JPH04170609A - Constant current circuit - Google Patents

Abstract

PURPOSE:To stabilize current flowing into an output terminal by feeding back a part of an output from a current mirror circuit to a band gap circuit through an internal current mirror circuit. CONSTITUTION:The current mirror circuit 1 is constituted of p-channel MOS transistors (TRs) Q1, Q3, Q5 and the band gap circuit 2 is constituted of TRs Q2, Q4, Q6 and a resistor R1. A feedback circuit 3 includes the 2nd current mirror circuit consisting of n-channel TRs Q7, Q9 whose sources are connected to a ground terminal (c) and a p-channel TR Q8 whose gate and source are respectively connected to the gate and source of the output TR Q5 and drain is connected to the drain of the TR Q9. Since the dispersion of production can be suppressed, an output current having a small dispersion can be extracted form an output terminal (b).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a constant current circuit of a constant current circuit integrated circuit.

[Conventional technology]

FIG. 4 is a circuit diagram showing an example of a conventional constant current circuit.

　゛ This constant current circuit has a power supply terminal a and an output terminal.

It has three terminals, a ground terminal C, and a power supply terminal a has three P-channel MOS transistors Q1. The sources of transistor Q, and Q, are connected, the gate of transistor Q1 is connected to an input node N, which is the intersection of the gate and drain of transistor Q, and the gate of transistor Qs, and the drain of transistor Q is connected to the output terminal The drain D of the transistor Q1, which is the output of the current mirror circuit, is connected to the drain and gate of the N-channel MOS transistor Q2, and the gate of the N-channel MOS transistor Q4.
The source of transistor Q4 is connected to ground terminal C, and the source of transistor Q4 is connected to ground terminal C.
The source of the transistor Q is connected to the ground terminal C via the resistor R1, and the drain of the transistor Q is connected to the input node N of the current mirror circuit l, which is the gate and drain of the P-channel MOS transistor Q. N channel MOS
Transistor Q2, N-channel MOS transistor Q
4. It is composed of a bandgap circuit consisting of a resistor R1.

In general, constant current circuits are required to have high accuracy in setting current, including variations in power supply potential, resistance, offset of gate-source potential difference VQS of transistors, and the like.

[Problem to be solved by the invention]

In the conventional constant current circuit described above, the V of the MO3 transistor is
O2 potential and V. , is larger than the base-emitter voltage V of the bipolar transistor, and has the drawback that high accuracy cannot be required for the set constant current value.

Next, the operation of the circuit shown in FIG. 4 will be explained. First, when a potential is applied between the power supply terminal a and the ground terminal C, a current ID8Q3 flows through the P-channel MOS transistor Q on the input node N side of the current mirror circuit 10, and at the same time, the current ID8Q3 flows through the P-channel MOS transistor Q1. A current I t+sa+ flows.

Then, at the same time a current I nsa□ flows through the N-channel MOS transistor Q2 of the bandgap circuit 2, N
A current flows through the channel MO3 transistor Q4 and draws a current through the transistor Q, and the current increases as much as the current is drawn, resulting in a circuit operation in which current flows through the transistor Q1.
Assuming that all transistors operate in a saturated state, convergence is achieved using the following equation (1).

VOSO4vasQ4 Ioso+ =□ ・・・・・・(1) ・・・・・・(2) Here, μ,: Mobility of n-channel MOS transistor, μ,: Mobility of p-channel MOS transistor,
ε. ! = oxide film dielectric constant, tox: oxide film thickness, L: MO3
Gate length of transistor, W: Gate width of MO3 transistor, V? : Threshold potential of the MOS transistor, that is, a current that satisfies equations (1) and (2) flows through the bandgap circuit 2 and the current mirror circuit 1. Therefore, the current IDIQ5 flowing through the output terminal is the (3rd)
The current of the equation can be extracted.

That is, as can be seen from equations (1) to (3) above, V? of each MOS transistor? , L, W, R1, etc., the current I flowing through the bandgap circuit 2
D804 has manufacturing variations. Also, from equation (3), the variation in the drain current IDSQ4 of the transistor Q is the drain current IDSQ4 of the transistor Q. 3 and the gate-source potential difference VG8Q3, which directly affects the output current S08, resulting in a large variation.

[Means to solve the problem]

The constant current circuit of the present invention includes a current mirror circuit having two monoconductivity type MO8) line transistors whose sources are commonly connected to a first power supply, and whose respective drains are connected to the drains of the two MOS transistors. and a pad gap circuit having two opposite conductivity type MOS transistors, one of whose sources is connected to a second power supply via a resistor, and a constant current is supplied from the input node N of the current mirror circuit through the six transistors. In the constant current circuit that outputs a current to an output terminal, the bandgap circuit includes means for negatively feeding back a current corresponding to the potential of the input node N to the source of either of the two MOS transistors of the bandgap circuit. It is configured with

〔Example〕

Next, embodiments of the present invention will be specifically described with reference to the drawings.

FIG. 1 is a circuit diagram of a first embodiment of the constant current circuit of the present invention.

P-channel MOS transistor Q 1r Q s r
Q constitutes a current mirror circuit, and transistors Q2. Q, , Qs and the resistor R1 constitute a bandgap circuit, and the feedback circuit 3 includes N-channel transistors Q7, . . . , whose sources are connected to the ground terminal. It has a second current mirror circuit of QQ, and a P-channel transistor Q whose gate and source are connected to the gate and source of the output transistor Q5, respectively, and whose drain is connected to the drain of the transistor Q.

Next, the operation of the circuit will be explained.

When a potential is applied between the power supply terminal a and the ground terminal C, a current IDSQ3 flows through the P-channel MOS transistor Q of the current mirror circuit 1, and at the same time, a current IDSQI flows through the P-channel MOS transistor Q1 and the P-channel MOS transistor Q8. flows, and then the N-channel MOS transistor Q2 . of the bandgap circuit 2 flows. Qe
, Qe respectively have a current I D8Q□r I D8Q61
As I,)so* flows, N channel*le MOS
Transistor Q4 and NMOS transistor Q draw current from transistor Q and transistor Q2, respectively.

Transistor Q3 is subtracted by transistor Q4.
The current increases by D804, and the current flowing through transistor Q1 and transistor Q8 increases.

On the other hand, transistor Q2 is transistor Q y rQ9
The current flow through transistor Q6 is reduced by the current drawn by the internal current mirror circuit of Q6. sQ6 decreases and the gate-source potential difference V. SQa becomes smaller, the voltage applied to resistor R1 becomes smaller, and current I flowing through transistor Q4 decreases.

Since the operation is performed with this negative feedback, assuming that all transistors are operating in a saturated state, the following (
4) It converges according to Eq. Drain current of transistors Q, , Qs I Dso4* I n5a3” Iosa
3''' ...(4) Since the current satisfying the equations (4) and (2) flows through the bandgap circuit 2 and the current mirror circuit 1, the current I D8QS flowing through the output terminal is expressed as the equation (5). It is determined by the formula.

As can be seen from this equation (5), especially the MOS transistor Q1. Q 2 , Q s , Q 4 no L
1W 1V T There are manufacturing variations, but if N
L of channel MOS transistors Q 2 and Q 4
Even if the ratio of /W shifts and the bandgap potential increases as a result, I vso4 increases, and I D8Q3 and I
D90s increases, N-channel MOS transistor Q*
, Qt's internal current mirror circuit increases ID8Q□, and the current flows through transistor Q6. sQ decreases, and the gate-source potential difference V. 3. , which acts to correct the bandgap voltage.

Therefore, since manufacturing variations are suppressed, I nl0
The output current IDI has smaller variations. , can be taken out from the output terminal.

FIG. 2 is a circuit diagram of a second embodiment of the present invention, in which the feedback circuit 3
As a, the drain of the P-channel transistor Q8 is directly fed back to the source of the transistor Q4 of the bandgap circuit, omitting the internal current mirror circuit in FIG. 1, so the circuit is simple.

FIG. 3 is a circuit diagram of a third embodiment of the present invention, in which a resistor R2 is inserted between the drain feedback point F of the transistor Q6 of the bandgap circuit 2 of FIG.

〔Effect of the invention〕

As explained above, according to the present invention, the threshold value of each MOS transistor is This has the effect of stabilizing the current flowing to the output terminal against manufacturing variations in potential and gate dimensions, and potential fluctuations applied to the power supply terminal.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of the first embodiment of the present invention, FIG.
The figure is part 2 of the present invention. The circuit diagram of the third embodiment and FIG. 4 are circuit diagrams of an example of a conventional constant current circuit. Ql, Qs, Q5. Ql...P channel MOS transistor, Q2. QJ, Ql, Qr
, Qe...N-channel MOS transistor* R,, R2...Resistor, a...Power terminal, b...Output terminal, C... ...Grounding terminal. Agent Patent Attorney Oto Hara Figure 1 Figure 2 Figure 3 and Figure 4

Claims (1)

[Claims] 1. A current mirror circuit having two monoconductivity type MOS transistors whose sources are commonly connected to a first power supply;
a bandgap circuit having two opposite conductivity type MOS transistors each having a drain connected to the drain of the two MOS transistors and a source of at least one connected to a second power source via a resistor; In a constant current circuit that outputs a current from the input node N of the mirror circuit to the constant current output terminal via the output transistor,
The bandgap circuit supplies a current corresponding to the potential of the input node N to the two MOs of the bandgap circuit.
A constant current circuit characterized by having means for negative feedback to one of the sources of an S transistor.