US 6,147,567 A · Method and apparatus for providing analog and digitally controlled capacitances for synthesizing high-frequency signals for wireless communications

Abstract

A method and apparatus for synthesizing high-frequency signals is disclosed that overcomes integration problem associated with prior implementations while meeting demanding phase noise and other impurity requirements. In one embodiment, a phase-locked loop (PLL) frequency synthesizer is disclosed having a voltage controlled oscillator (VCO) with a variable capacitance that includes a discretely variable capacitance in conjunction with a continuously variable capacitance. The discretely variable capacitance may provide coarse tuning adjustment of the variable capacitance, and the continuously variable capacitance may provide a fine tuning adjustment of the variable capacitance. In a further detail, a digital control signal is disclosed to control the overall capacitance for the discretely variable capacitance circuit, and a variable control signal is disclosed to control an overall capacitance for the continuously variable capacitance circuit. In addition, the output frequency may be varied by adjusting either the digital control word or the variable control word.

Claims31

Dependent claims

A frequency synthesizer having at least one variable frequency output, the output frequency varying as a capacitance within the synthesizer varies, comprising:

a differential amplifier having a positive side voltage node and negative side voltage node;
a positive side discretely variable capacitance circuit including a plurality of capacitor circuits;
a negative side discretely variable capacitance circuit including a plurality of capacitor circuits paired with the capacitor circuits in the positive side discretely variable capacitance circuit;
wherein the paired capacitor circuits comprise:
a positive side capacitor circuit coupled to the positive side voltage node;
a positive side switch circuit coupled to the positive side voltage node;
a negative side capacitor circuit coupled to the negative side voltage node;
a negative side switch circuit coupled to the negative side voltage node;
and
an additional switch circuit coupled between the positive side and negative side circuits to reduce an overall switch resistance when the negative side switch circuit and the positive side switch are in a conductive state;
and
wherein the positive and negative side switch circuits selectively include the positive and negative side capacitor circuits within the overall capacitance for the discretely variable capacitance circuit depending upon at least one control signal applied to the positive and negative side switch circuits.

9 more elements

A wireless communication system, comprising:

a frequency synthesizer having at least one variable frequency output, comprising:
a differential amplifier having a positive side voltage node and a negative side voltage node;
a positive side discretely variable capacitance circuit including a plurality of capacitor circuits;
a negative side discretely variable capacitance circuit including a plurality of capacitor circuits paired with the capacitor circuits in the positive side discretely variable capacitance circuit;
wherein the paired capacitor circuits comprise:
a positive side capacitor circuit coupled to the positive side voltage node;
a positive side switch circuit coupled to the positive side voltage node;
a negative side capacitor circuit coupled to the negative side voltage node;
a negative side switch circuit coupled to the negative side voltage node;
and
an additional switch circuit coupled between the positive side and negative side circuits to reduce an overall switch resistance when the negative side switch circuit and the positive side switch are in a conductive state;
and
wherein the positive and negative side switch circuits selectively include the positive and negative side capacitor circuits within the overall capacitance for the discretely variable capacitance circuit depending upon at least one control signal applied to the positive and negative side switches;
and
mixing circuitry coupled to receive an input signal and to receive the output signal from the frequency synthesizer and to produce an output signal at a desired frequency.

12 more elements

A method for operating frequency synthesizer having at least one variable frequency output, the output frequency varying as a capacitance within the synthesizer varies, comprising:

providing a differential amplifier having a positive side voltage node and a negative side voltage node;
providing a discretely variable capacitance circuit, comprising:
a plurality of positive side capacitor circuits;
and
a plurality of negative side capacitor circuits paired with the plurality of positive side capacitor circuits;
wherein the paired capacitor circuits comprise:
a positive side capacitor circuit coupled to the positive side voltage node;
a positive side switch circuit coupled to the positive side voltage node;
a negative side capacitor circuit coupled to the negative side voltage node;
a negative side switch circuit coupled to the negative side voltage node;
and
an additional switch circuit coupled between the positive side and negative side circuits to reduce an overall switch resistance when the negative side switch circuit and the positive side switch are in a conductive state;
and
controlling the output frequency of the frequency synthesizer utilizing the positive and negative side discretely variable capacitance circuits.

11 more elements

Dependencies are inferred from the claim text.

Method and apparatus for providing analog and digitally controlled capacitances for synthesizing high-frequency signals for wireless communications

Life of this patent

Method and apparatus for providing analog and digitally controlled capacitances for synthesizing high-frequency signals for wireless communications

Life of this patent

Abstract

Claims31