JPS6114174Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a current amplifier, which can be reliably driven at a low voltage by connecting first and second constant current sources to the input side and output side transistors, respectively. The purpose is to provide a current amplifier.

FIG. 1 shows a circuit diagram of an example of a conventional current amplifier. In the same figure, in order to obtain an output current (current supplied to load 2) I ₂ that is several times larger than the input current (signal input) I ₁ flowing through input signal source 1, the output side transistor T _r2 is connected to the input side A transistor having a larger emitter junction area than the transistor T _r1 is used, or a plurality of transistors connected in parallel are used. In this case, in this type of current amplifier, it is necessary to reduce the saturation voltage between the emitter and collector of the output side transistor T _r2 in order to improve the power supply voltage utilization rate, and for this purpose, the output side transistor T _r2 is connected to the input side transistor. The emitter junction area is extremely large compared to T _r1 . That is,
Generally, the emitter junction area ratio of transistors T _r1 and T _r2 is set to a larger ratio than the ratio of input current I ₁ to output current I ₂ (hereinafter referred to as current amplification factor), for example, 1:10. In order to obtain a current amplification factor of , transistors T _r1 and T _r2 are used with an emitter junction area ratio of 1:100. However, since it is not possible to obtain a current amplification factor of 1:10 as it is, a transistor T _r is connected between the emitter of the transistor T _r1 and the emitter of the transistor T _r2 .
_3. Connect T _r4 and current mirror circuit 3, etc.
A potential difference is created between the emitter of the transistor T _r1 and the emitter of the transistor T _r2 so that a current of 1:10 flows through the transistors T _r1 and T _r2 , and a difference is created in the voltage between the base and emitter of each transistor. The conduction state of _r1 and T _r2 was controlled.

However, in this conventional current amplifier, many elements such as the transistors T _r3 and T _r4 and the current mirror circuit 3 are connected to create a potential difference between the emitter of the transistor T _r1 and the emitter of the transistor T _r2 . The voltage between the base of transistor T _r1 and ground is (transistor T _r
1 base-emitter voltage) + (transistor T _r
Therefore, a large driving voltage is required between the power supply and _the ground, and it cannot be driven at a low voltage. However, it had drawbacks such as being difficult to integrate into ICs, etc.

There are other conventional current amplifiers that create a potential difference between the base of the input transistor and the output transistor base.
Like the conventional example shown in FIG. 1, this device also had drawbacks such as not being able to be driven at a low voltage.

The present invention eliminates the above-mentioned drawbacks, and an embodiment thereof will be described below with reference to FIG. 2.

FIG. 2 shows a circuit diagram of an embodiment of the current amplifier according to the present invention. In the figure, the same components as in FIG. 1 are given the same reference numerals. In the same figure, the emitter of the input transistor T _r1 and the output transistor T _r2
The emitter of the transistor T r1 is connected to the load 2, and a constant current source 4 for controlling the current amplification factor is connected between the base of the transistor T _r1 and the power supply +B. A diode-connected PNP transistor T _r5 and a constant current source 5 for controlling the current amplification factor are connected between the input signal source 1 and the ground, and the base of the transistor T _r5 is connected to the base of the transistor T _r6 . are connected, and the emitter of transistor T _r6 is connected to the base of transistor T _r1 .

The input current _I1 is supplied to the collector of the input transistor _Tr1 , the base of the output transistor _Tr2 , and the emitter of the transistor _Tr5 , and the output current _I2 is taken out from the emitter of the output transistor _Tr2 .

In the present invention, instead of creating a potential difference between the emitter of the input transistor T _r1 and the emitter of the output transistor T _r2 , the transistor T _r1
A potential difference is generated between the base of the transistor T _r2 and the base of the transistor T r2 so that (base potential e ₁ of the transistor T _r1 )>(base potential e ₂ of the transistor T _r2 ). In this case, if the emitter junction areas of the transistor T _r6 connected to the base of the transistor T _r1 and the transistor T _r5 connected to the base of the transistor T _r2 are the same, the ratio of the input current I ₁ to the output current I ₂ is That is, the current amounts of the constant current sources 4 and 5 are made different and adjusted appropriately so that the current amplification factor becomes a predetermined value _.
6 base-emitter voltage)>(transistor T _r
5 base-emitter voltage). Furthermore, if the emitter junction areas of the transistor T _r6 and the transistor T _r5 are different depending on the current amplification factor, the amount of current of each of the constant current sources 4 and 5 is adjusted so that the current amplification factor becomes a predetermined value. Adjust as appropriate so that they are the same, and the above relationship is established.

Here, current amplification factor = I ₂ /I ₁ = n, ratio of emitter junction area A ₁ of transistor T _r1 to emitter junction area A ₂ of transistor T _r2 = A ₂ /A ₁ = N, constant current source 4 The current flowing through constant current source 5 is I ₄ , and the current flowing through constant current source 5 is I ₅
The constant current source is set so that the following relationship is satisfied: I ₂ = NI ₅ (I ₁ − I ₅ )/I ₄ ≒ NI ₅ /I ₄・I ₁ (I ₁ ≫ _{I 5} ) NI ₅ /I ₄ = n Adjust and select the current amounts in 4 and 5, respectively. At this time, since e ₁ > e ₂ and there is a difference in the voltage between the base and emitter of transistors T _r1 and T _r2 , the constant current source 4
By adjusting the amount of current of each of transistors T _r1 and T r2 , the conduction states of transistors T r1 and T _r2 are controlled, and a predetermined current amplification factor can be obtained.

As described above, according to the present invention, since only the transistor T _r5 and the constant current source 5 are connected between the collector of the input side transistor T _r1 and the ground, the voltage is lower than that of the conventional example shown in FIG. It can be driven by voltage.

Note that the same effect can be obtained even if a transistor with a polarity opposite to that of the transistor in the above embodiment is used.

Temperature compensation can also be provided by the substantially diode-connected transistor T _r1 .

As described above, the current amplifier according to the present invention connects the emitters of the input and output transistors, and connects the first transistor to the base of the input transistor.
a constant current source and the emitter of the first transistor are connected, and a second transistor whose base is connected to the base of the first transistor and the collector of the input transistor and the base of the output transistor.
Since the emitter of the transistor is connected, the collector of the second transistor is connected to this base connection point, and the second constant current source is connected to this collector, the voltage between the base and emitter of the input transistor and the output The circuit that creates a difference in the voltage between the base and emitter of the side transistors can be a simple circuit such as one constant current source for controlling the current amplification factor. Since the above-mentioned constant current source is simply connected to the transistor that provides the base-emitter voltage of the input side and output side transistors, the circuit has the advantage of being able to operate at a lower voltage than conventional circuits. have

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an example of a conventional current amplifier, and FIG. 2 is a circuit diagram of an embodiment of the current amplifier according to the present invention. 1...Input signal source, 4, 5...Constant current source, 2...
...Load, T _r1 ...Input side transistor, T _r2 ...
Output side transistors, T _r5 , T _r6 ...transistors.

Claims (1)

[Scope of utility model registration request] It has an input side transistor and an output side transistor whose emitter junction area or the number of connected transistors is larger than that of the input side transistor, and there is a difference in the base-emitter voltage of each of the input side and output side transistors. A current amplifier that amplifies an input current generated and supplied to the collector of the input transistor and the base of the output transistor with a predetermined current amplification factor, and extracts an output current from the emitter of the output transistor, The emitters of the input side transistor and the output side transistor are connected to each other, and the emitter of the first constant current source and the first transistor are connected to the base of the input side transistor, and the collector of the input side transistor and the emitter of the first transistor are connected to the base of the input side transistor. The emitter of a second transistor whose base is connected to the base of the first transistor is connected to the base of the output side transistor, and the base of the first transistor and the second transistor are connected to each other.
A current amplifier comprising: a collector of the second transistor connected to a connection point with a base of the transistor; and a second constant current source connected to the collector of the second transistor.