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US 4,724,407 AGranted
Integrated filter circuit having switchable selected parallel filter paths
AssigneeHitachi, Ltd.
InventorsKuniaki Miura, Isao Fukushima, Yoshinori Okada, Mitsuru Kudo, Takashi Kubota
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Abstract
An integrated filter circuit including at least integrated resistances and integrated capacitances, said integrated filter circuit comprising a plurality of filter circuits connected in parallel and in which at least either resistance values or capacitance values are different, a switch for switching said parallel filter circuits, and means for controlling said switch to select one of said parallel filter circuits.
Claims6
An integrated filter circuit having at least integrated resistors and integrated capacitors comprising:
- (a) a first filter having an input and an output, a desired first center characteristic frequency f.sub.r1, and an actual first center characteristic frequency which is determined by first resistance and first capacitance values respectively of said integrated resistors and integrated capacitors, said values of first resistance and first capacitance being subject to variation from a desired value;
- (b) a second filter having an input and an output, a desired second center characteristic frequency f.sub.r2, and an actual second center characteristic frequency which is determined by second resistance and second capacitance values respectively of said integrated resistors and integrated capacitors, said values of second resistance and second capacitance being subject to variation from a desired value;
- (c) filter switching means, coupled to at least one of the input and output of said first and second filters, for selecting the first filter when the actual center characteristic frequency of the first filter is higher than the frequency f.sub.r1 or the actual center characteristic frequency of the second filter is higher than f.sub.r2 and for selecting the second filter when the actual center charcteristic frequency of the first filter is lower than f.sub.r1 or the actual center characteristic frequency of the second filter is lower than f.sub.r2 ;
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- (d) means for varying the actual center characteristic frequency of the filter selected by the filter switching means by varying a variable capacitance diode means to obtain a desired characteristic frequency.
2 more elements
An integrated filter circuit comprising:
- (a) an input terminal supplied with an input signal;
- (b) an output terminal providing an output signal;
- (c) filter circuit means connected between said input terminal and output terminal to receive said input signal and provide said output signal, said filter circuit means comprising an integrated circuit having a desired filter characteristic with an actual center characteristic frequency f, said filter circuit means having
- (i) a first filter circuit having a desired center characteristic frequency f.sub.r1, an input and an output, and first resistor means and first capacitance diode means, said first resistance means and first capacitance diode means respectively having first resistance and first capacitance values providing an actual first center characteristic frequency;
- and
- (ii) a second filter circuit having a desired center characteristic frequency f.sub.r2, an input and an output, and second resistor means and second capacitance diode means, said second resistor means and second capacitance diode means respectively having second resistance and second capacitance values providing an actual second center characteristic frequency;
- (d) filter selecting means, coupled to at least one of the inputs or outputs of said first and second filters for selectively connecting one of said first and second filter circuits with said input terminal or output terminal, said filter selecting means including switching means wherein under a first filter circuit selecting condition, said switching means selects said second filter circuit when the actual center characteristic frequency of said first filter is less than f.sub.r1 and under a second filter selecting condition, said switching means selects said first filter when the actual center characteristic frequency of said second filter circuit is equal to or greater than f.sub.r2 ;
- (e) adjusting means, connected to said first and second variable capacitance diode means of said first and second filter circuits, for changing capacitance values of said variable capacitance diode means;
- and
- (f) wherein said switching means selects the one of said first and second filter circuits having a center characteristic frequency closer to f than the center frequency characteristic frequency of the other filter and said adjusting means adjusts said capacitance value of said variable capacitance diode means of the selected one of the first and second filter circuits to obtain said actual characteristic frequency f.
7 more elements
Dependencies are inferred from the claim text.