Hitachi, Ltd.

Renesas Technology Corp.

Hitachi Ulsi Systems Co., Ltd.

Masanori Otsuka

Kazuo Yamakido

Koichi Seki

Masao Hotta

Yoichiro Kobayashi

Takao Okazaki

Yuji Hatano

Yukihito Ishihara

Yuko Tamba

Takafumi Kikuchi

Norimitsu Nishikawa

Etsuji Yamamoto

Yasuyuki Murakami

Shinya Sano

An AD converter which uses no buffer for receiving the input signals or uses the buffer having relaxed requirements concerning the range of input signals and the output impedance. Voltage at the connection points of a resistor ladder in which a plurality of resistor elements are connected in series, are compared with a reference voltage by a plurality of voltage comparators, a first current circuit is provided on the high potential side of the resistor ladder, a second current circuit is provided on the low potential side thereof, and analog input voltages are fed by providing an input terminal at any place of the resistor ladder except both ends thereof.

Analog to digital converter with voltage comparators that compare a reference voltage with voltages at connection points on a resistor ladder

In a mobile wireless communication end device having an electric power source including a cell, and a signal processing part and a transmitting-receiving part, to which electric power is applied from the electric power source, operation is performed in operation mode selected previously by the user when voltage of the electric power source is dropped. The signal processing part and the transmitting-receiving part have a normal operation mode operating at normal electric power and a low power operation mode operating at electric power lower than the normal operation mode. The mobile wireless communication end device includes operation mode setting apparatus for previously setting the operation mode of the device, observing apparatus for observing the voltage of the cell of the electric power source and generating a low power operation request signal when the voltage becomes a prescribed value or less, and apparatus for changing the signal processing part and the transmitting-receiving part to low power operation mode, when the low power operation mode is set by the operation mode setting means and the low power operation request signal is generated by the observing apparatus.

Mobile communication end device with low power operation mode

The number of current sources and switches necessary for a plurality of unit D/A converters using equal reference currents, are drastically reduced to reduce the parasitic capacitance coupled to current output lines, by converting a plurality of digital signals of a predetermined bit, which are divided from an input digital signal, into an analog current unit D/A converters and by converting the analog current in a manner to correspond to the weights of the corresponding input digital signals, thereby to synthesize the currents. The fixed reference digital signal is inputted to the D/A converter for cancelling offsets. The offsets of a plurality of analog output signals in positive and opposite phases obtained by branching the output of the D/A converter are individually detected. After this, the DC offset values of the individual analog outputs are used as offset adjusted negative feedback signals for a desired value. One of them is the digital signal to be fed back to the input portion of the D/A converter whereas the other is the analog signal to be fed to a path portion obtained by branching the output of the D/A converter.

Converter, offset adjustor, and portable communication terminal unit

Growing community of inventors

Tachikawa, Japan

Masanori Otsuka