JPS62260212A - Reference current source circuit - Google Patents

Abstract

PURPOSE:To remarkably reduce the influence of the Early's effect caused by the deviation of current amplification factor beta and the variation of power supply voltage, by using a feedback means to apply the feedback to a reference current value setting transistor. CONSTITUTION:A pnp transistor (TR) 11 detects the Early's effects of both TRs 4 and 5 and the variation of the current amplification factor beta and produces a detection increase current I0. An npn TR 12 and a resistance 13 convert the current I0 into the voltage information to supply it to the bases of the TRs 4, 5 and 6. Thus a loop is formed with these TRs 11 and 12 and resistance 13. While an npn TR 14 serves as a current source TR and supplies a current Iy. The TR 14 also drives a load 16. Then a resistance 15 serves as an emitter resistance and decides the current Iy.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a circuit that generates a reference current, particularly a reference current that has excellent stability against fluctuations in power supply voltage and whose current changes little with respect to deviations in the current amplification factor β of transistors. This relates to the generation circuit.

2. Description of the Related Art FIG. 3 shows a reference current generating circuit commonly used in the prior art. This reference current generation circuit has a current mirror composed of PNP transistors 1 and 2, which have almost the same characteristics, and transistors 1 and 2, and supplies a current I for driving the load. PNP) transistor 3
and NPN transistors 4 and 5 that determine the reference current value.
．． 6 and a resistor 7 that determines a reference current value. Note that 8 is a load connected to the collector circuit of the PNP transistor 6, 9 is a power supply terminal, and 1o is a ground terminal.

In the reference current generating circuit configured as above, the current I (=
If we pay attention to the relationship between I6) and the combined current of transistors 4.6 and the current flowing through the transistors at the same time, the following relational expression holds true.

Transistor 2 has the well-known relational expression below as a current mirror. Here βP is PNP)
This is the current amplification factor of the transistor.

Further, the reference current source composed of transistors 4, 5.6 and a resistor is as follows.

Here, vBE is the base eminota of each transistor.
is the saturation current of the transistor, and E is the emitter current of each transistor. If it is assumed that each transistor is equal, equation (7) holds true.

Further, the relationship between IE and IE6 is expressed via PNP current mirror transistors 1 and 2 as follows.

Applying equations (8) and (9) to equation (7), this process E
If βP and βN are both close to infinity, the formula can be expressed as αO', which will be shown later.
It is said that it is not affected by fluctuations in the power supply voltage vcc.

Since the current I8 is connected under almost the same conditions as I2 in equations (1) to 00, 12FI'=IE holds true and is used as a base fishing current source. The right term of equation (7) is the transistor 4.5 and the resistance of the circuit in Figure 3? (R7)
is the base voltage of transistors 4 and 6 due to the current flowing in , and the peak is the expression of the base voltage and emitter current of transistor 6.

FIG. 4 is a characteristic diagram of this relational expression. The horizontal axis is the current flowing through transistors 4 and 5.6 (IE, E6),
The vertical axis is the voltage at the point where the bases of these transistors are commonly connected, that is, the base voltage (VB).
From equation (7), curve I shows the characteristics of the right term, and curve 1
indicates ecstasy. Assuming that the current amplification factor β of the transistor is a value close to infinity, the current I shown in the circuit of FIG.

and I can be considered to be approximately I, =: I2 from equation (1),
Across the range, IE and IEe also settle to equal values. That is, the point A is the point where the curves 1 and II in FIG. 4 intersect at the same current. This is the value expressed by equation 10 as follows.

Problems to be Solved by the Invention In such a conventional configuration, the current amplification factor of the transistor is finite and not very large, and furthermore, if this circuit is formed as an integrated circuit,
When mass production is performed, there is a problem in that the IE value fluctuates due to variations in β. Another drawback is that it is relatively strongly influenced by power supply voltage fluctuations due to the Early effect of each transistor. Let's analyze it in detail below.

Problem 1: Influence of β Values often used in practice for equation 01: VT = 28 mV, R
Substituting 1:450Ω, βN: 100, βP=60, the current IE is = 57.77X0.6298 = 36.38 (μA) ■ Taking the value as the center value and considering the variation, βN = 50~
200. By substituting the βp30~1000 conditions, the minimum value “Emin” and the maximum value “El−1” of the electrician E [however, βN=
so, βP30] = 57.77X0.5865 = 33.82 (μA) ・Yamakawa... αυ
[However, βN=200βp=100) =57.77X0.6632 =38.31 (μA) ・Yamakawa... (2
). That is, it can be seen that there is a deviation of approximately +6%-7ch from the center value.

This deviation in the current source means a deviation in the gain of the amplifiers in multiple stages within the integrated circuit, and in the case of a configuration that attempts to obtain a gain of approximately 80 dB, the following effects occur.

Obtaining a gain of 80 dB with a single stage amplifier is unsuitable from the viewpoint of circuit stability, and generally four stages of amplifiers each having a gain of about 2 odB are often directly connected.

The gain Gv of the differential amplifier per stage is expressed by the following formula.

Assuming that gmd is the transconductance of the differential amplifier, and RL is the load impedance I is the current source current of the differential amplifier, RL and VT are invariant to the influence of β, so
At this time, if there is no question, it is clear that the deviations of +6% and -7% of the value will directly become the deviation of the gain. Gy = 2
If odB = 10 times, the deviation is from 10.5 times to 9.3 times, and is rewritten from 20.4 dB to 19.4 dB. Since this is four stages, it is directly added to 80 dB, resulting in a deviation of ±2 dB.

In common sense, the permissible deviation is often about ±3 dB, and this often becomes a problem under conditions where it is possible to predict other deviations.

Problem 2: Influence of the Early effect As is well known, the Early effect is a phenomenon in which the depletion layer is affected by fluctuations in voltage between the collector and emitter of a transistor, and the ratio of base current to collector current changes. This can be generally expressed by equation 03.

Here, IC is the collector current of the transistor, vcE is the voltage between the collector and emitter, vBE is the voltage between the base and emitter, and V″A is the early voltage.

If these early effects are considered in the conventional circuit shown in FIG. 3, the following can be analyzed. transistors 1 and 6
is a so-called diode connection in which the collector and base are directly connected, and since vcE is constant, it is not affected by the Early effect. However, transistors 2.4 and 5
, by the power supply voltage vcc of the power supply terminal 9, vc
Since E fluctuates, it affects Equations (8) and (9), respectively, and the relationship between IE, 11σHIE, and E2 has approximately the following effects.

vcE(1) and vcE(2) are the varying potential differences of CE.

Current element conditions, actual value of power supply fluctuation vCE (1)
-VCE (2): 5V, Vp, = , aoVSI
B=4, 8X 10-16(A), VT=26m
V, VB E: Substituting 654mV into aa2,
=, -@40.3 (μA) 4° = 6.03 μA [μA], so it can be inferred that the fluctuation was 12.5%.

The variation of transistor 4.6 is added as a result of this. Furthermore, since a similar amount of variation is added to the transistor 2, even if βP and βN of the 00 formula are assumed to be infinite, the variation of the 00 formula is added.

IEa = 57.71n2 (〒+o, 12) (μA) IE
, = IΣ (β is infinite) = 46.5 (μA) ``Ea is the current value ∆ which fluctuated due to the Early effect is I
E6. This is the change made to E. When the effect of ΔI/I does not exist, IE=40μA, so this appears as a 16.2% fluctuation in the ratio of Ea and E.

As already mentioned with regard to the effect of β, this is too large to be acceptable as a fluctuation range when used as a current source for a multistage differential amplifier. In other words, it is clear that the integrated circuit including the circuit shown in FIG. 3 is not suitable for use in equipment where the power supply fluctuates widely, such as equipment using dry batteries.

The problem of β can be analyzed using Figure 4 as follows.

When β is a finite and relatively small value, I>I, and the IE acting in the direction of "2" Ee is approximately expressed by the following equation.

As a result, the state is balanced in the state of IE>E6, and from point A in FIG. 4 it settles in the direction of IE>"Ee, that is, point 8.

Also, Early's problems can be diagrammed in a similar way.

Assuming that β is infinite, Equation 06 is 'E6/I
Let E = 1. If vCE now rises from a low voltage of 1v to 6v, this means that ΔI has increased. this is! Σ and I4, IE and! , respectively, and IE<I2. It will move in the direction of E<I, and will work in balance with the ``E ku'' Ee.
In other words, it settles at 0 points.

The present invention provides a reference current source circuit that can significantly reduce the influence of the Early effect caused by the deviation of the current amplification factor β and power supply voltage fluctuations described above.

Means for Solving the Problems In the reference current source circuit of the present invention, the bases of a first transistor and a second transistor whose collectors and bases are shorted are connected in common, and the emitters of both transistors are connected to a power supply terminal. The collector, base, and emitter of the current mirror circuit section are connected in common, and the collector common connection point is connected to the collector of the jgl transistor, and the emitter common connection point is connected through a current value determining resistor. third and fourth transistors connected to a reference potential point and having complementary polarity to the first and second transistors, the collectors of which are connected to the collectors of the second transistors, and the bases of which are connected to the collectors of the third and fourth transistors; a fifth transistor whose base common connection point is connected to the reference potential point and whose emitter is connected to the reference potential point, and whose polarity is complementary to the first and second transistors; and a collector connection point between the first, third and fourth transistors. a sixth transistor whose base is connected to the third, fourth, and fifth transistors to detect the difference current generated at the same coupling point;
The structure is equipped with a means to return to the base.

Function: In the reference current source circuit of the present invention, feedback is applied to the reference current value setting transistor by the feedback means, and a function of reducing deviation in the current source current value is provided.

Embodiment FIG. 1 shows the configuration of a reference current source circuit according to an embodiment of the present invention.

The basic configuration consisting of circuit elements and circuit parts numbered from 1 to 10 is almost the same as the basic configuration of the conventional circuit shown in FIG. The PNP transistor ~11 detects the Early effect of the transistor 4.6 and the fluctuation of the current amplification factor β, and generates a detected increased current I□. NPN)U/The raster 12 and the resistor 13 increase the detected increased current I□ written as,
It is a means for converting voltage information and supplying it to the bases of transistors 4, 5, and 6. It forms one loop with transistor 11, and becomes a component that solves the above-mentioned problem.

Further, the (NPN) transistor 14 is a current source transistor serving as means for supplying current air, and drives the load 16. The resistor 15 is an emitter resistor provided to determine the above-mentioned current air.

The operation and effects will be explained according to the above configuration.

The circuit section consisting of transistors 4, 6.6 and resistor 7 has almost the same basic configuration as shown in Fig. 3, where the emitter current IE is expressed by the formula (IG'). In Fig. 3, the collector of transistor 6 and Although the bases are connected to form a diode, in the circuit of the present invention, the transistor 12 is diode-connected.In order to explain its function in FIG. 1, various analyzes will be made as follows.

These are the same circuit parts as in FIG. 1 and have the same formulas. Also, engineering E6 and engineering. By substituting I2 in equation (1), the relationship between E and E is (to).If the Q9 equation is made into the relational expression of E6/IE, the relationship between E and I□ is E/β= Because it is more I
=I-I-I-'-・・・・・・・・・・ 2D
The relational expression 1B-β is obtained. Substituting this into equation (a) yields. Furthermore, by substituting the contents of equation (c) into equation (7), the following relational expression can be obtained. In this equation, even if a change in β occurs in transistors 1 and 2, feedback is applied due to the relationship of Iα′, and the term 1rs2() is the β2 of transistor 1.
This means that the error is reduced to 1/1. Note that the currents O and O form a current mirror with each other, and the feedback effect can be changed depending on what value this ratio is set to.

Let's consider qualitative behavior here. First, “E6
Let us assume a position where /IE are approximately equal. At point D of the circuit in FIG. 1, transistor 1 is
A base current of 1 is flowing, and the relationship with IO is IBXβ
Since P = ko, ko increases or decreases depending on the value of IB, causing the base-collector potential of the transistor 12 to rise or fall. Let's temporarily set I□=2I and R13=2R (however, R13 and R7 are the resistance values of resistors 13 and 7).

By the way, the base of transistor 12 is transistor 4,
It is connected to a 5.6 base. Therefore, IE="
It becomes stable at the point E6 = 2 0. The curve in Figure 4 shows these positions, and the constant relationships are the same as the circuit in Figure 3. In this stable state IE = 2 2 I
O is considered to be point A. By the way, let's consider that some kind of influence occurs, for example, a change in β, and the ratio of IE6/E is changed and moved to the B point side. This is because “Ee−ΔIEe<”s! The result is B+ΔIB. By increasing the base current. = I B xβ increases and the base-collector voltage of the transistor 12 increases, and the base voltage VB at the common base connection point, that is, the vertical axis in FIG. 4 increases and tries to return to point A. On the other hand, due to the fluctuation of β, “Ea+ΔIE
>I6, conversely, I-I, -ΔI, = - ΔIB. This circuit state means that the point is 0 in FIG. In this case, −ΔIB causes I
Since B rapidly decreases and I()=IBXβP also decreases, the collector-base voltage of transistor 12 decreases,
Since this is a drop in the common base point potential VB, it works to approach point A.

In addition, an early effect occurs, and the current 1. , IA is about to change, then in the equilibrium state of IE6=engine, I
When C+ΔIC occurs and becomes I2+ΔI2, I-
I, -ΔI,=IB-ΔIB, and IB decreases. This change in base current causes the base potential of the transistor 12 to drop, which disrupts the equilibrium of IEe=E and works to keep I2 constant.
Equilibrium is reached again at point E where IEe is slightly smaller than . This means that the loop works so that IB=I-I is always constant. As described above, in the circuit of the present invention,
For all transistor fluctuations, an operation is performed to suppress the error to one part of the loop gain.
Changes in the current value of the reference current source due to the Early effect and fluctuations in β can be kept to a minimum.

Here, quantitative considerations are added by substituting actual numerical values into the Q equation.

vT=26mV, R7=450Q1βP=30~100
Try adding the conditions.

Also, if you set IO//I=2, =57.77
1n2 (0,9966) = 57.77X0.688
6 = 39.78 (μA) ・・・・・・・・・・・・ (
to) = 57.77X 1n2 (0,99514) = 39
．． 95 (μA) ・・・・・・・・・・・・ (
C) = 57.771n2 (0,9996) = 40.0
2 (μA〕 ・・・・・・・・・ Kanko)
.

FIG. 2 shows an embodiment in which the scope of use is further expanded. In FIG. 2, the elements added to FIG. 1 are a capacitor 17 for preventing feedback loop oscillation, a resistor 18 for raising the common base potential of transistors 4, 5, 6, 12, and 14, and a reference current source. The diodes 19, 20, 21 and the resistor 22 constitute a starter for applying a start potential to VB of the circuit. Although it is not a component of the present invention, it is desirable to add a starter when implementing the invention. Note that the configuration of the starter is not particularly limited. In FIG. 2, if the power supply voltage VCC of the power supply terminal 9 is a low value, for example, below the threshold voltage of the transistor, the transistors 1 to 6, 11°12.14.1
3 is not in the active state, and even if vU continues to rise, no current flows through the loop of transistors 1, 2, and 4 to 6. On the other hand, the potential becomes equivalent to that of a diode, and current begins to flow through each of the transistors 1.2 and 4°5.6, forming a loop. Note that if the common base potential VB rises, the diode 1 is connected so that the current 1o flowing through the transistor 12 does not flow into the diodes 20 and 21.
9 is connected.

In the embodiment shown in FIG. 1, the common base point potential VB corresponds to vBE of the transistor 6, and can only be raised to about 0.8V at most. This limits the current value of a current source such as transistor 14. For example, as mentioned in the explanation of FIG. 1, if E6 is set to be about 40 μ8, if the transistor 14 is required to function as a current source larger than this, it will become unreasonable in terms of design. It is necessary to use a device with an emitter area several times larger than that of the transistor 6, or to change the settings of the IE6 itself, resulting in a lack of flexibility in application. If a resistor 18 (R18) is added to the connection point between the emitter of the transistor 6 and the resistor 7 as in the circuit shown in FIG. 2, the common base point potential VB can be raised as shown by. In addition, resistance 13
If is determined to a value of I=21° in accordance with the settings shown in FIG. 1, the feedback loose condition will not change.

If the value of resistor 22 is chosen to be 5Ω, the current IR2□ flowing through this resistor is lR22=I E+ I R6” 80
IIA, and the common base point potential VB is 4
00 mV, making it possible to set the current flowing through the transistor 14 in a fairly wide range.In addition, the oscillation prevention capacitor 17 can be added to any of the feedback loops, as long as the oscillation is stopped. The stray capacitance of the device may be used instead.

Effects of the Invention As described above with reference to FIG. 1, the effect of the present invention is that even if power supply voltage fluctuations occur, which is one of the operational environmental conditions, the Early effect of the transistor is reduced. It is possible.

Furthermore, even if the current amplification factor β of the transistor varies significantly, the range of variation in the current value of the current source can be reduced.

This has a great effect when used as a large number of reference current sources, for example, it not only has the effect of reducing the deviation of the total gain, but also minimizes the sensitivity deviation of the oscillation circuit, demodulation circuit 9 phase comparator, etc. It is also effective in suppressing the situation.

Furthermore, in the configuration shown in Fig. 1, if the relationship between equation (2) and α is appropriately selected, it acts negatively against the fluctuation of βP, and βP
When is a small value, it is also possible to set the current value of the current source to be large. Here, engineering. Let us assume that /I is 1.0. If vT and R7 in the formula are set to the same values as shown above, βP = 30 to 1oO, then = 67.7Xln2 (1,0311) = 41.76
(μA) ...Mountain... (c) = 57.7.
xJn2 (1,0098)=40.56 (μA)
・・・・・・・・・・・・You can get a sword. Note (2
) The result of the equation is the current value when β is low, and the four holes are the current values when β is high. In this way, 1.8′ is “ma”
It can be set to a higher value than w', and it becomes possible to conversely correct the decrease in sensitivity due to the decrease in β in other circuits.

The configuration of the present invention has been explained using an example in which the transistor 11 is connected to point D, which is a feedback point, and is used as an inverting current amplifier, but the same can be done with a configuration using a voltage conversion element, such as a MOS transistor, as an alternative element. results. Numerical analysis requires a somewhat different representation. For example, 1B does not exist, so
■, A feedback loop works so that = I,
The potential at point D is determined by I□ due to the voltage-current conversion element.
It becomes stable by settling on a bias point where = 2I.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the basic configuration of a reference current source circuit of the present invention, FIG. 2 is a circuit diagram showing another embodiment of the present invention, and FIG. 3 is a circuit diagram showing the configuration of a conventional reference current source circuit. 4 are characteristic diagrams showing the current-voltage characteristics of the current source. 1 to 3...PNP for current mirror configuration)
Ransistor, 4 to 6... NPN for determining current value
Transistor, 7... Resistor for determining reference current value, 8°16... Load, 9... Power supply terminal, 10... Ground terminal, 11. 12...
- Transistor for forming a feedback loop, 13.
15... Resistor for determining current value, 14...
・Current source transistor, 17... Capacitor for oscillation prevention, 18... Resistor for increasing base bias, 19-21... Diode for start-up circuit configuration, 22... ...Resistance for starting circuit configuration. Name of agent: Patent attorney Toshio Nakao and 1 other person 1~
3-One Sword〉Tomiller Yusei's PNP) Ranjista 4
~6---NP that curses the destruction ~ Transistor 7-g
' 渣j (Marujoto's origin - 8.16 - rental 13.15 - 11 electric 1ktL decision Mf) resistor 14 ---
Voltage source transistor 1st figure 17 --- Oscillation fat stop shoulder connector 18 --- Base bias and necessary resistors 19 to 21 ---
-Tanode 22-m1 for Wing Mohan 1 Prefecture Rumorsaki! l+1i
ffN41 Yoshianno, l circle fig. 2 fig. 3 fig. 4

Claims (3)

[Claims] (1) The bases of the first transistor and the second transistor whose collectors and bases are short-circuited are commonly connected, and the emitters of both transistors are connected to the power supply terminal, and the collector, base, and emitter are connected to each other. They are commonly connected, a collector common connection point is connected to the collector of the first transistor, an emitter common connection point is connected to a reference potential point via a current value determining resistor, and the first and second transistors are connected in common. and third and fourth transistors of complementary polarity, a collector connected to the collector of the second transistor, a base connected to a base common connection point of the third and fourth transistors, and an emitter connected to a reference potential point, respectively. , a fifth transistor having complementary polarity to the first and second transistors, a control electrode connected to a collector coupling point of the first, third and fourth transistors, and a difference current generated at the coupling point; a sixth transistor that detects
A reference current source circuit comprising means for feeding back a voltage corresponding to a difference current detected by the sixth transistor to the third, fourth and fifth bases. (2) The reference current source circuit according to claim 1, wherein the sixth transistor is a bipolar transistor. (3) The reference current source circuit according to claim 1, wherein the sixth transistor is a field effect transistor.