JPS6040207B2 - temperature compensated dc amplifier - Google Patents

Description

[Detailed description of the invention] The present invention relates to temperature compensated current amplifiers.

First, the operation of the current amplifier, which is the object of temperature compensation, will be explained with reference to FIG. A, is an operational amplifier. An idealized operational amplifier can be treated as having infinite input impedance, zero output impedance, and infinite current amplification. VR1 and VR2 are variable resistors for gain adjustment, and are connected in series between a constant voltage source +V and a ground point. The output terminal voltage V of variable resistor VR, and the output terminal voltage V2 of VR2 are connected to diode D, which will be described later.
, and D2, a sufficiently large current is supplied to each variable resistor so that it hardly changes due to the current flowing through D2. A diode D is connected between the non-inverting input terminal of the amplifier A and the output terminal of VR, and a diode D2 is connected between the negative input terminal and the output terminal of VR2. Signal power weakening is applied to the non-inverting input terminal,
The amplified output current 12 is fed back to the inverting input terminal. In a circuit having such a configuration, since the input voltages at both input terminals of amplifier A are equal, the following relationship holds true. V.

, 10V, =V. 20V2...{
1) However, Vo: Voltage drop across diode D due to current 1. Vo2: Voltage drop across diode D2 due to current 12. If each diode has the same characteristics, the following relationship holds true.

VO. =k-kou/n-go...[21V 戊=k
Character/n person...{3} However, k: Boltzmann's constant T: Absolute temperature q: Electron charge 11: Input current 12: Amplified feedback current Z1s: Saturation current m (3) From formula ls, V.

,,V. If you delete 2, harm = eXp magazine (V "V2)
．．・・・． ...t41'4}Formula 12 is 1, no's ex
This shows that Z is multiplied by p·q(V, -V2)/kT.

This type of amplifier is useful in fields such as photocurrent measurement because it is possible to obtain any amplification factor by appropriately setting V and V2, and it is also possible to extract a voltage logarithmically compressed input current by using the circuit configuration. It is widely used in In particular, in the technical field of cameras, this is applied to a circuit that determines another element according to the photocurrent by assigning any two factors such as film sensitivity, aperture value, and shutter speed to V1 and V2. However, as can be seen from equation {4}, when V, -V2 is set constant, the current amplification factor changes according to changes in absolute temperature. Therefore, unless V, -V2 is increased in response to the rise in absolute temperature, the amplification factor will fluctuate. FIG. 8 shows the temperature characteristics of the forward voltage of the diode. FIGS. 2 and 3 show specific application examples in which the current amplifier circuit of the type described above is subjected to temperature compensation by a thermistor.

FIG. 2 shows an example in which the DC amplifier circuit is applied to a circuit for amplifying a photoelectric current and extracting a voltage Vo proportional to the amplified DC current.

The circuit that provides the voltages V and V2 includes a constant voltage source CVS, a resistor and thermistor Th, and variable resistors VR, , VR2.
It consists of

In such a configuration of the compensation circuit, the potentials of V and V2 increase as the absolute temperature increases. If this rate of increase is exactly proportional to the rise in absolute temperature, the current amplification factor will not have a coefficient of temperature, but in the case of compensation using a thermistor, there will be a slight undulation as shown in curve a in Figure 7. will be left behind. That is, with such compensation, it is impossible to completely compensate for temperature changes within a wide range. FIG. 3 shows a circuit in which the DC amplifier shown in FIG. 1 is applied to an electric shutter circuit.

The temperature compensation circuit has the same configuration as shown in FIG. The photocurrent 1 of the solar cell PC is amplified by an operational amplifier A3.
A3 is provided with a circuit including a capacitor C, and when SW is opened in synchronization with the opening of the shutter, the capacitor C is charged with an amplified current 12. As a result, the voltage at the output terminal of A3 gradually increases and when it reaches the reference voltage of comparator A4, the current flowing to IJ relay R is turned off and the shirt relay is closed. In the above-described applications, it is necessary to accurately amplify a wide range of photocurrents, and it is desirable that temperature compensation be performed within a range of considerable temperature changes.

The present invention was made to solve these problems, and its purpose is to provide a current amplification circuit that is completely temperature compensated by supplying a bias voltage that changes in proportion to absolute temperature. It's about doing. To achieve the above object, the temperature compensated DC amplifier according to the present invention comprises a first PN junction structure connected to one input terminal of the operational amplifier, in which a feedback circuit is formed from the output to the inverting input terminal. the first and second PN junction structures in order to provide a signal current in the forward direction and obtain a current proportional to the signal current in the forward direction of the second PN junction structure connected to the other input terminal or output terminal; A current amplifier configured to apply a bias voltage to its other end, the base voltage of a transistor of a bias voltage generation circuit that generates the bias voltage being fixed to a constant value with respect to a reference potential point, and the emitter voltage of the transistor being fixed to a constant value. Insert a resistor and set the voltage (V) between the terminals of the resistor.

) to (V.

) (V BEO) However, V axis: 0 of the semiconductor of the transistor at absolute zero
Voltage corresponding to energy band gap V BEO
: Base-emitter voltage V of the transistor at the reference temperature To.

: By setting the voltage between the terminals of the resistor at an arbitrary temperature T (=To+△T), a voltage proportional to the absolute temperature is generated between the terminals, and all or part of the voltage proportional to the absolute temperature is It is connected as a bias voltage to the other ends of the first and second PN junction structures, and is configured to determine the degree of amplification of the signal voltage according to the bias voltage.

With such a configuration, complete temperature compensation is achieved and the object of the invention is fully achieved.

The present invention will be described in more detail below with reference to the drawings and the like.

FIG. 4 shows an embodiment of a temperature compensated DC amplifier according to the invention. The temperature characteristic correction of this current amplification circuit uses the temperature characteristic between the base and emitter of the transistor to extract a voltage in proportion to the absolute temperature. The principle of this correction circuit will be explained in detail using the circuit shown in FIG. 5A as an example. The voltage Vr applied across the resistor R3 is R3
- It is given by V8/(R30R4) and is constant regardless of temperature. Base-emitter voltage V of transistor Q3
BE and emitter current IE (=lc, but hfe of Q3>
>1) is expressed by the following formula.

IC=QTnexp [old days (VBE-V axis)].・・・．
・Collector current lco and base emitter voltage VBBo at a certain reference temperature are expressed by the following equation.

I.C.

=QT8eXp [Left (V side - V strange...shelf {5},
[6} In formula, lc: temperature T.

Collector current lco at K: Collector current Q at reference temperature T8K: Constant determined by structure T: Absolute temperature (〇K) T.

: Reference absolute temperature (OK) q: Electronic charge k: Borckmann constant VBE: Base-emitter voltage V8 at temperature TK.

. :Base-emitter voltage n at reference temperature ToK:
A constant determined by the manufacturing method V&: Voltage corresponding to the energy band gap of Si at absolute zero If we calculate VBE using the formula '5}, '6}, we get VBE=V&(・-voice) 10V legs (voice) 10 potatoes ln (harm)
10 ln (agriculture)...'7) In the above equation, the last two terms are small compared to the others, so if we ignore them, V
BE=V side (・-voice) W side (voice) ‐‐‐‐‐‐(71'
0 In FIG. 5A, the voltage drop across resistor R8 is equal to the sum of VBE of transistor Q and R518, so the following equation holds.

Vr=VBG+IER5......{
8 - If we partially differentiate this equation with respect to absolute temperature, Vr is a voltage that is independent of temperature and is determined by the division ratio of R3 and R4, as mentioned above, so we can obtain the following equation.

・・・．・・・-If we partially differentiate the {9} formula [7}' in the same way, we get Gei = - etc. + * ....・R5 from side type and working type. Nose thousand.

(vg.-v skin).・・１． - It can be seen from Equation (11) that the rate of change in emitter current IE with respect to absolute temperature is constant. If Vo(T) is the voltage between both terminals of the resistor R5 inserted in the emitter at a temperature T higher than the reference temperature To by ΔT, Vo(T) is given by the following equation.

However, in the following formula, Vo is used synonymously with Vo(L).

V. (T)=V. 10R5 (61E/6T)△T. ...
(99) When transformed using Equation 11, V is obtained.

(T)V.

Ten (△T/T) (V soft one V BEO). ...---(1
00) In order for Vo(T) to be a voltage proportional to absolute temperature, the following relationship needs to hold between Vo(T) and Vo.

V.

(T)/V. =T/T.

=(T. ten △T)/T. ．． ．． ．． ．． ．． ．． (101) Said (
From equations (100) and (111), VO NiV Utaichi V BE0
・・・．・・・・・・． - If (112) is established, a voltage proportional to absolute temperature can be obtained.

This means that the voltage across the resistor R5 inserted in the emitter is Vg,
There is no other choice than to make it one V BEO.

At this time, the emitter current IE of the transistor Q is proportional to the absolute temperature. This will be further explained with reference to equation (11).

In equation (11), the reference temperature is 30 PK, and Vgo=
1.2V, v BEO=0.6V.

JR5 (61E/6T) = (1.2
-0.6)・(1/300) =2nV/.

In other words, the voltage across the terminals of the resistor R5 changes by 2hV for a change in temperature of 10K.

Therefore, if a 1.2V voltage is connected to the base so that a voltage of 0.6V is generated at the emitter, a voltage proportional to the absolute temperature can be obtained from the resistor inserted outside the emitter as described above. I can do it.

If the current amplification factor hfe of transistor Q3>>1, then I
Since E=lc may be used, the rate of change ΔV/ΔT of the voltage V (FIG. 5A) with respect to absolute temperature is given by the following equation.

However, R? indicates the resistance value of the sum of the resistance values of variable resistors VR and VR2.

One-. −． (V song one VBEO),. …． (1 poem = R7△
△Sheep turtle TI.

2) Since the right side of equation (12) is a constant unrelated to temperature, V'
It can be seen that it changes in proportion to the absolute temperature.

Also V,. Since V2 is a part of V, V2 - V, changes in proportion to absolute temperature. Therefore, as shown at the beginning (
4} formula expq/kT (V, -V2) is a constant value independent of temperature, and the current amplification factor is kept constant. The change in V or V2 with respect to temperature is a straight line. This state (
Straight line a) is shown in FIG. 7 in comparison with curve b in the case of thermistor correction. The temperature compensation circuit can be similarly constructed using an NPN transistor Q4 as shown in FIG. 5B. FIG. 6 is a circuit diagram showing a second embodiment of the DC amplifier according to the present invention.

A base-emitter diode of transistor Q7 is used instead of diode D, and a base-emitter diode of transistor Q is used instead of diode D2. This configuration has the advantage that it is not necessary to supply a large current to the variable resistors VR, VR2. From the above explanation, it can be seen that in the current amplification circuit according to the present invention, complete temperature correction is performed. This temperature correction is always performed accurately even if the gain of the current amplifier circuit (which can be arbitrarily set by adjusting the value of V, -V2) is changed. Therefore, if the DC amplifier circuit according to the present invention is applied to the application example described with reference to FIGS. 2 and 3, accurate brightness measurement or control using the same can be performed. Various modifications can be made to the embodiments described in detail above.

For example, as shown in Figure 3, the feedback circuit also has a capacitor C.
It is also possible to configure using . Even in that case, complete temperature compensation is possible. In short, the scope of the present invention shall extend to all of the claims.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an amplifier that is subject to temperature compensation, FIGS. 2 and 3 are circuit diagrams showing application examples of the aforementioned amplifier, and FIG. 4 is an implementation of a temperature compensated current amplifier according to the present invention. A circuit diagram showing an example, FIG. 5A is a circuit diagram for explaining the compensation circuit of the circuit shown in FIG. 4, FIG. 5B is a circuit diagram showing another configuration example of the temperature compensation circuit, and FIG. 7 is a circuit diagram showing a second embodiment of the temperature compensated current amplifier according to the present invention, FIG. 7 is a graph showing temperature compensation characteristics, and FIG. 8 is a graph showing temperature characteristics of a general diode. TA A,, N, A3... operational amplifier, A4...
...Comparator, D,,D2"""Diode,,R
,, R2, R3, R8...Resistor, RL...
...Relay, Th...Thermistor, C...Capacitor, Q,,Q2,Q3,Q4,Q,Q7,Q8...
...Transistor, CVS... Constant voltage power source. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] 1. Applying a signal current in the forward direction to a first PN junction structure connected to one input terminal of an operational amplifier in which a feedback circuit is formed from the output to the inverting input terminal, and Alternatively, a bias voltage is applied to the other ends of the first and second PN junction structures in order to obtain a current proportional to the signal current in the forward direction of the second PN junction structure connected to the output terminal. In the current amplifier, the base voltage of a transistor of a bias voltage generation circuit that generates the bias voltage is fixed constant with respect to a reference potential point, a resistor is inserted into the emitter of the transistor, and the voltage between the terminals of the resistor ( By setting V_0) as below, a voltage proportional to the absolute temperature is generated between the terminals, and all or part of the voltage proportional to the absolute temperature is applied to the other ends of the first and second PN junction structures. 1. A temperature-compensated DC amplifier, characterized in that the temperature-compensated DC amplifier is connected to a bias voltage as a bias voltage, and is configured to determine an amplification degree of the signal voltage according to the bias voltage. (V_0) = (Vg_0 - VBEO) where, Vg_0: voltage corresponding to the energy band gap of the semiconductor of the transistor at absolute zero VBEO: base-emitter voltage of the transistor at reference temperature T_0 V_0: arbitrary temperature T Voltage between terminals of the resistor at (=T_0+△T)