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US 4,755,761 AGranted
Zero intermediate-frequency demodulator
AssigneeGeneral Electric Company
InventorRobert T. Ray, Jr.
Life of this patent
Estimating the term…
Abstract
A zero intermediate-frequency (IF) demodulator includes a pair of mixers receiving a quadrature local oscillator signal, for converting the FM-modulated input signal to an in-phase I baseband signal and a quadrature-phase Q baseband signal; each I and Q signal is then delayed and the I and Q signals and the delayed I.sub.d and Q.sub.d signals are arithmetically processed to generate first and second modulation-related signals, which are summed to provide the recovered modulation as an output signal. The arithmetic processing may use additive and/or multiplicative operations.
Claims19
A zero-intermediate frequency demodulator, comprising:
- means for generating a local oscillator (LO) signal at a frequency f.sub.o substantially equal to the average frequency of an input signal having the instantaneous frequency f.sub.i thereof modulated by transmitted information;
- means, receiving said LO signal, for converting the input signal to a pair of simultaneous signals including an in-phase baseband I signal and a quadrature-phase baseband Q signal;
- means for operating upon each of the respective I and Q signals with a substantially similar first transfer function H to produce respective baseband I.degree. and Q.degree. signals;
- a pair of arithmetic processing means each for operating upon a selected pair of the I, I.degree., Q and Q.degree. signals to generate an associated one of first and second signals each having an amplitude related to the instantanous modulation on the input signal, each including:
- means for performing a selected one of the respective operations of adding and subtracting a first one of the selected pair of signals respectively to and from the other signal of the selected pair, to provide a resulting signal;
- and multiplication means for squaring the resulting signal to obtain the associated one of the first and second signals;
- first summer means for summing the first and second signals to provide the recovered modulation as a first summer output signal;
- and
- output means, receiving at least the first summer output signal, for providing a demodulator output signal containing the information recovered from the input signals modulation.
6 more elements
A zero-intermediate-frequency demodulator, comprising:
- means for generating a local oscillator (LO) signal at a frequency f.sub.o substantially equal to the average frequency of an input signal having the instantaneous frequency f.sub.i thereof modulated by transmitted information;
- means, receiving said LO signal, for converting the input signal to a pair of simultaneous signals including an in-phase baseband I signal and a quadrature-phase baseband Q signal;
- means for delaying each of the respective I and Q signals by substantially the same delay time t.sub.d to provide respective baseband I.sub.d and Q.sub.d signals;
- a first multiplier means for providing a first signal as the product (I.multidot.Q.sub.d) of the I and Q.sub.d signals;
- a second multiplier means for providing a second signal as the product (Q.multidot.I.sub.d) of the Q and I.sub.d signals;
- first summer means for adding the negative of the second signal to the first signal, to provide the recovered modulation as a first summer output signal;
- and
- output means, receiving at least the first summer output signal, for providing a demodulator output signal containing the information recovered from the input signal modulation, and with the demodulator output signal amplitude proportional to
- sin (2.pi.[f.sub.i -f.sub.o ]t.sub.d).
6 more elements
A zero-intermediate-frequency demodulator, comprising:
- means for generating a local oscillator (LO) signal at a frequency f.sub.o substantially equal to the average frequency of an input signal having the instantaneous frequency f.sub.i thereof modulated by transmitted information;
- means, receiving said LO signal, for converting the input signal to a pair of simultaneous signals including an in-phase baseband I signal and a quadrature-phase baseband Q signal;
- means for delaying each of the respective I and Q signals by substantially the same delay time t.sub.d to provide respective baseband I.sub.d and Q.sub.d signals;
- a first multiplier means for providing a first signal as the product (I.multidot.I.sub.d) of the I and I.sub.d signals;
- a second multiplier means for providing a second signal as the product (Q.multidot.Q.sub.d) of the Q and Q.sub.d signals;
- first summer means for summing the first and second signals to provide the recovered modulation as a first summer output signal;
- and
- output means, receiving at least the first summer output signal, for providing a demodulator output signal containing the information recovered from the input signal modulation.
5 more elements
A zero-intermediate-frequency constant-phase frequency-shift-keyed (CPFSK) demodulator, comprising:
- means for generating a local oscillator (LO) signal at a frequency f.sub.o substantially equal to the average frequency of an input signal having the instantaneous frequency f.sub.i thereof of CPFSK-modulated by transmitted information;
- means, receiving said LO signal, for converting the input signal to a pair of simultaneous signals including an in-phase baseband I signal and a quadrature-phase baseband Q signal;
- first means for delaying each of the respective I
- by substantially similar time intervals .tau., where .tau. is substantially equal to the time interval in which one bit of CPFSK data is transmitted, to produce respective baseband I.sub.d and Q.sub.d signals;
- second means for delaying each of the respective I and Q signals by substantially similar time intervals 2.tau. to produce respective baseband I.sub.2d and Q.sub.2d signals;
- means receiving I, I.sub.d, I.sub.2d, Q, Q.sub.d and Q.sub.2d signals for generating each of first through fourth signals respectively as the (I.multidot.I.sub.2d), (Q.multidot.I.sub.d), (I.multidot.Q.sub.d) and (Q.multidot.Q.sub.2d) product signals;
- first summer means for subtracting the third signal from the second signal to provide a first summer output signal proportional to
- sin (2.pi.[f.sub.i -f.sub.o ].tau.);
- second summer means for summing the first and fourth signals to provide a second summer output signal proportional to
- cos (2.pi.[2(f.sub.i -f.sub.o)].tau.);
- and
- means, receiving the first and second summer output signals, for correcting frequency offset errors and providing a demodulator output signal containing the information recovered from the input signal modulation.
9 more elements
A zero-intermediate-frequency demodulator, comprising:
- means for converting an analog input signal, having the frequency thereof modulated by information, to a sequence of alternating in-phase I and quadrature-phase Q multi-bit digital data words, at a sampling rate determined by a sample signal and at least twice the bandwidth of the modulating information;
- arithmetic processing means for digitally providing alternating sequential data words representing a first product of the I data word and a delayed Q data word and then a second product of the Q data word and a delayed I data word;
- means for digitally adding the first and second product data words to obtain an output data word representing the information recovered from the input signal modulation;
- control means for providing the sample signal and for synchronizing all operations of the converting, processing and adding means;
- and
- means for converting the data of the output data word to the amplitude of an analog output signal.
3 more elements
A zero-intermediate-frequency demodulator, comprising:
- means for generating a local oscillator (LO) signal at a frequency f.sub.o substantially equal to the average center frequency f.sub.c of an input signal having the instantaneous frequency f.sub.i, thereof modulated by transmitted information;
- means receiving said LO signal, for converting the input signal to a pair of simultaneous signals including an in-phase baseband I signal and a quadrature-phase baseband Q signal;
- ADC means for converting each of the substantially simultaneous baseband analog in-phase I and quadrature-phase Q signals in a multi-bit digital data word, at a sampling rate determined by a sample signal and at least twice the base bandwidth of the modulating information;
- arithmetic processing means, receiving the sample signal, the logical inverse of the sample signal and the digital I and Q data words, for digitally providing alternating sequential data words representing a first product of the I data word and the Q data word delayed by a time interval t.sub.d inversely proportional to one-fourth the center frequency f.sub.c, and then a second produce of the Q data word and the I data word delayed by the T.sub.d time interval;
- means for digitally adding the first and second product data words to obtain an output data word representing the information recovered from the input signal modulation;
- control means for providing the sample and inverse sample signals to synchronize all operations of the ADC, processing and adding means;
- and
- means for converting the data of the output data word to the amplitude of an analog output signal.
5 more elements
Dependencies are inferred from the claim text.