JP3022384B2 - Temperature compensation circuit for gain control amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature control circuit of a gain control amplifier for compensating a temperature characteristic of the gain control amplifier.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram showing a configuration of a temperature compensation circuit of a conventional gain control amplifier.

In FIG. 3, a gain control amplifier 1 includes a first differential circuit 17 composed of transistors Q13 and Q14, a second differential circuit 18 composed of transistors Q15 and Q16, A transistor Q11 having a collector connected to each emitter of Q14 and a base connected to the input terminal 13;
A constant current source 11 connected to the emitter of the transistor Q1 and outputs a constant current; a transistor Q12 having a collector connected to each emitter of the transistors Q15 and Q16 and a base connected to the input terminal 14; The second constant current source 12 is connected to the emitter and outputs a constant current.

The base of the transistor Q13 and the base of the transistor Q16 are commonly connected at a connection point A, and the base of the transistor Q14 and the base of the transistor Q15 are commonly connected at a connection point B. The collector of the transistor Q13 is connected to the resistor R12 and the output terminal 15, and the collector of the transistor Q16 is connected to the resistor R13 and the output terminal 16. Further, the transistor Q
The emitter of the transistor 11 and the emitter of the transistor Q12 are connected via a resistor R11.

[0005] With such a circuit configuration, the gain control amplifier 1 amplifies a voltage input between the input terminals 13 and 14 with a predetermined gain Av, and outputs the amplified voltage between the output terminals 15 and 16. Note that the gain Av is determined at the connection points A and B
Is determined by the voltage difference between the gain control voltages respectively applied to the control signals.

On the other hand, the temperature compensation circuit 4 includes a first diode array 41 and a second diode array 42 each including a plurality of (n) diodes connected in series, and a current flowing through the first diode array 41. A variable current source 43 for determining I _GC , a constant current source 44 for supplying a constant current I ₀ to the second diode array 42, and a gain control amplifier for outputting a voltage (output voltage) on the cathode side of the first diode array 41. A first buffer 45 for applying to the first connection point A
And a second buffer 46 for applying a voltage (output voltage) on the cathode side of the second diode array 42 to a connection point B of the gain control amplifier 1.

The gain control amplifier 1 and the temperature compensation circuit 4 are each supplied with a DC voltage V _C from a voltage source 47.

Next, the operation of the gain control amplifier 1 and the temperature compensation circuit 4 shown in FIG. 3 will be described.

The gain Av of the gain control amplifier 1 can be expressed by the following equation (1).

[0010]

(Equation 1)Here, Avmax is the maximum gain of the gain control amplifier 1,
_GCIs the voltage V at the connection point A _AAnd voltage V at connection point B_BVoltage difference
(V_A-V_B), V_TIs v_T= KT / q (k: Boltzma
Constant, T: absolute temperature, q: electron charge)
You. Note that A_GCIs the voltage difference V in equation (1)_GCIndicates a term containing
A_GCHas v_TIs included.

The temperature compensating circuit 4 uses the current I _GC to
Of a voltage generated on the cathode side of the diode array 41 and output to the connection point A of the gain control amplifier 1 via the first buffer 45, the voltage generated by the current I ₀ to the cathode side of the second diode array 42 Second buffer 46
To the connection point B of the gain control amplifier 1.

[0012] At this time, the voltage difference between the connection point A and the connection point of the gain control amplifier _{1 B V GC (= V A} -V B) can be represented by the following formula (2).

[0013]

(Equation 2) Here, by substituting equation (2) into equation (1),

[0014]

(Equation 3) Get.

As can be seen from the equation (3), the voltage V is applied to the connection points A and B by the temperature compensation circuit 4.
_By applying _A and V _B , the v _T component is removed from the characteristic of the gain Av of the gain control amplifier 1, and the temperature fluctuation is eliminated.

The ratio of the current I ₀ of the constant current source 44 to the current I _GC of the variable current source 43 (I _GC / I ₀ ) is represented by A _GC.
Change rate | ΔA _GC / Δ (I _GC / I ₀ ) | is the voltage difference V _GC
The magnitude (= A ′ _GC ) of the gain control sensitivity with respect to is shown. The magnitude A ′ _GC of the gain control sensitivity is as follows from Expression (3).

[0017]

(Equation 4) As an example, if I ₀ is substituted for I _GC in equation (4), (I _GC
= I ₀ ),

[0018]

(Equation 5) Get. That is, the current ratio (I _GC / I _O ) between the constant current source 44 and the variable current source 43 (here, I ₀ is fixed and I _GC
The made variable, and the control current I _GC) is converted into a voltage by a diode connected in series, by which is input to the gain control amplifier 1, a temperature from the magnitude A _'GC gain control sensitivity Variations can be eliminated (see equations (3) and (4)).

As can be seen from equation (5), the decrease in gain control sensitivity (due to logarithmic reduction) due to the use of a plurality of diodes connected in series is caused by the number n of diodes.
Can be improved by increasing.

[0020]

However, in the temperature compensation circuit of the conventional gain control amplifier as described above, FIG.
As can be seen from the circuit connection shown in (1), the number of diodes connected in series is limited by the voltage value of the voltage source, and as a result, the improvement of gain control sensitivity is limited.

The temperature characteristics of the n diodes appear as they are at the connection points A and B of the gain control amplifier, and the value is -2.0 to -1.5 per diode.
mV / ° C. For example, when four diodes are stacked, -8.0 to-
Since a voltage having a temperature characteristic of 6.0 mV / ° C. is output, there is a problem that it is difficult to set a gain control voltage (bias setting) of the gain control amplifier.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems of the prior art, and has been made in order to solve the problems that occur in the temperature compensation circuit of a gain control amplifier using a diode. It is an object to provide a temperature compensation circuit.

[0023]

To achieve the above object, a temperature compensation circuit of a gain control amplifier according to the present invention comprises a first differential circuit and a second differential circuit having input portions connected in parallel. And amplifying the voltage difference input between the two input terminals with a gain determined by a voltage difference between two gain control voltages commonly input to the first differential circuit and the second differential circuit. A first transistor and a second transistor constituting a differential circuit in a temperature control circuit of a gain control amplifier for compensating a temperature characteristic of a gain control amplifier output between two output terminals; And a first current source for setting a current flowing through the second transistor, and an emitter of the first transistor and an emitter of the second transistor, respectively. A second current source for setting a total current flowing through the first transistor and the second transistor; a second current source connected to a base of the first transistor via a first resistor; A reference voltage source for outputting a predetermined constant voltage serving as one of the gain control voltages, a second resistor connected between the base of the second transistor and the reference voltage source, and the second transistor An emitter follower that receives the collector voltage of the second transistor as an input and outputs the other gain control voltage of the gain control amplifier, an output of the emitter follower, and a base of the second transistor; A third resistor that feeds back the output voltage of the emitter follower to the base of the second transistor at a resistance ratio to the resistor;
It is characterized by having.

At this time, the first current source is a variable current source that can change an output current, and the second current source is
A constant current source that outputs a constant current may be provided, and the first current source and the second current source may be variable current sources each capable of changing an output current.

In the temperature compensation circuit of the gain control amplifier configured as described above, since the first transistor and the second transistor form a differential circuit, the temperature compensation circuit of the first transistor and the second transistor The voltage between the bases is determined by the current ratio between the first current source and the second current source. Here, the output voltage of the emitter follower is fed back to the base of the second transistor based on the resistance ratio of the second resistor and the third resistor, so that the first transistor and the second transistor are output from the emitter follower. A voltage is output which is obtained by multiplying the voltage between the bases of the transistors by the resistance ratio of the second resistor and the third resistor. Therefore, the magnitude of the gain control sensitivity is determined by the current ratio between the first current source and the second current source and the resistance ratio between the second resistor and the third resistor.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

In the following, only the configuration of the temperature compensation circuit is different from the conventional one. The circuit configuration of the gain control amplifier is the same as that of the related art, and a detailed description thereof will be omitted.

(First Embodiment) FIG. 1 is a circuit diagram showing a configuration of a first embodiment of a temperature compensation circuit of a gain control amplifier according to the present invention.

In FIG. 1, a temperature compensating circuit 2 includes a differential circuit 26 including transistors Q21 and Q22,
A variable current source 21 connected to the collector of the transistor Q22 and determining a current I _GC flowing through the transistor Q22;
The emitter of the transistor Q21 and the transistor Q
22 are connected to the respective emitters of the transistor Q2.
1, a control constant current source 22 to the total current flowing through Q22 is fixed to a constant current I _0, it is connected via a resistor R21 to the base of the transistor Q21, a reference voltage source for outputting a predetermined reference voltage V _R 25 and a resistor R2 connected between the base of transistor Q22 and reference voltage source 25.
2 and an emitter follower, and the transistor Q22
Transistor Q2 that outputs the output voltage of differential circuit 26 output from the collector of
3 is connected between the collector of the transistor Q23 and the base of the transistor Q22.
And a constant current source 23 for feeding a constant current to the transistor Q23.
And is constituted by.

The resistor R21 is connected to the transistor Q21.
And is set to a resistance value equal to the resistance value of the resistors R22 and R23 connected in parallel. Further, the DC voltage V _C is supplied from the voltage source 24 to the gain control amplifier 1 and the temperature compensation circuit 2, respectively.

In such a configuration, the operation of the temperature compensation circuit 2 of the present embodiment will be described next.

The gain Av of the gain control amplifier 1 can be expressed by equation (1) as in the prior art.

The transistor Q2 of the temperature compensation circuit 2
1, the collector current ratio of Q22 is I _GC/ (I₀-I_GC)
Therefore, the voltage between the bases of the transistors Q21 and Q22 is
Pressure (V_{twenty one}-V_{twenty two}) Is as follows.

[0034]

(Equation 6) Base voltage (V ₂₁ -V _22), the resistors R22, R23
(The resistances are r2 and r3, respectively) and are output to the connection point B via the transistor Q23.

Since the reference voltage V _R is applied to the connection point A from the reference voltage source 25, the voltage difference V _GC (= V _A −V _B ) between the connection points A and _B is as follows. Become.

[0036]

(Equation 7) Assuming α = (r2 + r3) / r2, equation (7) is added to equation (1).
Substituting

[0037]

(Equation 8) Get. Therefore, as can be seen from equation (8), the v _T component having the temperature characteristic is removed from the gain Av characteristic of the gain control amplifier 1 as in the conventional case, and the gain of the gain control amplifier 1 does not fluctuate with temperature.

Here, the magnitude of gain control sensitivity A '_GCTo
A '_GC= | ΔA_GC/ Δ (I_GC/ (I ₀-I_GC)) |
Is obtained as follows.

[0039]

(Equation 9) As an example, the I _GC of formula (9), and substituting I _GC = I _0/2,

[0040]

(Equation 10)Get. That is, the variable current source 21 and the constant current source 22
Current ratio I_GC/ (I₀-I _GC) (Here I₀And fix
I_GCIs variable, and I_GCIs the control current).
It is converted to the voltage between the bases of the transistors Q21 and Q22.
Is input to the gain control amplifier 1 after being multiplied by the resistance ratio.
Thus, the magnitude A 'of the gain control sensitivity is the same as in the prior art._GCFrom temperature
The characteristic is removed (see equations (8) and (9)).

Further, since the temperature compensation circuit 2 of the present embodiment does not use a plurality of diodes connected in series as in the prior art, the improvement in gain control sensitivity is limited by the voltage value of the voltage source. Instead, the magnitude A ′ _GC of the gain control sensitivity can be set freely (to a large value) by the resistance ratio of the resistors R22 and R23.

Next, consider the temperature fluctuations of the voltage V _{A at} the connection point _A and the voltage V _{B at} the connection point B.

As can be seen from the circuit connection shown in FIG.
Voltage V _A at the connection point A is the voltage V _R of the reference voltage source 25. The voltage V _{B at} the connection point B is expressed by the following equation.

[0044]

[Equation 11] Voltage V _R of reference voltage source 25, resistance ratio α = (r2 + r3)
Assuming that / r2 and the current ratio I _GC / (I ₀ −I _GC ) have no temperature dependence, the temperature characteristic of the voltage V _{B at} the connection point B is determined only by v _T. Therefore, its value is Δ
v _T /ΔT=k/q≒0.09 mV / ° C., which is a very small value as compared with the conventional temperature compensation circuit using a plurality of diodes connected in series. That is, in the temperature compensation circuit of the gain control amplifier of the present embodiment, the gain control voltage output from the temperature compensation circuit 2 does not have such a large temperature dependence as in the related art, so that the bias setting of the gain control amplifier becomes easy. .

(Second Embodiment) FIG. 2 is a circuit diagram showing a configuration of a temperature compensation circuit of a gain control amplifier according to a second embodiment of the present invention.

The temperature compensation circuit of the gain control amplifier of the present embodiment differs from the first embodiment in that the control constant current source connected to the emitter side of the transistor constituting the differential circuit is changed to a variable current source. Is different.

In FIG. 2, the temperature compensation circuit 3 includes a differential circuit 36 including transistors Q31 and Q32,
A first variable current source 31 connected to the collector of the transistor Q32 and determining a current I _GC1 flowing through the transistor Q32; and a total current flowing through the transistors Q31 and Q32 respectively connected to the emitter of the transistor Q31 and the emitter of the transistor Q32. The second to determine I _GC2
Connected to the variable current source 32 is connected through a resistor R31 to the base of transistor Q31, a reference voltage source 35 for outputting a predetermined reference voltage V _R, the base of the transistor Q32, and between the reference voltage source 35 Resistor R3
2 and an emitter follower, and the transistor Q32
Transistor Q3 that outputs the output voltage of differential circuit 36 output from the collector of
3 is connected between the collector of the transistor Q33 and the base of the transistor Q32.
And a constant current source 33 for flowing a constant current through the transistor Q33.
And is constituted by.

The resistor R31 is connected to the transistor Q31
And is set to a resistance value equal to the resistance value of the resistors R32 and R33 connected in parallel. Further, the DC voltage V _C is supplied from the voltage source 34 to the gain control amplifier 1 and the temperature compensation circuit 3, respectively.

In such a configuration, the resistance value of the resistor R32 is r2, the resistance value of the resistor R33 is r3, and α
= (R2 + r3) / r2, and the gain Av of the gain control amplifier 1 and the magnitude A ′ _GC of the gain control sensitivity are obtained as in the first embodiment, as follows.

[0050]

(Equation 12)

[0051]

(Equation 13) For example, the current I _GC1 of the first variable current source 31 is fixed,
If the current I _GC2 of the second variable current source 32 is used as the control current, a control current versus gain characteristic opposite to that of the first embodiment can be obtained.

As can be seen from equations (12) and (13), in the case of this embodiment as well, the temperature characteristic is obtained from the characteristics of the gain Av and the gain control sensitivity of the gain control amplifier 1 as in the first embodiment. The v _T component is removed, and the gain control amplifier has no temperature fluctuation.

[0053]

Since the present invention is configured as described above, the following effects can be obtained.

Since the gain control sensitivity of the gain control amplifier is determined by the resistance ratio between the second resistor and the third resistor of the temperature compensation circuit, the voltage is different from that of the conventional temperature compensation circuit using a diode. The source voltage does not limit the gain control sensitivity improvement.

Further, since the gain control voltage does not have a large temperature dependency unlike the conventional temperature compensation circuit using a diode, the bias setting of the circuit (setting of the gain control voltage) becomes easy.

[Brief description of the drawings]

FIG. 1 shows a first example of a temperature compensation circuit of a gain control amplifier according to the present invention.
FIG. 2 is a circuit diagram illustrating a configuration of an example.

FIG. 2 shows a second embodiment of the temperature compensation circuit of the gain control amplifier of the present invention.
FIG. 2 is a circuit diagram illustrating a configuration of an example.

FIG. 3 is a circuit diagram showing a configuration of a temperature compensation circuit of a conventional gain control amplifier.

[Explanation of symbols]

Reference Signs List 1 gain control amplifier 2, 3 temperature compensation circuit 11 first constant current source 12 second constant current source 13, 14 input terminal 15, 16 output terminal 17 first differential circuit 18 second differential circuit 21 variable Current source 22 Control constant current source 23, 33 Constant current source 24, 34 Voltage source 25, 35 Reference voltage source 26, 36 Differential circuit 31 First variable current source 32 Second variable current source Q11 to Q16, Q21 To Q23, Q31 to Q33
Transistors R11 to R13, R21 to R23, R31 to R33
Resistor

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H03F 1/30 H03F 3/45

Claims (3)

(57) [Claims] An input portion includes a first differential circuit and a second differential circuit connected in parallel, and is commonly input to the first differential circuit and the second differential circuit. A gain control amplifier for amplifying a voltage difference input between two input terminals with a gain determined by a voltage difference between two gain control voltages and compensating for a temperature characteristic of the gain control amplifier that outputs between two output terminals. In the temperature compensation circuit, a first transistor and a second transistor that constitute a differential circuit, and a first current source that is connected to a collector of the second transistor and sets a current that flows through the second transistor Respectively connected to the emitter of the first transistor and the emitter of the second transistor;
And a second current source for setting a total current flowing through the second transistor; a first resistor connected to a base of the first transistor via a first resistor; A reference voltage source that outputs a predetermined constant voltage serving as a control voltage; a second resistor connected between the base of the second transistor and the reference voltage source; a collector voltage of the second transistor And an emitter follower that outputs the other gain control voltage of the gain control amplifier, and an output of the emitter follower, which is connected between a base of the second transistor and the second resistor. A third resistor for feeding back an output voltage of the emitter follower to a base of the second transistor in a resistance ratio. Temperature compensation circuit. 2. The temperature compensation circuit for a gain control amplifier according to claim 1, wherein said first current source is a variable current source capable of changing an output current, and said second current source is a constant current source. A temperature compensation circuit for a gain control amplifier, wherein the temperature compensation circuit is a constant current source that outputs a current. 3. The temperature compensation circuit for a gain control amplifier according to claim 1, wherein said first current source and said second current source are variable current sources each capable of changing an output current. A temperature compensation circuit for a gain control amplifier.