JPS62126662A - Constant current circuit - Google Patents

Abstract

PURPOSE:To make it possible to vary the value of a constant current, by connecting IG-FETs to each of resistors, which are connected in series, in parallel, and inputting signals, which are selectively conducted, to the gates of said IG-FETs. CONSTITUTION:A first power source VDD is connected to the source of a first- conductivity type first IG-FET 21. The gate and the drain of the FET 21 are connected to the drain of a second-conductivity type second IG-FET 31 and the gate of a first-conductivity type third IG-FET 22. The drain of the third IG-FET 22 is connected to the gate and the drain of a second-conductivity type fourth IG-FET 32 and the gate of the second IG-FET 31. The source of the second IG-FET 31 and the source of the fourth IG-FET 32 are connected to a second power source VSS. The source of the third IG-FET 22 is connected to one end of a resistor R. The other end of the resistor R is connected to the first power source VDD. The resistor R in such a constant current circuit is formed by the series connection of a plurality of resistors R1-Rn. First- conductivity type fifth IG-FETs 11-1n are connected to the individual resistors. Conducting signals I11-I1n are selectively inputted to these gates.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a constant current circuit, and more particularly to a constant current circuit that makes it possible to vary a constant current value by controlling a resistance value.

[Conventional technology]

BACKGROUND ART Integrated circuit devices used in small electronic wristwatches, electronic desk calculators, and the like employ a system in which power supplied from outside the integrated circuit device is first boosted or stepped down through a boost circuit or step-down circuit before being supplied. In this power supply system, power fluctuations from an external power supply device directly affect the integrated circuit, making the operation of the integrated circuit unstable.

Considering the above points, many integrated circuit devices in recent years have a built-in constant voltage power source as shown in FIG. 2. That is, the constant current circuit 1 is driven by the voltage difference between the voltage VDD and Vss supplied from the outside, and the current of the constant current circuit 1 is passed through the current-voltage conversion circuit 2, and the voltage obtained in the conversion circuit 2 is It is stabilized by the stabilizing circuit 3 and a constant voltage output is obtained at the output terminal 4.

[Problem that the invention seeks to solve]

However, in the constant current circuit that creates the reference current of the constant voltage power supply built into the integrated circuit device, the current value is uniquely determined by the characteristics of the constituent transistors, resistors, diodes, etc., and it is difficult to manufacture the integrated circuit device. It is not possible to change the current value of the constant current circuit afterwards. It is possible to vary the current value by installing a variable resistor etc. outside the integrated circuit in advance, but this increases the number of external devices and is not suitable for devices with high packaging density such as small electronic wristwatches and electronic desk calculators. This will be extremely disadvantageous. Furthermore, an adjustment process is required for component costs and manufacturing, leading to an increase in costs.

[Means for solving problems]

The constant current circuit of the present invention connects a first power source to the source of a first IG-FET of a tenth conductivity type, and
The gate and drain of the ET are connected to a second IG of a second conductivity type.
- the drain of the FET and the third IG-F of the first conductivity type;
E'r, and the drain of the third IG-FE'r is connected to the gate and drain of the fourth IG-FET of the second conductivity type and the gate of the second IG-FET. , the source of the second IG-FET and the fourth IG-FET
The source of the FET is connected to a second power supply, and the third I
Connect the source of G −F E jI′ to one end of the resistor,
In a constant current circuit in which the other end of the resistor is connected to the first power source, the resistor is configured by connecting at least two or more resistors in series, and a first resistor is connected in parallel to each of the series-connected resistors.
A fifth TG-FET of conductivity type is connected to the l0-F'E
It is characterized by inputting a signal which selectively makes the gate of 'r conductive.

〔Example〕

The present invention will be explained in detail below using the drawings. 1st
The figure shows one embodiment of the present invention, a P-channel insulated gate field effect transistor (IG-
One end of the resistor R1 that controls the source and reference current of the resistor R1 is connected to the first power supply VDD supplied from the outside, and the other end of the resistor R1 is connected in series up to the resistor Rn.
The other end of n is connected to the source of the P channel IG-FET 22. The sources of the P-channel IG-FETs 11-In are connected to one ends of the resistors R1-Rn, respectively, and the resistors R1-Rn are
The drains of IG-pE'rtl to 1n are connected to the other end of the resistor Rn, respectively. The gate and drain of the IG-FET 21 are connected to the gate of the IG-FET 22 and the drain of the N-channel IG-FET 31.
The gate of ET31 is connected to the gate and drain of N-channel IG-FET32 and the drain of IG-FET22, and the sources of IG-PE'r31 and 32 are connected to the second power supply Vs+s. When control signals 11 to In are input to the gates of IG-FETs 11 to In, and a low potential level (hereinafter referred to as -J, a) is applied to each control signal, the IG
-FETI 1~1n becomes conductive (hereinafter referred to as 1ON1), and the resistance value 1'1%rn of the resistors R1~Rn paired with ON IG-FETII~1n is selectively zeroed. I can do things. That is, the resistance value (h 1
+r, 20...+rn), and the constant current 10 is expressed by the following equation.

Here, q is the electron charge, k is the Bon-Raman constant, T is the absolute temperature, and m21. m22. m31. m32 is each I
This is a constant expressed by the channel size ratio (channel width/channel length) of G-FETs 21, 22, 31, and 32.

By applying the logical outputs of the storage circuits, etc. inside the integrated circuit device to the control signals 111 to Iln, it is possible to obtain a constant current according to the state of the storage circuits, etc.

By updating the contents of a predetermined memory circuit after assembling a small wristwatch or electronic desktop calculator, it becomes possible to easily vary the constant current value.

Instead of giving the control signals Ill to Iln from a storage circuit or the like inside the integrated circuit device, input terminals are provided in the integrated circuit device so that signals are added from the outside and the control signals (1)
It goes without saying that the current value of the constant current circuit can be varied by giving m Lw to 1 to Iln.

Incidentally, in the embodiment, T O-FET 11 to I n were explained as P channel type P E jr, but the resistors R1 to 'R
n is inserted between the source of IG-FET 31 and the second power supply Vsg, and the source of IG-FET 22 is connected to VD of the first power supply.
The same effect can be obtained by making the FET connected to D and connected in parallel to the resistor an N-channel FET, inputting the control signal to the gate of the FE'[', and applying a high potential to the control signal. It's obvious.

〔Effect of the invention〕

According to the present invention, the resistance value in a constant current circuit driven by an externally applied power source can be arbitrarily selected by a control signal, and a constant current circuit capable of varying the constant current value can be realized.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is a block diagram showing an integrated circuit device including a conventional constant current circuit. 11~In, 21, 22-+m+p channel 7 channel IG-PET, 31, 32...--N-t
r channel IG-FE'['. ■1~In...Control signal, R1-Rn...
··resistance.

Claims (1)

[Claims] A first power source is connected to the source of a first IG-FET of a first conductivity type, and the gate and drain of the first IG-FET are connected to the drain and drain of a second IG-FET of a second conductivity type. connected to the gate of the third IG-FET of the first conductivity type;
The drain of the third IG-FET is connected to the fourth IG-FET of the second conductivity type.
The gate and drain of the IG-FET and the second IG-FET
- connected to the gate of the FET, the source of the second IG-FET and the source of the fourth IG-FET connected to a second power supply, and the source of the third IG-FET connected to one end of the resistor; and the other end of the resistor is connected to the first power source. 1. A constant current circuit, characterized in that a fifth IG-FET of one conductivity type is connected to the gate of the IG-FET, and a signal is input to selectively conduct the gate of the IG-FET.