Fujitsu Corporation

Denso Corporation

Fujitsu Semiconductor Limited

Fijitsu Limited

Yoshihiro Kizaki

Toshihiko Kasai

Shinya Udo

Masatoshi Kokubun

Hidenobu Ito

Katsuyuki Yasukouchi

Osamu Kudo

Hiroyuki Satake

Tomoyuki Kumeta

A switching power device includes: a main circuit having a switching element and a coil that adjusts a current flowing through the coil and outputs a voltage; an output voltage detection circuit that outputs a first voltage; an error amplification circuit that outputs an error signal in response to a difference between the first voltage of the output voltage detection circuit and a second voltage; an oscillation circuit that outputs an oscillation signal; a driving circuit that outputs the driving signal to the switching element in response to a comparison result by comparing the oscillation signal of the oscillation circuit and the error signal of the error amplification circuit; and a soft-start control unit that controls the second voltage in response to the first voltage of the output voltage detection circuit when the first voltage reaches a soft-start threshold voltage between a standard detection voltage and a start detection voltage.

Switching power device

An operational amplifier capable of offset cancel in a shorter period, as well as a line driver capable of shortening one horizontal period and a liquid crystal display device are provided. In the operational amplifier of the invention, a time necessary for feed back control can be shortened than usual by a constitution that an output voltage VO in one horizontal period Hwhich is one horizontal period before is defined as a reference voltage in an offset cancel preparatory period HC, thereby changing the output voltage VO() only by the offset voltage VO() by the feed back control. In the line driver of the invention, the operational amplifier not used for the output of display data Dto Dconducts offset cancel operation and it is successively shifted on every one horizontal period. Since it is no more necessary to incorporate the offset cancel preparatory period in the output period, one horizontal period can be shortened further.

Operational amplifier, line driver, and liquid crystal display device

When both step-up PWM control and step-down PWM controls are executed, the offset of the ON/OFF switching timing for step-up PWM control and/or the offset of ON/OFF switching timing for step-down PWM control are changed to become identical. By synchronizing ON/OFF switching timing for step-up PWM control and ON/OFF switching timing for step-down PWM control, the loss on switching can be reduced.

DC-DC converter with step-up and step-down control capable of varying the offset voltage of the PWM triangle

In an input transistor of current mirror circuit, it is intended to prevent the current generated by Early effects from appearing in the output current of the current mirror circuit. Having an Early voltage detectorof same connection and structure as a driver circuit, and connected in parallel to the driver circuit, the current flowing in input transistor Qof the Early voltage detectoris detected. Output current (current IQ) of Early voltage detectoris added to input current (current IQ) of driver circuit. As a result, in input current (current IQ) of current mirror circuit, current &#x3b1; due to Early voltage effects can be canceled. At the same time, current &#x3b1; due to Early voltage effects generated in input transistor Qof current mirror circuitis prevented from appearing in output current (current IQ) of current mirror circuit

Early effect cancelling circuit, differential amplifier, linear regulator, and early effect canceling method

In an operational transconductance amplifier (OTA), resistors are bridge-connected to source terminals of MOSFETs that form a differential pair of the OTA. Capacitors are connected in parallel between the resistors in order to remove a DC signal component. The C-R circuit forms a high pass filter in order to intercept the DC component. Accordingly, even if there is a difference in transistor characteristic between the MOSFETs, a DC offset voltage does not appear in differential output terminals of the OTA and an output error can be eliminated. When the OTA is used in an AGC amplifier, an output dynamic range of the AGC amplifier can be made wide owing to the removal of the DC offset voltage.

Operational transconductance amplifier and AGC amplifier using the same

A bias circuit generates a first voltage at a first node. A second current source generates, according to the first voltage, a power supply current to be supplied to an internal circuit including transistors. A correcting transistor in a correcting circuit supplies the first node with a correcting current generated according to a constant voltage. Because of this, the first voltage is adjusted according to the correcting current. Therefore, the operating speed of the internal circuit is prevented from changing, being dependent on the variation of the threshold voltage and temperature variation of a transistor. As a result, the yield can be improved, independently of the variation of the threshold voltage among semiconductor integrated circuit chips, which occurs in a fabrication process. Further, temperature dependency of the operating speed of the internal circuit can be reduced, which can improve the yield of the semiconductor integrated circuit.

Semiconductor integrated circuit

The operational transconductance amplifier comprises a MOS field-effective transistor that controls the mutual conductance. The central voltage measurement circuit and the voltage addition circuit shift a gate voltage of the MOS field-effective transistor by an amount equal to the deviation of a source voltage of the MOS field-effective transistor caused by an input offset voltage Voff.

Growing community of inventors

Kasugai, Japan

Yoshihiro Kizaki