Integrated filter circuit having switchable selected parallel filter paths

Claim 2

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 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 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 r1 or the actual center characteristic frequency of the second filter is higher than f r2 and for selecting the second filter when the actual center charcteristic frequency of the first filter is lower than f r1 or the actual center characteristic frequency of the second filter is lower than f r2 ; and (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.

Claim 3

An integrated filter circuit according to claim 1, wherein said first and second filters include control circuits coupled to said first and second variable capacitance diode means to apply a control voltage for changing capacitance values of said first and second variable capacitance diode means, respectively.

Claim 4

An integrated filter circuit in accordance with claim 1 wherein said filter switching means includes: (a) switching means for connecting an input of said filter circuit and an output of said filter circuit respectively to the input and output to one of said first and second filters; (b) frequency discriminating means, coupled to the output of said filter circuit, for comparing the actual center characteristic frequency of the first filter with f r1 and for producing the control signal having a first magnitude when the actual center characteristic frequency is ≧f r1 and having a second magnitude when the actual center characteristic is <f r1 ; and (c) means, coupled to an output of said frequency discriminating means and responsive to the magnitude of the control signal, for causing the selection of the first filter when the control signal is of the first magnitude and for causing the selection of the second filter when the control signal is of the second magnitude.

Claim 5

An integrated filter circuit in accordance with claim 1 wherein said filter switching means includes: (a) switching means for connecting an input of said filter circuit and an output of said filter circuit respectively to the input and output to one of said first and second filters; (b) frequency discriminating means, coupled to the output of said filter circuit, for comparing the actual center characteristic frequency of the second filter with f r2 and for producing the control signal, the control signal having a first magnitude when the actual center characteristic frequency is ≧f r2 and a second magnitude when the actual center characteristic frequency <f r2 ; and (c) means, coupled to an output of said frequency discriminating means and responsive to the magnitude of the control signal, for causing the selection of the first filter when the control signal is of the first magnitude and for causing the selection of the second filter when the control signal is of the second magnitude.

Claim 6

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 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 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 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 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.

Claim 7

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 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 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 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 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.

Claim 8

An integrated filter circuit in accordance with claim 5 wherein said switching means comprises: frequency discriminating means coupled to the output terminal for discriminating between an actual frequency and a desired frequency by comparing the actual center characteristic frequency of said first and second filter circuits with the desired center characteristic frequency; and a switching circuit for receiving an output from said frequency discriminating means for selecting said filter circuit in accordance with the output of said frequency discriminating means.