Method and apparatus for noise compensation in an oscillator circuit
AssigneeSilicon Laboratories Inc.
InventorsLigang Zhang, Yunteng Huang
Life of this patent
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Abstract
A variable capacitance circuit includes a first and a second capacitor. A switch having an associated first nonlinear capacitance, selectively couples the first and second capacitors. To compensate for the first nonlinear capacitance, a second nonlinear capacitance is coupled to the switch that has a capacitance value responsive to a change in voltage that moves in a direction of change opposite to a direction of change of the first nonlinear capacitance.
Claims21
A method compensating for noise in a controllable oscillator, comprising:
- providing a first and a second capacitor respectively coupled to first and second tank circuit nodes;
- providing a switch between and selectively coupling the first and second capacitors according to a value of a control signal supplied to the switch, the switch having an associated first nonlinear capacitance that varies with a voltage at a third node coupled to the switch;
- and
- compensating for the first nonlinear capacitance with a second nonlinear capacitance coupled to the switch, the second nonlinear capacitance responsive to a change in the voltage at the third node to move a capacitance value of the second nonlinear capacitance in a direction opposite a direction of change of the first nonlinear capacitance in response to the change in the voltage.
An apparatus comprising:
- a variable capacitance circuit comprising:
- a first and a second capacitor;
- a switch having a first nonlinear capacitance associated therewith, the switch responsive to an applied voltage at a control terminal of the switch to selectively couple the first and second capacitors;
- and
- a second nonlinear capacitance coupled to the switch having a capacitance value that, responsive to a change in voltage at a node connecting the first and second nonlinear capacitances, moves in a direction of change opposite to a direction of change of the first nonlinear capacitance in response to the change in voltage.
An oscillator circuit comprising:
- a variable capacitance circuit including a first and second capacitor coupled by a switch having a channel region of a first conductivity type and responsive to a first value of a control signal supplied to the switch to cause the first and second capacitors to be coupled between first and second nodes of the oscillator circuit and responsive to a second value of the control signal to cause the first and second capacitors to be decoupled;
- and
- means for compensating for a first nonlinear capacitance associated with the switch, the means for compensating including a second non-linear capacitance formed by one or more devices having a channel region of a second conductivity type, the second non-linear capacitance also coupled to the switch.
A method for making an integrated circuit, comprising:
- forming a first and a second capacitor respectively coupled to first and second tank circuit nodes;
- forming a switch having a channel region of a first conductivity type between the first and second capacitors and to selectively couple the first and second capacitors, the switch having an associated first nonlinear capacitance that varies with voltage;
- and
- forming a compensation circuit having a channel region of a second conductivity type coupled to the switch and having a second nonlinear capacitance whose change in capacitance value in response to a change in the voltage moves in a direction opposite the first nonlinear capacitance.
Dependencies are inferred from the claim text.