Dual conversion FM receiver using phase locked direct conversion IF
First Claim
1. A direct, dual conversion receiver for processing radio signals frequency modulated on a carrier frequency comprising:
- translating bandpass filter means having a signal input, an output, and down- and up-conversion frequency inputs;
first and second frequency sources, coupled to said down- and up-conversion frequency inputs respectively of said translating bandpass filter means;
means for receiving and supplying said frequency modulated radio signals to said signal input of said translating bandpass filter means;
means coupled to said output of said translating bandpass filter means for amplifying and amplitude limiting the output signal of said translating bandpass filter means; and
phase lock loop means for controlling the frequency of said frequency source coupled to said translating filter means down-conversion input to equal the carrier frequency of the signal supplied to said translating filter means signal input and for demodulating said amplitude limited signal and providing a demodulated output.
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Accused Products
Abstract
A receiver for frequency modulated signals, having down-conversion to a baseband, zero intermediate frequency for selectivity, followed by up-conversion to a non-zero IF for amplification, limiting, and demodulation.
A phase-lock loop locks the frequency of the down-conversion source to the center frequency of the signal coupled to the baseband IF, converting the signal to precisely zero frequency. This avoids the beat note often found in direct conversion systems. The phase-lock loop additionally provides inherent demodulation of the FM signal.
The received FM signal is coupled to the baseband IF through a radio frequency amplifier for improved sensitivity and local oscillator isolation, or through a first IF comprising a mixer, local oscillator, filter, and amplifier.
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Citations
17 Claims
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1. A direct, dual conversion receiver for processing radio signals frequency modulated on a carrier frequency comprising:
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translating bandpass filter means having a signal input, an output, and down- and up-conversion frequency inputs; first and second frequency sources, coupled to said down- and up-conversion frequency inputs respectively of said translating bandpass filter means; means for receiving and supplying said frequency modulated radio signals to said signal input of said translating bandpass filter means; means coupled to said output of said translating bandpass filter means for amplifying and amplitude limiting the output signal of said translating bandpass filter means; and phase lock loop means for controlling the frequency of said frequency source coupled to said translating filter means down-conversion input to equal the carrier frequency of the signal supplied to said translating filter means signal input and for demodulating said amplitude limited signal and providing a demodulated output. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A direct, dual conversion receiver for processing radio signals frequency modulated on a carrier frequency comprising:
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translating bandpass filter means having a signal input, an output, and down- and up-conversion frequency inputs; first and second frequency sources, coupled to said down- and up-conversion frequency inputs respectively of said translating bandpass filter means; means for receiving and supplying said frequency modulated radio signals to said signal input of said translating bandpass filter means; means coupled to said output of said translating bandpass filter means for amplifying and amplitude limiting the output signal of said translating bandpass filter means; and phase lock loop means for controlling the frequency of said frequency source coupled to said translating filter means down-conversion input to differ by a predetermined offset from the carrier frequency of the signal supplied to said translating filter means signal input and for demodulating said amplitude-limited signal and providing a demodulated output. - View Dependent Claims (8, 9, 10, 11, 12, 13)
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14. The method of processing a received radio signal frequency modulated on a carrier frequency comprising the steps of:
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supplying said received radio signal to each of two substantially identical paths; down-converting the signal supplied to each of said paths by mixing with quadrature outputs of a first frequency source means to translate said signals in phase quadrature to baseband; lowpass filtering the signal in each of said paths to provide filtered, baseband signals; mixing said filtered baseband signals with quadrature outputs of a second frequency source having a predetermined frequency to produce two intermediate frequency signals; summing said intermediate frequency signals to produce a single intermediate frequency signal; amplifying and amplitude-limiting said single intermediate frequency signal; applying said amplitude-limited intermediate frequency signal to a phase lock loop means that both controls the frequency of said first frequency source and demodulates said intermediate frequency signal. - View Dependent Claims (15)
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16. The method of processing a received radio signal frequency modulated on a carrier frequency comprising the steps of:
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supplying said received radio signal to each of two substantially identical paths; down-converting the signal supplied to each of said paths by mixing with quadrature outputs of a first frequency source means to translate said signals in phase quadrature to a predetermined offset frequency below the range of modulation frequencies; lowpass filtering the signal in each of said paths to provide lowpass filtered signals; mixing said lowpass filtered signals with quadrature outputs of a second frequency source having a predetermined frequency to provide two intermediate frequency signals; summing said intermediate frequency signals to produce a single intermediate frequency signal; amplifying and amplitude limiting said single intermediate frequency signal; applying said amplitude-limited intermediate frequency signal to a phase lock loop means that both controls the frequency of said first frequency source and demodulates said intermediate frequency signal. - View Dependent Claims (17)
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Specification