Hitachi, Ltd.

Hitachi Vlsi Engineering Corp.

Toshiro Tsukada

Tatsuji Matsuura

Eiki Imaizumi

Seiichi Ueda

Michio Hara

Hisashi Tsuruoka

Toru Baji

Shinya Ohba

Toshimasa Kihara

Hiroshi Sato

Katsuaki Takagi

Kunihiko Usui

Yuichi Nakatani

A voltage comparator is provided including a differential amplifier, first, second and third switches, and first and second capacitors. A fourth switch is connected in series between the second and third switches and an input terminal of the differential amplifier. A first input voltage is sampled and held at the first capacitor through the first switch and at the second capacitor through the second and fourth switches, respectively. Thereafter, since the third switch is turned on and the fourth switch is turned off, the first input voltage is sampled and held at the input capacitor of the differential amplifier. Thereafter, the third switch is turned off and the fourth switch turned on. As a result, an on and off operation of the fourth switch is controlled so that a second input voltage which has been sampled at the second capacitor immediately before the switch is turned off is applied to the input capacitor of the differential amplifier.

Voltage comparator

According to the present invention, the number of elements of a signal processing circuit or the like can be drastically reduced by conducting a time-multiplex processing. In a transversal filter having a coefficient of symmetry of 16 taps, for example, the prior art requires about 58,000 transistors. In case four signal processing cores (i.e., SPC) having a function of four taps are used, the number of transistors required can be reduced to about 34,000 by a duplexing process. In case two SPCs having a function of eight taps are used, the number can be reduced to about 19,000 by a quadplexing process. In case, moreover, one SPC having a function of sixteen taps is used, the number can be reduced to about 13,000 by an octaplexing process. Here, the reason why the number of elements is not halved even if the number of the SPCs is halved is that the number of elements to be used in control circuits, memories and so on increases.

Digital video signal processor

In a serial-parallel A/D converter, at least two sets of comparators are provided for the conversion of the low-order bits and are operated in a cyclic fashion. Since the subsequent input can be subjected to the A/D conversion without waiting for the determination of the low-order bits, the conversion speed is increased.

Analog-to-digital converter

An analog-to-digital converter comprising a capacitive element for storing an analog input signal, a discharge means for discharging the charge stored in said capacitive element, a means for counting the number of clockpulses between the time of discharge starting and the time at which the voltage at the output of said capacitive element reaches a certain detection level, and a bias voltage supply means for supplying a bias voltage in order to bring the voltage at the output terminal of said capacitive element at the discharge starting time above said detection level.

The constant-current circuit consists of two MISFETs connected in series and a gate bias circuit for these MISFETs. The drain voltage of the first MISFET is maintained substantially constant by the source voltage of the second MISFET. The first MISFET does not sustain the channel length modulation, because its drain voltage is substantially constant. Consequently, a constant output current is obtained through the drain of the second MISFET.

Analog-to-digital converter employing constant-current circuit

An analog-to-digital converter comprising a capacitor for storing an analog input signal, a constant current discharging circuit coupled with the capacitor for discharging the charge stored therein, a level detection circuit connected to the input terminal of the capacitor, a counter connected to the output terminal of the level detection circuit for counting the number of clock-pulses between the time of discharge start and the time when the voltage at the input terminal of the capacitor drops to a detection level of the level detection circuit, a bias voltage supply means connected in series with the capacitor for adding a bias voltage to the voltage at the input terminal of said capacitor, and a switch connected in parallel with the capacitor for short-circuiting the capacitor when the voltage at the input terminal of said capacitor drops to the detection level.

Growing community of inventors

Hachioji, Japan

Toshiro Tsukada