A temperature-compensated amplifier circuit including an amplifier section having first and second transistors which are connected at their collectors to a power source terminal through first and second resistors, and having d.c. biased bases coupled to signal source terminals; a current source including a third transistor having a collector coupled with the emitters of the first and second transistors and a grounded emitter; a fourth transistor having an emitter coupled with the power source terminal through a third resistor; a fifth transistor connected at the emitter to the power source terminal and at the base to the base of the fourth transistor; a sixth transistor having both base and collector commonly coupled to the collector of the fourth transistor and grounded at the emitter; and a seventh transistor connected at the collector to the base and the collector of the fifth transistor, at the base to the bases of the third and sixth transistors and grounded at the emitter. The emitters of the sixth and seventh transistors are formed so as to have a predetermined area ratio thereby controlling the current in the forth and fifth transistors. The first to third resistors are formed to have substantially equal temperature characteristics.

This invention relates to a temperature-compensated amplifier circuit with 
a minimum variation of its characteristic with respect to temperature 
change. 
Various amplified circuits using components whose characteristics may 
easily change with temperature change such as diodes, transistors and 
resistors have been provided. Many attempts have been made to prevent the 
amplification factor of those amplifier circuits from varying with 
temperature change. However, most of them are unsuccessful in that the 
temperature compensating effect is insufficient with complex circuit 
construction. 
Accordingly, an object of the invention is to provide a 
temperature-compensated amplifier circuit with a relatively simple circuit 
construction and a minimum variation of the amplification factor with 
respect to temperature change. 
According to one aspect of the invention, there is provided a 
temperature-compensated amplifier circuit comprising: an amplifier 
section; load resistive means coupled with the amplifier section; 
temperature compensating resistive means having substantially the same 
temperature characteristics as the load resistive means; and a current 
source for feeding a first current to the temperature compensating 
resistive means and for feeding a drive current having a given ratio to 
the first current to the amplifier section.

Referring now to FIG. 1, there is shown an embodiment of a 
temperature-compensated amplifier circuit according to the invention. In 
FIG. 1, a differential amplifier section 1 includes a couple of 
transistors TR1 and TR2. These transistors TR1 and TR2 are connected at 
the emitters to each other. The transistor TR1 is connected at the base to 
a first signal source 2 which is d.c. biased and at the collector to one 
end of a load resistor R1. The transistor TR2 is connected at the base to 
a second signal source 3 which is d.c. biased and at the collector to one 
end of another load resistor R2. The load resistors R1 and R2 are equal to 
each other in temperature characteristic. The resistors R1 and R2 are 
commonly connected at the other ends. 
In the temperature-compensated amplifier circuit shown in FIG. 1, a power 
source section includes third to sixth transistors TR3 to TR6. The emitter 
of the third transistor TR3 is coupled with a power source terminal Vcc, 
via a resistor R3. The transistor TR4 is connected at the emitter to the 
power source terminal Vcc, at the base to the base of the transistor TR3 
and to the collector of the transistor TR4 per se and at the collector to 
the other end of the resistors R1 and R2. The transistor TR5 is connected 
at the base to the collector of the transistor TR3 and the collector of 
the transistor TR5 per se, and grounded at the emitter. A transistor TR6 
of a multi-emitter type is connected at the base to the collector of the 
transistor TR5, at the collector to the emitters of the transistors TR1 
and TR2, and grounded at emitters. The transistors TR5 and TR6 are so 
fabricated that the emitter area ratio of the transistor TR5 to transistor 
TR6 is 1:N. Accordingly, the collector currents I1 and I2 of the 
transistors TR3 and TR4 are related by an equation (1): 
EQU I2=N.times.I1 (1) 
The base-emitter voltage V.sub.BE1 and V.sub.BE2 of the transistors TR3 and 
TR4 have the following difference .DELTA.V.sub.BE : 
##EQU1## 
where k is Boltzmann constant, q is the charge quantity of an electron and 
T is an absolute temperature. 
The difference voltages .DELTA.V.sub.BE is also expressed as follows: 
EQU .DELTA.V.sub.BE =R3.times.I1 (3) 
From the equations (2) and (3), the following equation is obtained: 
##EQU2## 
In the equation (4), (k/q)ln N is independent from temperature and hence it 
can be expressed as a constant P. From this, the equation (4) can be 
rewritten as follows: 
##EQU3## 
In the equation (5), when I1 is partially differentiated with respect to T, 
the following equation is given: 
##EQU4## 
The amplification factor GA of the amplifier section 1 is given 
EQU GA=-gm.multidot.R.sub.L (7) 
where R.sub.L is a resistance of each of the resistors R1 and R2 and 
##EQU5## 
Therefore, the equation (7) can be rewritten as follows: 
##EQU6## 
By partially differentiating GA with respect to T, the following equation 
is obtained: 
##EQU7## 
In order that the amplification factor GA is independent from temperature 
T, the condition 
##EQU8## 
must be satisfied. That is, 
##EQU9## 
The equation (10) can be rewritten as follows: 
##EQU10## 
From the equation (1), the following equation is obtained: 
##EQU11## 
By substituting equation (12) into equation (6), the following equation is 
given: 
##EQU12## 
From equations (1), (5) and (13), the following equation is obtained: 
##EQU13## 
If the equation (14) coincides with the equation (11), the amplification 
factor GA is not affected by temperature change. In other words, when the 
resistors are equalized in the temperature characteristic, that is, 
##EQU14## 
is satisfied, a good temperature compensation of the amplification factor 
GA can be attained in the amplifier section 1. 
When substituting equations (1) and (4) for equation (8), the following 
equation is obtained: 
##EQU15## 
As seen from equation (15), the amplification factor GA is determined by 
the area ratio of emitters of the transistors TR5 and TR6, and the 
resistance ratio of the resistor R3 and the resistor R1 or R2. 
When circuit elements such as transistors and resistors are fabricated with 
relative conditional values such as predetermined area ratios and 
resistance ratios, an ordinary integrated circuit technology relatively 
easily realizes the fabrication, satisfying the conditions required. 
Therefore, the temperature-compensated amplifier circuit may be easily 
fabricated so that the amplification factor GA is little affected by 
temperature change. 
Another embodiment of the temperature-compensated amplifier circuit of the 
invention is illustrated in FIG. 2. In FIG. 2, the same reference symbols 
are used to designate like circuit elements in FIG. 1, and the description 
thereof is omitted, for the purpose of simplification. In the amplifier 
circuit in FIG. 2, the collectors of transistors TR1 and TR2, these 
constituting an amplifier section, are connected through resistors R1 and 
R2 commonly to the power source terminal Vcc and not to the collector of 
the transistor TR4. The collector of the transistor TR4 is coupled with 
the collector of a transistor TR7 of multi-emitter type like a transistor 
TR6. The base of the transistor TR7 is connected to the base of a 
transistor TR5, and to the base of a transistor TR8 of which the collector 
is connected to the emitters of the transistors TR1 and TR2 and the 
emitter is grounded. The amplifier circuit further includes transistors 
TR9 and TR10. The collector of the transistor TR9 is grounded and the 
emitter and the base are respectively connected to the base and the 
collector of the transistor TR4. The transistor TR10 is connected at the 
base and emitter to the collector and the base of the transistor TR5, and 
at the collector to the power source terminal Vcc. The transistors TR9 and 
TR10 are used to compensate for error in the ratio of the currents I1 and 
I2 due to the base currents flowing into the bases of the transistors TR3, 
TR4, TR5, TR7 and TR8. 
As in the amplifier in FIG. 1, the collector currents I1, I2 and I3 of the 
transistors TR3, TR4 and TR8 and the amplification factor GA of the 
amplifier section 1 in the FIG. 2 circuit are given 
##EQU16## 
where the ratio of emitter areas of the transistors TR5 and TR8 is 1/N and 
##EQU17## 
Therefore, it is possible to keep the amplification factor GA constant with 
respect to temperature change, by equalizing the temperature 
characteristics of the resistors R1 to R3. 
FIG. 3 shows a modification of the temperature-compensated amplifier 
circuit in FIG. 2. The amplifier circuit of FIG. 3 is substantially equal 
to that of FIG. 2, except that the resistor R3 and the emitter of the 
transistor TR4 are grounded, the base of the transistor TR8 is connected 
to the bases of the transistors TR3 and TR4 instead of the bases of the 
transistors TR5 and TR7, the emitter of the transistor TR8 is grounded 
through a resistor R5 and the emitters of the transistors TR5 and TR7 are 
connected to the power source terminal Vcc. 
In this example, the transistor TR7 is of multi-collector type and has 
collectors as M times as the collector of the transistor TR5. Accordingly, 
the collector currents I1 and I2 of the transistors TR3 and TR4 are given 
##EQU18## 
When both sides of the equation (20) are partially differentiated with 
respect to T, the following equation is obtained: 
##EQU19## 
Hence, the rate of variation in current I1 with respect to temperature 
change, 
##EQU20## 
is given 
##EQU21## 
The ratio variation in current I1 with respect to temperature change, 
##EQU22## 
is also equal to that of the current I2. 
The emitter current I3 of the transistor TR8 is given by the following 
equation: 
##EQU23## 
When both sides of the equation (23) is partially diferentiated with 
respect to T, the following equation is given: 
##EQU24## 
where 
##EQU25## 
The equation (24) is rewritten as follows: 
##EQU26## 
For obtaining an effective temperature compensation in the amplifier 
section 1, 
##EQU27## 
should be made equal to 
##EQU28## 
and therefore the following conditional equation is obtained from equation 
(26): 
##EQU29## 
From the equation (27), it is clearly understood that, when the 
temperature coefficient of the resistor R5 is equal to that of the 
resistor R3, the amplifier section 1 is well temperature-compensated. 
A modification of the FIG. 3 example is illustrated in FIG. 4. In the 
circuit shown in FIG. 4, the emitters of transistors TR3 and TR4 are 
connected to each other, through a resistor R3. A transistor TR11 is 
connected at the collector to the junction between the emitter of the 
transistor TR4 and the resistor R3, at the emitter to the ground, and at 
the base to the collector of the transistor TR11 per se and to the base of 
the transistor TR8. The FIG. 4 circuit is advantageous in that 
sufficiently effective temperature compensation is obtained and that a 
larger drive current is permitted to flow through the amplifier section 1. 
Possible is the insertion of a resistor having the same temperature 
coefficient as resistors R3, R1 and R2 between the emitter of the 
transistor TR11 and ground. 
A modification of the FIG. 2 amplifier circuit is shown in FIG. 5. In this 
circuit, transistors TR5, TR7 and TR8 are similarly connected to each 
other. The resistance ratio among resistors R7 to R9 respectively 
connected between the emitters of these transistors and ground, determines 
the current ratio of the currents flowing through the collector-emitter 
paths of the transistors TR5, TR7 and TR8. In this case, it is required 
that the resistors R7 to R9 be so selected that they have substantially 
the same temperature coefficient and the voltage drops across the 
resistors R7 to R9 are set larger than the base-emitter voltages V.sub.BE 
of the transistors TR5, TR7 and TR8. This makes it possible to neglect the 
difference between the base-emitter voltages of the transistors TR5, TR7 
and TR8 due to currents respectively flowing through the transistors TR5, 
TR7 and TR8. Accordingly, the ratio of currents flowing through the 
transistors TR5, TR7 and TR8 is determined by the ratio of the resistances 
of the resistors R7, R8 and R9. 
FIG. 6 shows a modification of the FIG. 3 circuit, in which a plurality of 
amplifier sections 1 are indivisually driven. In the amplifier circuit in 
FIG. 6, a current corresponding to that flowing through a resistor R3 
flows through a current path including a transistor TR12 and a diode D1. 
The junction between the diode D1 and the transistor TR12 is connected to 
the base of a transistor TR8. Current flowing through the diode D1, i.e. 
the current corresponding to current flowing through the resistor R3, 
flows through the current path of the transistor TR8. In this way, the 
current path of a combination of the transistor TR12 and the diode D1 is 
provided in each amplifier circuit section 1. Accordingly, the amplifier 
sections 1-1 and 1-2 are driven by individual control signals, 
respectively. In this point, this example is advantageous. 
Still another embodiment of the invention is shown in FIG. 7. This example 
is substantially equal to the FIG. 2 example, except that the amplifier 
section 1 includes a transistor TR13 connected at the base to the junction 
between the collectors of the transistors TR5 and TR3, at the collector to 
the power source terminal Vcc via a resistor R11, and at the emitter to 
ground. Making the temperature coefficient of the resistor R11 coincide 
with that of a resistor R3, enables the amplification factor of the 
transistor TR13 to be kept substantially constant with respect to 
temperature change. 
FIG. 8 shows a still another embodiment of this invention in which a 
plurality of amplifier sections 1-1 and 1-2 are connected in cascade 
fashion. The ratio of the current flowing through the current path of a 
transistor TR6 to that flowing through the current path of the transistor 
TR3, is determined by the resistances of resistors R13 and R14. The 
resistor R12 functions like the resistor R3 in the FIG. 1 circuit. 
A temperature-compensated amplifier circuit according to further embodiment 
of the invention is illustrated in FIG. 9. The temperature compensation 
circuit includes a transistor TR15 connected at the collector to the 
emitters of transistors TR1 and TR2, these constituting an amplifier 
section 1, and a series circuit including a resistor R16 and diodes D2-1 
to D2-n. The anode of the diode D2-1 is connected to the base of the 
transistor TR15. 
In the FIG. 9 circuit, the amplification factor GA of the amplifier section 
1 is given by the following equation: 
##EQU30## 
where Ie is current flowing through the collector-emitter path of the 
transistor TR1 or TR2. 
By partially differentiating both sides of the equation (28) with respect 
to T, the following equation is obtained: 
##EQU31## 
Now suppose that 
##EQU32## 
in the equation (29) and the equation (29) can be rewritten as follows: 
##EQU33## 
Satisfying the equation (30) may restrict the variation of the 
amplification factor of the amplifier section 1 in FIG. 9 due to 
temperature change, to a great extent. 
Current I.sub.D flowing through the path including resistor R16 and diodes 
D2-1 to D2-n is related with the current 2Ie flowing through the 
collector-emitter path of the transistor TR15, as given below. 
EQU Ie=m I.sub.D (31) 
Hence, 
##EQU34## 
Accordingly, from the equations (30) and (32), the following equation is 
obtained: 
##EQU35## 
This provides a sufficiently effective temperature compensation effect in 
the circuit in FIG. 9. 
The current I.sub.D flowing through the diodes D2-1 to D2-n is given 
##EQU36## 
where V.sub.FD is a forward voltage drop of each diode D2-1 to 
##EQU37## 
is derived out from equation (34) 
##EQU38## 
Since the temperature characteristics of the resistors R1 and R2, and 
resistor R16 are equal, the following equation is given: 
##EQU39## 
Substituting equations (33) and (36) into equation (34), n can be derived 
from the equation (34) as follows: 
##EQU40## 
From the equation (37), it is clearly understood that, if the operation 
voltage V.sub.C1 and the operation temperature T are given, the number n 
of diodes to be efficiently used can be calculated. Accordingly, when thus 
calculated number n of diodes are used, the variation of the amplification 
factor by temperature change in the circuit under discussion, can be 
minimized. 
FIG. 10 shows an even further embodiment of the invention. In this 
embodiment, the ratio of the current flowing through a series circuit 
including a resistor R16 and a series of diodes D2-1 to D2-n to the 
current flowing through the current path of a transistor TR15, is 
determined by a resistor R17 connected between the cathode of the diode 
D2-1 and ground and another resistor R18 between the emitter of the 
transistor TR15 and ground. Resistors having the same temperature 
coefficient are used for the resistors R17 and R18 and the resistances 
thereof are so selected as to be larger than the forward voltage drop 
across the diode D2-1 and the base-emitter voltage of the transistor TR15. 
The temperature-compensated amplifier circuit shown in FIG. 10 can attain 
the temperature compensating effect similar to that of FIG. 9 circuit. 
FIG. 11 shows another embodiment of the temperature-compensated amplifier 
circuit according to the invention. In the circuit, the amplifier section 
1 includes a transistor TR16 which is connected at the collector to the 
power source terminal V.sub.C2 via a load resistor R19, at the emitter to 
ground and at the base to the anode of the diode D2-1 via a resistor R20. 
In this circuit, too, the temperature coefficients of resistors R16, R19 
and R20 are selected to be equal. The temperature compensating effect 
resulting from this example is similar to that of the FIG. 9 example. 
FIG. 12 shows a modification of the temperature-compensated amplifier 
circuit shown in FIG. 9. The FIG. 12 circuit is substantially equal to the 
FIG. 9 one, except that the resistor R16 is eliminated, a resistor R21 is 
connected between the cathode of the diode D2-1 and ground, and a 
multi-emitter type transistor TR17 is used which is connected at the base 
to the cathode of the diode D2-n, at the emitter to the power source 
terminal V.sub.C1 and at the collector to ground by way of a diode D3. The 
base of the transistor TR15 is connected to the anode of the diode D3. 
While the invention has been described relating to some examples, it is not 
limited to them alone. For example, in the embodiment using a differential 
amplifier for the amplifier section 1 such as a FIG. 1 circuit, the 
resistor R2 and the transistor TR2 may be omitted and the amplifier 
section may be constructed by a single transistor. 
In the embodiment shown in FIG. 1, for example, the transistor TR6 is 
formed as a multi-emitter transistor to conduct a current having a 
predetermined rate with respect to a current flowing through the 
transistor TR5. However, it is possible to form the transistor TR6 by an 
ordinary transistor whose emitter area is predetermined times larger than 
that of the transistor TR5. 
Further, in the embodiment shown in FIG. 2, the transistors TR9 and TR10 
are used, but the transistors TR9 and TR10 can be omitted and the 
collector and base of each of the transistors TR4 and TR5 can be directly 
connected as shown in FIG. 13.