Digital down converter and method
First Claim
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1. A digital down converter, comprising:
- (a) a data input;
(b) sine and cosine multipliers, each with a multiplicand input coupled to said data input;
(c) a sin/cos generator with sine output coupled to a multiplier input of said sine multiplier and with cosine output coupled to a multiplier input of said cosine multiplier;
(d) a phase generator with output coupled to a phase input of said sin/cos generator;
(e) a lowpass filter with first and second filter inputs coupled to product outputs of said sine and cosine multipliers, respectively;
(f) an output formatter with first and second format inputs coupled to first and second filter outputs of said lowpass filter, respectively;
(g) control logic coupled to said phase generator, said lowpass filter, and said formatter, wherein control words held in said control logic determine (i) the phase output of said phase generator and (ii) the output format of said formatter, said control words including ones which effectively couple said data input directly to said lowpass filter.
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Abstract
A digital down converter for extracting a signal from a complex digital signal wherein the real and imaginary components of the complex digital signal are each modulated to shift the center frequency of the desired signal to zero frequency, decimated digitally to limit the bandwidth of each to the bandwidth of the desired signal and filtered to alter the shape thereof. The digital down converter includes a formatter for arranging the output of the desired signal in one of multiple output formats and a controller for programmably controlling the modulation, decimation and filtering and for selecting the desired output format.
207 Citations
18 Claims
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1. A digital down converter, comprising:
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(a) a data input; (b) sine and cosine multipliers, each with a multiplicand input coupled to said data input; (c) a sin/cos generator with sine output coupled to a multiplier input of said sine multiplier and with cosine output coupled to a multiplier input of said cosine multiplier; (d) a phase generator with output coupled to a phase input of said sin/cos generator; (e) a lowpass filter with first and second filter inputs coupled to product outputs of said sine and cosine multipliers, respectively; (f) an output formatter with first and second format inputs coupled to first and second filter outputs of said lowpass filter, respectively; (g) control logic coupled to said phase generator, said lowpass filter, and said formatter, wherein control words held in said control logic determine (i) the phase output of said phase generator and (ii) the output format of said formatter, said control words including ones which effectively couple said data input directly to said lowpass filter. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method of extracting a desired signal of specified bandwidth from a digital signal comprising the steps of:
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(a) providing a complex digital input signal having a real component and an imaginary component, each of said components comprised of a series of discrete time samples; (b) individually modulating said real and imaginary components such that the center frequency of one sideband of said desired signal is down converted to zero frequency; (c) decimating said real and imaginary components to thereby limit the bandwidth of each to the bandwidth of said desired signal; (d) formatting said real and imaginary components according to one of multiple output formats; (e) programmably controlling the modulation and decimation of said real and imaginary components and the bandwidth of said desired signal. - View Dependent Claims (8, 9, 10, 11, 12)
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13. A digital down converter which extracts a desired signal of specified bandwidth from a complex digital signal having an original sample rate comprising:
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a modulator section for individually down converting the real and imaginary components of said complex digital signal such that the center frequency of said desired signal is zero frequency; a filter section for limiting the bandwidth of said real and imaginary components by decimating the sample rate of each to thereby produce a real desired signal component and an imaginary desired signal component, each with a sample rate less than said original sample rate; formatter means for arranging said real desired signal component and said imaginary desired signal component in one of multiple serial output formats; and control means for programmably controlling said modulator section, said filter section and said formatter means. - View Dependent Claims (14, 15, 16, 17)
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18. A digital down converter which extracts a desired signal of specified bandwidth from a complex digital signal having a real component, an imaginary component and an original sample rate comprising:
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a sin/cosine generator for producing at least two out-of-phase modulation signals; a phase generator for producing a phase increment represented by a digital word which is sent to said sine/cosine generator for altering the phase of said modulation signals; plural multipliers for modulating said real and imaginary components by multiplying said real component by one of said modulation signals and multiplying said imaginary component by another of said modulation signals to thereby down convert said real and said imaginary components such that the center frequency of said desired signal is zero frequency; a decimation section having a specified decimation rate for decreasing the sample rate of said real and imaginary components and thereby producing a sampled real component and a sampled imaginary component with a sample rate less than said original sample rate; a scaling section for changing the magnitude of said sampled real component and said imaginary component by a factor corresponding to said specified decimation rate; a formatter section for arranging said sampled real component and said sampled imaginary component in one of multiple serial output formats; and control means for programmably controlling said sine/cosine generator, said phase generator, said decimation section, said scaling section and said formatter section.
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Specification