| 摘要 |
PROBLEM TO BE SOLVED: To ensure isolation between transmission and reception while enhancing the value and reducing the size of a circuit and power consumption by decreasing the number of high frequency VCOs and intermediate frequency VCOs. SOLUTION: In the synthesizer circuit of a dual mode transmitting/receiving circuit communicating in two different radio frequency bands, an IF local signal is generated by dividing the frequency of oscillation signal of a VCO2 for IF individually for transmission and reception. With regard to an RF local signal corresponding to a high frequency side system (W-CDMA), oscillation signal of a VCO1 for RF is utilized as it is. With regard to an RF local signal corresponding to a low frequency side system (DCS-1800), frequency of oscillation signal of the VCO2 for IF is divided by N3 through a frequency divider 9 to produce a signal having a frequency corresponding to the frequency shift width which is then mixed and shifted to generate the oscillation signal of the VCO1 for RF. |
