Communications receiver having a switchable filter input stage
First Claim
Patent Images
1. A multichannel communications receiver characterized by a reduced level of nonlinear distortion comprising:
- an input terminal for receiving signals broadcast over a plurality of communication channels;
channel selection means developing a first control signal representing a selected one of said plurality of channels and a second control signal representing a band of channels encompassing said selected channel, said band of channels having a bandwidth less than said plurality of channels;
an input stage coupled to said input terminal comprising a plurality of non-tunable circuit components including switchable filter means responsive to said second control signal for assuming a highpass filter characteristic or a lowpass filter characteristic, said filter means comprising an arrangement of inductors and capacitors, a first switching means and a second switching means being responsive to said second control signal for causing said inductors and capacitors to assume said highpass filter characteristic or said lowpass filter characteristic, at least one of said switching means being characterized by a parasitic reactance coupled across said filter means, said receiver comprising compensating means coupled across said filter means for reducing the effect of said parasitic reactance; and
frequency conversion means coupled to the output of said input stage and responsive to said first control signal for processing the passed band of channels so as to develop an output signal having a predetermined frequency representing only said selected channel.
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Abstract
A multichannel communications receiver, e.g. a CATV converter, includes a switched filter for reducing third order intermodulation distortion by limiting the number of channels processed by the receiver. In a preferred embodiment, the filter is switchable between a highpass and a lowpass configuration by a control signal supplied to two switching diodes. The input and output of the filter are coupled by a mutual inductance which partially compensates for the effect of parasitic inductance at higher frequencies.
20 Citations
17 Claims
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1. A multichannel communications receiver characterized by a reduced level of nonlinear distortion comprising:
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an input terminal for receiving signals broadcast over a plurality of communication channels; channel selection means developing a first control signal representing a selected one of said plurality of channels and a second control signal representing a band of channels encompassing said selected channel, said band of channels having a bandwidth less than said plurality of channels; an input stage coupled to said input terminal comprising a plurality of non-tunable circuit components including switchable filter means responsive to said second control signal for assuming a highpass filter characteristic or a lowpass filter characteristic, said filter means comprising an arrangement of inductors and capacitors, a first switching means and a second switching means being responsive to said second control signal for causing said inductors and capacitors to assume said highpass filter characteristic or said lowpass filter characteristic, at least one of said switching means being characterized by a parasitic reactance coupled across said filter means, said receiver comprising compensating means coupled across said filter means for reducing the effect of said parasitic reactance; and frequency conversion means coupled to the output of said input stage and responsive to said first control signal for processing the passed band of channels so as to develop an output signal having a predetermined frequency representing only said selected channel. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A multichannel CATV converter having an improved intermodulation distortion characteristic comprising:
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an input terminal for receiving signals broadcast over a plurality of CATV channels; channel selection means developing a first control signal representing a selected one of said plurality of CATV channels and a second control signal representing a band of channels encompassing said selected channel, said band of channels having a bandwidth less than said plurality of channels; an input stage coupled to said input terminal comprising a plurality of non-tunable circuit components including switchable filter means comprising a reactive network formed of an arrangement of inductors and capacitors, a first switching diode and a second switching diode, said second control signal being developed for selectively causing only said first diode or only said second diode to be conductive at one time such that said reactive network is selectively configured for only passing a highband or a lowband respectively of said plurality of CATV channels, at least one of said diodes being characterized by a parasitic reactance coupled across said filter means, said converter comprising compensating means coupled across said filter means for reducing the effect of said parasitic reactance; and frequency conversion means coupled to the output of said input stage and responsive to said first control signal for processing the passed band of channels so as to develop an output signal having a predetermined frequency representing only said selected CATV channel. - View Dependent Claims (9, 10, 11, 12, 13)
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14. A multichannel CATV converter having an improved intermodulation distortion characteristic comprising;
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an input terminal for receiving signals broadcast over a plurality of CATV channels; channel selection means developing a first control signal representing a selected one of said plurality of CATV channels and a second control signal representing a band of channels encompassing said selected channel, said band of channels having a band width less than said plurality of channels; an input stage coupled to said input terminal comprising a plurality of non-tuneable circuit components including switchable filter means comprising a reactive network formed of an arrangement of inductors and capacitors, a first switching means and a second switching means, said first and second switching means being responsive to said second control signal for causing said reactive network to assume a filter characteristic for only passing the band of channels represented thereby, at least one of said switching means being characterized by a parasitic reactance coupled across said filter means; compensating means coupled across said filter means for reducing the effect of said parasitic reactance; and frequency conversion means coupled to the output of said input stage and responsive to said first control signal for processing said passed band of channels so as to develop an output signal having a predetermined frequency representing only said selected CATV channel. - View Dependent Claims (15, 16)
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17. A switchable filter for reducing intermodulation distortion levels in a multichannel communications receiver comprising;
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an input terminal for receiving signals broadcast over a plurality of communications channels; an output terminal; first and second series connected capacitors coupled between said input and output terminals; first and second series inductors coupled between said input and output terminals; a third capacitor coupled between the common junction of said first and second inductors and a reference potential; a third inductor coupled between the common junction of said first and second capacitors and said reference potential; first and second switching diodes for selectively shunting only the common junction of said first and second capacitors or only the common junction of said first and second inductors to reference potential, whereby to selectively establish either a lowpass or a highpass filter characteristic respectively between said input and output terminals, at least one of said switching diodes being characterized by a parasitic reactance coupled across said input and output terminals; and compensating means for inductively coupling the broadcast signals received at said input terminal to said output terminal in phase opposition to the received broadcast signals coupled across said input and output terminals by said parasitic reactance.
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Specification