Frequency synthesizer

• US 20100301910A1
• Filed: 05/18/2010
• Published: 12/02/2010
• Est. Priority Date: 05/26/2009
• Status: Active Grant

• Current Assignee: Renesas Electronics Corporation
• Original Assignee: NEC Electronics Corporation (Renesas Electronics Corporation)
• Inventors: Matsuno, Noriaki, Hu, Weiliang
• Granted Patent: US 8,217,690 B2
• Time in Patent Office: Days
• US Class Current: 327/156
• CPC Class Codes: H03L 1/022 by indirect stabilisation, i.e. by generating an electrical correction signal which is a function of the temperature H03L1/021 takes precedence
• CPC Class Codes: H03L 2207/06 Phase locked loops with a controlled oscillator having at least two frequency control terminals
• CPC Class Codes: H03L 7/099 concerning mainly the controlled oscillator of the loop
• CPC Class Codes: H03L 7/18 using a frequency divider or counter in the loop H03L7/20, H03L7/22 take precedence

Abstract

A frequency synthesizer comprises a VCO group; a phase comparator; and a loop filter. Each VCO includes a varactor and a capacitor bank including a plurality of weighted capacitance elements, and a plurality of switches turned ON and OFF based on a control signal. Also provided a temperature compensation including a varactor correction potential generation circuit, a correction potential generation circuit for parasitic capacitance of the capacitor bank, a variable gain amplifier in which weighting processing, based on a control signal of the capacitor bank, is performed on an output potential of the correction potential generation circuit, and an adder circuit that adds the output voltage of the correction potential generation circuit of the varactor and output voltage of the variable gain amplifier, and the varactor of the VCO is controlled by output (correction potential) of the adder circuit.

Claims

1. A frequency synthesizer apparatus comprising:

a voltage controlled oscillator circuit that varies oscillation frequency thereof by a control voltage supplied thereto, the voltage controlled oscillator circuit including;

a variable capacitance element; and

a capacitor bank that includes a plurality of weighted capacitance elements and a plurality of switches controlled turned ON and OFF based on a plurality of control bit signals corresponding to the plurality of capacitance elements, respectively;

a phase comparator that performs phase comparison between an output signal fed back from the voltage controlled oscillator circuit and a reference signal supplied thereto, the output signal from the voltage controlled oscillator circuit being fed back directly or via a frequency divider to an input of the phase comparator;

a loop filter that generates a control voltage for supply to the voltage controlled oscillator circuit, based on a result of the phase comparison; and

a temperature compensation block that includes;

a first correction potential generation circuit that generates a correction potential for parasitic capacitance of the capacitor bank of the voltage controlled oscillator circuit;

a second correction potential generation circuit that generates a correction potential for the variable capacitance element;

a weighting circuit that performs weighting processing, based on the control bit signals, on an output potential of the second correction potential generation circuit; and

a combining circuit that combines an output voltage of the first correction potential generation circuit and an output voltage of the weighting circuit,

the variable capacitance element of the voltage controlled oscillator circuit having capacitance thereof controlled by an output of the combining circuit of the temperature compensation block.

2. The frequency synthesizer apparatus according to claim 1, wherein the temperature compensation block further comprises

a circuit that generates a voltage corresponding to the control bit signals, and

the weighting circuit comprises

a variable gain amplifier that have a gain varied by the voltage generated corresponding to the control bit signals.

3. The frequency synthesizer apparatus according to claim 1, wherein the first correction potential generation circuit comprises:

a replica circuit of the capacitor bank;

an other fixed capacitor,

the replica circuit having a capacitor being charged for a prescribed time with a prescribed current, while the other fixed capacitor being charged for the same prescribed time with the same prescribed current; and

a differential amplifier circuit that detects and outputs a voltage difference between terminal voltages of the capacitor of the replica circuit and the other fixed capacitor.

4. The frequency synthesizer apparatus according to claim 1, wherein the weighting circuit comprises

a parallel resistor array including a plurality of resistor-sets, connected in parallel, each register-set having a resistor and a switch connected in series to the resistor, the switch being turned ON and OFF by the control bit signal, and

the combining circuit comprises

a variable resistor with a resistance thereof varied by an output of the second correction potential generation circuit, the variable resistor being connected in parallel to the parallel resistor array, and connected to the variable capacitance element.

5. The frequency synthesizer apparatus according to claim 1, wherein, in the temperature compensation block,

the weighting circuit comprises

a resistor array including a plurality of resistor-sets connected in series, each resistor-set having a resistor and a switch connected in parallel to the resistor, the switch being turned ON and OFF by the control bit signal and shortening the resistor when ON, and

the combining circuit comprises

a variable resistor having a resistance thereof varied by an output of the second correction potential generation circuit, the resistor array being connected in series to the variable resistor and being connected to the variable capacitance element.

6. The frequency synthesizer apparatus according to claim 1, wherein the weighting circuit comprises

a digital-to-analog conversion circuit that receives an output voltage of the first correction potential generation circuit as a reference voltage, and outputs a voltage according to the control bit signals.

7. The frequency synthesizer apparatus according to claim 1, wherein the voltage control oscillation circuit comprises:

a variable capacitance element that receives an output voltage of the second correction potential generation circuit; and

another variable capacitance element that receives an output voltage of the weighting circuit.

8. The frequency synthesizer apparatus according to claim 1, further comprising

a circuit that combines an output voltage of the weighting circuit in the temperature compensation block, an output voltage of the second correction potential generation circuit, and an output of the loop filter, the combined voltage being applied to the variable capacitance element of the voltage control oscillation circuit.

9. The frequency synthesizer apparatus according to claim 1, comprising, as the first correction potential generation circuit,

a voltage source designed so that the temperature dependency of an output voltage of the first correction potential generation circuit has a certain desired value.

10. The frequency synthesizer apparatus according to claim 1, wherein the sign of a change of an oscillation frequency of the voltage control oscillation circuit and the sign of a change of an oscillation frequency of the voltage control oscillation circuit by the first and second correction potential generation circuits, are mutually opposite.