Matsushita Electric Industrial Co., Ltd.

Kenichi Tatehara

Norihide Kinugasa

Kiyoshi Nakamori

Toshiya Akagi

Kenji Koishi

Yuichi Kamioka

Naoyuki Nakamura

Yoshiyuki Miyabata

Ikuo Hidaka

Kazuyuki Ohmi

Haruhiko Mizuno

A current summing type D/A converter having a configuration of two or more steps is provided. In a D/A converter block of the first step, by adding current segments, upper bits are D/A converted, and one of the current segments in the first step is further supplied to a D/A converter block in a second step to be shunt by the D/A converter block in the second step, so that lower bits are D/A converted. The output current in the first step and the output current in the second step are then added each other. According to the foregoing method, the D/A conversion may be performed without causing a differential linearity error.

Current summing digital-to-analog converter

A laser diode driving device of the present invention can appropriately shorten the rising time and the falling time of a laser diode drive current in a range from a small current region to a large current region. In synchronization with the addition of an original input current from an input constant current source to the laser diode drive current amplifier, a differentiated current is added to the input current through a differentiation circuit and a pull-in type V-I conversion circuit, whereby the rising of a laser diode drive current is made abrupt. Furthermore, by increasing a gate potential of an input PchMOS transistor constituting the laser diode drive current amplifier by a differentiation circuit and a push-out type V-I conversion circuit in synchronization with the disconnection of an input current, the falling of a laser diode drive current is made abrupt.

Laser diode driving device

In order to improve the robustness against electrostatic discharge, when power source terminal and ground terminal are open, of a semiconductor device having a first, a second and a third inverter that are connected in a cascade arrangement, the semiconductor device is provided not only with a first input protection circuit for guiding positive electrostatic discharges, that are applied from outside to a signal input terminal, to a power source line, and a second input protection circuit for guiding negative electrostatic discharges, that are applied from outside to the signal input terminal, to a ground line, but also an internal protection circuit for guiding electrostatic discharges that have been guided by the first input protection circuit to the power source line and flow from a P-channel MOS transistor in the second inverter towards the third inverter, to the ground line.

Semiconductor device

The laser drive device of this invention includes a laser, first and second current sources, a current amplifier, and first and second transistors. When the first transistor is OFF, a first current from the first current source is supplied to the current amplifier, where the current is amplified to generate a laser current to be supplied to the laser. Thus, the laser is turned ON. During this time, the second transistor is ON, allowing a second current to flow from a power supply node into the second current source. When the first transistor is ON, the entire or part of the first current flows into the second current source through the first transistor. This reduces the current supplied to the current amplifier and thus the laser current, resulting in turning OFF the laser. During this time, the second transistor is OFF. The values of the first and second currents are determined by a set current value. The value of the laser current supplied to the laser during the ON-state of it is determined by the first current. Therefore, by adjusting the set current value, a desired value of laser current can be supplied to the laser. Having the current amplifier, the values of the first and second currents are smaller than the value of the laser current. This suppresses an increase in power consumed by the first and second power sources and the first and second transistors when the laser current increases.

Laser drive device

The digital-analog converter circuit includes: a high-order D-A converter circuit unit ( ) for outputting a first voltage (Va) and a second voltage (Vb) both resulting from D-A conversion of the high-order five bits of a 13-bit input code to first and second output nodes ( ) through two buffers ( ) having the same characteristics, respectively; a low-order D-A converter circuit unit ( ) for receiving the voltages on these two output nodes as reference voltages of an R-2R ladder circuit ( ) and conducting D-A conversion of the low-order eight bits of the input code for output to a third output node ( ); a sample-and-hold unit ( ) for selectively sampling and holding the voltage on the third output node ( ), i.e., the D-A conversion output of the 13-bit input code, according to a value of the input code; and an output unit ( ) for multiplying the sampled and held D-A conversion output voltage by a gain with respect to an arbitrary central voltage. Thus, a D-A converter circuit capable of outputting a desired analog voltage with high accuracy even when a large number of bits are converted is implemented with a small chip area.

High-precision D-A converter circuit

In an optical disc apparatus, a semiconductor SLD driving device is mounted on an optical pickup in order to realize a high speed switching of drive current for a semiconductor laser diode (SLD), necessary for recording data. The SLD is placed. within 5 cm from the SLD driving device. The driving device becomes a heat source due to driving current of the SLD, and increases a temperature of the optical pickup. Since the temperature rises proportionally to power consumption, power saving is required. A voltage supplied to the driving device is controlled to be a minimum level necessary for keeping the driving device still working on basic functions. The SLD driving device is mounted to the optical pickup, and this driving device handles N pieces of input signals for setting semiconductor laser power and N pieces of switch-timing-input-signals for selecting respective input signals. A supplied voltage is controlled so that a voltage supplied to the output section of the driving device is a minimum value necessary for keeping the output section still operating. A power source is placed outside of the pickup.

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Osaka, Japan

Kenichi Tatehara