Abstract: To implement a filter circuit with low noise and a low cutoff frequency in a smaller area, a filter circuit has a first circuit which receives an input signal supplied to an input terminal, amplifies the signal, and outputs the amplified signal to an output terminal, a first differential amplification circuit for receiving the output signal of the first circuit through a first capacitance element, a first resistance element for forming a negative feedback path between the input and output of the first differential amplification circuit, and a second resistance element for forming a negative feedback path between the output of the first differential amplification circuit and the input of the first circuit.

Abstract: Variable operating currents are generated in relation to input signal power and output signal power and achieving both low noise and low power consumption. Emitter follower circuits are attached to output terminals of a frequency divider for generating a local signal. By adjusting the currents flowing through the emitter follower circuits, the amounts of currents flowing into mixers is adjusted. When the amounts of currents of local signals flowing into the mixers increases, the effect of noise suppression is expected. The amounts of the currents flowing through the emitter follower circuits is changed depending on the amplification factor of variable amplifiers.

Abstract: The invention provides a control method for generating variable operating currents in relation to input signal power and output signal power and achieving both low noise and low power consumption. Emitter follower circuits are attached to output terminals of a frequency divider for generating a local signal. By adjusting the currents flowing through the emitter follower circuits, the amount of currents flowing into mixers is adjusted. When the amount of currents of local signals flowing into the mixers increases, the effect of noise suppression is expected. The amount of the currents flowing through the emitter follower circuits is changed depending on the amplification factor of variable amplifiers.

Abstract: The communication semiconductor integrated circuit includes serial-signal processing circuits having low-pass filters and variable gain amplifier circuits cascade-connected in series. The low-pass filters constituting the serial-signal processing circuit each include a variable capacitance circuit composed of capacitance elements and switching elements connected in series to the capacitance elements, respectively, and capable of selecting the capacitance elements to change capacitance of the low-pass filter. A reference clock signal is supplied to the circuit containing the low-pass filters upon turning on of a power supply, for example, to determine a deviation of a delay time in the circuit to a design value and on and off states of the switching elements of the variable capacitance circuit are set so that the deviation of the delay time is minimized.

Abstract: Receiving properties are greatly improved by varying and outputting an output voltage of I/Q signals, which correspond to an input level in a semiconductor integrated circuit device for baseband processing. When a portable terminals system reaches a training period after power is supplied thereto, a switch is turned on and another switch is turned off and a digital comparator compares an adjustment voltage outputted from an output-voltage adjustment circuit and a reference voltage of a baseband circuit to output comparison results thereof. A control circuit controls and adjusts, based on the comparison results, a voltage-controlled unit so that an adjustment voltage may become nearly equivalent to the reference voltage of the baseband circuit. Thereby the output level of the I signals (, Q signals) outputted from the RF processing unit is corrected, and the output levels of the I signals (, Q signals) are set to be equivalent to that of the reference voltage of the baseband circuit.