Class Codes: H04L 7/033 using the transitions of the received signal to control the phase of the synchronising-signal-generating means, e.g. using a phase-locked loop
• CPC Class Codes: H04M 1/573 Line monitoring circuits for detecting caller identification
• CPC Class Codes: H04M 11/06 Simultaneous speech and data transmission, e.g. telegraphic transmission over the same conductors
• CPC Class Codes: H04M 19/001 Current supply source at the exchanger providing current to substations
• CPC Class Codes: H04M 19/02 providing ringing current or supervisory tones, e.g. dialling tone or busy tone

Abstract

A method and apparatus are provided for reducing the amplitude of signals that often are inadvertently coupled to a telephone line from an isolation barrier system, or that cause undesirable interference within the circuitry of the isolation barrier system. Such signals have undesirable peaks in the frequency domain (spectral peaks) due to the existence of periodicities in the data signal that is transmitted across the isolation barrier. Such spectral peaks are reduced by this invention, which comprises randomizing or scrambling the data signal before it crosses the isolation barrier, and descrambling the data after it has crossed the isolation barrier. In one embodiment, the data signal is scrambled by combining it with a random bit stream (or a pseudo random bit stream), which effectively “whitens” the resulting scrambled signal, thus removing spectral peaks that exist in the original data signal. After the scrambled signal passes across the isolation barrier, it is descrambled by reversing the original scrambling operation. In preferred embodiments, both the scrambling and the descrambling steps are performed by combining the incoming signal with synchronized pseudo-random bit patterns using “exclusive-or” logical operations.

Claims

1. An isolation system for providing a digital communication channel across an isolation barrier between a data input terminal and a data output terminal, the isolation system comprising:

a data randomizing circuit connected to receive a digital data input signal from the input terminal and to output a randomized data signal to be communicated across the isolation barrier; and

a data de-randomizing circuit coupled to receive the randomized data signal through the isolation barrier and to form a digital data output signal.

2. The system of claim 1, further comprising:

an encoder circuit connected to receive the randomized data signal from the data randomizing circuit, the encoder circuit including logic circuitry for combining the randomized data signal with control signals, the encoder circuit providing a digital encoded signal at an encoder output that is coupled to a first side of the isolation barrier; and

a decoder circuit connected to receive (a) the digital encoded signal from a second side of the isolation barrier, and (b) a clock signal, the decoder circuit adapted to separate the digital encoded signal into control signals and a randomized output data signal, the data de-randomizing circuit receiving the randomized output data signal.

3. The system of claim 2, further comprising a driver circuit connected between the encoder output and to the first side of the isolation barrier, the driver circuit adapted to receive the encoded signal and to apply it to the first side of the isolation barrier.

4. The system of claim 2, further comprising a clock recovery circuit connected to the second side of the isolation barrier to receive an isolated encoded signal therefrom, the clock recovery circuit providing a clock signal synchronized with the digital encoded signal received on the second side of the isolation barrier.

5. The system of claim 1, wherein the isolation barrier comprises one or more isolation capacitors.

6. The system of claim 1, wherein the data randomizing circuit comprises an “

exclusive-or”

circuit having one input connected to receive the digital data input signal and another input connected to receive a random digital signal from a random signal generator.

7. The system of claim 6, wherein the random digital signal is a pseudo-random digital signal.

8. The system of claim 7, wherein the random signal generator comprises a pseudo-random signal generator including a linear feedback shift register.

9. The isolation system of claim 1, further comprising an digital-to-analog converter connected to receive the digital data output signal and having an output connected to provide an analog data output signal to the data output terminal.

10. An isolation system for providing a digital communication channel for data signals and control signals, the isolation system comprising:

an isolation barrier;

a data randomizing circuit connected to receive said data signals and to output a randomized data signal;

a multiplexer located on one side of the isolation barrier and connected to receive the randomized data signal and the control signals, the multiplexer providing a multiplexed digital signal that is connected to the isolation barrier;

a demultiplexer located on the other side of the isolation barrier and connected to receive the multiplexed digital signal from the isolation barrier, the demultiplexer having a randomized data signal output and a control signal output; and

a data de-randomizing circuit connected to receive the randomized data signal from the demultiplexer and to form a digital data output signal, the digital data output signal being presented at an output terminal of the isolation system.

11. The system of claim 10, wherein the isolation barrier comprises one or more isolation capacitors.

12. The system of claim 10, wherein the data randomizing circuit comprises an “

exclusive-or”

circuit having one input connected to receive the digital data input signal and another input connected to receive a random digital signal from a random signal generator.

13. The system of claim 12, wherein the random signal is a pseudo-random signal.

14. The system of claim 13, wherein the random signal generator comprises a pseudo-random signal generator including a linear feedback shift register.

15. The system of claim 10, further comprising an analog-to-digital converter having an output connected to an input of the data randomizing circuit, the analog-to-digital converter adapted to receive an analog input signal connected to an input of the isolation system and to provide a corresponding digital representation of the analog input signal at said analog-to-digital converter output.

16. A method of transmitting a digital data signal across an isolation barrier, comprising:

randomizing the digital data signal to form a randomized data signal;

combining the randomized data signal with control information to form a digital encoded signal;

driving the digital encoded signal across the isolation barrier;

receiving an isolated encoded signal from the isolation barrier;

separating the isolated encoded signal into an isolated data signal and isolated control information; and

de-randomizing the isolated data signal to recover said digital data signal.

17. The method of claim 16, comprising driving the digital encoded signal across a capacitive isolation barrier.

18. The method of claim 16, further comprising recovering a clock signal from the isolated encoded signal to provide a recovered clock signal, and synchronizing the isolated encoded signal with the recovered clock signal.

19. The method of claim 16, wherein the randomizing step comprises generating a first random bit sequence and combining it in a logical operation with the digital data signal to form the randomized data signal.

20. The method of claim 19, wherein the logical operation is an “

exclusive or”

operation.

21. The method of claim 19, further comprising generating the first random bit sequence using a linear feedback shift register, and wherein the random bit sequence is a pseudo-random bit sequence.

22. The method of claim 20, wherein the de-randomizing step comprises generating a second random bit sequence that is identical to the first random bit sequence and combining the second random bit sequence in a logical operation with the isolated data signal to recover the digital data signal.