Integrated burst FSK receiver

• US 20050249307A1
• Filed: 09/29/2004
• Published: 11/10/2005
• Est. Priority Date: 05/10/2004
• Status: Active Grant

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Krafft, Steve, Kwentus, Alan, Jaffe, Steven, Yu, Tommy
• Granted Patent: US 7,903,764 B2
• Time in Patent Office: Days
• US Class Current: 375/272
• CPC Class Codes: H03D 3/004 wherein the demodulated signal is used for controlling an oscillator, e.g. the local oscillator
• CPC Class Codes: H03D 3/007 by converting the oscillations into two quadrature related signals H03D3/245 takes precedence
• CPC Class Codes: H03D 7/165 at least two frequency changers being located in different paths, e.g. in two paths with carriers in quadrature combined with amplitude demodulation H03D1/2245, combined with angle demodulation H03D3/007; N-path filters H03H19/002
• CPC Class Codes: H04L 27/2334 using filters

Abstract

An integrated burst FSK receiver is provided to receive and interpret an RF signal using FSK modulation. The integrated burst FSK receiver uses a programmable RF local oscillator to mix a received signal down to an IF range or baseband, where it is filtered and sampled for subsequent digital processing. Digital filtering and detection are employed to improve overall bit error rate performance and receiver sensitivity. A programmable digital low-pass or band-pass filter can also be used to suppress interference. A matched filter correlator can be used for detection and symbol timing adjustment in one mode, while an adaptive frequency comparator can be used in another mode. Circuits are provided that estimate carrier offset, frequency deviation and signal strength. These measurements can then be used to optimize the receiver performance. A method for receiving and interpreting an RF signal using FSK modulation is also provided.

Claims

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

an RF converter for converting an RF signal to a digital sampled signal;

a frequency determiner coupled to said RF converter to generate a frequency indicator signal based on the digital sampled signal; and

a detector coupled to said frequency determiner for producing a decision based on the frequency indicator signal.

2. The FSK receiver of claim 1, wherein said RF converter comprises:

a first programmable gain amplifier for amplifying an RF signal;

a mixer coupled to said first programmable gain amplifier for shifting the amplified RF signal to an IF or baseband frequency;

a second programmable gain amplifier coupled to said mixer for amplifying the downconverted signal;

a bandpass filter coupled to said second programmable gain amplifier and centered at the mix-down frequency for filtering the amplified downconverted signal;

a third programmable gain amplifier coupled to said bandpass filter for amplifying the filtered amplified downconverted signal; and

an analog to digital converter coupled to said third programmable gain amplifier for producing a digital sampled signal from the filtered amplified signal.

3. The FSK receiver of claim 1, wherein said frequency determiner comprises:

a first mixer that receives an IF frequency and a carrier offset frequency for producing a frequency adjustment for centering a received digital sampled signal with the IF frequency;

a second mixer that receives the digital sampled signal and is coupled to said first mixer for adjusting the center frequency and splitting I and Q signal components from the received digital sampled signal;

a first anti-aliasing filter coupled to an I signal component output of said second mixer for filtering out images generated by an analog to digital conversion;

a first down-sampler coupled to the I signal component output for down sampling the I signal component of the received digital sampled signal;

a first filter coupled to said first down-sampler;

a second anti-aliasing filter coupled to the Q signal component output of said second mixer for filtering out images generated by an analog to digital conversion;

a second down-sampler coupled to the Q signal component output for down sampling the Q signal component of the received digital sampled signal;

a second filter coupled to said second down-sampler;

a rectangular to polar conversion module coupled to said first and second filters for producing an amplitude and phase of the received digital sampled signal; and

a derivative module for receiving the phase of the received digital sampled signal from said a rectangular to polar conversion module to produce a frequency indicator signal of the received digital sampled signal.

4. The FSK receiver of claim 3, wherein the carrier offset is provided by said detector.

5. The FSK receiver of claim 3, wherein said first and second filters are low pass filters.

6. The FSK receiver of claim 3, wherein said first and second filters are bandpass filters.

7. The FSK receiver of claim 1, wherein said frequency determiner comprises:

a first mixer that receives an IF frequency and a carrier offset frequency for producing a frequency adjustment for centering a received digital sampled signal with the IF frequency;

a second mixer that receives the digital sampled signal and is coupled to said first mixer for adjusting the center frequency and splitting I and Q signal components from the received digital sampled signal;

a plurality of bandpass filters for separating the received digital sampled signal into a plurality of signals located at different frequencies; and

a frequency indicator detector coupled to the outputs of said plurality of bandpass filters for determining a frequency indicator signal of the received digital sampled signal.

8. The FSK receiver of claim 7, wherein the carrier offset is provided by said detector.

9. The FSK receiver of claim 1, wherein said frequency determiner comprises:

a mixer that receives an IF frequency for producing a frequency adjustment for centering a received digital sampled signal with the IF frequency;

a local oscillator coupled to said mixer for providing a center frequency;

a loop filter coupled to said mixer and said local oscillator that follows the center frequency and provides an estimate of a frequency of the said received digital sampled signal.

10. The FSK receiver of claim 1, wherein said detector comprises:

a slicer for generating a hard decision value from a received frequency indicator signal;

a threshold comparator for generating a final data decision by comparing the hard decision value with a programmable threshold; and

a sample module for sampling the final data decision.

11. The FSK receiver of claim 1, wherein said detector comprises:

a header detector for detecting the type of message to be decoded;

a data detector for detecting the value associated with a received frequency; and

a sample centering module for providing a sample time to said data detector for improving the precision of a sample rate used to sample the value of a received frequency indicator signal.

12. The detector of claim 11, wherein said header detector comprises:

a first header correlator for correlating a received frequency indicator signal with a first known header;

a first peak detector for detecting a peak output from said first header correlator;

a second header correlator for correlating the received frequency indicator signal with a second known header;

a second peak detector for detecting a peak output from said second header correlator; and

a header selector for determining the header type associated with the frequency indicator signal coupled to the outputs of the first and second peak detectors.

13. The detector of claim 12, wherein said header selector determines a reference time for when the header is received.

14. The detector of claim 12 further comprising a carrier offset detector coupled to the header selector for generating a carrier offset frequency associated with a received frequency.

15. The detector of claim 12, wherein said data detector comprises:

a first data correlator for correlating a received frequency indicator signal with a first known data value;

a first sampler for sampling the output of said first data correlator, wherein the sampling time is provided by said sample centering module;

a second data correlator for correlating the received frequency indicator signal with a second known data value;

a second sampler for sampling the output of said first data correlator, wherein the sampling time is provided by said sample centering module; and

a decision generator for determining a value associated with the received frequency indicator signal.

16. The detector of claim 12, wherein said sample centering module comprises:

a multiplexer coupled to said data detector that transmits the received frequency indicator signal;

a peak detector coupled to said multiplexer for determining a peak detection time of the received frequency indicator signal;

a first adder coupled to said peak detector that subtracts a sample time from the peak detection time;

a loop filter coupled to said adder; and

a second adder coupled to said filter and said first adder that receives a time increment equal to an expected time increment between signals and adds the expected time increment to the peak detection time to produce the sample time for a subsequent received frequency indicator signal.

17. An integrated circuit that receives FSK modulated signals comprising an FSK receiver of claim 1.

18. A satellite set top box that receives FSK modulated signals comprising an FSK receiver of claim 1.