Rohm Co., Ltd.

Ichiro Yokomizo

Hiroyuki Funahashi

Yoichi Tamegai

Sachito Horiuchi

Noboru Kagemoto

Hironori Nakahara

Yutaka Shibata

Mayuka Matsumae

Yoshiyuki Karasawa

A selector circuit outputs one of a first input voltage or a second input voltage via an output terminal. A first transistor and a second transistor are provided in series between a first input terminal and the output terminal. A third transistor and a fourth transistor are provided in series between a second input terminal and the output terminal. A control unit controls the ON/OFF operations of the first transistor through the fourth transistor. The back gates of the first transistor and the second transistor are connected such that at least one body diode of the first transistor Mand at least one body diode of the second transistor are arranged in opposing directions. The back gates of the third transistor and the fourth transistor are connected in the same way.

Selector circuit

A current-voltage conversion circuit which converts a current to be detected into a voltage, includes a detection resistor, amplifier circuit having a first operational amplifier, and an offset adjusting current source having a third resistor and a fourth resistor which are capable of trimming. The offset adjusting current source causes an offset adjustment current to flow in the offset resistor. The current value of the offset adjustment current is controlled by adjusting the resistance of the third resistor and the fourth resistor. A voltage at a node between the first transistor and the second resistor is output.

Current-voltage conversion circuit

Trimming by disconnecting a fuse connected in parallel to a feedback resistor of an amplifier circuit would cause a variation in voltage value due to a remaining resistance component. A voltage generator circuit is provided therein with a D/A converter circuit of an R-2R ladder resistor network type circuit. The D/A converter circuit is provided with a first switch circuit to an eighth switch circuit, corresponding to each bit, which are switched to set a digital value. Each switch circuit, which is provided with a fuse for providing a fixed voltage value, allows the fuse to be disconnected to fix the voltage value to a value obtained by inverting the initial value. The setting circuit controls the switching operation of each switch circuit, thereby simulating an electrical state of a fuse being disconnected before the fuse is actually disconnected.

Method and circuit for producing trimmed voltage using D/A converter circuit

A DC/DC converter is provided with a DC power source; a reference voltage generating circuit; an amplifier which receives an electric power from the DC power source and outputs an electric power of which voltage is controlled so as to assume a target voltage value by stepping down the voltage of the electric power from the DC power source depending on a difference between the reference voltage and a detection voltage; an oscillation circuit which generates signals having a specific frequency; a voltage boosting circuit which receives the output of the amplifier and the output of the oscillation circuit, causes switching of the output of the amplifier at the specific frequency to charge a first capacitor, and performs voltage boosting by transferring the electric charges-charged in the first capacitor through complementary ON/OFF switching with respect to the former switching into a second capacitor after raising substantially upto n/m time voltage (wherein n>m and n and m are integers equal to or more than 2) and charging the same therewith; and an output voltage detection circuit which generates the detection voltage depending on the output voltage of the boosting circuit, whereby a voltage of substantially n/m times of the target voltage value is generated from the voltage boosting circuit.

DC/DC converter

An equalizer includes first and second differential amplifiers which have a common output and respective separate current sources, a first negative feed back circuit which feeds back a voltage signal extracted from the common output to the first differential amplifier, a second negative feed back circuit which feeds back the voltage signal to the second differential amplifier, and a filter circuit which is provided at either the first or the second negative feed back circuit and which differentiates frequency characteristics during signal amplification in the first and second differential amplifiers. Frequency characterstic is selected through selection of one of the current values of the respective current sources in response to a sound quality adjusting signal.

Equalizer and audio device using the same

An equalizer includes first and second differential amplifiers which have a common output and respective separate current sources, a first negative feed back circuit which feeds back a voltage signal extracted from the common output to the first differential amplifier, a second negative feed back circuit which feeds back the voltage signal to the second differential amplifier, and a filter circuit which is provided at either the first or the second negative feed back circuit and which differentiates frequency characteristics during signal amplification in the first and second differential amplifiers. A frequency characteristic is selected through selection of one of the current values of the respective current sources in response to a sound quality adjusting signal.

Growing community of inventors

Kyoto, Japan

Ichiro Yokomizo