Voltage controlled oscillator with controlled capacitance ratio in positive feedback loop to broaden bandwidth

Claim 2

A voltage controlled oscillator comprising: resonant circuit means having at least a coil and a first variable capacitance diode, and for resonating within predetermined variable frequency ranges; active circuit means having an input, an output, and an active element connected between said input and said output, said input being connected to said resonant circuit means in order to receive a resonant output therefrom; variable capacitance ratio means having a second variable capacitance diode and at least one capacitor and connected in a positive feedback manner between said input and said output of said active circuit means in order to oscillate said active element of said active circuit means at a resonant frequency of said resonant circuit means; and variable control means for changing a resonant frequency of said resonant circuit means to thereby apply a control voltage to said first and second variable capacitance diodes and for controlling a capacitance ratio between said at least one capacitor and said second variable capacitance diode in said variable capacitance ratio means, so that an oscillator frequency of said active element can be changed substantially linearly over a wide bandwidth of no less than one octachord in accordance with a variation in said control voltage, to thereby retain the amount of positive feedback at a predetermined level against the oscillator frequency of said active circuit means.

Claim 3

A voltage controlled oscillator according to claim 1, wherein said coil has two ends, and said resonant circuit means includes two variable capacitance diodes respectively connected in a reverse bias manner between both ends of said coil and a standard electric potential point; said control voltage being supplied from another variable control means to one end of said coil; and said resonant output and said control voltage being extracted from another end of said coil.

Claim 4

A voltage controlled oscillator according to claim 1, wherein: said coil of said resonant circuit means has first and second ends; said at least one capacitor of said variable capacitance ratio circuit means includes first and second capacitors; said variable capacitance ratio circuit means includes a variable capacitance diode connected in a reverse bias manner between an end of said coil and a standard electric potential point by means of a choke coil; said first capacitor is connected between said input and said output of said active circuit means; and said second capacitor is connected between a connecting point of said variable capacitance diode and said choke coil, and said active circuit means.

Claim 5

A voltage controlled oscillator according to claim 1, further comprising: buffer circuit means for receiving an output from said active circuit means and for outputting said output at almost a linear level over the whole bandwidth of the oscillatory frequency of said active element.

Claim 6

A voltage controlled oscillator comprising: resonant circuit means having at least a coil and a first variable capacitance diode, and for resonating within predetermined variable frequency ranges; active circuit means having an input, an output, and an active element connected between said output and said input, said input being connected to said resonant circuit means in order to receive a resonant output therefrom; coupling control means having a first capacitor for connecting at least said resonant circuit means to said active circuit means as a capacitance coupling, and a second variable capacitance diode for adjusting the strength of said capacitance coupling in accordance with a resonant frequency of said resonant circuit means; variable capacitance ratio means having at least a third variable capacitance diode and a second capacitor connected in a positive feedback manner between said input and said output of said active circuit means in order to oscillate said active element of said active circuit means at a resonant frequency of said resonant circuit means; and variable control means for changing a resonant frequency of said resonant circuit means to thereby apply a control voltage to said first, second and variable capacitance diodes and for controlling a capacitance ratio between said first capacitor and said second variable capacitance diode of said variable capacitance ratio means, so that an oscillator frequency of said active element can be changed substantially linearly over a wide bandwidth of no less than one octachord in accordance with a variation in said control voltage, to thereby retain the strength of the capacitance coupling between said resonant circuit means and said active circuit means substantially at a predetermined level in accordance with a resonant frequency of said resonant circuit means and to retain an amount of positive feedback at a predetermined value against the oscillator frequency of said active element.

Claim 7

A voltage controlled oscillator comprising: resonant circuit means having at least a coil and a first variable capacitance diode, and for resonating within predetermined variable frequency ranges; active circuit means having an input, an output, and an active element connected between said output and said input, said input being connected to said resonant circuit means in order to receive a resonant output therefrom; coupling control means having a first capacitor for connecting at least said resonant circuit means to said active circuit means as a capacitance coupling, and a second variable capacitance diode for adjusting the strength of said capacitance coupling in accordance with a resonant frequency of said resonant circuit means; variable capacitance ratio means having at least a third variable capacitance diode and a second capacitor connected in a positive feedback manner between said input and said output of said active circuit means in order to oscillate said active element of said active circuit means at a resonant frequency of said resonant circuit means; and variable control means for changing a resonant frequency of said resonant circuit means to thereby apply a control voltage to said first, second and variable capacitance diodes and for controlling a capacitance ratio between said first capacitor and said second variable capacitance diode of said variable capacitance ratio means, so that an oscillator frequency of said active element can be changed substantially linearly over a wide bandwidth of no less than one octachord in accordance with a variation in said control voltage, to thereby retain the strength of the capacitance coupling between said resonant circuit means and said active circuit means substantially at a predetermined level in accordance with a resonant frequency of said resonant circuit means and to retain an amount of positive feedback at a predetermined value against the oscillator frequency of said active element.

Claim 8

A voltage controlled oscillator according to claim 5, wherein said coil has two ends, and said resonant circuit means includes: two variable capacitance diodes respectively connected between both ends of said coil and a standard electric potential point; said control voltage from said variable control means being applied to one end of said coil; and said control voltage and said oscillator output being extracted from another end of said coil.

Claim 9

A voltage controlled oscillator according to claim 6 wherein said coupling means includes: a variable capacitance diode arranged in a reverse bias manner and connected in series with a third capacitor and between said another end of said coil and said standard electric potential point; a choke coil connected to said variable capacitance diode; and a third capacitor connected between said input of said active circuit means and a connecting point of said variable capacitance diode and said choke coil.

Claim 10

A voltage controlled oscillator according to claim 6 wherein: said third variable capacitance diode is connected in a reverse bias manner between said another end of said coil and said standard electric potential point by means of a choke coil; and said variable capacitance ratio means further includes: a fourth capacitor connected between said input and said output of said active circuit means; and a fifth capacitor connected between the connecting point of said choke coil and said variable capacitance diode, and said active circuit means.

Claim 11

A voltage controlled oscillator according to claim 5, further comprising: buffer circuit means for receiving an output from said active circuit means and for outputting said output at almost a linear level over the whole bandwidth of the oscillatory frequency of said active element.