Frequency synthesis architecture in a satellite receiver

• US 6,091,931 A
• Filed: 06/18/1997
• Issued: 07/18/2000
• Est. Priority Date: 06/18/1997
• Status: Expired due to Term

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: LSI Logic Corporation (Broadcom, Inc.)
• Inventors: Ben-Efraim, Nadav, Keate, Christopher
• Primary Examiner(s): Harvey, David E.
• Application Number:
  US08/878,328
• Time in Patent Office: 1,126 Days
• Field of Search: 348/726, 348/731, 348/725, 348/732, 348/733, 455/3.2, 455/191.1, 455/191.2, 455/191.3, 455/197.2, 455/197.3, 455/198.1, 455/199.1
• US Class Current: 455/3.02
• CPC Class Codes: H03D 7/166 using two or more quadrature frequency translation stages
• CPC Class Codes: H03J 1/0008 using a central processing unit, e.g. a microprocessor digital tuning in general H03J5/0245
• CPC Class Codes: H03J 7/065 the counter or frequency divider being used in a phase locked loop
• CPC Class Codes: H04N 7/20 Adaptations for transmission via a GHz frequency band, e.g. via satellite

Abstract

An improved DBS receiver front end architecture having a tuner chip and a demodulator/decoder chip. The tuner chip and the demodulator/decoder chip each include portions of a digital tuning frequency synthesizer. The frequency synthesizer comprises one or more digital counters which are implemented on the demodulator/decoder chip, and an oscillator which is implemented on the tuner chip. This advantageously avoids digital noise interference with the tuner chip while providing a reduced part count. Briefly, the present invention concerns a DBS receiver front end which includes a tuner chip and a demodulator/decoder chip which cooperate to perform a frequency synthesis function. The tuner chip has a tuning oscillator coupled to a tank circuit having an adjustable resonance frequency, and a downconverter coupled to receive a tuning frequency signal provided by the tuning oscillator. The demodulator/decoder chip has a programmable counter configured to count cycles of the tuning frequency to provide a frequency-divided signal to a phase detector. The phase detector compares the frequency-divided signal to a reference frequency, and is coupled to adjust the resonance frequency of the tank circuit to cause the tuning frequency to have a frequency which is a multiple of the resonance frequency. The demodulator/decoder chip also has a decoder which receives the baseband signal and converts it to a decoded signal.

Claims

1. A DBS receiver front end comprising:

a tuner chip which includes;

a tuning oscillator coupled to a tank circuit having an adjustable resonance frequency;

a downconverter coupled to the tuning oscillator to receive a tuning frequency signal, wherein the downconverter is further coupled to receive a receive signal, wherein the downconverter is configured to responsively provide a product signal, wherein the tuner chip is configured to convert the product signal into a baseband signal; and

a demodulator/decoder chip which includes;

a programmable counter coupled to count cycles of the tuning frequency signal, wherein the programmable counter is configured to responsively provide a frequency-divided signal to a phase detector, wherein the phase detector is configured to compare the frequency-divided signal with a reference frequency, and wherein the phase detector is coupled to adjust the resonance frequency of the tank circuit to cause the tuning frequency signal to have a frequency which is a multiple of the reference frequency; and

a decoder operably coupled to receive said baseband signal and configured to convert the baseband signal to a decoded signal.

2. The DBS receiver front end of claim 1, wherein the tuner chip further includes:

a prescaler coupled to receive the tuning frequency signal from the tuning oscillator, wherein the prescaler is configured to provide a reduced frequency signal to the programmable counter; and

a charge pump coupled to the phase detector and configured to responsively provide a correction voltage to a loop filter which determines the resonance frequency of the tank circuit.

3. The DBS receiver front end of claim 2, wherein the tuner chip includes the phase detector, and wherein the tuner chip further includes:

a crystal oscillator configured to provide a crystal oscillation signal; and

a reference divider configured to provide the reference frequency by frequency-dividing the crystal oscillation signal.

4. The DBS receiver front end of claim 2, wherein the downconverter comprises:

a phase-shift network which converts the tuning frequency signal into a zero-phase signal and a 90-degree-phase signal;

a first mixer coupled to combine the zero-phase signal with the receive signal to provide a first product signal; and

a second mixer coupled to combine the 90-degree-phase signal with the receive signal to provide a second product signal.

5. The DBS receiver front end of claim 4, wherein the tuner chip further comprises:

a dual lowpass filter coupled to receive said first and second product signals and responsively produce said baseband signal; and

a gain control amplifier coupled to receive said baseband signal from the lowpass filter, wherein the gain control amplifier multiplies the baseband signal by an adjustable gain to produce a baseband signal with a constant-maximum.

6. The DBS receiver front end of claim 2, wherein the demodulator/decoder chip includes the phase detector, and wherein the demodulator/decoder chip further includes:

a crystal oscillator configured to provide a crystal oscillation signal; and

a reference divider configured to provide the reference frequency by frequency-dividing the crystal oscillation signal.

7. The DBS receiver front end of claim 2, wherein the demodulator/decoder chip further comprises:

an analog-to-digital converter coupled to convert the baseband signal into a digital baseband signal;

a filter coupled to filter the digital baseband signal to produce a filtered signal, wherein the filter is configured to maximize a signal to noise ratio of the filtered signal, and wherein the filtered signal is coupled to the decoder for conversion to a decoded signal.

8. The DBS receiver front end of claim 7, wherein the baseband signal may have a frequency offset error, and wherein the demodulator/decoder chip further includes:

a frequency offset estimator coupled to receive the filtered signal and responsively produce a frequency offset error estimate; and

a microcontroller configured to read the frequency offset error estimate and responsively determine a correct setting for the programmable counter.

9. A tuner chip which comprises:

a tuning oscillator coupled to a tank circuit having an adjustable resonance frequency;

a downconverter coupled to the tuning oscillator to receive a tuning frequency signal, wherein the downconverter is further coupled to receive a receive signal, wherein the downconverter is configured to responsively provide a product signal, wherein the tuner chip is configured to convert the product signal into a baseband signal;

a prescaler coupled to receive the tuning frequency signal from the tuning oscillator, wherein the prescaler is configured to provide a reduced frequency signal to an off-chip programmable counter;

a phase detector coupled to the off-chip programmable counter to receive a frequency-divided signal and configured to compare the frequency divided signal to a reference frequency; and

a charge pump coupled to the phase detector and configured to responsively provide a correction voltage to a loop filter which determines the resonance frequency of the tank circuit.

10. The tuner chip of claim 9, wherein the tuner chip further includes:

a crystal oscillator configured to provide a crystal oscillation signal; and

a reference divider configured to provide the reference frequency by frequency-dividing the crystal oscillation signal.

11. The tuner chip of claim 10, wherein the downconverter comprises:

a phase-shift network which converts the tuning frequency signal into a zero-phase signal and a 90-degree-phase signal;

a first mixer coupled to combine the zero-phase signal with the receive signal to provide a first product signal; and

a second mixer coupled to combine the 90-degree-phase signal with the receive signal to provide a second product signal.

12. The tuner chip of claim 11, wherein the tuner chip further comprises:

a dual lowpass filter coupled to receive said first and second product signals and responsively produce said baseband signal; and

a gain control amplifier coupled to receive said baseband signal from the lowpass filter, wherein the gain control amplifier multiplies the baseband signal by an adjustable gain to produce a baseband signal with a constant-maximum.

13. A method for synthesizing a tuning frequency in a DBS receiver front end having a tuner chip and a demodulator/decoder chip, wherein the method comprises:

coupling a tuning oscillator on the tuner chip to a tank circuit;

configuring a prescaler on the tuner chip to produce a reduced frequency signal from a tuning frequency signal provided by the tuning oscillator;

programming a counter on the demodulator/decoder chip to count a desired number of reduced frequency signal cycles for each cycle of a frequency divided signal provided by the counter;

configuring a phase detector to compare a reference frequency signal with the frequency divided signal to provide a phase difference signal;

coupling the phase difference signal to a charge pump on the tuner chip;

coupling the charge pump to provide a correction voltage to a loop filter; and

coupling the loop filter to control a resonance frequency of the tank circuit.

14. The method of claim 13, wherein the phase detector is on the demodulator/decoder chip, and wherein the method further comprises coupling a reference divider on the demodulator/decoder chip to a crystal oscillator to provide the reference frequency signal.

15. The method of claim 13, wherein the phase detector is on the tuner chip, and wherein the method further comprises coupling a reference divider on the tuner chip to a crystal oscillator to provide the reference frequency signal.