A cellular phone system realizes highly-functional communication by voice communication, TV telephone, and the wireless Internet with a third-generation cellular phone and is further developing to realize higher speed and higher functions. To realize such various services, standards such as EDGE (Enhanced Data rate for GSM Evolution) obtained by improving the communication speed of GSM (Global System for Mobile Communication), W-CDMA (Wideband Code Division Multiple Access), and LTE (Long Term Evolution) have been devised.
With increase in the number of the frequency bands used and the number of users and diversification of the communication system, GSM of the 900 MHz band and DCS (Digital Cellular System) of the 1.8 GHz band are used in Europe. On the other hand, in the U.S., PCS (Personal Communication Service) of the 1.9 GHz band and GSM of 850 MHz are used. In addition, there are W-CDMA and LTE using 1.5 GHz, the 2 GHz band, and 2.5 GHz, and a cellular phone has to be used in multiple bands and multiple modes as precondition.
To be used in multiple bands and multiple modes as described above, a high frequency antenna switch module has to have a large-scale circuit such as a DP9T (Double Pole 9 Throw) circuit.
FIGS. 30A and 30B are circuit diagrams schematically showing a switch circuit constructed as an SPDT (Single Pole Double Throw) switch in a switch module. In the GSM and LTE, the TDD (Time Division Duplex) method is used. Consequently, transmission (TX) and reception (RX) have to be frequently switched. For example, in the case of transmission (FIG. 30B), transistors M261 and M264 are turned on by applying positive voltage. On the other hand, transistors M262 and M263 are turned off by applying negative voltage. By the operation, an RF signal from a transmission circuit TX1 is transmitted to an antenna ANT via the on transistor M261 and is emitted as radio wave from the antenna ANT to the air. To cut off a leak signal of the RF signal from the transmission circuit TX1, in a reception circuit RX1, the transistor M263 is turned off and the reception circuit RX1 is connected to the ground GND by the transistor M264. On the other hand, in the case of reception (FIG. 30A), the transistors M262 and M263 are turned on by applying positive voltage. On the other hand, the transistors M261 and M264 are turned off by applying negative voltage. By the operation, an RF signal (the instantaneous voltage value is a few μ Vpp to a few m Vpp) received from the antenna ANT is transmitted to the reception circuit RX1 via the on transistor M263 and is connected to an RFIC (Radio Frequency Integrated Circuit) on the outside of the switch module. To prevent leakage of an RF signal received from the antenna ANT to the transmission circuit TX1, the transistor M261 is turned off and the transistor M262 is connected to the ground GND.
The reason why the negative voltage is applied to the off switch as described above is as follows. Since the power of the RF signal supplied from TX1 to the switch becomes about 1W at maximum, the instantaneous voltage applied to the drain terminal or the source terminal of a transistor in the switch reaches a few Vpp. To maintain the off state of the transistor even when the voltage reaching a few Vpp is applied, it is necessary to apply the negative voltage of about, for example, −2.5 V to the off transistor.
FIG. 31 illustrates a high frequency antenna switch module having a general configuration. A high frequency antenna switch module (1) includes a switch (7) body such as the SPDT switch, an I/O interface (2) receiving a control data signal SDATA from a BBIC (Base-Band Integrated Circuit) of a portable terminal and a system clock SCLK and controlling starting of the switch module, switching of switch ports, setting of stand-by, and the like, a decoder (3) receiving a control signal CNT from the I/O interface and generating a switch control signal SWCNT adapted to actual switching of switches, and a negative voltage generation circuit (6) supplying a negative voltage output signal NVG_OUT to the switch (7).
For example, as described in the following literature of Jeongwon Cha et al., the negative voltage generation circuit (6) is construed by a clock generator, a charge pump circuit, and a capacitive element of large area. The charge pump circuit is driven by a clock generated by the clock generator, and negative charges output from the charge pump are accumulated in the capacitive element, thereby generating negative voltage.
Jeongwon Cha et al, “Analysis and Design Techniques of CMOS Charge-Pump-Based Radio-Frequency Antenna-Switch Controllers”, IEEE Transactions on Circuits and Systems-I, Vol. 56, No. 5, May 2009, pp. 1053-1062
Japanese Patent Application Laid-Open Publication No. 2009-27487 discloses a technique of separately preparing a charge discharging path constructed by an FET (Field Effect Transistor) and a diode for a gate terminal of a transistor as a component of the switch and the GND terminal to prevent positive charges accumulated in a parasite capacitor Cgs between the gate terminal and the source terminal of the transistor in the switch from flowing in a charging capacitor in a negative voltage circuit, thereby suppressing rise in a negative voltage generated at the time of switching ports of the switch and shortening the time of the switch ports switching.
A ninth embodiment in Japanese Patent Application Laid-Open Publication No. 2010-103971 discloses another technique. A fluctuation in a boosted voltage is detected by a comparator. When the boosted voltage value fluctuates to a predetermined value, the frequency of a clock generator in a booster circuit is increased and operated to promptly reset the boosted voltage to the original value. When the boosted voltage rises to a predetermined value, the clock frequency is reset to the original frequency. With the configuration, by increasing the clock frequency only at the timing of the switch ports switching, without enlarging the area of the charging capacitor Cc in the booster circuit, increase in power consumption can be suppressed.