Patent ID: 7626459
Filing Date: 2009-12-01
Classification: H03F,H03G,H04B

Abstract:
1. A mobile communication terminal a high frequency circuit block of which comprises: a transmitting section that transmits a high frequency signal; a receiving section that receives a high frequency signal; a synthesizer section; and a shared device section, wherein: said transmitting section comprises: an up converter that converts a modulation signal having an intermediate frequency into a transmission frequency signal; a variable gain high frequency amplifier circuit that includes a gain control circuit and amplifies the output signal of said up converter; a high frequency switch a common terminal of which is connected to the output terminal of said variable gain high frequency amplifier circuit, and which switches the high frequency signal path depending on the transmission frequency; a first band pass filter an input terminal of which is connected to one switching terminal of said high frequency switch, and which extracts a signal in a first transmission band; a first high power high frequency amplifier circuit that includes a fixed gain and amplifies a high frequency signal outputted from said first band pass filter; a first isolator that provides the output of said first high power high frequency amplifier circuit to said shared device section; a second band pass filter an input terminal of which is connected to the other switching terminal of said high frequency switch, and which extracts a signal in a second transmission band; a second high power high frequency amplifier circuit that includes a fixed gain and amplifies a high frequency signal outputted from said second band pass filter; and a second isolator that provides the output of said second high power high frequency amplifier circuit to said shared device section, and wherein: said gain control circuit of said variable gain high frequency amplifier circuit comprises: a signal input terminal and a signal output terminal; a first variable resistor circuit connecting said signal input terminal to said signal output terminal; a second variable resistor circuit connected in parallel to said signal input terminal and a first ground terminal; a third variable resistor circuit connected in parallel to said signal output terminal and a second ground terminal; a control terminal connected respectively to said first, second, and third variable resistor circuits; a first reference voltage terminal connected to said first variable resistor circuit; and a second reference voltage terminal connected to said second and third variable resistor circuits, in which: the DC resistance between said signal input terminal and said signal output terminal is infinity; the DC resistance between said signal input terminal and said first ground terminal is infinity; the DC resistance between said signal output terminal and said second ground terminal is infinity; and on the basis of the relation between the voltage of said control terminal, the voltage of said first reference voltage terminal, and the voltage of said second reference voltage terminal, the resistance values of said first, second, and third variable resistor circuits are adjusted continuously, so that the signal level on said signal output terminal is continuously adjusted relative to the signal level inputted to said signal input terminal.