JPS60810B2 - antilogarithmic amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an antilogarithm amplifier using a semiconductor PN junction as an antilogarithm conversion element, and in particular to an antilogarithm amplifier capable of correcting deviation from antilog linearity due to physical properties of the antilogarithm conversion element. This is what I did.

Note that anti-log linearity means that the input voltage V
On a graph where i is linear and the output voltage Vo is log, the input/output characteristics are a straight line, that is, logVo=A
A characteristic described in the form Vj+B.

However, A and B are constants here. Generally, anti-logarithmic amplifiers are required to have a wide dynamic range and good anti-log linearity. However, in antilogarithmic amplifiers that use semiconductor PN junctions as antilogarithmic conversion elements, the antilogarithmic linearity collapses as shown in Figure 3b due to the collective physical properties of the PN junction, and the effective range of antilogarithmic conversion is limited. It's coming. That is,
The voltage V-current 1 characteristic of the PN junction is 1=ls[exp{
q(V-IR)/kT}-1].

Here, ls is the reverse saturation current, q is the amount of electron charge, k is the Bormann constant, r is the Kelvin temperature, and R is the ohmic resistance of the PN junction. In the equation showing the voltage-current characteristics above, the last term (reverse saturation current ls) is a small current (several pA or less)
The IR term (ohmic resistance voltage drop) is the cause of deterioration of the anti-log linearity in the large current (approximately 1 skin A or more) region. However, the reverse saturation current ls
is very small compared to the normally handled current 1, so the above voltage-current characteristic equation can be approximated to the following equation. 1=lsex
p[q(V-IR)/kT]1} The ohmic resistance voltage drop IR in the characteristic equation [1} is the cause of creating an effective limit in the large current region, and in the past, the upper limit of an antilogarithmic amplifier was determined fatefully. , it was no longer possible to perform extensive anti-logarithmic transformations.

Furthermore, in order to obtain anti-log linearity over a wide range, a semiconductor element was used that had a small inverse saturation current ls and a particularly small ohmic resistance R of the PN junction. For this reason, the antilogarithmic conversion element becomes expensive, and as a result, an antilogarithmic amplifier having a wide range of linearity has to be expensive. The present invention has been made to eliminate the above-mentioned drawbacks, and embodiments thereof will be described below with reference to the drawings.

In Fig. 1, 1 is a known constant current circuit that flows out a constant current lr, and 2 and 3 are N circuits with well-matched voltage-current characteristics.
PN type transistors Tr2, Tr3, 8, and 9 are operational amplifiers with high input impedance and low offset voltage, 4 is a negative feedback resistor Rf of the operational amplifier 9, and 5 is a positive resistance temperature coefficient whose resistance value increases in proportion to temperature. 6 is the input resistance Ri, 7 is the positive feedback resistor Rc, 10 and 11 are capacitors and resistors that maintain good frequency stability of this anti-logarithmic amplifier, and 12 and 13 are the input terminals of this anti-logarithmic amplifier, respectively. , is the output terminal. Note that NPN transistors 2 (Tr2), 3
(Tr3) and a resistor 5 (Rp) having a positive temperature coefficient of resistance are selected so that they are in equilibrium at the same temperature. Further, the operational amplifier 14 forms an addition/inversion circuit, and the operational amplifier 9 and the negative feedback resistor 4 (Rf) form a current-voltage conversion circuit. The embodiment shown in FIG. 1 has a configuration in which a positive feedback circuit including a positive feedback resistor 7 (Rc) is provided in a known antilogarithm calculation circuit. Next, the operation of this circuit will be explained.

Since both NPN transistors 2 (Tr, ) and 3 (Tr2) have their collector potentials kept at the same potential as their base potentials, they operate as simple PN junctions and follow the voltage-current equation {1}. The base-emitter voltages of transistors 2 (Tr, ) and 3 (T [2) are respectively defined as VBE and VBE2, the collector currents are respectively lc and IC2, and the ohmic resistances are R and R2, respectively, and the reverse saturation current is Let lslt ls2 respectively, then lc,=ls
,exp[q(VBE,-1,R,)/KT](2}l
c2=ls2exp[q(VBE2-12R2)/kT
]{3} holds true.

By the way, in this case, since the constant current circuit 1 is configured to supply the constant current lr and the input impedance of the arithmetic amplifier 8 is determined to be sufficiently high, it is possible to set lcl=lr. Also, the current flowing through the negative feedback resistor 4 (Rf) is
If it is o, then lc2=lo may be set as above. Therefore, the expressions '2) and '3} are "lr=ls,exp[q
(VBE.-lrR,) nokT〕■lo=ls2exp
[q(VBE2-loR2) no kT] becomes '5'.

By the way, if we take the ratio of the '5} formula and the ■ formula, we get Obi: Instrument eXp [
In the past {(vBE2-VBE・)-(10R2-lrR・)
}]. Here, transistors 2 (Tr2), 3 (
Since the characteristics of Tr3) are well matched, IS231S・
3.R, you may set R2=R, and the above formula is band=eXp[
In the past {(vBE2-vBE,)-R(10-lr)}]
(6) can be approximated. Therefore, lo=Ire
xp[q {(VBE2-VBE,)-R(lo-lr
)}/kT] '71.

Further, the base potential of the transistor 2 (Tr2), that is, the output voltage of the operational amplifier 14 is 1 (Rp/Ri)Vi1 (
Rp/Rc)Vo, and these transistors 2(T
Since the emitters of r,) and 3 (Tr2) are common, vBE2-vBE,=Kishu flea v.

(8) holds true.

Since the output voltage Vo is equal to Rflo, (7), '8)
From the formula, the output voltage Vo is v. =Rf, reXp [Gun Elementary School (Study Abroad-R) 10 books r] (9).
Of the terms in the side equation, Rlr' is constant regardless of the input voltage Vi and is sufficiently small compared to the voltage drop R1o due to the ohmic resistance R in the range where the current lo is large, so it has almost no effect on the deterioration of anti-log linearity. Therefore, the formula [9} is v.=RflreXp [word duck vi+
It can be approximated as (R Shizukuyume-R)10}]o■. Now, in the working equation, if Rc is set so that Rc=RpRf/ROD, (10-equation is V.

= R flre

Further, due to the problem of temperature stability, the temperature term of the resistance 5 (Rp) having a positive resistance temperature coefficient is canceled out according to equation 02 if the resistance value increases in proportion to temperature. Furthermore, from the OU equation, the positive feedback resistor 7 (Rc) is the resistor Rp
Therefore, if you select a temperature-sensitive resistor that satisfies the OU equation as Rc, the temperature stability of anti-log linearity will also be compensated for.In the middle of approximating from the formula ■ to the Tane equation, In cases where the voltage drop Rh due to the ohmic resistance R cannot be ignored,
If there is a need to further improve linearity, this R1r
I need to delete it.

An example in this case is shown in FIG. In Figure 2, 1
The elements and circuit configurations from 14 to 14 correspond to those shown in FIG. i, and have similar functions. 15 is a resistor Rr, and 16 is an operational amplifier 14 via a resistor 15 (Rr).
This is a correction voltage application terminal connected to the inverting input terminal of.

A correction voltage -Vr is applied to the correction voltage application terminal 16. Here, the base potential of the transistor 2 (Rr,) is 1 (Rp/Ri)Vi-(Rp/Rc)V. Ten (Rp
/Rr)Vr, and VBE2-VBE. : Agriculture Vi+
Ashiji〉.

Ichimantei Vr03 is established. The relationship of Vo=Rflo and {
7} and 03], the output voltage Vo is "v.

=Rf・. eXp [Ku {group vi ten (R zero sa - R) ten ten (R1 r - 蓑W})] leg. Now, in the 04 formula,
If Rr and Vr are set so that Rr/Vr=Rp/R1r ■, the female formula can obtain formula 02 without approximation using the OU formula and formula 09,
The two ohmic resistances R of transistors 2 (Tr, ) and 3 (Tr2) will be erased.

At this time, the correction voltage Vr is set to a constant voltage, and Rr=Rp
If a temperature-sensitive resistor that satisfies Vr/R1r is selected as Rr, the temperature stability of anti-log linearity is also compensated. Transistor 2 (
In addition to the methods described above, methods for canceling the voltage drop R1r due to the ohmic resistance R of Tr, ) include superimposing a negative DC voltage on the input voltage Vi, and applying a positive DC voltage to the non-inverting input terminal of the operational amplifier 14. There are many ways to do this, but all have the same result. Also, in the rigid type,
The value of positive feedback resistor 7 (Rc) is RC<RPRf no R
If the output voltage when set to be female is Yo, and the output voltage when set to satisfy the OU formula is Vo, band = eXp [<R zero - R
)) becomes blood, and the larger the value of the output voltage V'o becomes, the more it exceeds the inverse logarithmic function of the input voltage Vi.

In other words, if positive feedback is applied excessively, an anti-logarithmic amplifier can be realized in which the larger the output voltage, the greater the deviation from anti-log linearity as shown in Figure 3c. In other words, when controlling a linear VC○ (voltage controlled oscillator) at the output with an arithmetic differential voltage corresponding to the key that determines the pitch of a musical tone, the above-mentioned inverse logarithmic amplifier with excessive positive feedback If you use
It can be obtained from O. FIG. 4 shows an embodiment in which a resistor adder circuit consisting only of lamps is used as means for applying positive feedback to the input. Each of the elements and circuits shown in FIGS. 1 to 13 correspond to those shown in FIG. 1 and have the functions of the same machine. However, unlike 5 (Rp) in Figure 1, the resistance RT with a positive temperature coefficient of resistance shown by 5 does not increase linearly with temperature, but has a predetermined nonlinear positive resistance value. It has a temperature coefficient of resistance of
Further, the circuit configuration is slightly different from that shown in FIG. 1, in that the base of transistor 2 (Tr2) is grounded, and the base of transistor 3 (Tr3) serves as an input to the anti-logarithm calculation circuit section. This is to make the input characteristic of the device positive as in the embodiment shown in FIG. The constant current circuit 1 consists of a terminal 15 for applying a constant voltage source +VB and a resistor Rs for voltage-current conversion, and since the non-inverting input of the operational amplifier 8 is grounded and negative feedback is applied, The inverting input of the operational amplifier 8 becomes the ground potential (virtual ground), and as a result, the collector of the transistor 2 (Tr2) has lr=VB/R.
A constant current of s flows. Transistors 2 (Tr,), 3 (
Tr3) also holds formulas '4} to [7}, and if the input voltage and output voltage are Vi and Vo, respectively, then the base voltage of transistor 3 (Tr3), that is, VBE2-VBE
, is tRTRC RTRi
■R old C+RT
(RC1Ri) Vi+RiRC+RT (RC1R.

Becomes Vo. Also, the output voltage Vo is equal to Rflo, so v.

=RflreXp [word {K, vi ten (K2Rf-R)1
01RI}] It becomes the leg. however,
RTRc RTRiK,=Ri
RC + RT (RC + Ri), K2 NiR government C + RT (RC
It is 10RD.

Among the terms in the ■ equation, R1r can be ignored for the same reason as the approximation from the ■ equation to the tane equation, and the side equation is ``v.: Rfl female p [magazine {
K, vi+(K2Rf-R)10}]
(It can be approximated to 2). Now, in the formula (2), RC=R
(If Rc is set so that it becomes 20, the formula ■ becomes v.

= Rflreexp (word, K, Vi) (22!, so the error term that destroys the L antilog linearity disappears, and the linearity in a large current range can be greatly improved.) Also, due to the problem of temperature stability, the The resistance temperature coefficient resistance 5 (RT) is 22
Since the coefficient of Vi in the equation needs to maintain a constant value against temperature changes, RTRC ■K, = R
It is sufficient if it satisfies iRC+RT(RC+Rj)=MT.

However, M is a constant determined by the input/output characteristics. Furthermore, since the positive feedback resistor 7 (Rc) of the leg type includes the above-mentioned resistor RT, if a temperature-sensitive resistor that satisfies the leg type is selected as Rc, the temperature stability of anti-log linearity is also compensated. .
Now, in the middle of approximating from formula The case is also similar to the means shown in FIG.
By connecting a resistor corresponding to the resistor 15 (Rr) in the figure and applying an appropriate compensation voltage to the terminal of the resistor, using a method that results in the compensation voltage being superimposed on the input voltage Vi,
Elimination of the voltage drop R1r can be realized.

Furthermore, if the value of the positive feedback resistor 7 (Rc) is set to RC (in equation 20), the input/output characteristics will be as shown in Fig. 3 c, as in the case of Fig. 1. In this way, an anti-logarithmic amplifier can be realized in which the larger the output voltage, the greater the deviation from anti-logarithmic linearity, and the same effect as in the case of FIG. 1 can be expected.

The embodiment shown in FIG. 4 avoids drift and offset components of the operational amplifier 14 constituting the adder circuit shown in FIG.
The feature is that the adder circuit is made up of resistors without these variable elements. In addition, in the above embodiment, only the case where the input/output characteristic is positive, that is, the output voltage Vo is a positive increasing function of the input voltage Vi, has been described, but even in the opposite case, positive feedback will result. With this configuration, anti-log linearity can be corrected in exactly the same way.

In addition, in the examples, in FIGS. 1 and 2, the resistor Rp is
In the figure, the resistance RT is treated as a positive resistance temperature coefficient resistance, but from the viewpoint of temperature stability, in the embodiments shown in Figs. By using a negative temperature coefficient resistor whose value decreases in inverse proportion to temperature, the temperature term can be canceled out, and temperature compensation can be performed while the positive feedback resistor Rc remains a temperature-fixed resistance. In the embodiment shown in Fig. 4, if the resistor RT is fixed temperature-wise and the input resistor Ri and positive feedback resistor Rc are negative temperature coefficient resistors that satisfy equation 21), the temperature term can be canceled and temperature compensation can be achieved. becomes possible. As described above, the present invention can cancel out the voltage drop caused by the ohmic resistance of the semiconductor PN junction of the anti-logarithmic conversion element by applying positive feedback from the output, so that anti-log linearity can be obtained over a wider range. In particular, it is extremely valuable as it can remove the upper limit of the usable range due to the PN junction ohmic resistor. Furthermore, by simultaneously canceling out the ohmic resistance of the PN junction for temperature compensation, it is possible to obtain more perfect anti-log linearity.Also, by applying excessive positive feedback, the pitch pitch of a natural instrument such as a piano can be improved. It is also possible to obtain a voltage proportional to this, which has a very large effect.Furthermore, by applying too little positive feedback, it is possible to generate a pitched scale with a pinch like a honky-tonk. It has great utility in musical instruments, such as the ability to obtain voltage.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram of a specific embodiment of the present invention, and FIG.
The figure is a circuit configuration diagram of another specific embodiment of the present invention.
The figure is an input/output characteristic diagram for explaining anti-log linearity.
The figure is a circuit configuration diagram of another specific embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Constant current circuit, 2... First transistor, 3... Second transistor, 4...
... Member feedback resistance Rf, 5... Positive resistance temperature coefficient resistance, 6... Input resistance Ri 7... Positive feedback resistance Rc, 8... First operational amplifier "9
...Second operational amplifier, 14...Brother 3
operational amplifier, 15...resistor Rr. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Scope of Claims] 1. An antilogarithm calculation circuit using a semiconductor PN junction as an antilogarithm conversion element and a feedback circuit, wherein the antilogarithm calculation is performed from the output of the antilogarithm calculation circuit through the feedback circuit. An inverse logarithmic amplifier characterized by applying positive feedback to the input of the circuit. 2. Connect the output of the constant current circuit to the emitter of the first transistor via a resistor from the output of the first operational amplifier whose inverting input is connected to the base of the first transistor.
a first amplification circuit configured by connecting the collector of the first transistor to the non-inverting input of the operational amplifier, and connecting the collector of the first transistor to the inverting input of the first operational amplifier; The non-inverting input of the amplifier is connected to the base of the second transistor, the inverting input of the second operational amplifier is connected to the collector of the second transistor, and the inverting input is connected to the output of the second operational amplifier via a negative feedback resistor. and a second amplifier circuit connected to the base of the first transistor and the emitter of the second transistor. Input the connection point with the non-inverting input of the operational amplifier,
2. The antilogarithmic amplifier according to claim 1, which uses an antilogarithmic arithmetic circuit whose output is the output of the second operational amplifier. 3. The anti-logarithmic amplifier according to claim 2, wherein the positive feedback signal and the input signal are added by an addition circuit constituted by a third operational amplifier. 4 Negative feedback is applied from the output of the third operational amplifier whose non-inverting input is grounded to the inverting input via the negative feedback resistor Rp, and the positive feedback signal is applied to the resistor Rc, and the input signal is connected to the resistor Ri.
, an ohmic resistance of the second transistor is R, and a negative feedback resistance of the second operational amplifier is Rf. When the value of the resistance Rc is R
4. The anti-logarithmic amplifier according to claim 3, wherein the inverse logarithmic amplifier is set so that c=RpRf/R. 5. The inverse logarithmic amplifier according to claim 4, wherein the resistor Rp and the resistor Rc are resistors having a positive resistance temperature coefficient (positive temperature coefficient thermistor). 6. The anti-logarithmic amplifier according to claim 4, wherein a resistor having a negative temperature coefficient of resistance (a negative characteristic thermistor) is used as the resistor Ri. 7. The anti-logarithmic amplifier according to claim 2, wherein the positive feedback signal and the input signal are added by a resistor adding circuit made up of resistors. 8 Claim 2 in which the positive feedback signal, the input signal, and the correction signal are added by an adder circuit configured with a third operational amplifier.
Anti-logarithmic amplifier as described in section. 9 Negative feedback is applied from the output of the third operational amplifier whose non-inverting input is grounded to the inverting input via the negative feedback resistor Rp, and the positive feedback signal is passed through the resistor Rc and the input signal is passed through the resistor Ri to the third operational amplifier. further comprising an adder circuit configured to apply a predetermined correction voltage -Vr to the inverting input of the third operational amplifier via a resistor Rr; The ohmic resistance of the second transistor is R, and the negative feedback resistance of the second operational amplifier is Rf.
When the output current of the constant current circuit is Ir, the above resistance Rc
The value of Rc=RpRf/R, and the above resistance Rr
9. The anti-logarithmic amplifier according to claim 8, wherein the value of Rr is set to be Rr=RpVr/RIr. 10 Claim 9 in which a positive resistance temperature coefficient resistor (positive temperature coefficient thermistor) is used for the resistor Rp, the resistor Rc, and the resistor Rr.
Anti-logarithmic amplifier as described in section. 11. The anti-logarithmic amplifier according to claim 9, wherein a negative resistance temperature coefficient resistor (negative characteristic thermistor) is used as the resistor Ri. 12 Connect the output of the first operational amplifier whose non-inverting input is grounded via a resistor to the emitter of the first transistor whose base is grounded, and connect the collector of the first transistor to the inverting input of the first operational amplifier. , the inverting input of the first operational amplifier is grounded to a constant current source, respectively.
the output of a second operational amplifier whose non-inverting input is grounded is connected to the inverting input via a negative feedback resistor, and the inverting input of the second operational amplifier is connected to the collector of a second transistor. a second amplifier circuit consisting of;
The emitter of the first transistor and the emitter of the second transistor are connected, and an antilogarithm calculation circuit is used, the base of the second transistor being input and the output of the second operational amplifier being output. An antilogarithmic amplifier according to claim 1. 13. The anti-logarithmic amplifier according to claim 12, wherein the positive feedback signal and the input signal are added by an adder circuit constituted by a third operational amplifier. 14. The inverse logarithmic amplifier according to claim 12, wherein the positive feedback signal and the input signal are added by a resistor adding circuit made up of resistors. 15 One end of the resistor Rc and one end of the resistor Ri are connected to the other end of the resistor R_T whose one end is grounded, and a positive feedback signal is applied to the other end of the resistor Rc, and an input signal is applied to the other end of the resistor Ri. If the ohmic resistance of the second transistor is R and the negative feedback resistance of the second operational amplifier is Rf, then the value of the resistor Rc is as follows.
Rc=(RiR_T(Rf-R))/(R(Ri+R_
15. The inverse logarithmic amplifier according to claim 14, characterized in that the inverse logarithmic amplifier is set so that T)). 16. The antilogarithmic amplifier according to claim 15, wherein a positive resistance temperature coefficient resistor (positive temperature coefficient thermistor) is used for the resistor R_T and the resistor Rc. 17. The anti-logarithmic amplifier according to claim 15, wherein negative resistance temperature coefficient resistors (negative characteristic thermistors) are used for the resistor Ri and the resistor Rc. 18. The antilogarithmic amplifier according to any one of claims 1 to 17, wherein antilogarithmic linearity is corrected as positive feedback. 19. The antilogarithm according to any one of claims 1 to 17, characterized in that positive feedback is applied too little so that the larger the output, the greater the deviation from the antilogarithmic linearity in the smaller direction. amplifier. 20. The anti-logarithmic amplifier according to any one of claims 1 to 17, characterized in that positive feedback is excessively applied so that the larger the output, the greater the deviation from anti-logarithmic linearity in the larger direction. . 21 Claim 1 in which a pair of transistors with mutually matched voltage-current characteristics is used as an anti-logarithmic conversion element
21. The antilogarithmic amplifier according to any one of items 20 to 20.