Front end circuits of FM receivers
AssigneeNippon Gakki Seizo Kabushiki Kaisha
InventorMinoru Ogita
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Abstract
The front end circuit is constituted by first and second signal paths for transmitting a high frequency signal received by an antenna, and a transfer switch for selecting either one of the signal paths depending upon the state of the received signal, and a circuit for converting the frequency of either one of the selected signals to an intermediate frequency signal. Two signal paths have different filtering attenuating and amplifying characteristics, thereby providing an optimum condition for either a local or distant reception of radio wave signals.
Claims10
In a front end circuit of an FM receiver of the type wherein the frequency of a high frequency signal received from an antenna input circuit is converted to obtain an intermediate frequency signal, the improvement which comprises at least two alternate signal processing circuits having different characteristics in sensitivity and selectivity to be selected in compliance with a high frequency signal tuned by the antenna input circuit, a first one of said alternate signal processing circuits comprising means for providing relatively broader frequency band and relatively high signal to noise ratio processing for said high frequency signal, the other one of said alternate signal processing circuits comprising means for providing relatively narrower frequency band and relatively lower signal to noise ratio processing for said high frequency signal, said other one of said alternate signal processing circuits including filter means providing a relatively steeper and narrower band pass characteristic than that provided by said first one of said alternate signal processing circuits, both of said alternate signal processing circuits having band pass characteristics centered substantially about the same frequency, a frequency converter for converting the outputs of said processing circuits into an intermediate frequency signal, and transfer switch means for selectively connecting said first one of said alternate processing circuits to the input of said frequency converter when said received high frequency signal is of a relatively high intensity and for connecting said other one of said alternate signal processing circuits to the input of said frequency converter when said received high frequency signal is of a relatively low intensity, whereby the received high frequency signal is reproduced in the most suitable sensitivity and selectivity.
Dependencies are inferred from the claim text.