CCD demodulator/correlator
First Claim
1. A CCD demodulator/correlator for use in a direct sequence, spread spectrum receiver for demodulating a received signal to produce a demodulated signal and for correlating the demodulated signal with respect to a code signal to produce an output signal indicating the degree of correlation between the demodulated signal and the code signal, the demodulator/correlator comprising:
- (a) a demodulator comprising;
(i) at least one filter input site at which a received signal is sampled and converted into charge packets;
(ii) a CCD filter, the filter comprising a plurality of filter charge storage sites;
(iii) means for causing the charge packets to propagate along the filter charge storage sites; and
(iv) an output site at which the filter produces the demodulated signal in the form of a sequence of the charge packets; and
(b) a correlator comprising;
(i) a CCD delay line, the CCD delay line comprising a sequence of correlator charge storage sites, including a correlator input site;
(ii) means for coupling the demodulated signal to the correlator input site;
(iii) a matching circuit, the matching circuit comprising means for storing a code signal; and
(iv) means for combining charge packets stored in the correlator charge storage sites in accordance with the code signal to produce an output signal.
1 Assignment
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Accused Products
Abstract
A charge-coupled device (CCD) used as a demodulator and a correlator in the receiver of a spread spectrum radio system. The device implements both functions in the charge domain, thereby avoiding unnecessary conversions between voltage and charge that would normally be required if the functions were separately implemented. In its preferred form, the demodulator and correlator include an in-phase filter (170), a quadrature filter (172), delay circuits (174, 176), decimation circuits (181-184), correlators (191-194), and signal combiners (200, 202). The delay circuits are used in the preferred embodiment to compensate a time shift between the in-phase and quadrature channels that result from the minimum shift keying modulation used, but would not necessarily be required for other types of modulation. The decimation circuits match the data rate of the in-phase and quadrature filters to the data rate used by the correlators, which is determined as a function of chip rate used to spread the data. Each of the in-phase and quadrature channels are implemented in a CCD, which includes a "pipe organ" filter structure to implement the respective filters that process the analog input signal for each channel. Storage sites are configured as delay lines in the device.
63 Citations
17 Claims
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1. A CCD demodulator/correlator for use in a direct sequence, spread spectrum receiver for demodulating a received signal to produce a demodulated signal and for correlating the demodulated signal with respect to a code signal to produce an output signal indicating the degree of correlation between the demodulated signal and the code signal, the demodulator/correlator comprising:
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(a) a demodulator comprising; (i) at least one filter input site at which a received signal is sampled and converted into charge packets; (ii) a CCD filter, the filter comprising a plurality of filter charge storage sites; (iii) means for causing the charge packets to propagate along the filter charge storage sites; and (iv) an output site at which the filter produces the demodulated signal in the form of a sequence of the charge packets; and (b) a correlator comprising; (i) a CCD delay line, the CCD delay line comprising a sequence of correlator charge storage sites, including a correlator input site; (ii) means for coupling the demodulated signal to the correlator input site; (iii) a matching circuit, the matching circuit comprising means for storing a code signal; and (iv) means for combining charge packets stored in the correlator charge storage sites in accordance with the code signal to produce an output signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A CCD demodulator/correlator for use in a direct sequence, spread spectrum receiver having a code signal source, said CCD demodulator/correlator comprising:
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(a) demodulation filter means, in receipt of a received signal, for demodulating the received signal, producing a demodulated signal that is in a charge domain form; and (b) correlator means, coupled to receive the demodulated signal in the charge domain form, for correlating the demodulated signal with chips provided by a pseudorandom number generator code signal, to recover an intelligence bearing signal. - View Dependent Claims (10, 11)
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12. A method for demodulating and correlating a received signal in a direct sequence, spread spectrum receiver having a pseudorandom number generator that produces a code signal, said method comprising the steps of:
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(a) demodulating a received signal, producing a demodulated signal that is in a charge domain form; and (b) directly correlating the demodulated signal in the charge domain form, without any intermediate conversion between a voltage domain and the charge domain form, with a code signal to recover an intelligence bearing signal, said steps of demodulating and correlating being completed entirely in the charge domain to avoid conversion between the charge domain and the voltage domain.
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13. A method for demodulating and correlating a received signal to produce a demodulated signal and to correlate the demodulated signal with respect to a code signal, to produce an output signal indicating the degree of correlation between the demodulated signal and the code signal, said method being used in a direct sequence, spread spectrum receiver, comprising the steps of:
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(a) causing a plurality of charge packets to propagate along a plurality of filter charge storage sites, producing a demodulated signal; (b) coupling the demodulated signal to a correlator input site; (c) storing a code signal; and (d) combining charge packets stored in a plurality of correlator charge storage sites in accordance with the code signal to produce an output signal. - View Dependent Claims (14, 15, 16, 17)
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Specification