Tunable notch filter for image frequency and conducted local oscillator leakage rejection
First Claim
1. In an RF receiver generating an IF signal having desired and undesired components by heterodyning a local oscillator signal with a selected RF signal and an image frequency signal respectively, the improved tuning arrangement comprising:
- tuning means for generating a tuning voltage representing the selected RF signal; and
a filter circuit including a parallel resonant circuit having tunable means coupled to said tuning means and responsive to said tuning voltage for assuming in response to said tuning voltage a parallel resonance for establishing a maximum response at the frequency of said selected RF signal, said parallel resonant circuit further comprising a series resonance circuit including said tunable means for assuming in response to said tuning voltage a series resonance for establishing a notch near the frequency of said local oscillator signal so as to pass the selected RF signal while attenuating the local oscillator and image frequency signals.
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Accused Products
Abstract
A tunable notch filter for the front end of an RF receiver includes magnetically coupled input and output tunable stages each responsive to a tuning voltage provided thereto. Each of the input and output stages includes a respective series and parallel resonant circuit wherein the parallel resonant circuits are tuned to a selected RF frequency and the series resonant circuits are tuned to a frequency approximately equal to that of a local oscillator. By using the series resonant circuits to create a notch at a frequency approximating that of the local oscillator, conducted local oscillator leakage from the receiver'"'"'s antenna is substantially reduced and local oscillator image frequency rejection is substantially improved.
53 Citations
22 Claims
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1. In an RF receiver generating an IF signal having desired and undesired components by heterodyning a local oscillator signal with a selected RF signal and an image frequency signal respectively, the improved tuning arrangement comprising:
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tuning means for generating a tuning voltage representing the selected RF signal; and a filter circuit including a parallel resonant circuit having tunable means coupled to said tuning means and responsive to said tuning voltage for assuming in response to said tuning voltage a parallel resonance for establishing a maximum response at the frequency of said selected RF signal, said parallel resonant circuit further comprising a series resonance circuit including said tunable means for assuming in response to said tuning voltage a series resonance for establishing a notch near the frequency of said local oscillator signal so as to pass the selected RF signal while attenuating the local oscillator and image frequency signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. In an RF receiver generating an IF signal having desired and undesired components by heterodyning a local oscillator signal with a selected RF signal and an image frequency signal respectively, the improved tuning arrangement comprising:
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tuning means for generating a tuning voltage representing the selected RF signal; and filter means comprising a parallel circuit and a series circuit sharing a common varactor diode, the varactor diode being responsive to the tuning voltage for causing the parallel circuit to resonate for establishing a maximum response at the frequency of the selected RF signal and the series circuit to resonate for establishing a notch between the frequencies of the local oscillator and image frequency signals so as to pass the selected RF signal while attenuating the local oscillator and image frequency signals. - View Dependent Claims (10, 11)
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12. In an RF receiver including an antenna responsive to an RF signal incident thereon and a mixer responsive to the RF signal and coupled to a local oscillator and further responsive to a local oscillator frequency signal output therefrom for combining said RF and local oscillator frequency signals in a heterodyned manner for generating an IF signal, said RF receiver further including tuning means for generating a tuning voltage for tuning said RF receiver over a range of RF frequencies, a tunable notch filter comprising:
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an input stage coupled to the antenna for receiving the RF signal and including first coupled tunable parallel and series resonant circuits, wherein said input stage is coupled to the tuning means and is responsive to the tuning voltage received therefrom and wherein the tuning voltage tunes said first parallel resonant circuit to a desired frequency and tunes said first series resonant circuit to a notch frequency approximately equal to the frequency of the local oscillator signal; and an output stage magnetically coupled to said input stage and including second coupled tunable parallel and series resonant circuits, wherein said output stage is coupled to the mixer and to the tuning means and is responsive to the tuning voltage received therefrom and wherein the tuning voltage tunes said second parallel resonant circuit to said desired frequency and tunes said second series resonant circuit to said notch frequency. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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Specification