JPH0766298B2 - Constant current source circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to a constant current source circuit suitable for semiconductor integrated circuits.

[Conventional technology]

Various types of constant current source circuits using semiconductor elements have been proposed and put into practical use.

FIG. 6 is a circuit diagram for explaining a conventionally known constant current source circuit by the fixed bias method, in which M ₁ is a P channel MOS.
FET (hereinafter abbreviated as transistor M ₁ ), 2 is a bias circuit, 3 is a power supply (V ₁ ), 4 is a load resistor, R ₁ and R ₂ are resistors, _ID is a drain current flowing in the transistor M ₁ , V _GS is the gate-source voltage of the transistor M ₁ .

FIG. 7 is a static characteristic diagram of the gate-source voltage V _GS and the drain current I _D of the transistor M ₁ in the circuit of FIG.

As can be seen from the static characteristic diagram of FIG. 7, if the gate-source voltage V _GS of the transistor M ₁ is constant, the drain current I
_D also becomes constant, and a constant current I _D flows regardless of the magnitude of the load resistance R _L. Here, the gate voltage of the transistor M ₁ is determined by the resistance ratio of the resistors R ₁ and R ₂ and the voltage V ₁ of the power supply 3.

Therefore, if the voltage V ₁ of the power source 3 is constant, the voltage V _GS between the gate and source of the transistor M ₁ is kept constant, the transistor M ₁ operates as a constant current source.

However, in the above-mentioned conventional technique, the gate-source voltage V _GS vs. drain current I _D characteristic of the transistor M ₁ has manufacturing variations and temperature dependence, and consideration should be given to variations in the drain current due to them. Was not done.

[Problems to be solved by the invention]

As described above, there are large variations in the characteristics of transistors in the semiconductor manufacturing process. In addition, transistors have poorer temperature characteristics than resistors and capacitors. In the above-mentioned prior art, no consideration is given to variations in characteristics of the transistors and temperature variations, and there is a problem in that the current value of the constant current source fluctuates greatly (usually in a MOS / IC process, it is from two times to one half). It was

It is an object of the present invention to provide a constant current source circuit that suppresses current variations of a constant current source due to variations in transistor characteristics and temperature characteristics.

[Means for solving problems]

The above object is achieved by detecting the drain (collector) current I _D flowing through the transistor M ₁ which operates as a current source, such that the drain (collector) current I _D is constant transistor M ₁
It is achieved by controlling the gate (base) voltage of the.

In order to detect the drain (collector) current of the transistor M ₁ (first transistor), a second transistor paired with the transistor M ₁ and a drain (collector) side of the second transistor are connected. A first capacitor whose other end is grounded and a first switch connected in parallel with the first capacitor are provided, and these, the transistor M ₁ and the resistor R _L constitute a current mirror circuit. The first switch discharges the electric charge of the first capacitor at regular intervals. A sample and hold circuit for sampling and holding the voltage across the first capacitor for a fixed period in synchronization with the operation of the first switch is provided.
By comparing the sampled and held voltage with a voltage preset by the drain current of the second transistor and the capacitance value of the first capacitor, the second voltage
This is accomplished by determining the magnitude of the drain (collector) current of the second transistor and controlling the gate (base) voltage of the second transistor, that is, the gate (base) voltage of the transistor M ₁ .

[Action]

In the current detection circuit, the first switch discharges the electric charge of the first capacitor in a constant cycle.

It is stored in the first capacitor. By these operations, the drain (collector) that flows to the second transistor
The current can be detected from both ends of the first capacitor in the state of being converted into voltage.

The sample and hold circuit samples and holds the voltage across the first capacitor in synchronization with the first switch. The reference voltage generating circuit generates a constant voltage (reference voltage). The comparison circuit compares the output voltage of the sample and hold circuit with the reference voltage of the reference voltage generation circuit, and outputs a voltage (or current) according to the difference between these voltages. The smoothing circuit smoothes the output voltage of the comparison circuit. By applying the smoothed voltage to the gate (base) of the second transistor,
The drain (collector) currents of the second transistor and the transistor M ₁ (first transistor) operating as a current source can be controlled. That is, the drain (collector) currents of the transistor M ₁ (first transistor) and the second transistor are the capacitance value of the first capacitor of the current detection circuit, the sampling time of the sample and hold circuit, and the reference voltage generation. Since it is determined by the reference voltage of the circuit, a constant current can be obtained regardless of the characteristic variation of the transistor M ₁ .

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of a constant current source circuit according to the present invention, in which M ₁ and M ₂ are P-channel MOS / FE, respectively.
T (hereinafter, abbreviated as transistor). V ₁ and V ₂ are voltage sources, R ₁ is a resistor, R _L is a load resistor, C ₁ , C ₂ and C ₃ are capacitors, S ₁ and S ₂ are switch circuits, and A ₁ and A ₂ are respectively Shows an amplifier.

Further, 5 is a current detection circuit, 6 is a sample and hold circuit, 7 is a reference voltage generation circuit, 8 is a comparison circuit, and 9 is a smoothing circuit.

FIG. 2 is an operation waveform diagram of FIG. 1, where (a) is the conduction state of the switch circuit S ₁ , (b) is the conduction state of the switch circuit S ₂ , (c) is the voltage waveform at point X, ( d) shows the voltage waveform at the Y point.

First, the individual operation of each unit will be described.

In FIG. 1, the transistor M ₁ operates as a current source with the resistance R _L as a load. Next, the current detection circuit 5 will be described. The switch circuit S ₁ discharges the electric charge of the capacitor C _{1 in} a constant cycle.

The transistor M ₂ forms a current mirror with the transistor M ₁ by using the capacitor C ₁ as a load.

Therefore, the drain current of the transistor M ₂ is proportional to the drain current of the transistor M ₁ . The drain current of the transistor M ₂ flows into the capacitor C ₁ when the switch circuit S ₁ is in the non-conducting (OFF) state. At this time, the drain current of the transistor M ₂ can be detected as the voltage across the capacitor C ₁ .

Sample and hold circuit 6 samples the capacitor C ₂ by the switch circuit S ₂ operating voltage across the capacitor C ₁ of the current detection circuit 5 in synchronization with the switching circuit S _1, to hold.

The amplifier A ₁ operates as an impedance converter.
Here, the capacitance of the capacitor C ₁ of the current detection circuit 5 is
C _1, the drain current I _D2 of the transistor M _2, if the amount of time that the switch circuit S ₂ is conducting and t _2, the voltage V _C across the capacitor C ₂ is And the drain current of the transistor M ₂ becomes
It can be expressed as the voltage across C ₂ .

Reference voltage generating circuit 7, the (1) constant voltage equivalent to the drain current I _D2 of the transistor M ₂ than relationships (hereinafter, referred to as a reference voltage) to generate.

The comparison circuit 8 compares the reference voltage generated by the reference voltage generation circuit 7 with the voltage stored in the capacitor C ₂ of the sample and hold circuit 6, and outputs the result as a voltage. Here, the output impedance of the amplifier A ₂ becomes a high impedance state when the two comparison signal levels are equal.

The smoothing circuit 9 smoothes the output voltage output from the comparison circuit 8.

Next, the overall operation will be described.

The drain current of the transistor M ₁ is represented by the drain current of the transistor M ₂ of the current detection circuit 5, after the drain current of the transistor M ₂ is converted into a voltage by the capacitor C _1, both ends of the capacitor C ₁ Is sampled and held in the capacitor C ₂ of the sample and hold circuit 6. The sampled and held voltage is compared by the comparison circuit 8
It is compared with the reference voltage of the reference voltage generating circuit 7 by the amplifier A ₂ of. Here, considering the case where the voltage across the capacitor C ₂ is smaller than the reference voltage, the output of the amplifier A ₂ becomes a voltage close to the ground voltage. The output of the amplifier A ₂ performs the operation of discharging the electric charge accumulated in the capacitor C ₃ of the smoothing circuit 9. As a result, the voltage across the capacitor C ₃ decreases and the gate-source voltage of the transistors M ₁ and M ₂ increases. That is, the drain currents of the transistors M ₁ and M ₂ are increased.

Next, consider the case where the reference voltage and the voltage across the capacitor C ₂ are equal. At this time, the output of the amplifier A ₂ is in a high impedance state, and the voltage across the capacitor C ₃ of the smoothing circuit is held. During this time, the transistors M _1, the gate-source voltage of M ₂ is kept constant transistors M _1, M ₂ each drain current is a constant value.

Next, consider the case where the voltage across the capacitor C ₂ is higher than the reference voltage. At this time, the output of the amplifier A ₂ outputs a voltage close to the power supply voltage.

As a result, the voltage across the capacitor C ₃ increases and the gate-source voltage of the transistors M ₁ and M ₂ decreases. That is, the drain currents of the transistors M ₁ and M ₂ are reduced.

The fluctuation of the output of the amplifier A ₂ is smoothed by the smoothing circuit 9 and then applied to the gates of the transistors M ₁ and M ₂ .
The transistor M ₁ operates as a constant current source.

According to the first embodiment described above, it is possible to configure a constant current source circuit that is not affected by variations in transistor characteristics and temperature fluctuations.

Since the amplifier A ₁ is used as an impedance converter, it is obvious that a source follower or the like may be used instead of the amplifier. Further, since the resistor R _L is used as the load of the current source transistor, it is clear that an active element such as a transistor may be used instead of the resistor R _L.

FIG. 3 is a circuit diagram showing a second embodiment of the constant current source circuit according to the present invention, and those having the same functions as those in FIG. 1 are designated by the same reference numerals. M ₃ and M ₄ are N channel M respectively
OS • FET, V ₃ and V ₄ are voltage sources.

The operation of the second embodiment will be omitted because it can be easily understood from the description of the operation of the above embodiment.

According to this embodiment, it is possible to configure a constant current source circuit that is not affected by the characteristic variations of the MOS • FETs M ₃ and M ₄ and temperature fluctuations.

FIG. 4 is a circuit diagram showing a third embodiment of the constant current source circuit according to the present invention, and those having the same functions as those in FIG. 1 are designated by the same reference numerals. T ₁ and T ₂ are PNP type transistors, and R ₂ and R ₃ are resistors. The description of the operation of this embodiment will be omitted because it can be easily understood.

According to the third embodiment described above, it is possible to configure a constant current source circuit that is not affected by variations in transistor characteristics and temperature variations.

FIG. 5 is a circuit diagram showing a fourth embodiment of the constant current source circuit according to the present invention, and those having the same functions as those in FIGS. 1, 3, and 4 are designated by the same reference numerals. is there. T ₃ and T ₄ are NPN type transistors, respectively. The operation of this embodiment will be omitted because it can be easily understood from the description of the operation of the above embodiment.

According to the fourth embodiment described above, it is possible to configure a constant current source circuit which is not affected by variations in transistor characteristics and temperature fluctuations.

〔The invention's effect〕

As described above, according to the present invention, it is possible to configure a constant current source circuit in which there is no variation in current of a current source or variation in characteristics due to variations in characteristics of transistors due to variations in manufacturing of IC and variations in characteristics due to temperature variations. It is possible to provide a constant current source circuit having an excellent function, excluding the drawbacks of the technology.

[Brief description of drawings]

1 is a circuit diagram showing a first embodiment of the present invention, FIG. 2 is an operation waveform diagram of FIG. 1, FIG. 3 is a circuit diagram showing a second embodiment of the present invention, and FIG. FIG. 5 is a circuit diagram showing a third embodiment of the present invention, FIG. 5 is a circuit diagram showing a fourth embodiment of the present invention, and FIG.
FIG. 7 is a circuit diagram for explaining a conventionally known constant current source circuit, and FIG. 7 is a static characteristic diagram of the gate-source voltage and the drain current of the transistor M ₁ in FIG. 5 ... Current detection circuit, 6 ... Sample and hold circuit,
7: reference voltage generation circuit, 8: comparison circuit, 9: smoothing circuit, M ₁ , M ₂ ...... MOS / FET, A ₁ , A ₂ ...... amplifier, S ₁ , S ₂
... switch circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shuzo Matsumoto 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Prefecture Home Appliances Research Laboratory, Hitachi, Ltd. (72) Hironori Hanafusa 292, Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Tate Video Engineering Co., Ltd. (56) Reference JP-A-58-37719 (JP, A) JP-A-62-69230 (JP, A)

Claims (1)

[Claims] 1. A first and a second transistor connected in a current mirror form, a load driven by an output current of the first transistor, and a capacitor supplied with an output current of the second transistor. Switch means for discharging the charge charged in the capacitor at a predetermined frequency, hold means for holding the charge voltage of the capacitor for a predetermined period, and comparing the held voltage with a reference voltage to determine the difference between these voltages. A constant current source circuit, comprising: a control unit that controls the biases of the first and second transistors so as to decrease.