Linearized FM quadrature detector
AssigneeNational Semiconductor Corporation
InventorWilliam B. Jett, Jr.
Life of this patent
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Abstract
In an FM receiver a multiplier is driven from the IF limiter. The limiter also drives a single tuned circuit which produces a quadrature signal that drives a second port in the multiplier. When the quadrature signal is multiplied by the IF signal an FM detector results. The center frequency is determined by the frequency of the quadrature relationship and the extent of the resultant output curve is determined by the Q of the tuned circuit. The output response is linearized by varying the current in the multiplier as a function of the IF signal deviation.
Claims10
In an FM detector comprising a multiplier having input signal means, output signal means, current control means and means for coupling said multiplier to a source of signal in phase quadrature with with the signal coupled to said input signal means, the improvement comprising:
- means for varying the current in said current control means so tha the current in said multiplier increases as the input signal coupled to said input signal means deviates from its center frequency whereby the linearity of said detector is increased.
An FM detector comprising:
- a multiplier having first and second input ports, and output port and a source of operating current;
- means for driving said first port with a constant amplitude signal;
- a tuned circuit;
- means for driving said tuned circuit from said means for driving said first port in quadrature therewith;
- means for coupling said tuned circuit to said second port for supplying a quadrature signal thereto;
- and
- means for modulating said source of operating current in response to the deviation of said constant amplitude signal from the center frequency of said tuned circuit.
Dependencies are inferred from the claim text.