Digitally tunable capacitor
First Claim
1. A device, comprising:
- a first switchable capacitor having a first capacitance;
a second switchable capacitor having a second capacitance, the second switchable capacitor being connected in a parallel circuit with the first switchable capacitor, the parallel circuit having a tunable capacitance; and
a switch controller that is coupled to the first and second switchable capacitors, the switch controller being configured to switch the first and second switchable capacitors to adjust the tunable capacitance based on first and second (M+1)-ary pulse width modulated signals, (M being a positive integer), respectively, with each of the first and second (M+1)-ary pulse width modulated signals supplied by the switch controller; and
an offset switchable capacitor having an offset capacitance, the offset switchable capacitor being coupled to the switch controller and in parallel with the first switchable capacitor, wherein the switch controller generates an offset pulse width modulation signal to turn on the offset switchable capacitor for a full modulation period.
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Accused Products
Abstract
The disclosed device can contain a pair of switchable capacitors, one of which has the larger capacitance of the pair. Each of the switchable capacitors can include a capacitor in series with a switch. Both switchable capacitors can be connected in a parallel circuit that has a tunable capacitance. The ratio of the capacitances of the pair can approximately equal a ratio of mutually prime integers. In a particular case, the ratio of capacitances can approximately equal a ratio of two consecutive integers. The capacitance ratio can be called a weight or weight ratio. A switch controller can drive the pair of switchable capacitors with a pair of (M+1)-ary pulse width modulated signals, each of which has the same modulation period.
82 Citations
26 Claims
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1. A device, comprising:
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a first switchable capacitor having a first capacitance; a second switchable capacitor having a second capacitance, the second switchable capacitor being connected in a parallel circuit with the first switchable capacitor, the parallel circuit having a tunable capacitance; and a switch controller that is coupled to the first and second switchable capacitors, the switch controller being configured to switch the first and second switchable capacitors to adjust the tunable capacitance based on first and second (M+1)-ary pulse width modulated signals, (M being a positive integer), respectively, with each of the first and second (M+1)-ary pulse width modulated signals supplied by the switch controller; and an offset switchable capacitor having an offset capacitance, the offset switchable capacitor being coupled to the switch controller and in parallel with the first switchable capacitor, wherein the switch controller generates an offset pulse width modulation signal to turn on the offset switchable capacitor for a full modulation period. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. An apparatus, comprising:
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a tunable oscillator circuit that is configured to resonate substantially at a tunable oscillator period; a first switchable capacitor having a first capacitance; a second switchable capacitor having a second capacitance, the second switchable capacitor being connected in parallel with the first switchable capacitor to form a parallel circuit, the parallel circuit being coupled to the tunable oscillator circuit and having a tunable capacitance; a switch controller that is coupled to the first and second switchable capacitors, the switch controller being configured to switch the first and second switchable capacitors to adjust the tunable capacitance based on first and second (M+1)-ary pulse width modulated signals, (M being a positive integer), respectively, with each of the first and second (M+1)-ary pulse width modulated signals supplied by the switch controller; and an offset switchable capacitor having an offset capacitance, the offset switchable capacitor being coupled to the switch controller and in parallel with the first switchable capacitor, wherein the switch controller generates an offset pulse width modulation signal to turn on the offset switchable capacitor for a full modulation period. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. A method of adjusting a tunable capacitance, comprising:
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generating a first (M+1)-ary pulse width modulation signal and a second (M+1)-ary pulse width modulation signal (M being a positive integer) having a first and a second duty cycle, respectively, and an offset modulation signal using a switch controller; and switching a first and a second switchable capacitor with the first and second (M+1)-ary pulse width modulation signals, respectively, by the switching controller, to adjust a tunable capacitance, the switch controller being coupled to the first and second switchable capacitors, the first and second switchable capacitors having a first capacitance and a second capacitance, respectively, the first switchable capacitor being disposed in parallel with the second switchable capacitor, the first switchable capacitor being in parallel with an offset switchable capacitor having an offset capacitance, the first and second capacitance having a weight ratio that is substantially equal to a ratio of mutually prime integers, wherein the switch controller generates an offset pulse width modulation signal to turn on the offset switchable capacitor for a full modulation period. - View Dependent Claims (23, 24, 25, 26)
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Specification