Direct conversion radio receiver for FM signals
AssigneeInternational Standard Electric Corporation
InventorsIan A. W. Vance, John K. Goatcher
Life of this patent
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Abstract
A radio receiver for FM signals having a demodulation system to produce an approximation to an analog output by either measuring the time intervals between successive zero crossings in the I.F. (FIG. 1, FIG. 2B) or by filtering pulses produced at each zero crossing of the I.F. (FIG. 1, FIG. 2A). The demodulator includes two signal pathways in quadrature phase relation, the second signal either lagging or leading the first signal in dependence on whether the received signal frequency is above or below a local oscillator frequency. The modulation frequency can carry analog information separate and apart from the on-off (digital) information.
Claims16
In or for a radio receiver for receiving frequency modulated signals with a varying frequency difference from a carrier frequency, and in which mixing with a local oscillator is used to produce quadrature baseband channels, a demodulator circuit comprising a first channel in which a first baseband signal at the difference frequency will appear, a second channel in which a second baseband signal at the difference frequency will appear in quadrature with respect to the first channel and lagging or leading the first baseband signal in dependence upon the received signal frequency being above or below the local oscillator frequency, respectively;
- and means for converting the outputs of said channels into an analog signal having an amplitude representative of the difference frequency.
Dependencies are inferred from the claim text.