SEMICONDUCTOR INTEGRATED CIRCUIT

• US 20100052795A1
• Filed: 08/12/2009
• Published: 03/04/2010
• Est. Priority Date: 08/28/2008
• Status: Abandoned Application

• Current Assignee: Renesas Electronics Corporation
• Original Assignee: Renesas Technology Corporation (Renesas Electronics Corporation)
• Inventors: Uozumi, Toshiya, Kitamura, Tomomitsu, Norimatsu, Takayasu, Nakamura, Takahiro, Yamawaki, Taizo
• Application Number:
  US12/540,248
• Publication Number:
  US 20100052795A1
• Time in Patent Office: Days
• US Class Current: 331/10
• CPC Class Codes: H03B 5/1215 the current source or degeneration circuit being in common to both transistors of the pair, e.g. a cross-coupled long-tailed pair
• CPC Class Codes: H03B 5/1228 the amplifier comprising one or more field effect transistors
• CPC Class Codes: H03B 5/1243 the means comprising voltage variable capacitance diodes
• CPC Class Codes: H03B 5/1265 switched capacitors
• CPC Class Codes: H03B 5/1293 having means for achieving a desired tuning characteristic, e.g. linearising the frequency characteristic across the tuning voltage range
• CPC Class Codes: H03J 2200/10 Tuning of a resonator by means of digitally controlled capacitor bank
• CPC Class Codes: H03J 3/20 of single resonant circuit by varying inductance only or capacitance only

Abstract

The present invention provides a semiconductor integrated circuit capable of reducing a chip occupied area and reducing variations in control gain of a digitally controlled oscillator. The semiconductor integrated circuit is equipped with the digitally controlled oscillator. The digitally controlled oscillator comprises oscillation transistors and a resonant circuit. The resonant circuit comprises inductances, a frequency coarse-tuning variable capacitor array and a frequency fine-tuning variable capacitor array. The frequency coarse-tuning variable capacitor array comprises a plurality of coarse-tuning capacitor unit cells. The frequency fine-tuning variable capacitor array comprises a plurality of fine-tuning capacitor unit cells. The capacitance values of the coarse-tuning capacitor unit cells of the frequency coarse-tuning variable capacitor array are set in accordance with a binary weight 2^M−1. The capacitance values of the fine-tuning capacitor unit cells of the frequency fine-tuning variable capacitor array are also set in accordance with a binary weight 2^N−1.

Claims

1. A semiconductor integrated circuit comprising:

a digitally controlled oscillator,

wherein the digitally controlled oscillator comprises oscillation transistors and a resonant circuit,

wherein the resonant circuit comprises inductances, a frequency coarse-tuning variable capacitor array and a frequency fine-tuning variable capacitor array,

wherein the frequency coarse-tuning variable capacitor array at least comprises a plurality of coarse-tuning capacitor unit cells corresponding to a first predetermined number, which are respectively controlled by coarse-tuning digital control signals having the number of bits corresponding to the first predetermined number,

wherein the frequency fine-tuning variable capacitor array at least comprises a plurality of fine-tuning capacitor unit cells corresponding to a second predetermined number, which are respectively controlled by fine-tuning digital control signals having the number of bits corresponding to the second predetermined number,

wherein capacitance values of the coarse-tuning capacitor unit cells of the frequency coarse-tuning variable capacitor array are set in accordance with a binary weight, and

wherein capacitance values of the fine-tuning capacitor unit cells of the frequency fine-tuning variable capacitor array are set in accordance with a binary weight.

2. The semiconductor integrated circuit according to claim 1,

wherein a minimum frequency transition width of the frequency fine-tuning variable capacitor array is set smaller than that of the frequency coarse-tuning variable capacitor array.

3. The semiconductor integrated circuit according to claim 2,

wherein the frequency fine-tuning variable capacitor array comprises a plurality of capacitor arrays controlled by the fine-tuning digital control signals respectively.

4. The semiconductor integrated circuit according to claim 3,

wherein the capacitor arrays are arranged symmetrically about a center line.

5. The semiconductor integrated circuit according to claim 2,

wherein the fine-tuning capacitor unit cells of the frequency fine-tuning variable capacitor array respectively comprise unit capacitors corresponding to a number set in accordance with a binary weight, and

wherein the unit capacitors respectively have capacitance areas identical to one another.

6. The semiconductor integrated circuit according to claim 2,

wherein the oscillation transistors at least comprise a first transistor and a second transistor, and the inductances at least comprise a first inductance and a second inductance,

wherein an output electrode of the first transistor and a control input electrode of the second transistor are coupled to one end of the first inductance, whereas an output electrode of the second transistor and a control input electrode of the first transistor are coupled to one end of the second inductance,

wherein the other end of the first inductance and the other end of the second inductance are coupled to an operating potential point, and

wherein the frequency coarse-tuning variable capacitor array and the frequency fine-tuning variable capacitor array are coupled in parallel between the one end of the first inductance and the one end of the second inductance.

7. The semiconductor integrated circuit according to claim 6,

wherein one ends of unit cells of the fine-tuning capacitor unit cells of the frequency fine-tuning variable capacitor array are respectively coupled to the one end of the first inductance through independent first branch signal wires, and

wherein the other ends of the unit cells of the fine-tuning capacitor unit cells of the frequency fine-tuning variable capacitor array are respectively coupled to the one end of the second inductance through independent second branch signal wires.

8. The semiconductor integrated circuit according to claim 6,

wherein unit cells of the coarse-tuning capacitor unit cells of the frequency coarse-tuning variable capacitor array and unit cells of the fine-tuning capacitor unit cells of the frequency fine-tuning variable capacitor array respectively comprise first capacitors whose one ends are coupled to the one end of the first inductance, second capacitors whose one ends are coupled to the one end of the second inductance, and switching transistors each coupled between the other end of the first capacitor and the other end of the second capacitor.

9. The semiconductor integrated circuit according to claim 6,

wherein the digitally controlled oscillator is provided in a digital PLL comprising a phase frequency detector, a digital loop filter and a divider, and

wherein an oscillation frequency of the digitally controlled oscillator is controlled by an output of the digital loop filter.

10. The semiconductor integrated circuit according to claim 9, further comprising at least either one of a receiver for receiving an RF receive signal therein and generating a reception baseband signal by frequency downconversion, and a transmitter for generating an RF transmit signal by frequency upconversion of a transmission baseband signal,

wherein the digital PLL is operated as a frequency synthesizer for generating at least either one of a reception local signal based on the frequency downconversion of the receiver and a transmission local signal based on the frequency upconversion of the transmitter.

11. A semiconductor integrated circuit comprising:

a digitally controlled oscillator,

wherein the digitally controlled oscillator comprises oscillation transistors and a resonant circuit,

wherein the resonant circuit comprises inductances, a channel selection acquiring variable capacitor array and a follow-up tuning variable capacitor array,

wherein the channel selection acquiring variable capacitor array at least comprises a plurality of channel selection acquiring capacitor unit cells corresponding to a first predetermined number, which are respectively controlled by channel selection acquisition digital control signals having the number of bits corresponding to the first predetermined number,

wherein the follow-up tuning variable capacitor array at least comprises a plurality of follow-up tuning capacitor unit cells corresponding to a second predetermined number, which are respectively controlled by follow-up tuning digital control signals having the number of bits corresponding to the second predetermined number,

wherein capacitance values of the channel selection acquiring capacitor unit cells of the channel selection acquiring variable capacitor array are set in accordance with a binary weight, and

wherein capacitance values of the follow-up tuning capacitor unit cells of the follow-up tuning variable capacitor array are set in accordance with a binary weight.

12. The semiconductor integrated circuit according to claim 11,

wherein a minimum frequency transition width of the follow-up tuning variable capacitor array is set smaller than that of the channel selection acquiring variable capacitor array.

13. The semiconductor integrated circuit according to claim 12,

wherein the follow-up tuning variable capacitor array comprises a plurality of capacitor arrays respectively controlled by the follow-up tuning digital control signals.

14. The semiconductor integrated circuit according to claim 13,

wherein the capacitor arrays are arranged symmetrically about a center line.

15. The semiconductor integrated circuit according to claim 12,

wherein the follow-up tuning capacitor unit cells of the follow-up tuning variable capacitor array are respectively comprised of unit capacitors corresponding to a number set in accordance with a binary weight, and

wherein the unit capacitors respectively have capacitance areas identical to one another.

16. The semiconductor integrated circuit according to claim 12,

wherein the oscillation transistors at least comprise a first transistor and a second transistor, and the inductances at least comprise a first inductance and a second inductance,

wherein an output electrode of the first transistor and a control input electrode of the second transistor are coupled to one end of the first inductance, whereas an output electrode of the second transistor and a control input electrode of the first transistor are coupled to one end of the second inductance,

wherein the other end of the first inductance and the other end of the second inductance are coupled to an operating potential point, and

wherein the channel selection acquiring variable capacitor array and the follow-up tuning variable capacitor array are coupled in parallel between the one end of the first inductance and the one end of the second inductance.

17. The semiconductor integrated circuit according to claim 16,

wherein one ends of unit cells of the follow-up tuning capacitor unit cells of the follow-up tuning variable capacitor array are respectively coupled to the one end of the first inductance through independent first branch signal wires, and

wherein the other ends of the unit cells of the follow-up tuning capacitor unit cells of the follow-up tuning variable capacitor array are respectively coupled to the one end of the second inductance through independent second branch signal wires.

18. The semiconductor integrated circuit according to claim 16,

wherein unit cells of the channel selection acquiring capacitor unit cells of the channel selection acquiring variable capacitor array, and unit cells of the follow-up tuning capacitor unit cells of the follow-up tuning variable capacitor array respectively comprise first capacitors whose one ends are coupled to the one end of the first inductance, second capacitors whose one ends are coupled to the one end of the second inductance, and switching transistors each coupled between the other end of the first capacitor and the other end of the second capacitor.

19. The semiconductor integrated circuit according to claim 16,

wherein the digitally controlled oscillator is provided in a digital PLL comprising a phase frequency detector, a digital loop filter and a divider, and

wherein an oscillation frequency of the digitally controlled oscillator is controlled by an output of the digital loop filter.

20. The semiconductor integrated circuit according to claim 19, further comprising at least either one of a receiver for receiving an RF receive signal therein and generating a reception baseband signal by frequency downconversion, and a transmitter for generating an RF transmit signal by frequency upconversion of a transmission baseband signal,

wherein the digital PLL is operated as a frequency synthesizer for generating at least either one of a reception local signal based on the frequency downconversion of the receiver and a transmission local signal based on the frequency upconversion of the transmitter.