JPS598033A - Semiconductor integrated circuit device - Google Patents

Abstract

PURPOSE:To decrease the number of external parts, by incorporating an MOSFET which receives the voltage from a solar battery at its drain into a semiconductor IC together with a voltage comparator which compares the source voltage of the MOSFET with the reference voltage. CONSTITUTION:An MOSFETQ and a voltage comparator OP are incorporated into a semiconductor IC LSI which constitutes an electronic calculator that works on a solar battery E. The voltage -VE of the battery E is received at the drain of the MOSFETQ, and the source voltage -VDD of the FETQ is supplied to a noninverse input of the comparator OP to be compared with the reference voltage -Vref applied to the noninverse input. The output of this comparison is applied to the gate of the FETQ. Thus the impedance of the FETQ is controlled, and the voltage VDD is controlled so as to be coincident with the voltage Vref. Then a fixed level of voltage is supplied to a digital control circuit LOG. The display output of the LOG is transmitted to a liquid crystal display device LCD to perform a specific display. The clamp voltage can be set at an optional level by the voltage Vref.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor integrated circuit device driven by a solar cell.

Conventionally, as shown in FIG. 1, an electronic desktop calculator that is driven by a thick @kameike has been known. In this electronic desktop calculator, the voltage supplied from the solar cell E depends on the amount of incident light. Therefore, an external light emitting diode (LED) is used to clip overvoltage. Therefore, there are disadvantages in that the price is high (and the voltage setting is completely determined by the EDO forward voltage).

SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor integrated circuit device in which the number of external components is reduced and the power supply voltage can be set arbitrarily.

Other objects of the invention will become apparent from the following description and drawings. FIG. 2 shows a circuit diagram of an embodiment of the invention.

In the figure, a portion surrounded by a dotted line is a semiconductor integrated circuit device L S 1, which is formed on one semiconductor substrate by a known semiconductor manufacturing method.

The symbol E indicates a solar cell.

To reduce the power supply impedance, capacitor C
are installed in parallel. In this example.

The voltage generated by the solar cell E is directly supplied to the semiconductor integrated circuit device LSI, and a voltage clamp circuit as described below is provided inside the semiconductor integrated circuit device LSI.

The voltage −VF, which is supplied by the solar cell E, is MOS
It is applied to the drain D of the FET (insulated gate field effect transistor) Q. The voltage comparator OP receives the voltage of the source S of MO8F'E'l'Q at its inverting input (-), receives the reference voltage vref at its non-inverting input (+), and transfers its output to the MO8FETQ By transmitting the signal to the gate G of the MO8FETQ, control the impedance of the MO8FETQ to make the voltage EIa''-VDD of the source S match the reference voltage vref.

The black box is indicated by the symbol LOG.

Although not particularly limited, it is a digital control circuit constituting an electronic overlay computer, and is operated by being supplied with power by the voltage -vDD through the MO8FETQ. The display output of this LQU is transmitted to the liquid crystal display word [LCD] indicated by a black box, although not particularly limited, and a predetermined display is performed.

In this example, the voltage from the solar cell E is −■. becomes larger, and the internal power supply voltage -Vl)D becomes equal to the reference voltage Vre.
When the wL pressure comparator OP tries to become larger than f, the wL pressure comparator OP becomes larger than M
The IP address of O8FETQ is increased to clamp the internal power supply voltage -VDD to a constant voltage. In this embodiment, the voltage clamp means is connected to the semiconductor integrated circuit device LS.
Since it is built into the I, the number of external parts can be reduced and the price can be lowered.

Furthermore, the voltage at which the voltage clamp starts is the reference voltage vre.
It can be set arbitrarily by f.

In addition, in the case of using LCl as one display device as in this embodiment, the brightness fluctuates due to the increase in the internal capacitance of the semiconductor integrated circuit device LSI, resulting in poor display quality.
In addition to making things worse, there are other problems such as the non-selection output level rising and causing erroneous display. Therefore, in a semiconductor integrated circuit device having an LCD driving circuit, the internal power supply voltage -
It is necessary to stabilize the voltage of vDD.

When using an enhancement type MOS FET, the voltage from the solar cell E is used as the power supply voltage of the voltage comparator OP. It should be possible to operate it with Alternatively, when the voltage comparator OP is operated with the internal power supply voltage -vDD, a startup MQ8FET that is turned on until the internal Fg voltage -DD rises to a predetermined voltage is installed in parallel with the above MO8FETQ. do it.

If a depletion type MO8FETQ is used, the starting circuit is unnecessary.

Further, the voltage comparator OP may be provided with an input offset voltage (III) voltage, and this may be used as the reference voltage Vref. In this case, the non-inverting input (+) side is grounded.

Furthermore, the reference voltage vref may be set near the lower limit operating voltage of the internal logic circuit, and the drive voltage for the liquid crystal display may be formed into a three-value or four-value voltage using a voltage doubler circuit. .

Further, the polarity of the WL pressure may be a positive polarity.

This invention can be widely used in semiconductor integrated circuit devices whose power supply voltage is generated by five solar cells.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of the prior art. FIG. 2 is a circuit diagram showing an example of the present invention. OF...voltage comparator, LOG...digital control circuit, LCI)...liquid crystal display device, LSI...semiconductor integrated circuit device.

Claims (1)

[Claims] 1. MOSFE whose drain receives voltage from a solar cell
T, a voltage comparator that compares the source voltage of this MOSFET with a predetermined reference voltage and transmits the output voltage to the gate of the MO8FET to make the source voltage a constant voltage;
A semiconductor integrated circuit device characterized in that it includes an electronic circuit that operates by receiving voltage supply from the source of the MO8FET. 2. The semiconductor integrated circuit device according to claim 1, wherein the electronic circuit includes a liquid crystal display device drive circuit. 3. The semiconductor integrated circuit device according to claim 2, wherein the electronic circuit constitutes an electronic desktop calculator.