Patent ID: 7647033

Claim:
A semiconductor integrated circuit device for communication, comprising: a PLL circuit which constitutes a frequency synthesizer including, a reference frequency oscillator which generates a reference frequency signal having a reference oscillation frequency; a phase comparator having one input terminal supplied with the reference frequency signal formed from the reference frequency oscillator; an RF voltage-controlled oscillator which responds to an output of the phase comparator; and a divider connected between an output terminal of the RF voltage-controlled oscillator and the other input terminal of the phase comparator; an RF transmission voltage-controlled oscillator which generates an RF transmit frequency signal used for an RF transmit signal for RF communication; and a level converter which converts an amplitude level of an oscillation output signal of the reference frequency signal of the reference frequency oscillator to an input amplitude level of the phase comparator in the PLL circuit, wherein an RF transmit frequency of the RF transmit frequency signal generated from the RF transmission voltage-controlled oscillator is set in response to an oscillation frequency of an RF oscillation output signal generated from the RF voltage-controlled oscillator in the PLL circuit, wherein the level converter includes a voltage amplifier which amplifies the reference frequency signal of the reference frequency oscillator, and wherein the voltage amplifier is configured in a circuit form of a self-bias type voltage amplifier including a coupling capacitor having one end supplied with the reference frequency signal of the reference frequency oscillator, an amplifying transistor having an input electrode connected to the other end of the coupling capacitor and having an output electrode supplied with an operating voltage via a load, and a bias element connected between the output electrode and input electrode of the amplifying transistor.