FSK demodulator system and method

• US 20050089120A1
• Filed: 09/07/2004
• Published: 04/28/2005
• Est. Priority Date: 09/09/2003
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Hunt, William, Quinlan, Philip E., Mulvaney, Kenneth J., Crowley, Patrick G.
• Granted Patent: US 7,397,300 B2
• Time in Patent Office: Days
• US Class Current: 375/335
• CPC Class Codes: H03D 3/007 by converting the oscillations into two quadrature related signals H03D3/245 takes precedence
• CPC Class Codes: H03D 3/02 by detecting phase difference between two signals obtained from input signal H03D3/28 - H03D3/32 take precedence; muting in frequency-modulation receivers H03G3/28; limiting arrangements H03G11/00
• CPC Class Codes: H04L 27/144 with demodulation using spectral properties of the received signal, e.g. by using frequency selective- or frequency sensitive elements
• CPC Class Codes: H04L 27/1525 using quadrature demodulation
• CPC Class Codes: H04L 27/156 with demodulation using temporal properties of the received signal, e.g. detecting pulse width

Abstract

An FSK demodulator system with tunable spectral shaping including a pair of quadri-correlators responsive to first and second quadrature signals, one of the pair deriving first and second signals representative of the frequency deviation of the quadrature signals at even integer multiples of the frequency deviation and for resolving the modulated FSK data represented by the quadrature signals and the other of the pair deriving first and second signals representative of the frequency deviation of the quadrature signals at odd integer multiples of the deviation frequency and for resolving the modulated FSK data represented by the quadrature signals, and a delay control circuit for setting a delay to each of the pair of quadri-correlators to control the first and second signals representative of the frequency deviation of the quadrature signals derived by each of the pair of quadri-correlators and generate a tuned spectral response at both even and odd integer multiples of the frequency deviation.

Claims

1. An FSK demodulator system with tunable spectral shaping comprising:

a pair of quadri-correlators responsive to first and second quadrature signals, one of said pair deriving first and second signals representative of the frequency deviation of said quadrature signals at even integer multiples of said frequency deviation and for resolving the modulated FSK data represented by said quadrature signals and the other of said pair deriving first and second signals representative of the frequency deviation of said quadrature signals at odd integer multiples of said deviation frequency and for resolving the modulated FSK data represented by said quadrature signals; and

a delay control circuit for setting a delay to each of said pair of quadri-correlators to control said first and second signals representative of the frequency deviation of said quadrature signals derived by each of said pair of quadri-correlators and generate a tuned spectral response at both even and odd integer multiples of said frequency deviation.

2. The FSK demodulator system of claim 1 further including an analog-to-digital converter responsive to first and second quadrature signals at a predetermined IF frequency varied by positive and negative frequency deviations for generating digital said first and second quadrature signals.

3. The FSK demodulator system of claim 1 further including a plurality of scaling circuits responsive to said pair of quadri-correlators for introducing programmable scaling coefficients to the output of each of said pair correlators to weight said first and second signals representative of the frequency deviation generated by each of said pair of correlators to generate a composite tuned spectral response that combines said even and odd integer multiples of said frequency deviation.

4. The FSK demodulator system of claim 1 in which one of said pair of quadri-correlators includes a cosine correlator.

5. The FSK demodulator system of claim 1 in which one of said pair of quadri-correlators includes a sine correlator.

6. The FSK demodulator system of claim 5 in which said delay circuit generates a programmable delay for said sine correlator which is equal to τ

₁, where

${\mathrm{\tau <br><br>}}_1=\frac{1}{4<br><br>\left(f_{\mathrm{dev}}\right)},$

and where f_dev is said frequency deviation.

7. The FSK demodulator system of claim 4 in which said delay circuit generates a programmable delay for said cosine correlator which is equal to τ

₂, where

${\mathrm{\tau <br><br>}}_2=\frac{1}{4<br><br>\left(f_{\mathrm{dev}}\right)},$

and where f_dev is said frequency deviation.

8. The FSK demodulator system of claim 2 in which said frequency deviation is optimized to equal the said IF frequency divided by a predetermined number.

9. The FSK demodulator system of claim 8 in which said predetermined number is chosen from the group consisting of:

an odd integer, an even integer, and a real number.

10. The FSK demodulator system of claim 1 in which said frequency deviation has a frequency in the range of about 100 Hz to 5 MHz.

11. The FSK demodulator system of claim 3 in which said scaling coefficients are values between −

1 and +1.

12. The FSK demodulator system of claim 3 further including an adder circuit responsive to said plurality of scaling circuits for linearly combing the outputs of said pair of correlators to provide a said composite spectral response and maximize the output signal-to-noise ratio.

13. The FSK demodulator system of claim 2 in said IF frequency is greater than zero.

14. The FSK demodulator system of claim 2 in which said IF frequency is in the range of about 100 kHz to 10 MHz.

15. The FSK demodulator system of claim 2 in which the said IF frequency is zero.

16. The FSK demodulator system of claim 2 in which said analog-to-digital converter includes a limiter.

17. The FSK demodulator system of claim 2 in which said analog-to-digital converter includes a one bit analog-to-digital converter.

18. The FSK demodulator system of claim 2 in which said analog-to-digital converter includes a saturated analog-to-digital converter.

19. The FSK demodulator system of claim 4 in which said cosine correlator is responsive to first and second quadrature signals and generates a cosine frequency response.

20. The FSK demodulator system of claim 4 in which the ratio of an IF frequency to said frequency deviation is an odd integer multiple.

21. The FSK demodulator system of claim 4 in which the ratio of an IF frequency to said frequency deviation is a real number.

22. The FSK demodulator system of claim 5 in which said sine correlator is responsive to first and second quadrature signals and generates a sinusoidal frequency response.

23. The FSK demodulator system of claim 5 in which the ratio of an IF frequency to said frequency deviation is an even integer multiple.

24. The FSK demodulator system of claim 5 in which the ratio of an IF frequency to said frequency deviation is a fractional number or a real number having a fractional part greater than zero.

25. The FSK demodulator system of claim 1 in which each of said pair of quadri-correlators includes first and second delay circuits responsive to said first and second quadrature signals for generating delayed first and second quadrature signals, first and second multiplier circuits responsive to said first and second quadrature signals and first and second delayed quadrature signals for deriving first and second signals representative of the frequency deviation of the quadrature signals, and a summer circuit responsive to said first and second signals representative of the frequency deviation of said quadrature signals for resolving the digital values represented by said quadrature signals.

26. The FSK demodulator system of claim 3 in which said system operates at a modulation index in the range of about 0.1 to 50.

27. The FSK demodulator system of claim 26 in which said delay and said scaling coefficients are adjusted to maximize the output signal-to-noise ratio over a modulation index in the range of about 0.1 to 50.

28. The FSK demodulator system of claim 1 in which said FSK demodulator system enables FSK demodulation, and/or Gaussian Frequency Shift Keying (GFSK) demodulation and/or Minimum Shift Keying (MSK) demodulation, and/or Phase Shift Keying (PSK) demodulation.

29. The FSK demodulator system of claim 12 further including a low pass filter responsive to said adder circuit for removing noise and harmonics from said tuned spectral response.

30. The FSK demodulator system of claim 29 further including a slicer circuit responsive to said low pass filter for recovering said modulated FSK data and generating a recovered bit stream.

31. The FSK demodulator system of claim 30 further including a digital PLL responsive to said recovered bit stream for generating a clock signal and a data signal.

32. The FSK demodulator system of claim 2 further including a quadrature receiver responsive to a high frequency FSK signal varied by positive and negative frequency deviations which represent modulated FSK data for converting said high frequency FSK signal to said first and second quadrature signals at said predetermined IF frequency.

33. An FSK demodulator system with tunable spectral shaping comprising:

a limiter responsive to a first and second quadrature signals at a predetermined IF frequency varied by a positive and negative frequency deviations for generating digital first and second quadrature signals;

a pair of quadri-correlators responsive to said digital first and second quadrature signals, one of said pair deriving first and second signals representative of the frequency deviation of said quadrature signals at even integer multiples of said frequency deviation and for resolving the modulated FSK data represented by said quadrature signals and the other of said pair deriving first and second signals representative of the frequency deviation of said quadrature signals at odd integer multiples of said deviation frequency and for resolving the modulated FSK data represented by said quadrature signals; and

a delay control circuit for setting a delay to each of said pair of quadri-correlators to control said first and second signals representative of the frequency deviation of said quadrature signals derived by each of said pair of quadri-correlators and generate a tuned spectral response at both even and odd integer multiples of said frequency deviation.

34. An FSK demodulator system with tunable spectral shaping comprising:

an analog-to-digital converter responsive to first and second quadrature signals at a predetermined IF frequency varied by positive and negative frequency deviations for generating digital first and second quadrature signals;

a sine and cosine pair of quadri-correlators responsive to said digital first and second quadrature signals each of said pair deriving first and second signals representative of the frequency deviation of said quadrature signals at even or odd integer multiples or sub-multiples of said frequency deviation about said IF frequency and for resolving the modulated FSK data represented by said quadrature signals;

a delay control circuit for setting a delay to each of said sine and cosine pair of quadri-correlators for controlling said first and second signals representative of the frequency deviation of said quadrature signals; and

a plurality of scaling circuits responsive to said sine and cosine pair of quadri-correlators for introducing programmable scaling coefficients to the output of each of said pair correlators to weight said first and second signals representative of the frequency deviation generated by each of said pair of correlators to generate a composite tuned spectral response that combines said even and odd integer multiples of said frequency deviation.

35. The FSK demodulator system of claim 34 further including an adder circuit responsive to said plurality of scaling circuits for lineally combining the outputs of said sine and cosine pair of quadri-correlators to generate said composite spectral response.

36. The FSK demodulator system of claim 34 further including a qaudrature receiver responsive to a high frequency FSK signal varied positive and negative frequency deviations which represent modulated FSK data for converting said high frequency FSK signal to said first and second quadrature signals at said predetermined IF frequency.

37. The FSK demodulator system of claim 34 in which said analog-to-digital converter includes a limiter.

38. The FSK demodulator system of claim 34 in which said analog-to-digital converter includes a saturated analog-to-digital converter.

39. An FSK demodulator system with tunable spectral shaping comprising:

a analog-to-digital converter responsive to a first and second quadrature signals at a predetermined IF frequency varied by a positive and negative frequency deviations for generating digital first and second quadrature signals;

a sine and cosine pair of quadri-correlators responsive to said digital first and second quadrature signals each of said pair deriving first and second signals representative of the frequency deviation of said quadrature signals at even or odd integer multiples or sub-multiples of said frequency deviation about said IF frequency and for resolving the modulated FSK data represented by said quadrature signals;

a delay control circuit for setting a delay to each of said sine and cosine pair of quadri-correlators for controlling said first and second signals representative of the frequency deviation of said quadrature signals;

a plurality of scaling circuits responsive to said sine and cosine pair of quadri-correlators for introducing programmable scaling coefficients to the output of each of said pair correlators to weight said first and second signals representative of the frequency deviation generated by each of said pair of correlators; and

an adder circuit responsive to said plurality of scaling circuits for lineally combining the outputs of said sine and cosine pair of quadri-correlators to generate a composite spectral response that combines said even and odd integer multiples of said frequency deviation.

40. An FSK demodulator system with tunable spectral shaping comprising:

a plurality of correlators, each said correlator including a sine and cosine correlator responsive to first and second quadrature signals at a predetermined IF frequency varied by positive and negative frequency deviations, each of said sine and cosine correlators deriving first and second signals representative of the frequency deviation of said quadrature signals at even or odd integer multiples or sub-multiples of said frequency deviation about said IF frequency and for resolving the modulated FSK data represented by said quadrature signals;

a delay control circuit for setting a programmable delay to each of said sine and cosine correlators for controlling and maximizing said first and second signals representative of the frequency deviation of said quadrature signals; and

a plurality of scaling circuits responsive to each of said sine and cosine correlators for introducing programmable scaling coefficients to the output of each of said sine and cosine correlators to weight said first and second signals representative of the frequency deviation generated by each of said sine and cosine correlators and generate a lineally combined composite spectral response that combines the outputs of each of said plurality of correlators and approximates a matched filter response.

41. An FSK demodulator system with tunable spectral shaping comprising:

a analog-to-digital converter responsive to a first and second quadrature signals at a predetermined IF frequency varied by a positive and negative frequency deviations for generating digital first and second quadrature signals;

a plurality of correlators, each said correlator including a sine and cosine correlator responsive to said digital first and second quadrature signals at a predetermined IF frequency, each of said sine and cosine correlators deriving first and second signals representative of the frequency deviation of said quadrature signals at even or odd integer multiples or sub-multiples of said frequency deviation about said IF frequency and for resolving the modulated FSK data represented by said quadrature signals;

a delay control circuit for setting a programmable delay to each of said sine and cosine correlators for controlling and maximizing said first and second signals representative of the frequency deviation of said quadrature signals; and

a plurality of scaling circuits responsive to each of said sine and cosine correlators for introducing programmable scaling coefficients to the output of each of said sine and cosine correlators to weight said first and second signals representative of the frequency deviation generated by each of said sine and cosine correlators and generate a lineally combined composite spectral response that combines the outputs of each of said plurality of correlators and approximates a matched filter response.

42. The FSK demodulator system of claim 41 further including an adder circuit responsive to said plurality of scaling circuits for lineally combining the outputs of each of said plurality of correlators for generating said lineally combined composite response.

43. The FSK demodulator system of claim 41 in which said analog-to-digital converter includes a limiter.

44. The FSK demodulator system of claim 41 in which said analog-to-digital converter includes a saturated analog-to-digital converter.

45. The FSK demodulator system of claim 41 further including a low pass filter response to said adder circuit for removing noise and harmonics from said lineally combined composite response.

47. The method of claim 45 further including the step of introducing scaling coefficients to weight said first and second signals representative of the deviation frequency at even or odd integer multiples or sub-multiples the frequency deviation about a predetermined IF frequency to generate a composite spectral response that combines said even and odd integer multiples of said deviation frequency.

46. An FSK demodulator method comprising the steps of:

deriving first and second signals representative of the frequency deviation of first and second quadrature signals at even integer multiples of the frequency deviation and resolving the modulated FSK data represented by the quadrature signals;

deriving first and second signals representative of the frequency deviation of first and second quadrature signs at odd integer multiples of the frequency deviation and resolving the modulated FSK data represented by the quadrature signals; and

setting a delay to control the first and second signals representative of the frequency deviation at the even and odd multiples of the frequency deviation to generate a tuned spectral response at both even and odd integer multiples of the frequency deviation.