Patent ID: 7929594

Claim:
A semiconductor integrated circuit for communication, comprising: a D/A converter circuit which converts digital I and Q signals for transmission supplied from a baseband circuit into analog I and Q signals for transmission; a transmission circuit which modulates, using the converted I and Q signals, a carrier and transmits the modulated carrier; a reception circuit which generates, by demodulating received signals, received analog I and Q signals; an A/D converter circuit which converts the received analog I and Q signals thus generated into received digital I and Q signals; and a clock generation circuit which generates a reference clock signal required to generate a high-frequency signal for use in modulation processing performed in the transmission circuit and demodulation processing performed in the reception circuit, wherein the clock generation circuit is provided with a voltage-controlled oscillator circuit which oscillates, when a quartz oscillator is connected thereto, at a frequency dependent on a natural frequency of the quartz oscillator and a control voltage applied thereto, and wherein the voltage-controlled oscillator circuit is configured such that a result obtained by converting, in an internal D/A converter circuit, digital frequency control information supplied from the baseband circuit is applied as the control voltage to the voltage-controlled oscillator circuit and the voltage-controlled oscillator circuit oscillates at a frequency corresponding to the control voltage, further comprising, in addition to the D/A converter circuit, a second D/A converter circuit which converts the digital frequency control information into an analog signal, and wherein the second D/A converter circuit is provided with a first conversion section which generates multi-level voltages corresponding to several high-order bits of an input digital signal and a second conversion section which receives the voltages generated in the first conversion section and generates multi-level voltages corresponding to bits other than the several high-order bits of the input digital signal.