Tuning system for a digital satellite receiver with fine tuning provisions
First Claim
1. Apparatus for processing digital signals modulated on to ones of a plurality of RF carrier signals, comprising:
- a RF input for receiving said plurality modulated RF carrier signals;
.a tuning control phase locked loop including a local oscillator for generating a local oscillator signal;
a mixer coupled to said RF input and to said local oscillator for producing an IF signal modulated with digital signals corresponding to a selected RF signal of said plurality of RF signals;
an IF filter having a center frequency;
said IF signal having a nominal frequency corresponding to said center frequency of said IF filter;
a digital signal demodulator including a carrier recovery loop means for demodulating said IF to produce said digital signals carried by said IF signal; and
means for controlling the operation of said tuning control phase locked loop in response to at least one control signal generated by said carrier recovery loop which indicates the status of operation of said carrier recovery loop;
said controlling means controlling said tuning control phase locked loop to (1) establish an initial local oscillator frequency corresponding to said selected RF signal during an acquisition mode starting when said selected RF signal is initially selected and ending when said second closed loop is properly demodulating said IF signal, and (2) change the local oscillator frequency from said initial local oscillator frequency to a reduce a frequency offset of said IF signal from said nominal IF frequency during a fine tuning mode;
said controlling means further selectively changing the relative response times of said tuning control phase locked loop and said carrier recovery loop during said fine tuning mode to allow said carrier recovery loop to track frequency changes of said IF signal due to changes of said local oscillator frequency and thereby maintain the proper demodulation of said IF signal.
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Accused Products
Abstract
An economical tuning system for a digital satellite television receiver includes a phase locked loop (PLL) tuning control IC of the which is normally used in a tuning system of a conventional terrestrial broadcast or cable television reciever to control the frequency of the local oscillator (LO). Unfortunately, the PLL IC is only capable of changing the frequency of the LO in relatively large steps. As a result, the operation of a carrier recovery loop which demodulates the digitally encoded IF signal produced by the tuner may be interrupted during a fine tuning mode because the carrier recovery loop may not be able to track frequency changes of the LO. To reduce such possibility, the integrator filter associated with the PLL IC is modified to decrease the rate of change of the LO frequency during the fine tuning mode.
55 Citations
20 Claims
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1. Apparatus for processing digital signals modulated on to ones of a plurality of RF carrier signals, comprising:
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a RF input for receiving said plurality modulated RF carrier signals;
.a tuning control phase locked loop including a local oscillator for generating a local oscillator signal; a mixer coupled to said RF input and to said local oscillator for producing an IF signal modulated with digital signals corresponding to a selected RF signal of said plurality of RF signals; an IF filter having a center frequency;
said IF signal having a nominal frequency corresponding to said center frequency of said IF filter;a digital signal demodulator including a carrier recovery loop means for demodulating said IF to produce said digital signals carried by said IF signal; and means for controlling the operation of said tuning control phase locked loop in response to at least one control signal generated by said carrier recovery loop which indicates the status of operation of said carrier recovery loop; said controlling means controlling said tuning control phase locked loop to (1) establish an initial local oscillator frequency corresponding to said selected RF signal during an acquisition mode starting when said selected RF signal is initially selected and ending when said second closed loop is properly demodulating said IF signal, and (2) change the local oscillator frequency from said initial local oscillator frequency to a reduce a frequency offset of said IF signal from said nominal IF frequency during a fine tuning mode; said controlling means further selectively changing the relative response times of said tuning control phase locked loop and said carrier recovery loop during said fine tuning mode to allow said carrier recovery loop to track frequency changes of said IF signal due to changes of said local oscillator frequency and thereby maintain the proper demodulation of said IF signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. Apparatus for processing digital signals modulated on to ones of a plurality of RF carrier signals, comprising:
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a RF input for receiving said plurality modulated RF carrier signals; a first closed loop means including a local oscillator for generating a local oscillator signal; a mixer coupled to said RF input and to said local oscillator for producing an IF signal modulated with digital signals corresponding to a selected RF signal of said plurality of RF signals; an IF filter having a center frequency;
said IF signal having a nominal frequency corresponding to said center frequency of said IF filter;a digital signal demodulator including a second closed loop means for demodulating said IF to produce said digital signals carried by said IF signal; and means for controlling the operation of said first closed loop means in response to at least one control signal generated by said second closed loop means which indicates the status of operation of said second closed loop means; said controlling means controlling said first closed loop means to (1) establish an initial local oscillator frequency corresponding to said selected RF signal during an acquisition mode starting when said selected RF signal is initially selected and ending when said second closed loop is properly demodulating said IF signal, (2) maintain said initial local oscillator frequency during a steady-state mode, and (3) change the local oscillator frequency from said initial local oscillator frequency to a reduce a frequency offset of said IF signal from said nominal IF frequency during a fine tuning mode; said controlling means further controlling said first closed loop means to increase the response time of said first closed locked loop means to allow said second closed loop means to track frequency changes of said IF signal due to frequency changes of said local oscillator and thereby maintain the proper demodulation of said IF signal during said fine tuning mode. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19)
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20. Apparatus for processing digital signals modulated on to ones of a plurality of RF carrier signals, comprising:
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a RF input for receiving said plurality modulated RF carrier signals; a first closed loop means including a local oscillator for generating a local oscillator signal; a mixer coupled to said RF input and to said local oscillator for producing an IF signal modulated with digital signals corresponding to a selected RF signal of said plurality of RF signals; an IF filter having a center frequency;
said IF signal having a nominal frequency corresponding to said center frequency of said IF filter;a digital signal demodulator including a second closed loop means for demodulating said IF to produce said digital signals carried by said IF signal; and means for controlling the operation of said first closed loop means in response to at least one control signal generated by said second closed loop means which indicates the status of operation of said second closed loop means; said controlling means controlling said first closed loop means to (1) establish an initial local oscillator frequency corresponding to said selected RF signal during an acquisition mode starting when said selected RF signal is initially selected and ending when said second closed loop is properly demodulating said IF signal, (2) maintain said initial local oscillator frequency during a steady-state mode, and (3) change the local oscillator frequency from said initial local oscillator frequency to a reduce a frequency offset of said IF signal from said nominal IF frequency during a fine tuning mode; said first closed loop means having a first response time during said acquisition mode, a second response time greater than said first response time during a steady state mode, and a third response time greater than said second response time during said fine tuning mode.
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Specification