JPS6051313A - Equivalent variable resistance circuit - Google Patents

Abstract

PURPOSE:To suppress a nonlinear distortion to obtain an equivalent variable resistance circuit which can be operated with a low voltage, by connecting one terminals of two current mirror circuits and connecting them to a constant current circuit and connecting the other terminals to another current mirror circuit. CONSTITUTION:Pairs of transistors TRs Q11 and Q12, TRs Q13 and Q14, and TRs Q15 and Q16 constitute current mirror circuits respectively, and collector currents of individual TRs are equal and comes to I/2. When the emitter dynamic resistance is denoted as re and the current amplification factor of NPN TRs Q11-Q14 is denoted as betaN and that of PNP Ts Q15 and Q16 is denoted as betaP , an equivalent resistance R viewed from a point D in a figure is as indicated by a formula I , and the equivalent resistance is VT/I if the thermal voltage is denoted as VT and betaN and betaP are larger than 1. Thus, a nonlinear distortion is suppressed to obtain the equivalent variable resistance circuit which can be operated with a low voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in an equivalent variable resistance circuit using transistors.

[Technical background of the invention and its problems]

2. Description of the Related Art Conventionally, an equivalent variable resistance circuit configured as shown in FIG. 1 is known as an equivalent variable resistance circuit using semiconductor elements that is widely used in general electronic equipment including audio equipment.

In other words, this is the most basic configuration in which a current source S and a diode D are connected in series between the power supply vcc and the reference potential point GND, and when a current of This takes advantage of the fact that the operating resistance r of D depends on the thermal voltage vT and the electric current r=''- (2).

The resistance seen from the ω point shown in the diagram is the above r,
By controlling the current source S and varying the current (2), an equivalent variable resistance r can be obtained.

However, in actual use, when a current of Δi flows into the input terminal at the point (A) shown in the figure, the current flowing through the diode D becomes 10 Δi, but since the voltage-current characteristic of the diode is an exponential function, The problem is that nonlinear distortion cannot be avoided.

For this reason, conventionally known devices are configured as shown in FIG. 2 to suppress nonlinear distortion.

In other words, this is a differential pair transistor Q1.

For Q2, a pair of current mirror transistors Q! between their respective collectors and the power supply vCc. , Q4 as a load, and their common emitter and reference potential point GND.
A pair of current mirror transistors Qs serving as a current source between them,
The same current as the input current I to the transistor Q5 also flows through the transistor Q6, and these are connected to the differential pair transistors Q1,
The operating current is Qz. Note that the pace of transistor Q2 is connected to an appropriate bias current source VrefK.

Considering the equivalent resistance r' when looking at the transistor Ql side from the point (A') shown in FIG. 2, if we ignore the collector resistance rC of the transistor Q4 since the transistor Q1 is diode-connected, It is the emitter operating resistance r of transistor Q1. Equal to r'-re(Qt) Cwhere re(Q4)
>> re (Ql) :). From this, Ic(Qs) I.sub.2 is obtained, and by controlling the current I flowing from point (B) in the figure, it becomes possible to vary the equivalent resistance r' as seen from point (A') in the figure.

By the way, in this case, if the current of transistor Q1 increases by Δi, then transistor Q1. Since Q2 has a differential configuration, the current of transistor Q2 decreases by Δi, and the current mirror pair transistor Q3
．． As Q4 increases, the current of transistor Q4 also decreases by Δi.

This shows that the input current from the diagram (A') is 2·Δi without changing the circuit, and in fact, the input current from the diagram (A')
Transistor Q when the input current from point ) is Δ(
The current change in l is 1·Δi.

In contrast, in the case of Figure 2 compared to Figure 1, only half the current change occurs at the same input current value, so it is possible to suppress the occurrence of nonlinear distortion in real life. This is what has become.

However, in the case of Fig. 2, there are many transistors connected in series between the power supply vcc and the reference potential point GND, so the voltage required for operation is at least one pace-emitter voltage VBIe and two collector-emitter voltages. Voltage VC
! , so that Vag + 2Vcx = VB
E (Q3) + Veffi (Qz) + VCE (
Ql)5- or Vmz (Qs) + VCE (Q4)
+V(1(Ql)#0.7V+2X0.2~0.3
V# is 1.1 to 1.3v, which poses a problem that it cannot be applied to devices that operate at a low voltage of 1v or less, which is required in recent small portable devices.

[Purpose of the invention]

Therefore, this invention was made in view of the above points, and is an extremely good equivalent variable resistor that is improved so that non-linear distortion can be suppressed and low voltage operation of 1 V or less is possible. The purpose is to provide circuits.

[Summary of the invention]

That is, the equivalent variable resistance circuit according to the present invention includes a pair of first and second current mirror transistors whose respective emitters are connected to a reference potential point or a power source, one end of which is connected to the power source or a reference potential point, and the other end of which is connected to the power source or the reference potential point. a current source connected in common to the non-diode-connected collectors of the first pair of current mirror transistors and the diode-connected collectors of the second pair of current mirror transistors; each emitter connected to the power source or the reference potential; and the collector on the diode-connected side is connected to the collector on the non-diode-connected side of the second current mirror pair of transistors, and the non-diode-connected collector is connected to the diode-connected side of the first current mirror pair of transistors. and a third pair of current mirror transistors connected to the collector of the transistor.

[Embodiments of the invention]

An embodiment of the present invention will be described in detail below with reference to the drawings.

That is, as shown in FIG. 3, the emitters of the pair of current mirror transistors Qlt + Qtz and Qts + Q14 are connected to the reference potential point GND.

Here, the transistor Q14 is connected to the power supply VCC through a collector-emitter path of a diode-connected transistor Q15.

Further, the transistor Q1□ is diode-connected and connected to the power supply vcc via the collector-emitter path of the transistor Q1g.

The collector of the transistor Q11 and the collector of the diode-connected transistor (hs) are commonly connected to the power supply VCC via a current source s11.

Note that in the above description, the transistors Q1s 1Q16 are also formed as a pair of current mirrors.

Therefore, in the above configuration, the transistor Qllr Q
lz and Qls t Q14 and Qls.

Since each Qlg is made up of a pair of current mirrors, each collector current IC(Qll) ~ IC(Qlg
) is IC(Qll) = IC(Q12) r I
C(Qlg) = IC(Q14)tIc(Qls
)=IC(Qlg).

And, from the circuit configuration, naturally “c((hl)=
Ic(Qlg) + IC(Q14) = Ic(
Qts), so in the end Ic(Ql
t) = Ic(Qtz) = Ic(Qlg)=
Ic(Qt4) −Ic(Qts)=Ic(Qt
s) is established.

Also, from the circuit configuration, Ic (Qlz) + Ic
Since the relationship (Qlg)=I holds true, each transistor Q! Operating current IC (Qll) ~ Ic (
Q□6) are all I/2.

Figure 4 shows point p (transistors Q1, Q) shown in Figure 3.
6 shows a simplified equivalent circuit at a low frequency when a voltage signal source ``in'' is connected between the common collector of 6) and the reference potential point GND.

Here, as described above, each transistor Qll to Q1s
Since the + operating currents are equal, their respective emitter operating resistances r8(Qlt) to ro(Qlg) are also equal to each other.

Then, the current amplification factor of the NPN transistors Qtt to Q14 is set to β, and the PNP transistor Qts +Q1
Letting that of g be β, and looking at the input current in and the input voltage vin, the following relationship holds true in FIG. 4: vin: βNroZg 9-.

Therefore, the equivalent resistance seen from point (D) in FIG. 3 is T Rζ-1■, and by controlling ■, a variable equivalent resistance R can be obtained.

Also, in FIG. 3, if there is an increase in the current Δi in the transistor Qll, then the transistor Q11+Q
Since 12 is a pair of current mirrors, the current on the transistor Q12 side also increases by Δi.

Then, the current of transistor Q1g decreases by that amount, and the current of transistors QCs, Q14 and Qls decreases by that amount.

Since each Qlg is a current mirror, the current of the transistor Q16 also decreases by Δi. This means that a current of 2·Δi flows from the point (not shown in the diagram), which does not cross the tab or handle.

10- This means that when the current inflow from point p) is Δi,
The operating current change of the transistor (ht) is i·Δi, which indicates that the occurrence of nonlinear distortion can be suppressed as in the case of FIG. 2.

FIG. 5 shows equivalent variable resistance characteristics obtained by computer analysis of the circuit shown in FIG. 3, and shows that almost theoretically linear characteristics can be obtained.

The circuit in Figure 3 connects the power supply VCC and the reference potential point GND.
Since the number of transistors connected in cascade between them is small, the voltage required for operation is vB + "cF, ("ro, 8~0.9
It is possible to operate at a low voltage of 1 V or less, so that only V) is required.

FIG. 6 shows another embodiment in which the transistors Q1t to Q16 shown in FIG.

0 and the reference potential point GND are connected inversely, and resistors R to R6 are inserted into the emitters of the pair of current mirror transistors Qlt' to Q16'. In this case, the equivalent variable resistance R' viewed from the common collector of the transistors Q14' + Qts' (point D' in the figure) has a characteristic equal to R in FIG. 3.

It goes without saying that the present invention is not limited to the embodiments described above and illustrated, and that various modifications and applications can be made without departing from the gist of the invention.

[Effects of the Invention] Therefore, as described in detail above, according to the present invention, an extremely good equivalent variable is achieved which is improved so that nonlinear distortion can be suppressed and low voltage operation of 1 V or less is possible. It becomes possible to provide a resistance circuit.

[Brief explanation of drawings]

1 and 2 are configuration explanatory diagrams showing a conventional equivalent variable resistance circuit, FIG. 3 is a configuration explanatory diagram showing an embodiment of the equivalent variable resistance circuit according to the present invention, and FIG. isometric diagram,
Figure 5 is a curve diagram showing the equivalent variable resistance characteristics of Figure 3;
The figure is a configuration explanatory diagram showing another embodiment of the present invention. Qsx"Qte...transistor, 811...current source, vcc...power supply, GND...reference potential point. 13- Figure 3 Figure 4 Figure 6 Decoy i4"1-]i2 Figure 5 Figure 6 Figure, 2

Claims (1)

[Claims] a pair of first and second current mirror transistors each having an emitter connected to a reference potential point or a power supply; one end connected to the power supply or reference potential point and the other end connected to the first transistor;
a current source commonly connected to the non-diode-connected collectors of the current mirror pair of transistors and the diode-connected collectors of the second current mirror pair of transistors, each emitter of which is connected to the power supply or reference potential point; , the collector on the diode connection side is connected to the second
a third pair of current mirror transistors connected to the collectors on the non-diode-connected side of the pair of current mirror transistors, and the non-diode-connected collectors are connected to the collectors on the diode-connected side of the first pair of current mirror transistors. An equivalent variable resistance circuit characterized by: