JPS60172810A - Balanced/unbalanced converting circuit - Google Patents

Abstract

PURPOSE:To improve converting accuracy even if a characteristic of a transistor (TR) has a difference and to decrease the number of components by constituting the circuit with a TR operated as an emitter follower, flowing the same current to the TR of the same conduction type and cancelling the difference between the base and emitter between the TRs. CONSTITUTION:A voltage nearly equal to a potential drop component V2 of a resistor 5 is applied across a resistor R2 via TRs Q3, Q4 constituting the emitter follower, the voltage is converted into a collector current of the TRQ4, the current is converted again into a voltage by a resistor R1 and outputted via the emitter follower comprising a TRQ2. On the other hand, the potential drop V1 of the resistor 4 is outputted via a TRQ1, a resistor R1 and the TRQ2. Since each emitter current of the TRs Q2, Q3 is equal to that of a constant current source IB, a base-emitter voltage VBE of both the TRs is made equal. The emitter current of the TRs Q4, Q1 is made nearly equal by setting sufficiently to a small value of the constant current IS, the relation of VBE1=VBE2 is attained. Moreover, the resistors R1, R2 are made equal. Then the balanced inputs V1, V2 are converted into an unbalanced signal V3.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a balanced/unbalanced conversion circuit for configuring a line current detection circuit in a line circuit with high precision and a small number of elements.

(Prior Art) A power supply section and a line current detection section of a conventional line circuit are shown in FIG. 1(a). The power supply section is a power supply control circuit 1. Power transistor 2.3. It consists of resistors 4, 5 and a local power source 6, and the collector current of the power transistor 2.3 is connected to a terminal device 9 via balanced lines 7, 8. A specific example of the power supply control circuit 1 is shown in FIG. 1(b), but its operation is not directly relevant here and will therefore be omitted.

On the other hand, the line current detection section is a balanced/unbalanced conversion circuit 10.
, comparator ll, reference voltage 12. Detection output terminal 13
and resistors 4 and 5, the operation of which is performed by the power supply control circuit 1.
By setting the resistors 1'4 and 15 (Fig. 1(b)) in the power transistors 1'4 and 15 (Fig. 1(b)) to have a high resistance, almost all the current flowing to the lines 7 and 8 passes through the power transistors 2 and 3f. Since the line current flows through the resistors 4 and 5, it can be detected as a potential drop across the resistors 4 and 5.

The potential drop across resistor 4.5 is converted to voltage 41 for both by balanced/unbalanced conversion circuit io, and comparator 1
1 and is compared with the reference voltage 12 and output as a binary signal to the OUT terminal 13 to detect on/off hook on the terminal device 9 side.

A specific example of the balanced/unbalanced conversion circuit IO is shown in Figure 1 (c
There is one using three differential amplifiers 16, 17, and 18 as shown in FIG. Its operation is such that the potential drop across the resistor 4.5 is detected by differential amplifiers 16 and 17, and their outputs are added together by differential amplifier 18 and output as an unbalanced signal.

By the way, such a flat/unbalanced conversion circuit has problems such as the large number of elements constituting each differential amplifier, and the fact that the local power supply 6 is generally as large as -48V, resulting in high power consumption. was there.

(Objective of the Invention) The present invention has been proposed to eliminate the above-mentioned drawbacks, and its purpose is to achieve flat/unbalanced conversion even if there is a difference in characteristics between an npn transistor and a pnp transistor. The object of the present invention is to realize a balanced/unbalanced conversion circuit with high precision and a small number of elements.

(Fourteenth aspect of the invention) In order to achieve the above object, the present invention provides an electronic balanced/unbalanced conversion circuit in which one of the equalized signals V1
is applied to the base of the first transistor Q1, and this first
The collector of the transistor Ql is connected to a constant potential point, and both ends of the first resistor R are connected to the emitter of the first transistor Ql, and to the emitter of the second transistor Q2 of a conductivity type complementary to the first transistor Ql. A constant current source 3 is connected to the emitter of the second transistor Q, and the other signal v2 of the second transistor Q is connected to the second transistor Q2 and the second transistor Q of the same voltage type. 3 to the base of the third transistor Q3, and this third transistor Q3
The emitter of the fourth transistor Q4 is connected to the collector of the second transistor Q2 and the base of a fourth transistor Q4 of the same electric type as the first transistor Q1, and the emitter of the fourth transistor Q4 is connected to the second resistor. The collector of the fourth transistor Q4 is connected to the base of the second transistor Q2, and the collector of the fourth transistor Q4 is connected to the base of the third transistor Q2 through the emitter of the second transistor Q2. Output signal) 4y,,! The gist of the invention is a balanced/unbalanced conversion circuit for heavy machinery.

Next, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the embodiment is merely an illustration, and it goes without saying that all modifications and improvements may be made without departing from the scope of the present invention.

Therefore, in order to reduce the number of constituent elements, the present invention is mainly composed of transistors that operate as emitter followers.
Is the same 1W and 'fAF for transistors of the same conductivity type? +If, l-, transistor I! Ilnohes-S
High precision is achieved by canceling out the differences in the voltage V□ between the vines.

FIG. 2 shows an embodiment of the present invention. Its composition is npn
Transistor Ql 1. , Qi, pnI) ) Transistor Q2゜Q, constant current source, , 8, and resistor R11R
It consists of 2.

Note that the balanced/unbalanced conversion circuit 10 in FIG.
This circuit replaces the balanced/unbalanced conversion circuit 10 shown in FIG. 1(a), and the other configuration is the same as that shown in FIG. 1(a).

The operation is such that the potential drop V2 across the resistor 5 passes through the terminal t+j and the transistor Q3+Q4 that constitutes the emitter follower, and a substantially equal voltage is applied across the resistor R2, which is converted into the collector current of the transistor Q4, and then again through the resistor R8. It is converted into a voltage and output via the emitter follower of transistor Q2. On the other hand, the potential drop of resistor 4 ■1
is outputted via terminals g and h through transistor Q4 + resistor R, . . . ) transistor Q2.

To express this in a formula, vs=v+ IVBIII-R+(("2"l■ngs
l lVB[c41)/Rz ) + I vBE21
--(1). However, Vyu1 is transistor Q
The base-emitter voltage was 1, and the base current of each transistor was ignored as it was small. Since the collector of the transistor Q2 and the emitter of the transistor Q3 are connected, the emitter current of the transistor Q2 and the emitter current of the transistor Q3 are both equal to that of the constant current source 8. Therefore, ■ BFi3 = ■ Rei 2 O Also, since the collector 1 of transistor Q4, the current flows to transistor Q1, the constant '1L flow 8's I1η
By setting sufficiently small, the emitter currents of transistor Q4 and transistor Q1 become almost equal, so that VB+! +4 and 0 and resistance R1
ML is set so that and R2 are equal. Therefore, by substituting these results into equation (1), v3=vl −
■2 (lvB+a+l 1vn1.141) (lv
Bg,l-1VB1! ! 21)=■1-V2...
(2) Tonashi, balanced human power V, , V2 is unbalanced signal V
It can be seen that it is converted to . Note that the constant current generator 8 is for startup purposes, and when 2 = 0, the collector current of the transistor Q4 becomes 0, but the constant current IB supplies the base current of the transistor Q2. It is for the purpose of

None of the assumptions used to derive equation (2) from equation (1) are easy to implement in integrated circuits.
That is, the base-emitter voltage vBl! between transistors of the same conductivity type. The variation in is as small as about several mV, and the resistor's specific accuracy can be obtained on the order of 1 inch, so the approximate expression (2) is quite accurate.

Although this embodiment has been described in the case of a bipolar transistor, it is needless to say that the same effect can be expected even when F-T is applied.

(Effects of the Invention) As explained above, the balanced/unbalanced conversion circuit of the present invention has a small number of components and is economical.
In the conventional circuit shown in c), if each differential amplifier requires about 20 elements, the total number of elements is about 60, but according to the present invention, the number of elements including the elements constituting the current source is reduced. This can be achieved with about 10 elements, and the effect is great. In addition, the base-emitter voltage V of transistors of the same conductivity type
If even the variation in ng is kept small, there is an advantage that balanced/unbalanced conversion can be performed with a very high degree of IIF, since the difference in transistor 'F' between input transistors has no effect on accuracy.

[Brief explanation of drawings]

FIG. 1(a) is a circuit diagram of the current supply section and line current detection section of a conventional line circuit, FIG. 1(b) is a specific circuit diagram of the power supply control circuit, and FIG. 1(c) is a balanced/ Specific circuit diagram of unbalanced conversion circuit. FIG. 2 is a specific circuit diagram showing an embodiment of the balanced/unbalanced conversion circuit according to the present invention. 1...Power supply control circuit, 2, 3...Power transistor,
4.5...Resistance, 7, 8...Line, 9...Terminal equipment, 1o, to'...Balanced/'unbalanced conversion circuit,
11... Comparator, 12... Reference voltage, 13...
Output terminal, 14.15...Resistance, 16.17.18...
・Differential amplifier, Q4 + Q4 ・'・npn transistor, Q2 + Q3 ・= pnp transistor s
IB + ■8...Constant current source, R□, R2...Resistor] Figure (a)

Claims (1)

[Claims] In the electronic flat/unbalanced conversion circuit, one of the balanced signals V1 is applied to the base of the first transistor Q1, and the collector of the first transistor Q is connected to a constant potential point.1. Both ends of the first resistor are connected to the emitter of the first transistor Q+ and the base of a second transistor Q2 of a conductivity type complementary to the first transistor Q+, and , is connected to the emitter of the second transistor Q2, and the other signal 2 of the balanced signals is applied to the base of a third transistor Q+1 having the same conductivity type as the second transistor Q2. The emitter of the transistor Q, and the collector of the second transistor Q2, and the first transistor Q,
and the base of a fourth transistor Q4 of the same conductivity type, and the emitter of this fourth transistor Q4 is connected to the collector current of the third transistor Q3 via a second resistor to another constant potential point. , the collector of the fourth transistor Q4 is connected to the base of the second transistor Q2, and the output signal is taken out from the emitter of the second transistor Q. conversion circuit.