Dual Threshold Demodulation in an Amplitude Modulation Radio Receiver

• US 20090247100A1
• Filed: 04/01/2008
• Published: 10/01/2009
• Est. Priority Date: 04/01/2008
• Status: Active Grant

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Meltzer, David, Padaparambil, Muralikumar A., Blum, Gregory A.
• Granted Patent: US 8,000,671 B2
• Time in Patent Office: Days
• US Class Current: 455/182.100
• CPC Class Codes: H03D 1/06 Modifications of demodulators to reduce distortion, e.g. by negative feedback
• CPC Class Codes: H03G 3/3052 in bandpass amplifiers (H.F. or I.F.) or in frequency-changers used in a (super)heterodyne receiver H03G3/32, H03G3/34 take precedence

Abstract

A method, algorithm, circuits, and/or systems for demodulation in an amplitude modulated (AM) radio receiver are disclosed. In one embodiment, a radio receiver can include an amplifier configured to receive a radio frequency (RF) input signal and a gain control signal, and provide an amplified signal, an automatic gain control (AGC) circuit configured to receive a high threshold comparator output and provide the gain control signal, a mixer configured to combine the amplified signal and a local oscillation signal and provide a mixed output, a high threshold comparator configured to compare the mixed output with a reference level and provide the high threshold comparator output, and a low threshold comparator configured to compare the mixed output with the reference level and provide an output of the radio receiver.

Claims

1. A radio receiver, comprising:

a) an amplifier configured to receive a radio frequency (RF) input signal and a gain control signal, and provide an amplified signal;

b) a mixer, configured to combine said amplified signal and a local oscillation signal and provide a mixed output;

c) a first threshold comparator configured to compare a baseband signal with a first comparator threshold level, and provide a first comparator output, said baseband signal being derived from said mixed output;

d) a second threshold comparator configured to compare said baseband signal with a second comparator threshold level, and provide a second comparator output coupled to an output of said radio receiver, said second comparator threshold level being of lower magnitude than said first comparator threshold level;

e) an automatic gain control (AGC) circuit, configured to receive said first comparator output and provide said gain control signal.

2. The radio receiver of claim 1, further comprising a phase locked loop (PLL) configured to generate said local oscillation signal from a reference clock.

3. The radio receiver of claim 1, further comprising a low pass filter (LPF) coupled to said mixed output, and configured to provide said baseband signal to said first threshold comparator and to said second threshold comparator.

4. The radio receiver of claim 1, wherein said RF input signal includes an amplitude modulated (AM) signal.

6. The radio receiver of claim 1, wherein the frequency of said local oscillation signal is substantially equal to a carrier frequency of said RF input signal.

7. The radio receiver of claim 1, wherein said first comparator output has a lower duty cycle than said second comparator output.

8. The radio receiver of claim 1, wherein said first comparator threshold level and said second comparator threshold level are adjustable.

5. (canceled)

9. An automatic gain control (AGC) loop circuit, comprising:

a) an amplifier configured to receive a radio frequency (RF) input signal and a gain control signal, and provide an amplified signal;

b) a mixer, configured to combine said amplified signal and a local oscillation signal and provide a mixed output;

c) a filter configured to receive said mixed output and provide a baseband signal therefrom, said baseband signal being converted into a digital, recovered, baseband signal by a comparison of said baseband signal with a first threshold level;

d) a threshold comparator configured to compare said baseband signal with a second threshold level higher than said first threshold level, and to provide a threshold comparator output;

e) an AGC block configured to receive said threshold comparator output and generate said gain control signal therefrom.

11. The circuit of claim 9, configured for heterodyne type demodulation of said RF input signal.

12. The circuit of claim 9, wherein said digital, recovered, baseband signal has a higher duty cycle than said threshold comparator output.

13. The circuit of claim 9, wherein said first threshold level and second threshold level are adjustable.

10. (canceled)

14. A method of demodulating a radio frequency (RF) input signal, comprising the steps of:

a) receiving said RF input signal in an amplifier of a radio receiver;

b) mixing an output of said amplifier with a local oscillation signal to form a mixed signal;

c) obtaining a recovered signal from said mixed signal;

d) performing a first comparison of said recovered signal with a first reference threshold level to provide a first signal, said first signal providing gain control for said amplifier; and

e) performing a second comparison of said recovered signal with a second reference threshold level to provide a digital, recovered, baseband signal, wherein said first reference threshold level is higher than said second reference threshold level.

16. The method of claim 14, wherein in step (c), said recovered signal is obtained by applying said mixed signal to a frequency filter.

17. The method of claim 14, further comprising adjusting said second reference threshold level to maintain a 50% duty cycle on said digital, recovered, baseband signal.

15. (canceled)

18. (canceled)

19. A radio receiver, comprising:

a) a first amplifier configured to receive a radio frequency (RF) input signal and provide an amplified signal;

b) a mixer configured to combine said amplified signal and a local oscillation signal and provide a mixed output;

c) a second amplifier configured to receive said mixed output and provide an intermediate frequency (IF) signal;

d) a first threshold comparator configured to compare said IF signal with a first reference threshold level, and provide a first comparator output; and

e) a second threshold comparator configured to compare said IF signal with a second reference threshold level, and provide a second comparator output coupled to an output of said radio receiver.

20. The radio receiver of claim 19, further comprising an automatic gain control (AGC) circuit configured to receive said first comparator output and produce a gain control signal.

21. The radio receiver of claim 20, wherein said second amplifier is further configured to receive said gain control signal.

22. The radio receiver of claim 19, wherein said second amplifier further comprises one or more filters configured to filter said mixed output.

23. The radio receiver of claim 19, further comprising one or more reference level generators configured to produce one or more of said reference threshold levels.

25. The radio receiver of claim 21, further comprising a phase locked loop (PLL) and an in-phase and quadrature signal generator configured to generate said local oscillation signal from a reference clock.

24. (canceled)

26. A signal digitizer with gain control, comprising:

a variable amplifier having an amplifier signal input, a gain control input, and configured to provide an amplified output;

a first threshold detector having a first detector input coupled to said amplified output, and a first detector output configured to output a first digital signal indicative of when a voltage level at said first input is above a first threshold level;

an automatic gain control (AGC) circuit having an AGC input coupled to receive said first detector output, and having an AGC output coupled to said gain control input of said variable amplifier;

a second threshold detector having a second detector input coupled to said amplified output, and having a second detector output configured to output a second digital signal indicative of when said a voltage at said second detector input is above a second threshold level that is lower than said first threshold level, said second detector output being an output of said signal digitizer.

27. The signal digitizer with gain control of claim 26, wherein said second detector input is configured to receive the same input as said first detector input.

28. The signal digitizer with gain control of claim 26, further having a reference level generator configured to output a reference level, wherein said first threshold level and said second threshold level are derived from said reference level.

29. The signal digitizer with gain control of claim 28, wherein:

said first threshold detector has a first reference input coupled to receive said reference level; and

said second threshold detector has a second reference input coupled to receive said reference level.

30. The signal digitizer with gain control of claim 26, said first digital signal has a duty cycle smaller than 50%.

31. The signal digitizer with gain control of claim 30, wherein said second digital signal has a duty cycle greater than the duty cycle of said first digital signal.

32. The signal digitizer with gain control of claim 30, wherein said second predefined threshold level is selectively adjustable, and said second predefined threshold level is adjusted to maintain a 50% duty cycle on said second digital signal.

33. The signal digitizer with gain control of claim 26, wherein said amplified output is directly coupled to said first detector input and to said second detector input.

34. The signal digitizer with gain control of claim 33, wherein said signal digitizer with gain control is part of a radio receiver having:

a mixer configured to mix a received radio input with a local oscillator signal to create a mixed signal; and

a filter configured to receive said mixed signal and to output a recovered signal;

said recovered signal being coupled to said amplifier signal input.

35. The signal digitizer with gain control of claim 26, wherein said amplified output is indirectly coupled through a mixer and a filter to said first detector input and to said second detector input.

36. The signal digitizer with gain control of claim 35, wherein;

said signal digitizer with gain control is part of a radio receiver having a local oscillator configured to provide a local oscillator signal to said mixer;

said amplifier signal input is a radio input;

said mixer is configured to provide a mixed signal; and

said filter is configured to receive said mixed signal to produce a recovered signal that is directly coupled to said first detector input and to said second detector input.