Apparatus and method for FSK demodulation with integrated time and frequency tracking

• US 7,508,890 B1
• Filed: 05/09/2005
• Issued: 03/24/2009
• Est. Priority Date: 08/23/2001
• Status: Active Grant

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Lamb, Aaron D., Malone, Lawrence J.
• Primary Examiner(s): PHU, PHUONG M
• Application Number:
  US11/124,913
• Time in Patent Office: 1,415 Days
• Field of Search: 375/334, 375/272, 375/335, 375/275, 329/300, 329/301, 329/302, 329/303
• US Class Current: 375/334
• CPC Class Codes: H04L 27/156 with demodulation using temporal properties of the received signal, e.g. detecting pulse width
• CPC Class Codes: H04L 27/16 Frequency regulation arrangements
• CPC Class Codes: H04L 7/007 detection of error based on maximum signal power, e.g. peak value, maximizing autocorrelation

Abstract

An FSK receiver comprising: 1) demodulation circuitry for receiving an incoming FSK signal and generating a baseband signal comprising an amplitude modulated symbol stream, of Logic 0 symbols and Logic 1 symbols having a data rate, R; 2) auto-correlation circuitry for sampling the baseband signal S times during each symbol and generating an auto-correlation function comprising a sample stream of N-bit samples having a data rate, S×R, and having positive-going peaks approximately coinciding with the center of the Logic 1 symbol in a 010 sequence in the baseband signal and negative-going peaks approximately coinciding with the center of the Logic 0 symbols in a 101 sequence in the baseband signal; and 3) decision circuitry for receiving the auto-correlation function and deciding a logic level of a first symbol as a function of: 1) a comparison of a signal level of a center sample of the first symbol and a mean signal level of the auto-correlation function and 2) a comparison of the signal level of the center sample of the first symbol and a signal level of a center sample of a second symbol preceding the first symbol.

Claims

1. A frequency-shift-keyed (FSK) receiver, comprising:

demodulation circuitry capable of receiving an incoming FSK signal and generating a baseband signal;

auto-correlation circuitry capable of sampling the baseband signal and generating an auto-correlation function, the auto-correlation function having a positive-going peak approximately coinciding with a center of a Logic 1 symbol in the baseband signal and having a negative-going peak approximately coinciding with a center of a Logic 0 symbol in the baseband signal; and

decision circuitry capable of deciding a logic level of a first symbol using the auto-correlation function wherein the decision circuitry is capable of deciding the logic level of the first symbol by comparing a signal level of a center sample of the first symbol and a mean signal level of the auto-correlation function.

2. The FSK receiver as set forth in claim 1, wherein the decision circuitry is capable of deciding the logic level of the first symbol further by at least one of:

comparing the signal level of the center sample of the first symbol and a signal level of a center sample of a second symbol preceding the first symbol; and

comparing the signal level of the center sample of the first symbol and a signal level of a center sample of a third symbol following the first symbol.

3. The FSK receiver as set forth in claim 2, wherein the decision circuitry is further capable of deciding the logic level of the second symbol by comparing the signal level of the center sample of the second symbol and the mean signal level of the auto-correlation function.

4. The FSK receiver as set forth in claim 3, wherein the decision circuitry is further capable of deciding the logic level of the third symbol by comparing the signal level of the center sample of the third symbol and the mean signal level of the auto-correlation function.

5. The FSK receiver as set forth in claim 4, wherein:

in response to determining that the second symbol, the first symbol, and the third symbol comprise a 010 sequence of symbols, the decision circuitry is capable of comparing the signal level of the center sample of the first symbol with at least one of (i) a signal level of a preceding sample of the first symbol and (ii) a signal level of a following sample of the first symbol to determine a location of the positive-going peak of the auto-correlation function corresponding to the first symbol.

6. The FSK receiver as set forth in claim 4, wherein:

in response to determining that the second symbol, the first symbol, and the third symbol comprise a 101 sequence of symbols, the decision circuitry is capable of comparing the signal level of the center sample of the first symbol with at least one of (i) a signal level of a preceding sample of the first symbol and (ii) a signal level of a following sample of the first symbol to determine a location of the negative-going peak of the auto-correlation function corresponding to the first symbol.

7. The FSK receiver as set forth in claim 4, wherein:

in response to determining that the positive-going peak or the negative-going peak does not coincide with the center sample of the first symbol, the decision circuitry is capable of advancing or delaying sampling of the baseband signal by at least one sample time period.

8. The FSK receiver as set forth in claim 1, wherein:

the positive-going peak approximately coincides with the center of the Logic 1 symbol in a 010 sequence in the baseband signal; and

the negative-going peak approximately coincides with the center of the Logic 0 symbols in a 101 sequence in the baseband signal.

9. A frequency-shift-keyed (FSK) device, comprising:

an antenna capable of providing an incoming FSK signal; and

an FSK receiver comprising;

demodulation circuitry capable of receiving the incoming FSK signal and generating a baseband signal;

auto-correlation circuitry capable of sampling the baseband signal and generating an auto-correlation function, the auto-correlation function having a positive-going peak approximately coinciding with a center of a Logic 1 symbol in the baseband signal and having a negative-going peak approximately coinciding with a center of a Logic 0 symbol in the baseband signal; and

decision circuitry capable of deciding a logic level of a first symbol using the auto-correlation function wherein the decision circuitry is capable of deciding the logic level of the first symbol by comparing a signal level of a center sample of the first symbol and a mean signal level of the auto-correlation function.

10. The FSK device as set forth in claim 9, wherein the decision circuitry is capable of deciding the logic level of the first symbol further by at least one of:

comparing the signal level of the center sample of the first symbol and a signal level of a center sample of a second symbol preceding the first symbol; and

comparing the signal level of the center sample of the first symbol and a signal level of a center sample of a third symbol following the first symbol.

11. The FSK device as set forth in claim 10, wherein the decision circuitry is further capable of deciding the logic level of the second symbol by comparing the signal level of the center sample of the second symbol and the mean signal level of the auto-correlation function.

12. The FSK device as set forth in claim 11, wherein the decision circuitry is further capable of deciding the logic level of the third symbol by comparing the signal level of the center sample of the third symbol and the mean signal level of the auto-correlation function.

13. The FSK device as set forth in claim 12, wherein:

in response to determining that the second symbol, the first symbol, and the third symbol comprise a 010 sequence of symbols, the decision circuitry is capable of comparing the signal level of the center sample of the first symbol with at least one of (i) a signal level of a preceding sample of the first symbol and (ii) a signal level of a following sample of the first symbol to determine a location of the positive-going peak of the auto-correlation function corresponding to the first symbol; and

in response to determining that the second symbol, the first symbol, and the third symbol comprise a 101 sequence of symbols, the decision circuitry is capable of comparing the signal level of the center sample of the first symbol with at least one of (i) a signal level of a preceding sample of the first symbol and (ii) a signal level of a following sample of the first symbol to determine a location of the negative-going peak of the auto-correlation function corresponding to the first symbol.

14. A method, comprising:

demodulating an incoming frequency-shift-keyed (FSK) signal and generating a baseband signal;

sampling the baseband signal and generating an auto-correlation function, the auto-correlation function having a positive-going peak approximately coinciding with a center of a Logic 1 symbol in the baseband signal and having a negative-going peak approximately coinciding with a center of a Logic 0 symbol in the baseband signal; and

deciding a logic level of a first symbol using the auto-correlation function wherein deciding the logic level of the first symbol comprises comparing a signal level of a center sample of the first symbol and a mean signal level of the auto-correlation function.

15. The method as set forth in claim 14, wherein deciding the logic level of the first symbol further comprises at least one of:

comparing the signal level of the center sample of the first symbol and a signal level of a center sample of a second symbol preceding the first symbol; and

comparing the signal level of the center sample of the first symbol and a signal level of a center sample of a third symbol following the first symbol.

16. The method as set forth in claim 15, further comprising:

deciding the logic level of the second symbol by comparing the signal level of the center sample of the second symbol and the mean signal level of the auto-correlation function; and

deciding the logic level of the third symbol by comparing the signal level of the center sample of the third symbol and the mean signal level of the auto-correlation function.

17. The method as set forth in claim 16, further comprising:

in response to determining that the second symbol, the first symbol, and the third symbol comprise a 010 sequence of symbols, comparing the signal level of the center sample of the first symbol with at least one of (i) a signal level of a preceding sample of the first symbol and (ii) a signal level of a following sample of the first symbol to determine a location of the positive-going peak of the auto-correlation function corresponding to the first symbol; and

in response to determining that the second symbol, the first symbol, and the third symbol comprise a 101 sequence of symbols, comparing the signal level of the center sample of the first symbol with at least one of (i) a signal level of a preceding sample of the first symbol and (ii) a signal level of a following sample of the first symbol to determine a location of the negative-going peak of the auto-correlation function corresponding to the first symbol.