JPS5922245B2 - Teiden Atsubias Cairo - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bias circuit suitable for integrated circuits, and in particular to a constant voltage source for driving a constant current transistor.

Various conventional constant voltage bias circuits have been devised to drive transistors, but most of them are either completely inoperable at low voltages such as the voltage of a single battery, or do not have good characteristics against wide voltage fluctuations. I can't maintain it.

FIG. 1a shows an example of the most commonly used constant current circuit. 1 is a diode-connected reference transistor, 2 and 3 are constant current transistors, and 4 is a resistor.

The emitter current of the transistor 1 is determined by the voltage applied to the terminal 5 and the resistor 4. If transistor 2|3 has the same emitter area as transistor 1, the emitter current of each transistor will be the same. The output voltage of terminal 8 is the base-emitter voltage of transistor 1, VBE0.
, and if the emitter current of transistor 1 is IE4, it is expressed by the following equation as well known. K.T.
1E1 VBE1=-1n-(1) ε Isl where Is is the saturation current, is the Boltzmann constant, ε is the electron charge, and T is the absolute temperature.

In this circuit, if the voltage applied to terminal 5 changes over a wide range, I
E also changes at the same rate. This change brings about a change in VBE as shown in equation (1), and the currents of transistors 2 and 3 connected to terminal 8 also change in the same way as IE due to the exponential variation in VBE. Therefore, stability against power supply voltage fluctuations cannot be expected. Further, the output resistance seen from the terminal 8 is given by the reciprocal of the mutual conductance gml of the transistor 1, as is generally well known. For example, even if 1mA is applied to transistor 1 at room temperature, the output resistance is 26Ω.
I only sit down at my desk. 10m to keep it below 2.6Ω
A current of more than A must be consumed.

This is too large to be used in battery operated devices. The disadvantage when the output resistance seen from the terminal 8 is large can be explained as follows. Now consider the case where transistor 2 is used as an active load of an amplifying element.
In addition, when the output amplitude of the amplifying element increases, the potential of the collector terminal 6 of the transistor 2 naturally changes greatly. This collector potential variation is transmitted to the base electrode by the base width modulation effect. Since this variation in the base potential is a variation in the terminal 8, the base potential of the transistor 3 also varies, and its collector current varies. The adverse effect of this mutual interference between transistors 2 and 3 becomes smaller as the output resistance of terminal 8 becomes smaller. Therefore, it is desirable that the output resistance of the terminal 8 be as small as possible, but the circuit shown in FIG. 1a is not suitable because it consumes a large amount of current. FIG. 1b is a circuit diagram of another conventionally used bias circuit.

In this circuit, the operating state is stabilized by a strong negative feedback effect that circulates from the base of the transistor 12 to the emitter and then from the base to the collector of the transistor 11. In the same circuit, the collector current of transistor 12 is the base-emitter potential difference VBEll(
(usually about 0.7 volts) and the value of the resistor 9 connected to the emitter of the transistor 12. The current of transistor 11 is VB from the voltage applied to terminal 15.
It is given by the ratio of the value obtained by subtracting E,l+Vゎ,2 and the value of the resistor 14. Therefore, if the voltage at terminal 15 fluctuates over a wide range, the current in transistor 11 also fluctuates, but the V
As seen in equation (1), BE,, is a logarithmic function change in the current fluctuation value, and VBE! ! The fluctuation of is suppressed to almost 0.
The fluctuation from 7 volts is small. For example, transistor 11
Even if the current of changes by 10 times, the change of VBEl is 0.06
It's a bolt. As mentioned above, since the current of the transistor 12 is given by the ratio of VBE,l and the resistor 9, its fluctuation is also greatly suppressed.

Therefore, transistor 13 has the same element dimensions as transistor 12,
If the value of resistor 10 is the same as that of resistor 9, its current value will be the same as that of transistor 12. Also, due to the strong negative feedback effect described above, the output resistance seen from the terminal 18 is only one part of the loop gain (approximately the ratio of the value of the resistor 14 to the emitter resistance of the transistor 11) compared to the case of FIG. It's getting smaller. Therefore, the circuit shown in Figure 1b is much more stable and superior in terms of characteristics than the circuit shown in Figure 1a, but the only drawback is that the voltage applied to terminal 15 must be at least 2 x VBE (approximately 164 volts). It is a must. Normally, it is desirable that the voltage be 2 volts or more. Therefore, it cannot be used in devices that operate on a single battery. An object of the present invention is to provide a constant voltage bias circuit that can be used with a low voltage power source, such as a 1.3 volt single battery, has low current consumption, and can ensure a constant output voltage over a wide range of variations in power supply voltage. It is to provide.

Another object of the present invention is to provide a constant voltage bias circuit with extremely low output impedance.

In other words, the objective is to provide a constant voltage bias circuit that can drive a plurality of constant current transistors while minimizing mutual interference. The present invention will be explained below with reference to Examples.

FIG. 2 is a circuit diagram showing an embodiment of the present invention. In the figure, the collector of the transistor 19 is connected to an applied voltage terminal 31 via a resistor 25, and the emitter is grounded as a common terminal, forming a common emitter type amplifier circuit as a whole. Transistor 22 is transistor 1
The emitter is connected to the terminal 31 and the collector is grounded via the resistor 27, forming a common emitter type amplifier circuit, and the collector of the transistor 22 is connected to the base electrode of the transistor 19. ing.
On the other hand, the transistors 20 and 21 have opposite conductivity types, and the transistor 20 and the transistor 19 have the same conductivity type, and the transistor 21 and the transistor 22 have the same conductivity type. and transistor 20 and transistor 2
1 have their collectors connected in series, and the collector of transistor 21 is directly connected to its base, forming a collector-base connected diode with its emitter as an anode. This diode serves as the collector load of transistor 20. It is connected between the terminal 31 and the terminal 31. Further, the cathode of the diode is connected to the base of the transistor 22. On the other hand, the emitter of the transistor 20 is a resistor 26
The base is connected to the collector of the transistor 19. If you connect as above,
Starting from the base of the transistor 22, passing through the collector thereof to the base of the transistor 19, and further passing from the collector of the transistor 19 to the base of the transistor 20,
A negative feedback circuit returning to the collector, ie, the base of the transistor 22, is formed.

Considering the loop gain in such a loop, since the transistors 22 and 19 are emitter-grounded amplifier circuits, a fairly high loop gain can be expected, forming a strong negative feedback circuit. Therefore, the operating point of each transistor is extremely stabilized. In such a stabilized state, the collector current of the transistor 22 is determined by the ratio of the base-emitter voltage VBEl9 of the transistor 19 and the value of the resistor 27, if the base current of each transistor is ignored. Moreover, if the emitter areas of diode-connected transistor 21 and transistor 22 are equal, their respective collector currents, that is, the collector current of transistor 20 and the collector current of transistor 22 are equal. Therefore, the collector currents of the transistors 23 and 24 whose bases and emitters are connected between the common base terminal 28 of the transistors 21 and 22 and the applied voltage terminal 31, respectively, are also the same if the emitter area is the same as that of the transistors 21 and 22. Similarly, they are equal. Further, the current flowing through the transistor 19 is given by the ratio of the voltage at the terminal 31 minus VBE2O and the voltage drop across the resistor 26 (usually set to about 0.1 volt) and the resistor 25. Therefore, this value will change at the same rate if the voltage applied to terminal 31 changes over a wide range. However, as explained with respect to the circuit of FIG. 1b, the base-emitter voltage VBE1 of transistor 19 does not change much and remains almost constant. Therefore, the collector current of transistor 22 is also approximately constant. Therefore, the collector currents of transistors 23 and 24 are also highly stabilized against fluctuations in the power supply voltage. Also, the minimum power supply voltage for stable operation of this circuit is VBE of transistor 21 and transistor 20.
Since it is the sum of the collector-emitter voltage VCE and the voltage drop VR26 across the resistor 26, it is approximately 0.7+0.1+0
．． 1 = approximately 0.9 volts is sufficient. The upper limit is determined by the withstand voltage of the transistor, so it is usually at least 7 volts or more. Therefore, this circuit configuration can operate over a very wide range of power supply voltages. Next, considering the output resistance as seen from the terminal 28, it can be made very small because it is essentially one part of the loop gain of the emitter resistance (the reciprocal of the mutual conductance Gm2l) of the diode-connected transistor 21 due to the strong negative feedback loop. .

For example, transistor 21 (and therefore transistor 22)
Assuming that the current is 100 μA, the loop gain at that time is approximately 4.
If it is 0 dB, the emitter resistance of transistor 21 is 2
The output resistance as seen from the terminal 28 is 1/100, that is, 1/100 of the loop gain, and is 2.6Ω. To obtain this value in FIG. 1a, 10 mA must be applied. Compared to this, current consumption can be significantly reduced. Actually, it is relatively easy to obtain a loop gain of about 40 dB with this circuit, and if a high resistance is used as the resistor 25, for example, a pinch resistor often used in integrated circuits,
It is possible to increase the loop gain and reduce current consumption. In general, pinch resistance has a large initial deviation (−
50 to +100%) has no significant effect on the current values of the transistors 21 and 22 even if the resistance values vary. Incidentally, the capacitor 32 is used to prevent oscillation of the negative feedback loop, and together with the resistor 26, stabilizes the loop circuit. The capacitance value varies depending on the current value of each transistor and the required loop gain, but it is several PF
~ several tens of PF. The capacitor 32 may be unnecessary if the current of each transistor is increased slightly and the resistor 26 is selected to be large to reduce the loop gain.
Even if the power supply voltage fluctuates over a wide range, the potential difference across the capacitor 32 remains approximately equal to VBE1, so that when integrated circuits are implemented, a P-N junction capacitance can be used without much inconvenience. The above explanation has been given for the case where the transistors 23 and 24 are PNP, but it will also be explained that the same applies to the case where the constant current transistor is NPN if all the conductivity types of the transistors in Fig. 2 are set to opposite conductivity types. Not even.

As described above, according to the present invention, there is provided a constant voltage bias circuit that operates on a single battery voltage, has a substantially constant output voltage even over a wide range of power supply voltage fluctuations, has low power consumption, and has a sufficiently small output resistance. is obtained.

[Brief explanation of the drawing]

1A and 1B are circuit wiring diagrams showing typical examples of conventional constant voltage bias circuits, and FIG. 2 is a circuit wiring diagram showing an embodiment of the present invention. 1, 2, 3, 11, 12, 13, 19, 20...
・NPN transistor, 21, 22, 23, 24...
...PNP transistor, 4, 14, 9, 10
, 25, 26, 27...Resistance, 5, 15, 31
...Applied voltage terminal, 8, 18, 28...
・Output voltage terminal, 29, 30... Output current terminal.

Claims (1)

[Claims] 1 A first transistor and a second transistor having opposite conductivity types each form a common emitter amplifier circuit with a resistive load, and a third transistor having the same conductivity type as the second transistor has the same conductivity type as the first transistor. A common emitter amplifier circuit is formed with a diode-connected conductivity type fourth transistor as a load, and a negative feedback loop is formed in which the first, second, and third transistors are connected in cascade, and the fourth transistor A constant voltage bias circuit characterized by receiving an output from the base of.