Method of recovering and decoding of Manchester coded data

• US 6,963,295 B1
• Filed: 07/02/2004
• Issued: 11/08/2005
• Est. Priority Date: 07/02/2004
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Greene, John C., Doddamane, Krishna
• Primary Examiner(s): JeanPierre, Peguy
• Assistant Examiner(s): LAUTURE, JOSEPH J
• Application Number:
  US10/884,429
• Time in Patent Office: 494 Days
• Field of Search: 341/70, 341/50, 341/51, 342/42
• US Class Current: 341/70
• CPC Class Codes: H03M 5/12 Biphase level code, e.g. split phase code, Manchester code; Biphase space or mark code, e.g. double frequency code

Abstract

A method and apparatus for accurately decoding a Manchester data stream having transition time distortion and noise spikes. Briefly, in an embodiment using a protocol where a falling edge at the mid-point of a bit represents a “1” bit and a rising edge at the mid-point represents a “0” bit, the coded data can be accurately determined by comparing the time period tp₁ from the start of the bit to the first falling edge and the time period tp₂ from the last rising edge to the end point of the bit. If tp₁ is less than tp₂, the bit represents a bit value of “0” and if tp₂ is less than tp₁, the bit represents a bit value of “1”.

Claims

1. A method of receiving and decoding transmitted Manchester-coded data signals comprising the steps of:

receiving a series of Manchester-coded bits at an interrogation unit;

determining a start point and an end point of each of said Manchester-coded data bits;

measuring a first time period between said start point and a selected first one of a negative and positive voltage transition that occurs during one of said Manchester-coded data bits after said start point;

measuring a second time period between the end point and the last of the other one of a negative and positive transition;

comparing said first time period and said second time period;

determining that said Manchester-coded data bit is representative of one of a “

0”

bit and a “

1”

bit if said first time period is less than said second time period; and

determining that said Manchester-coded data bit is representative of the other one of a “

0”

bit and a “

1”

bit if said first time period is greater than said second time period.

2. The method of claim 1 further comprising the steps of determining a time value (t₀) at the occurrence of said start point, a time value (t₁) at the occurrence of said first negative transition, a time value (t₂) at the occurrence of said first positive transition and a time value (t₃) at the occurrence of said end point, and wherein said step of measuring a first time period comprises determining the difference in time values t₀ and t₁ and said step of measuring a second time period comprises determining the difference in time values t₂ and t₃.

3. The method of claim 2 wherein a transition timing of said Manchester-coded data bit has been distorted.

4. The method of claim 2 wherein said Manchester-coded data bit has been distorted by noise.

5. The method of claim 2 wherein said Manchester-coded bits are provided by an RFID (Radio Frequency Identification Device).

6. The method of claim 1 wherein said first time period is between said start point and the first negative voltage transition and said second time period is between said end point and the last positive voltage transition.

7. The method of claim 6 wherein said data bit represents a “

0”

when said second time period is greater than said first time period.

8. The method of claim 1 wherein said first time period is between said start point and the first positive transition and the second time period is between the end point and the last negative voltage transition.

9. The method of claim 1 wherein a transition timing of said Manchester-coded data bit has been distorted.

10. The method of claim 1 wherein said Manchester-coded data bit has been distorted by noise.

11. The method of claim 1 wherein said Manchester-coded bits are provided by an RFID (Radio Frequency Identification Device).

12. An interrogation unit for receiving a series of Manchester-coded data bits from a transmitter comprising:

circuitry for providing a start point and an end point of each of said Manchester-coded data bits;

circuitry for detecting the occurrence of a selected first one of a negative and positive voltage transition after said start point;

a first device for measuring a first time period between said start point and said first voltage transition;

circuitry for detecting the occurrence of a last voltage transition, said last voltage transition being a last of a negative and positive voltage transition, that occurs after the first voltage transition and up to said end point;

a second device for measuring a second time period between said last voltage transition and said end point;

a comparison unit for comparing said first time period and said second time period; and

circuitry for determining that the Manchester-coded data bit is representative of one of a “

0”

bit and a “

1”

bit when said second time period is greater than said first time period and determining the Manchester-coded bit is representative of the other one of a “

0”

bit and a “

1”

bit when said first time period is greater than said second time period.

13. The interrogation unit of claim 12 wherein said circuitry for determining said start point, said circuitry for detecting said first occurrence of a negative transition, said circuitry for detecting said last occurrence of a positive transition, and said end point comprises first, second, third and fourth counters that count clock pulses for respectively determining a value t₀ at the occurrence of said start point, a value t₁ at the occurrence of said first negative transition, a value t₂ at the last occurrence of a positive transition and a value t₃ at the occurrence of said end point, wherein said first device for measuring said first time period is a first comparator unit for determining the difference in the number of clock pulses between values t₀ and t₁, and wherein said second device for measuring said second time period is a second comparator unit for determining the difference in the number of clock pulses between value t₂ and value t₃.

14. The interrogation unit of claim 13 wherein said transmitter is an RFID (Radio Frequency Identification Device).

15. The interrogation unit of claim 12 wherein said transmitter is an RFID (Radio Frequency Identification Device).