US 5,486,794 A · Variable frequency LC oscillator using variable impedance and negative impedance circuits

Abstract

A variable frequency oscillator which can be implemented entirely in a semiconductor chip, which is variable over a broad frequency range and which has relatively low phase noise, includes a variable impedance circuit, a reactive load connected to an output terminal pair of the variable impedance circuit, and a negative impedance circuit having an output terminal pair connected to the output terminal pair of the variable impedance circuit. In one embodiment, the negative impedance circuit has an input terminal pair connected to an input terminal pair of the variable impedance circuit to serve as a positive feedback path for the variable impedance circuit. In another embodiment, the negative impedance circuit includes a pair of level shifters which ensure that the variable impedance circuit is properly biased and works in a forward active region.

Claims15

Dependent claims

A variable frequency oscillator, comprising:

a variable impedance circuit having an input terminal pair, an output terminal pair and a control input pair for receiving a control voltage to vary impedance of said variable impedance circuit;
a reactive load connected to said output terminal pair of said variable impedance circuit, said variable impedance circuit being a capacitive impedance when said reactive load is an inductive load and being an inductive impedance when said reactive load is a capacitive load;
and
a negative impedance circuit having an output terminal pair connected to said output terminal pair of said variable impedance circuit and an input terminal pair connected to said input terminal pair of said variable impedance circuit, said negative impedance circuit serving as a positive feedback path for said variable impedance circuit.

1 more element

A variable frequency oscillator, comprising:

a variable impedance circuit including:
a first differential circuit having a transistor pair with a pair of input terminals, a pair of output terminals, and a pair of emitters;
a reactive element connected between said emitters of said transistor pair;
a first variable current attenuator having a pair of input terminals connected respectively to said output terminals of said transistor pair, a pair of output terminals, and a control input pair for receiving a first control voltage to vary current gain of said first variable current attenuator to vary correspondingly an impedance measured across said output terminals of said first variable current attenuator;
and a pair of level shifters, each of which having an input terminal connected to a respective one of said output terminals of said variable current attenuator, and an output terminal connected to a respective one of said input terminals of said transistor pair, said level shifters ensuring that said first differential circuit and said first variable current attenuator are properly biased;
a reactive load connected to said output terminals of said first variable current attenuator, said reactive element being a capacitive element when said reactive load is an inductive load and being an inductive element when said reactive load is a capacitive load;
and
a negative impedance circuit having an output terminal pair connected to said output terminals of said first variable current attenuator.

5 more elements

Dependencies are inferred from the claim text.

Variable frequency LC oscillator using variable impedance and negative impedance circuits

Life of this patent

Variable frequency LC oscillator using variable impedance and negative impedance circuits

Life of this patent

Abstract

Claims15