Abstract: A path switching FET and a shunt FET are separated from each other by a capacitor. The gates of the path switching FET and the shunt FET are controlled using an inverter circuit having a first internal power supply voltage (e.g., 2.5 V) as a power supply. The sources and drains of the path switching FET and the shunt FET are controlled using an inverter circuit having a second internal power supply voltage (e.g., 1.25 V) which is smaller than the first internal power supply voltage, as a power supply.

Abstract: A path switching FET and a shunt FET are separated from each other by a capacitor. The gates of the path switching FET and the shunt FET are controlled using an inverter circuit having a first internal power supply voltage (e.g., 2.5 V) as a power supply. The sources and drains of the path switching FET and the shunt FET are controlled using an inverter circuit having a second internal power supply voltage (e.g., 1.25 V) which is smaller than the first internal power supply voltage, as a power supply.

Abstract: The low-noise amplifier with through mode is configured such that a source grounded transistor and a gate grounded transistor are connected in cascode, and a load impedance element and a switching transistor are serially connected between the drain of the gate grounded transistor and a power supply, and a through pass circuit is connected between an input terminal and an output terminal. The gate voltage of the gate grounded transistor is regulated by a bias circuit and the voltage of a mode control terminal is converted by a level shifter to control the gate voltage of the switching transistor, whereby, in the case of using only transistors whose terminal-to-terminal breakdown voltages are each equal to or less than the power supply voltage, it becomes feasible to prevent voltages equal to or more than the terminal-to-terminal breakdown voltages from being applied between the terminals of each transistor.

Abstract: A filter automatic adjustment circuit is provided for adjusting a characteristic frequency of a main filter whose characteristic frequency is adjustable with a reference signal frequency served as a target frequency. A reference filter has modes selectively changed over, and filters an inputted reference signal. A phase difference detector detects a phase difference between an input signal inputted to the reference filter and an output signal from the reference filter, and outputs a signal having a duty ratio corresponding to a phase difference caused by the reference filter. A counter counts a duty ratio corresponding to the phase difference caused by the reference filter based on the output signal from the phase difference detector and the reference signal, and outputs a signal representing a counted duty ratio. A decoder decodes the output signal from the counter into a control signal for variation correction on the main filter.

Abstract: The invention provides a filter automatic adjustment apparatus and method, and a mobile telephone system, which realizes low power consumption while adjusting a characteristic frequency of a main filter having an adjustment function to a target frequency. The filter automatic adjustment apparatus includes: a phase difference detector 104 which outputs a signal having a duty ratio corresponding to a phase difference between an input signal and an output signal of a reference filter 103; a comparator 105 which converts the output signal of the phase difference detector into a rectangular wave; a counter 106 which consecutively counts a predetermined interval of the rectangular wave plural times; and a determination circuit 107 which selects a count value satisfying a predetermined criterion from the plural time count values, and the filter automatic adjustment apparatus adjusts the characteristic frequency of the main filter based on the selected count value.

Abstract: An automatic tuning apparatus for a filter includes a mode wherein a switching part is controlled so that a reference signal is inputted to the filter, a plural number of control signals are successively input to a control terminal of the filter, a tentative value of the control signal is determined based on respective amplitudes detected by an amplitude detection part as a “coarse tuning step”, a plural number of control signals are successively input in the vicinity of the tentatively determined value to a control terminal, and the value of the control signal is determined to be used in a mode as a “fine tuning step” based on respective phase differences detected by a phase comparator part”.

Abstract: The invention provides a filter automatic adjustment apparatus and method, and a mobile telephone system, which realizes low power consumption while adjusting a characteristic frequency of a main filter having an adjustment function to a target frequency. The filter automatic adjustment apparatus includes: a phase difference detector 104 which outputs a signal having a duty ratio corresponding to a phase difference between an input signal and an output signal of a reference filter 103; a comparator 105 which converts the output signal of the phase difference detector into a rectangular wave; a counter 106 which consecutively counts a predetermined interval of the rectangular wave plural times; and a determination circuit 107 which selects a count value satisfying a predetermined criterion from the plural time count values, and the filter automatic adjustment apparatus adjusts the characteristic frequency of the main filter based on the selected count value.

Abstract: Purposes to offer an automatic tuning apparatus for filter which enables an accurate tuning to be attained and is small size and low power consumption and a communication instrument using the above.