JPS5823761B2 - Directly connected multi-stage widening circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multi-stage amplifier circuit suitable for semiconductor integrated circuits, and particularly for semiconductor integrated circuits driven at low power supply voltages.

In semiconductor integrated circuits, since it is not possible to incorporate large-capacity coupling capacitors, direct-coupled multi-stage amplifier circuits in which stages are coupled in a DC manner are exclusively used.

For this reason, the bias potential of each stage is greatly restricted in relation to other stages.

Furthermore, since it is not possible to incorporate an inductance as a load in a semiconductor integrated circuit, a resistor or the like is mainly used.

In order to operate the transistor without saturating it, the DC voltage drop that occurs in the load resistance cannot be increased.
Load resistance must be reduced.

This problem is especially serious in semiconductor integrated circuits that are driven with low power supply voltages.

This low value of load resistance also results in low AC voltage gain.

As shown in FIG. 1, a conventional amplifier circuit uses a transistor 2 whose collector and base are short-circuited and a resistor 7 as the load of a differential amplifier 1.
Connect the base of the next stage transistor 3 to the short-circuit point of the base, and connect the emitter resistor 8 and load resistor 4 to this transistor 3.
There is a device in which the thermal stability of the bias of the transistor 3 is improved by connecting the transistor 3 in series.

The transistor 10 and the resistor 9 supply a constant current to the differential amplifier circuit 1. The collector of the transistor 3 is connected to the output terminal 6, and the circuit is driven by the power supply 5.

In such a conventional multi-stage amplifier circuit, the transistor 3
A current having a current density equal to the emitter current density of the transistor 2 is passed through the transistors 2 and 3, so that the base-emitter voltages of these transistors 2 and 3 are made equal to reduce the distortion factor.

In this case, the resistance values of the resistors 7 and 8 are designed to satisfy the following relationship using relatively low resistance values.

Here, 1°2+IE3 is the emitter current of transistors 2 and 3, R7 and R8 are the resistance values of resistors γ and 8, and SF3.
SF3 represents the effective emitter area of transistors 2 and 3, and m represents the ratio.

On the other hand, variations in the emitter currents of the transistors 2 and 3, which are balanced depending on manufacturing conditions, are corrected to a considerable extent by the emitter resistors γ and 8, and this correction is more effective as the resistance values of the emitter resistors 1 and 8 are larger.

This increase in resistance increases the voltage drop and reduces the undistorted maximum output.

On the other hand, the fact that the emitter current densities of transistors 2 and 3 are equal means that the DC current amplification rate of the circuit of transistors 2 and 3 is given by m in equation (1), and the amplification rate for the AC component is also equal to m.

Therefore, if an attempt is made to increase the degree of voltage increase by increasing the load resistance 4, there is a drawback that the undistorted maximum output voltage becomes smaller due to the DC voltage drop.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a multistage coupled amplification circuit that can increase the degree of amplification for AC components without increasing the DC voltage drop that occurs in the load resistance, and can obtain a large undistorted maximum output.

That is, according to the present invention, a first transistor including an input terminal, an output terminal, and a common terminal, a second transistor whose collector and base are short-circuited and which are connected to the output terminal of the first transistor; a first resistor whose one end is connected to the emitter of the second transistor; a third transistor whose base is connected to the output terminal of the first transistor; and a second resistor whose one end is connected to the emitter of the third transistor. , a load impedance whose one end is connected to the collector of the third transistor, and the first and second transistors.
and a power supply connected between the other end of the resistor and the other end of the load impedance, and the emitter current density of the third transistor is made larger than the emitter current density of the second transistor to increase the DC current. A multi-stage amplification circuit characterized by obtaining an AC current amplification factor larger than a width factor is obtained.

According to the present invention, as will be understood from the detailed description below, it is possible to obtain an AC current amplification rate greater than a DC current amplification rate.

Furthermore, this AC current amplification rate is determined by the ratio of the emitter current densities of the second and third transistors and the voltage drop of the first resistor. The emitter current of the transistor can be freely selected.

That is, the DC bias potential of the third transistor can be determined regardless of the AC current amplification rate, and it is possible to obtain a large distortion-free maximum output.

Next, the present invention will be explained in more detail with reference to the drawings.

First, the present invention will be explained using FIG. 1 in the same manner as the conventional multi-stage amplification circuit.

The circuit is the same as the conventional multistage amplifier circuit, but according to the present invention, the emitter current density of the transistor 3 is selected to be larger than the emitter current density of the transistor 2, for example, twice or more.

Now, let the emitter currents of transistors 2 and 3 be IP, 2 > IP3, respectively, and the base-emitter voltage be VBE2. vBE3, the resistance values of resistors 7 and 8 are R7, R8, resistor 8, the emitter of transistor 3,
When Kirchhoff's law is applied to the loop formed by the base, the base of transistor 2, the emitter, and the resistor γ, the following equation is obtained.

If the emitter junction area of transistor 3 is m times the emitter junction area of transistor 2, and the saturation current of transistor 2 is 13, then p: absolute value of electron charge: Boltzmann constant T: absolute temperature is obtained.

Therefore Here, if we differentiate equation (6) with respect to IP2, we get get.

Substituting equation (6) into equation (8) yields.

This equation (9) must be set so that the emitter current density ratio, that is, the AC current amplification rate in this case, is 105% or more of the DC current amplification rate, otherwise the purpose of the present invention will be compromised due to variations in the semiconductor device manufacturing process. Sometimes I can't reach my full potential,
Furthermore, if an attempt is made to obtain an unnecessarily large value, the temperature characteristics of the circuit will deteriorate.

Now, the emitter junction area of transistor 3 can be halved without changing the emitter currents of transistors 2 and 3, or the value of resistor 8 can be reduced without changing the emitter junction area of transistors 2 and 3. By doubling the emitter current, the emitter current density of transistor 3 can be made twice that of transistor 2, the voltage drop across resistor γ is 100 mV, and the absolute temperature is 300°K (27°C ), then from equation (8), the AC current amplification rate is 1.
It becomes 17 times.

Furthermore, as can be seen from equation (8), if the voltage drop across resistor 7 is reduced while the emitter current density of transistor 3 is made larger than the emitter current density of transistor 2, a larger AC current amplification factor can be obtained. However, on the other hand, if the voltage drop across this resistor γ is made too small, thermal stability and output linearity at the time of a large signal deteriorate.

Furthermore, as can be seen from equation (8), transistors 2 and 3
The AC current amplification rate is determined by the combination of the emitter current densities of and the relationship with the voltage drop of the resistor 1, and there is a wide degree of freedom in the emitter current of the transistor 3 that can be selected for a constant AC current amplification rate. be.

That is, the DC potential of the output terminal 6 can be determined regardless of the AC current amplification rate.

This also shows that by reducing the DC potential of the output terminal 6 to half the voltage of the power supply 5, for example, it is possible to extract an output signal with a large amplitude.

2 to 4 show other embodiments of the present invention,
A composite element is used in place of the transistors 2 and 3 in FIG.

That is, in FIG. 2, a PNP transistor 2 connected in the same type of Darlington is used instead of transistors 2 and 3 in FIG.
2゜23 is used, and the transistor 42 is connected using transistors 32 and 33, which are a different kind of Darlington connection of a PNP transistor and an NPN transistor (Fig. 3).
The bias is adjusted by resistor 34.35.

4, similarly to FIG. 3, transistors 42 and 43 are connected in different types of Darlington, and a diode 49 is connected between the terminal corresponding to the base and the terminal corresponding to the collector of the transistor 42. In FIG.

According to these embodiments, when the present invention is implemented in a semiconductor integrated circuit, a horizontal type P with a small emitter ground current increase hfe
NP transistors can also be used.

[Brief explanation of drawings]

FIG. 1 shows a conventional direct-coupled multistage amplifier circuit and a first embodiment of the present invention.
It is a circuit diagram explaining an actual case. 2 to 4 are circuit diagrams showing other embodiments of the present invention, respectively. 1... Differential amplifier, 2, 3, 10...
Transistor, 4, 7, 8, 9, 34, 35...
・Resistance, 5...Power supply, 6...Output terminal,
49...Diode, 22.23,32,33
, 42, 43... Composite transistor.

Claims (1)

[Claims] 1. A first transistor receiving a human input signal, a series circuit of a PN junction element and a first resistor connected between an output terminal of the first transistor and one power supply terminal, and a series circuit of a first resistor of the first transistor. a second transistor whose base is connected to the output terminal; a second resistor connected between the emitter of the second transistor and the one power supply terminal; and a second resistor whose base is connected to the output terminal; and a load impedance connected between the second transistor and the power supply terminal, and the emitter junction area of the second transistor is made smaller than the junction area of the PN junction element, or the resistance value of the second resistor is made smaller than the junction area of the second transistor. By making the resistance smaller than that of 1,
Without feeding back the collector output of the second transistor to the input, the emitter current density of the second transistor is made larger than the current density of the PN junction element to change the AC current amplification factor for the input signal to a DC current. A direct-coupled multi-stage amplifier circuit characterized by a higher amplification factor.