JPS62239216A - Constant current circuit - Google Patents

Abstract

PURPOSE:To stabilize a current characteristic against the fluctuation of a load and that of a power source voltage by comprising a circuit utilizing the differ ence between action points of the same conductive type fieled effect transistors. CONSTITUTION:The 2nd FFT32 is operated in the saturated area of a drain current, however the drain current is inclined to change due to the fluctuation of the load 4 and that of the power voltage VDD. At that time the drain voltage of the 1st FET31 changes, which leads the voltage across the gate and source of the 2nd FET to change. The action point of the 2nd FET fluctuates, and a change in the drain current of the 2nd FET is suppressed. With the aid of such an action the action point of the 1st FET31 is set in the saturated area of the drain current, whereby a constant current circuit with a stabler current characteristic can be constituted.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a constant current circuit in a semiconductor integrated circuit.

[Summary of the invention]

The unexploited aspect is that in the constant current circuit of a semiconductor integrated circuit, a circuit that utilizes the difference in the operating point of field effect plastic transistors of the same conductivity type is constructed. This makes the characteristic sound more stable.

[Conventional technology]

The fifth constant current circuit in conventional semiconductor integrated circuits
A typical example is the causal circuit.

FIG. 5 shows a circuit often used as a constant current source for an operational amplifier in a semiconductor integrated circuit. In Figure 5, P
Let β of channel transistor 1 be βP, threshold voltage kVTP, βtβN threshold voltage kVTN of N-channel transistor 2, β of N-channel transistor 5? Let βNB1 threshold IE pressure kVTN. Also, the power supply voltage t-V
np, the voltage of the ground line is 2°, and the N-channel transistor 3 operates in the sum region, then the load 4? The flowing current is expressed by the following equation (1).

(As is clear from the formula, this circuit is a constant current circuit that is unrelated to load fluctuations.

[The mesodic point that the invention attempts to solve]

Is the constant current circuit in Figure 5 the gate voltage of N-channel transistor 5? The drain 'J? of N-channel transistor 3 is kept constant. Constant current characteristics are obtained by utilizing the saturation error range characteristics of the L current.

However, at the tip, the drain current changes as the drain voltage changes (
The drain current does not remain constant as the load changes (mJ), and increases as the drain pressure increases.
The purpose is to solve all of the above problems, and to obtain a constant current circuit that exhibits stable characteristics against fluctuations in load and power supply voltage.

[Means for solving problems]

(υ) In the constant current circuit of the present invention, a) the first field effect transistor is connected in series with the second field effect transistor, and b) the gate electrode of the first field effect transistor is connected to the second field effect transistor. Effect transistor gate JL
C) the drain' of the second field effect transistor;
1Jic pole is connected to the load; and d) the first field effect transistor has a drain current saturation region as an operating point, and the M2 field effect transistor has a drain current saturation region as an operating point; Close.

(2) As a means for obtaining the operating points of the first and second field effect transistors, the threshold voltage V of the first field effect transistor and the threshold voltage VT of the field effect transistor of the 1lfI2 are determined. , the constant current circuit has a configuration similar to that of the constant current circuit described in claim 1, which makes the voltage higher than .

[Effect]

Effect of the constant current circuit of the present invention? In other words, when the drain voltage of the second field effect transistor increases due to a load change, the second field effect transistor operates in the saturation region, but the drain current increases slightly. At this time, the drain voltage of the first field effect transistor also increases, but the increase in the drain voltage of the first field effect transistor decreases the voltage between the gate and lease of the second field effect transistor, and It functions to reduce current flow at the drain of a field effect transistor.

Taking full advantage of this effect, the operating point of the first additive effect transistor is set to the first and second additive effect transistor thresholds (+t VTI e VT, k VTI > vTt
By setting it in the saturation region, it is possible to obtain very stable saturation characteristics of the drain current, creating a constant current circuit with better regulation characteristics than conventional ones. Obtainable.

〔Example〕

FIG. 1 shows one embodiment of the present invention.

Although FIG. 1 is configured with an N-channel MOEI field effect transistor (hereinafter referred to as MosrgT), a similar configuration is also possible with a P-channel MO8ET'KT.

51 is the first field effect transistor (hereinafter referred to as FET), 52 is the second FKT, 4 is the load and VRE, and G is the FET 31. The reference voltage applied to the gate electrode of EI''F2T32 can be applied inside the integrated circuit by setting it to mff like FKTl and FET2 in Fig. 5, or it can be applied from outside the integrated circuit. ! It is also possible to apply A voltage.

VBUB\i Fundamental root potential and cardiac root potential VSS as shown in Figure 11
It is possible to use a separate power supply, but it is also possible to use the same potential as V2O.

The second FET 32 is operated in the drain current saturation region, but the drain current changes due to fluctuations in the load 4 or fluctuations in the power supply voltage vDD. At this time, the first
The drain voltage of the FKT 31 changes, the voltage between the gate and lease of the second FKT changes, the operating point of the second FIT changes, and changes in the drain current of the second FF 3T are suppressed.

In the present invention, by setting the operating point of the 10th F'm'l' in the saturation region of the drain current, the above-mentioned effect can be effectively utilized, and the entire constant current circuit can be constructed with more stable current characteristics.

FIG. 2 shows one embodiment of the present invention.

Although FIG. 2 is composed of N-channel MO13FET, P-channel MO81F1! A similar configuration is also possible for :T.

55.54 Fl! iT+'l: Connected in series, the connection point thereof is connected to the gate electrode of FFXT at 51.52, and applies reference α pressure to FET at 51.52.

If the operating point i of FTAT55 is set in the same way as the operating point of FET 51, the potential at the connection point of FKT33 and FET54 will not be affected by fluctuations in VDD, and a stable potential will be obtained, which can be used as a reference voltage and can be used as a reference voltage. does not require a reference voltage supply from the Furthermore, by setting the current amplification rate of Fil:T54 to an excessive value, it is extremely stable even when the temperature changes! 1! It is possible to configure a flow circuit.

That is, the variation t% of the drain current of FICT31 and F'KT52 with respect to temperature I#T55 and Fll:T34
This is compensated by temperature changes in the potential at the connection point.

FIGS. 3 and 4 show an embodiment of the present invention.

The 31st embodiment has the same basic operation as the embodiment shown in FIG. 1, but the substrate potential is set to the same potential as the lease potential, and the fluctuation t of the threshold value due to the back gate bias is eliminated.

The embodiment shown in FIG. 4 has the same basic operation as the embodiment shown in FIG. 2, but the substrate potential is made the same as each lease potential of each transistor, and the fluctuation t in the threshold value due to the pack gate bias is eliminated.

〔Effect of the invention〕

According to the present invention, two transistors of the same conductivity type are connected in series, and the operating point of each transistor is appropriately set. You can get money. In addition, the circuit is very simple, and since the same 4', jl:W transistors are used, the load on the semiconductor bag layer process can be reduced, and the cost can be reduced significantly.

[Brief explanation of drawings]

Figure 41 - Circuit diagram showing an embodiment of the invention Figure 2 - Circuit diagram showing an embodiment of the invention Fig. 6 - Circuit diagram showing an embodiment of the invention [+lJ k Figure 4 -
Circuit diagram showing an example of the non-inventive example Fig. 2 - Circuit diagram showing a conventional example 1, 2.5.51.32.33.34...Field effect transistor 4...Load . More than that, the circuit diagram of the circuit B is 19, the circuit diagram is 1 circuit, t5D, 2 u, the 8th route is Q8, the circuit diagram is 3 times, and the circuit diagram is 3 times. Electricity is poor and counterfeit! Circuit discussion 51 blades

Claims (2)

[Claims] (1) In a constant current circuit using a semiconductor integrated circuit device, a) a first field effect transistor is connected in series to a second field effect transistor, and b) a gate electrode of the first field effect transistor. are commonly connected to the gate electrode of the second field effect transistor, c) the drain electrode of the second field effect transistor is connected to a load, and d) the first field effect transistor A constant current circuit characterized in that the second field effect transistor has a drain electrode saturation region as an operating point, and the second field effect transistor has a drain electrode saturation region as an operating point. (2) As a means for obtaining the operating points of the first and second field effect transistors, the threshold voltage V_T_1 of the first field effect transistor is set to the threshold voltage V_T_2 of the second field effect transistor. 2. The constant current circuit according to claim 1, wherein the constant current circuit is made to be higher than .