CN1661910A - Gain Control Circuit and Associated Gain Amplifier - Google Patents

Abstract

A gain amplifier comprises a gain control circuit for generating a gain control voltage according to a control voltage, and a variable gain amplification unit connected to the gain control circuit and an input voltage for adjusting an output signal output to a load according to the gain control voltage. The gain control circuit comprises a level adjusting unit with a fixed current source and generating a first voltage according to a control voltage; at least one first temperature compensation unit having a first temperature control (PTAT) current source for generating a second voltage according to a current operating temperature; and a voltage conversion unit for generating the gain control voltage according to the first and second voltages.

Description

Gain Control Circuit and Associated Gain Amplifier

technical field

The present invention relates to a control circuit, in particular to a gain control circuit and a related gain controller.

Background technique

As shown in FIG. 1, it is a conventional variable gain amplifier (variable gainamplifier) 50, wherein the gain control voltage V _CTRL is used to control the current ratio of the differential pair (differential pair) formed by transistors T ₉ and T ₁₀ , and then adjust the magnitude of the current I _L flowing through the load LD. In addition, the current I _L can be obtained by the following equation 1, wherein gm is the gain of the variable gain amplifier 50, V _RF is an input voltage, and V _T is a parameter.

I _rf =gm×V _RF

$I_L=I_{\mathrm{rf}}(1+\tanh \frac{V_{\mathrm{CTRL}}}{V_T})$ formula one

2 and 3 show the relationship between a linear gain control voltage V _CTRL and the gain in the amplifier 50 . As shown in FIG. 2, in the range of 0dB-20dB, the relationship curve RC between the gain control voltage V _CTRL and the gain is not linear. In order to obtain this relationship curve RC, a gain control circuit is needed to generate a corresponding gain control voltage V _CTRL according to an external control voltage, and the relationship between the external control voltage and the gain of the amplifier 50 is a logarithmic linear relationship (log- linear relationship).

Also, as shown in Equation 1, the current I _L is related to the parameter V _T , while $V_T=\frac{\mathrm{kT}}{q},$ Where k is Boltzmann's constant, T is the absolute temperature, and q is the charge quantity. Therefore, when the temperature changes, the current switching characteristics will change.

Contents of the invention

In view of this, the primary purpose of the present invention is to cause the external control voltage and gain of the variable gain amplifier to exhibit a log-linear relationship.

Another object of the present invention is to correct the temperature-affected change of the gain control of the variable gain amplifier.

To achieve the above object, the present invention provides a gain control circuit, including a level adjustment unit, with a fixed current source, generating a first voltage according to a control voltage; at least one first temperature compensation unit, with a first A temperature control (Proportional To Absolute Temperature; PTAT) current source is used to generate a second voltage according to the current working temperature; and a voltage conversion unit is used to generate a gain control voltage from the first and second voltages.

According to the stated purpose, the present invention further provides a gain amplifier, including a gain control circuit as described above, used to generate a gain control voltage according to a control voltage, and a variable gain amplification unit connected to the gain control circuit and An input voltage is used to adjust the output signal output to the load according to the gain control voltage.

In order to make the above and other purposes, features, and advantages of the present invention more comprehensible, a preferred embodiment is specifically cited below, together with the accompanying drawings, and is described in detail as follows:

Description of drawings

Figure 1 shows a traditional variable gain amplifier:

Figure 2 and Figure 3 show the relationship between the linear gain control voltage and the gain in the amplifier of Figure 1.

FIG. 4 is a schematic diagram of a variable gain amplifier of the present invention.

FIG. 5 shows the relationship curve between the control voltage and the gain control voltage, and the relationship curve between the control voltage and the gain in the present invention.

Fig. 6 is the first embodiment of the gain control circuit of the present invention

FIG. 7 is a second embodiment of the gain control circuit of the present invention.

FIG. 8 is a third embodiment of the gain control circuit of the present invention.

Symbol Description

50: variable gain amplifier; V _CTRL : gain control voltage;

R ₀ : resistance; LD: load;

T ₉ -T ₁₁ : transistors; V _RF : input voltage;

I _L , I _ac : current.

100, 100a, 100b, 100c: gain control circuits;

200: variable gain amplifier unit; 300: variable gain amplifier;

10: Level adjustment unit; 12: Voltage divider circuit;

20: temperature compensation unit; 30: voltage conversion unit;

V _AGC : control voltage; V _CTRL : gain control voltage;

V _RF : input voltage; LD: load;

T ₁ -T ₁₁ : transistors; I _tc : fixed current source;

I _e1 , I _e7 : current source; V ₀ : divided voltage;

R _e1 , R _e2 : resistive elements; V _dd : power supply voltage;

V ₁ : first voltage; V ₂ : second voltage;

V ₃ : the third voltage; V ₄ : the fourth voltage;

N ₁ -N ₆ : nodes; Gm1-Gm3: transconductors;

R ₀ -R ₇ , R _tc , R _ptat : resistance;

I _L , I _re1 , I _re2 , I ₁ -I ₆ : current;

I _ptat , I _ptat1 , I _ptat2 , I _ptat3 : Temperature-controlled current sources

Detailed ways

FIG. 4 is a schematic diagram of a variable gain amplifier of the present invention. As shown in FIG. 4 , the variable gain amplifier 300 of the present invention includes a gain control circuit 100 and a variable gain amplifying unit 200 . The gain control circuit 100 generates a gain control voltage V _CTRL according to a control voltage V _AGC . The variable gain amplifying unit 200 is connected to the gain control circuit 100 and an input voltage V _RF , and adjusts the output signal output to the load, such as the current IL flowing through the load _LD , according to the gain control voltage V _CTRL . For example, the gain control voltage V _CTRL is used to control the current ratio of the differential pair formed by the transistors T ₉ and T ₁₀ , thereby adjusting the magnitude of the current _IL flowing through the load LD, that is, adjusting the variable amplifying unit A buff size of 200.

5 is used to show the relationship curve RC ₁ between the control voltage V _AGC and the gain control voltage V _CTRL in the variable gain amplifier 300 of the present invention, and the relationship curve between the control voltage V _AGC and the gain of the amplifying unit 200 (gain) _RC2 . In the present invention, there is a log-linear relationship between the control voltage V _AGC input to the gain control circuit 100 and the gain of the gain amplification unit 200, so that the gain control voltage V _CTRL and the gain amplification The gain relationship of the unit 200 is shown by the curve RC in FIG. 2 .

In addition, in order to keep the gain control characteristic unchanged, when the temperature changes, the gain control voltage V _CTRL should also be adjusted with the temperature. Therefore, two different current sources are used in the present invention, one is a fixed current source, which does not change with temperature, and the other is a temperature controlled (PTAT) current source, which changes with temperature. Therefore, when the temperature rises, the gain control voltage V _CTRL also increases accordingly to compensate the influence caused by the V _T parameter, so as to maintain the gain control characteristic unchanged.

first embodiment

FIG. 6 is a first embodiment of the gain control circuit 100 of the present invention. As shown in FIG. 6, the gain control circuit 100a includes a level adjustment unit 10, which has a fixed current source I _tc , generates a first voltage V ₁ according to the control voltage V _AGC ; a temperature compensation unit 20, which has a temperature control The current source I _ptat is used to generate a second voltage V ₂ according to the current operating temperature; and a voltage converting unit 30 is used to generate the gain control voltage V _CTRL according to the first and second voltages V ₁ and V ₂ .

The level adjustment unit 10 includes a voltage dividing circuit 12 , a transistor T ₁ and a constant current source I _tc . The voltage divider circuit 12 is composed of resistors R ₁ and R ₂ for generating a divided voltage V ₀ according to the control voltage V _AGC . The transistor T ₁ has a control terminal connected to the divided voltage V ₀ , a first terminal connected to the ground voltage (GND), and a second terminal connected to the first node N ₁ through the resistor R _tc . The fixed current source I _tc is connected between the power supply V _dd and the first node N ₁ , wherein the current of the fixed current source I _tc does not change with temperature. The first voltage V ₁ obtained by dividing the control voltage V _AGC will control the conduction of the transistor T ₁ , adjust the current flowing through the resistor R _tc , and then adjust the potential on the first node N ₁ , that is, the first voltage V ₁ .

The temperature compensation unit 20 includes a transistor T ₂ and a temperature control current source I _ptat . The transistor T ₂ has a first terminal connected to the second node N ₂ via the resistor R _ptat , a control terminal and a second terminal connected to the ground voltage GND. The temperature-controlled current source I _ptat is connected between the power supply voltage V _dd and the second node N ₂ , wherein the current of the temperature-controlled current source I _ptat changes with temperature. When the temperature changes, the current generated by the temperature-controlled current source will change to adjust the current flowing through the resistor R _ptat , thereby adjusting the potential on the second node N ₂ , that is, the second voltage V ₂ .

The voltage conversion unit 30 includes a transconductor (transconductor) Gm ₁ , and two resistive elements R _e1 and R _e2 . The transconductor Gm ₁ is used to convert the first voltage V ₁ from the level adjustment unit 10 and the temperature compensation unit The second voltage V ₂ of 20 is converted into a first and a second current I _re1 , I _re2 . The resistive elements R _e1 and _Re2 will generate a voltage drop according to the first and second currents I _re1 and I _re2 . In this embodiment, the resistive elements R _e1 and R _e2 are respectively a resistor, but this is not intended to limit the present invention . The voltage difference between the node N ₃ and the node N ₄ is output to the variable gain amplifying unit 200 as the gain control voltage V _CTRL . The transconductor Gm1 includes a differential pair formed by transistors T ₃ and T ₄ , a resistor R ₃ and two current sources I _e1 and I _e2 . The control terminals of transistors T ₃ and T ₄ are respectively connected to the first and second voltages V ₁ and V ₂ , and the current ratio of the differential pair will be changed according to the first and second voltages V ₁ and V ₂ to adjust the flow through The currents I _re1 and I _re2 of the resistive elements R _e1 and R _e2 are used to adjust the gain control voltage V _CTRL .

Therefore, when the temperature rises, the temperature control current source I _pata will change the magnitude of the second voltage V ₂ to increase the gain control voltage V _CTRL to compensate the influence caused by the VT parameter, thereby maintaining the gain control characteristic unchanged.

second embodiment

FIG. 7 is a second embodiment of the gain control circuit 100 of the present invention. As shown in FIG. 7, the gain control circuit 100b includes a level adjustment unit 10, which has a fixed current source I _tc , generates a first voltage V ₁ according to the control voltage V _AGC ; a temperature compensation unit 20, which has a temperature control The current source I _ptat is used to generate a second voltage V ₂ according to the current operating temperature; and a voltage converting unit 30 is used to generate the gain control voltage V _CTRL according to the first and second voltages V ₁ and V ₂ . In this embodiment, the level adjustment unit 10 and the temperature compensation unit 20 are the same as those in the first embodiment, and will not be repeated here.

In this embodiment, the voltage converting unit 30 includes three transconductors Gm ₁ , Gm ₂ and Gm ₃ , and two resistive elements R _e1 and R _e2 , wherein the three transconductors Gm ₁ , Gm ₂ and Gm ₃ have different threshold voltage. The transconductors Gm ₁ -Gm ₃ are used to convert the first voltage V ₁ from the level adjustment unit 10 and the second voltage V ₂ from the temperature compensation unit 20 into first to sixth currents I ₁ -I ₆ . The resistive elements R _e1 and R _e2 will generate a voltage drop according to the first to second currents I ₁ -I ₆ , and the voltage difference between the node N ₃ and the node N ₄ is used as the gain control voltage V _CTRL and output to the variable gain Amplifying unit 200.

The transconductor Gm ₁ includes a differential pair formed by transistors T ₃ and T ₄ , resistors R ₃ and R ₆ , and two current sources I _e1 and I _e2 . The control terminals of transistors T ₃ and T ₄ are respectively connected to the first and second voltages V ₁ and V ₂ , and the current ratio of the differential pair will change according to the first and second voltages V ₁ and V ₂ to adjust the flow to the resistance The currents I _{1 and} I ₂ of the permanent elements Re1 and _Re2 . The transconductor Gm ₂ includes a differential pair composed of transistors T ₅ , T ₆ , resistors R ₄ , R ₇ , and two current sources I _e3 , I _e4 . The control terminals of transistors T ₅ and T ₆ are respectively connected to the first and second voltages V ₁ and V ₂ , and the current ratio of the differential pair will be changed according to the first and second voltages V ₁ and V ₂ to adjust the flow to The currents I ₃ , I ₄ of the resistive elements R _e1 , R _e2 . The transconductor Gm ₃ includes a differential pair consisting of transistors T ₇ and T ₈ , resistors R ₅ and R ₈ , and two current sources I _e5 and I _e6 . The control terminals of transistors T ₇ and T ₈ are respectively connected to the first and second voltages V ₁ and V ₂ , and the current ratio of the differential pair will be changed according to the first and second voltages V ₁ and V ₂ to adjust the flow to Currents I ₅ , I ₆ of the resistive elements R _e1 , R _e2 .

In this embodiment, due to the difference of the resistors R ₆ and R ₇ , the transconductors Gm ₁ , Gm ₂ and Gm ₃ respectively have a first, a second and a third threshold voltage. For example, when the voltage difference between the first and second voltages V ₁ and V ₂ exceeds a first predetermined level, only the transconductor Gm ₁ will generate the first voltage according to the first and second voltages V ₁ and V ₂ . , the second current I ₁ , I ₂ , and the transconductors Gm ₂ , Gm ₃ do not work, the current I _re1 will be equal to the first current I ₁ , and the current I _re2 will be equal to the second current I ₂ .

If the voltage difference between the first and second voltages V ₁ and V ₂ exceeds a second predetermined level, only the transconductors Gm ₁ and Gm ₂ will work, so that according to the first and second voltages V ₁ and V ₂ , The first, second, third, and fourth currents I ₁ , I ₂ , I _{3 ,} and I ₄ are generated, and the transconductor Gm ₃ does not work. At this time, the current I _re1 will be equal to the first current I ₁ and the second current. The sum of the three currents I ₃ , and the current I _re2 is equal to the sum of the second current I ₂ and the fourth current I ₄ .

If the voltage difference between the first and second voltages V ₁ , V ₂ exceeds a third predetermined level, the transconductors Gm ₁ , Gm ₂ , and Gm ₃ will all function to operate according to the first and second voltages V ₁ , V ₂ generates the first, second, third, fourth, fifth and sixth currents I ₁ , I ₂ , I ₃ , I ₄ , I ₅ and I ₆ , and the current I _re1 will be equal to the first current The sum of I ₁ , the third current I ₃ and the fifth current I ₅ , and the current I _re2 is equal to the sum of the second current I ₂ , the fourth current I ₄ and the sixth current I ₆ .

As shown in Figure 3, when changing in the low gain range, such as 0-5dB, the corresponding gain control voltage V _CTRL needs a larger change slope, and when changing in the high gain range, such as 10-20dB, the corresponding gain The control voltage V _CTRL needs a smaller change slope. Therefore, the present invention uses a plurality of transconductors with different threshold voltages to gradually start up when the gain is changed, so that the slope between the control voltage V _AGC and the corresponding gain control voltage V _CTRL becomes steeper to maintain the control voltage V AGC and the corresponding gain control voltage V _CTRL . Log-linear relationship between gains.

In addition, when the temperature rises, the temperature control current source I _pata will change the magnitude of the second voltage V ₂ to increase the gain control voltage V _CTRL to compensate the influence caused by the VT parameter and maintain the gain control characteristic unchanged.

Therefore, in the variable gain amplifier of the present invention, the relationship between the gain control voltage V _CTRL and the gain (gain) of the gain amplifying unit will obtain the relationship of the curve RC in Fig. 2, and the gain control characteristic will not be affected by the temperature Influence.

third embodiment

FIG. 8 is a third embodiment of the gain control circuit 100 of the present invention. As shown in FIG. 7 , the gain control circuit 100c includes a level adjustment unit 10 , three temperature compensation units 20 - 1 - 20 - 3 and a voltage conversion unit 30 .

The level adjustment unit 10 has a fixed current source I _tc and generates a first voltage V ₁ according to the control voltage V _AGC . The temperature compensation units 20-1-20-3 respectively have a temperature-controlled current source I _ptat1 -I _ptat3 for generating the second, third, and fourth voltages V ₂ , V ₃ , and V respectively according to the current operating temperature. ₄ . In this embodiment, each temperature compensation unit 20 - 1 - 20 - 3 is the same as that in the first embodiment, and will not be repeated here. The voltage conversion unit 30 is configured to generate a gain control voltage V _CTRL according to the first, second, third, and fourth voltages V ₁ , V ₂ , V ₃ , and V ₄ .

In this embodiment, the voltage converting unit 30 includes three transconductors Gm ₁ , Gm ₂ and Gm ₃ , and two resistive elements R _e1 and R _e2 , wherein the three transconductors Gm1 , Gm2 and Gm ₃ have different thresholds voltage, where the circuit structure of the transconductors Gm ₁ -Gm ₃ is the same as that in FIG. 7 .

The transconductor Gm ₁ is used to convert the first voltage V ₁ from the level adjustment unit 10 and the second voltage V ₂ from the temperature compensation unit 20 - 1 into a first to a second current I ₁ , I ₂ . The transconductor Gm ₂ is used to convert the first voltage V ₁ from the level adjustment unit 10 and the third voltage V ₃ from the temperature compensation unit 20 - 2 into a third to a fourth current I ₃ , I ₄ . The transconductor Gm ₃ is used to convert the first voltage V ₁ from the level adjustment unit 10 and the fourth voltage V ₄ from the temperature compensation unit 20 - 3 into fifth to sixth currents I ₅ , I ₆ . In other words, the transconductor Gm ₁ adjusts the currents I ₁ , I ₂ flowing to the resistive elements R _e1 , R _e2 according to the first and second voltages V ₁ , V ₂ . The transconductor Gm ₂ adjusts the currents I 3 , I ₄ flowing to the resistive elements _{R e1} , R _e2 according to the first and third voltages V ₁ , V ₃ . The transconductor Gm ₃ adjusts the currents I ₅ , _{I 6} flowing to the resistive elements R _e1 , R _e2 according to the first and fourth voltages V ₁ , V ₄ .

For example, the transconductors Gm ₁ , Gm ₂ , and Gm ₃ are used to generate first, second, third, fourth, fifth, and sixth currents at corresponding threshold voltages according to the first to fourth voltages. I ₁ , I ₂ , I ₃ , I ₄ , I ₅ and I ₆ . The current I _re1 is equal to the sum of the first current I ₁ , the third current I ₃ and the fifth current I ₅ , and the current I _re2 is equal to the sum of the second current I ₂ , the fourth current I ₄ and the sixth current I ₆ . The resistive elements R _e1 and R _e2 generate a voltage drop according to the currents I _re1 and I _re2 , and the voltage difference between the node N ₅ and the node N ₆ is output to the variable gain amplifier unit 200 as the gain control voltage V _CTRL .

As shown in Figure 3, when changing in the low gain range, such as 0-5dB, the corresponding gain control voltage V _CTRL needs a larger change slope, and when changing in the high gain range, such as 10-20dB, the corresponding gain The control voltage V _CTRL needs a smaller change slope. Therefore, the present invention uses a plurality of transconductors with different threshold voltages to gradually start up when the gain is changed, so that the slope between the control voltage V _AGC and the corresponding gain control voltage V _CTRL becomes steeper to maintain the control voltage V _{AGC and the corresponding gain control voltage V CTRL} . Log-linear relationship between gains.

In addition, when the temperature rises, the temperature control current sources I _pata1 , I _pata2 , and I _pata3 will change the magnitudes of the second, third, and fourth voltages V ₂ , V ₃ , and V ₄ respectively to increase the gain control voltage V _CTRL , It is used to compensate the influence caused by the VT parameter, so as to maintain the gain control characteristic unchanged.

Therefore, in the variable gain amplifier of the present invention, the relationship between the gain control voltage V _CTRL and the gain (gain) of the gain amplifying unit will obtain the relationship of the curve RC in Fig. 2, and the gain control characteristic will not be affected by the temperature Influence.

In summary, although the present invention has been disclosed as above with a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can carry out various methods without departing from the spirit and scope of the present invention. Changes and modifications, therefore, the protection scope of the present invention should be determined by the scope defined by the proposed claims.

Claims (16)

1. A gain control circuit comprising: A level adjustment unit, having a fixed current source, generates a first voltage according to a control voltage; At least one first temperature compensation unit has a first temperature-controlled current source for generating a second voltage according to the current operating temperature; and A voltage converting unit is used for generating a gain control voltage according to the first and second voltages. 2. The gain control circuit according to claim 1, wherein said voltage conversion unit comprises: a transconductor for converting the first and second voltages into a first and second current; and A first and second resistive element are used to convert the first and second currents into the gain control voltage. 3. The gain control circuit as claimed in claim 2, wherein the level adjustment unit further comprises: a voltage divider circuit connected to the control voltage to generate a first divided voltage; and A first transistor with a control terminal connected to the first divided voltage, a first terminal connected to a ground voltage, and a second terminal connected to a first node through a first resistor, wherein the fixed current source is connected to between a supply voltage and the first node. 4. The gain control circuit as claimed in claim 3, wherein the temperature compensation unit further comprises: a second transistor having a first terminal connected to a second node via a second resistor, and a second terminal and a control terminal connected to the ground voltage, wherein the first temperature-controlled current source is connected to the between the supply voltage and the second node. 5. The gain control circuit as claimed in claim 4, wherein said transconductor comprises a differential pair having differential input terminals connected to said first and second nodes respectively, wherein said first and second nodes The voltages on the two nodes are used as the first and second voltages. 6. The gain control circuit as claimed in claim 1, wherein said voltage conversion unit comprises: A first transconductor having a first threshold voltage, generating a first and second current when the voltage difference between the first and second voltages is greater than the first threshold voltage; a second transconductor having a second threshold voltage, generating a third current and a fourth current when the voltage difference between the first and second voltages is greater than the second threshold voltage; and A first and a second resistive element are used for generating the gain control voltage according to the current generated by the first and the second transconductor. 7. The gain control circuit as claimed in claim 1, further comprising a second temperature compensation unit having a second temperature-controlled current source for generating a third voltage according to the current operating temperature, wherein the The voltage conversion unit generates the gain control voltage according to the first, second and third voltages. 8. The gain control circuit as claimed in claim 7, wherein said voltage conversion unit comprises: A first transconductor, connected to the first temperature compensation unit, has a first threshold voltage, and generates a first and second threshold voltage when the voltage difference between the first and second voltages is greater than the first threshold voltage Second current; A second transconductor, connected to the second temperature compensation unit, has a second threshold voltage. When the voltage difference between the first and third voltages is greater than the second threshold voltage, a third and a second threshold voltage are generated. Four currents; and A first and second resistive element, connected to the first and second transconductors, for generating the gain control voltage according to the current generated by the first and second transconductors. 9. A gain amplifier comprising: A gain control circuit, used for generating a gain control voltage according to a control voltage, comprising: a level adjustment unit, having a fixed current source, generating a first voltage according to the control voltage; At least one first temperature compensation unit has a first temperature-controlled current source for generating a second voltage according to the current operating temperature; and a voltage converting unit, configured to generate the gain control voltage according to the first and second voltages; as well as A variable gain amplification unit is connected with the gain control circuit and an input voltage, and adjusts the output signal output to the load according to the gain control voltage. 10. The gain amplifier of claim 9, wherein the voltage conversion unit comprises: a transconductor for converting the first and second voltages into a first and second current; and A first and second resistive element are used to convert the first and second currents into the gain control voltage. 11. The gain amplifier as claimed in claim 10, wherein said level adjustment unit further comprises: a voltage divider circuit connected to the control voltage to generate a first divided voltage; and A first transistor with a control terminal connected to the first divided voltage, a second terminal connected to a first node through a first resistor, and a first terminal connected to a ground voltage, wherein the fixed current source is connected to between a supply voltage and the first node. 12. The gain amplifier of claim 11, wherein the temperature compensation unit further comprises: a second transistor having a first terminal connected to a second node via a second resistor, and a second terminal and a control terminal connected to the ground voltage, wherein the first temperature-controlled current source is connected to the between the supply voltage and the second node. 13. The gain amplifier as claimed in claim 12, wherein said transconductor comprises a differential pair having differential input terminals connected to said first and second nodes respectively, wherein said first and second The voltage on the node is used as the first and second voltages. 14. The gain amplifier of claim 9, wherein the voltage conversion unit comprises: A first transconductor having a first threshold voltage, generating a first and second current when the voltage difference between the first and second voltages is greater than the first threshold voltage; a second transconductor having a second threshold voltage, generating a third current and a fourth current when the voltage difference between the first and second voltages is greater than the second threshold voltage; and A first and second resistive element are used for generating the gain control voltage according to the first, second, third and fourth currents generated by the first and second transconductors. 15. The gain amplifier as claimed in claim 9, further comprising a second temperature compensation unit having a second temperature-controlled current source for generating a third voltage according to the current operating temperature, wherein the voltage The converting unit generates the gain control voltage according to the first, second and third voltages. 16. The gain amplifier of claim 15, wherein the voltage conversion unit comprises: A first transconductor, connected to the first temperature compensation unit, has a first threshold voltage, and generates a first and second threshold voltage when the voltage difference between the first and second voltages is greater than the first threshold voltage Second current; A second transconductor, connected to the second temperature compensation unit, has a second threshold voltage. When the voltage difference between the first and third voltages is greater than the second threshold voltage, a third and a second threshold voltage are generated. Four currents; and A first and second resistive element, connected to the first and second transconductors, used for generating the first, second, third and first transconductors according to the first and second transconductors four currents, generating the gain control voltage.

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