A temperature-insensitive bias circuit

Abstract

The present invention belongs to the technical field of radio frequency circuits, and relates to a bias circuit that is insensitive to temperature, comprising first to fourth transistors, first to seventh resistors, and two DC power supplies. The first, second, and third transistors form a feedback loop for adaptive biasing of an HBT transistor. When the first transistor needs to amplify a signal, the second and third transistors form a feedback loop, and automatically increase the bias current in the base region of the first transistor, thereby improving the linearity of the first transistor. In order to make the bias circuit insensitive to ambient temperature, the fourth transistor acts as a thermal feedback circuit to keep the current of the entire circuit from changing with temperature. In order to prevent the fourth transistor from causing other effects on the circuit, a capacitor can be added to the base region of the fourth transistor. This prevents it from causing other effects on the circuit, and further reduces the influence of the thermal feedback loop on the linearization feedback loop.

Description

Technical Field

[0001] The present invention belongs to the technical field of radio frequency circuits, and in particular, relates to a bias circuit that is insensitive to temperature changes. Background Art

[0002] The power amplifier in the communications field is one of the key units in the wireless communication link. Its function is to amplify the electrical signal of the modulated information to a certain power level, and to stimulate the back-end antenna to generate the corresponding electromagnetic wave signal to realize wireless signal transmission.

[0003] In the design of power amplifier circuits, in order for the amplifier composed of semiconductor devices such as transistors and MOS tubes to amplify the signal voltage without distortion, it is necessary to ensure that these devices are in a specific working state, that is, their operating points should be set, and the setting of these operating points can be achieved through external circuits, which are called bias circuits.

[0004] In high-frequency monolithic microwave integrated circuits for mobile phones, heterojunction bipolar transistor technology is mostly used for manufacturing because of its advantages such as single power supply, easy matching, good linearity, and high power density. For the current mainstream GaAs HBT process, since the thermal conductivity of gallium arsenide is very low and it will continue to decrease with the increase of temperature, when the power amplifier works in a large signal state, it will generate considerable power dissipation and accumulate more heat, which is the self-heating effect. Since the base-emitter junction of the transistor can be regarded as equivalent to a PN junction, the increase in temperature will cause the electrons in the emission region to be thermally excited, and the total number of drifting electrons will gradually increase with the increase in temperature. Temperature affects the parameters of the transistor, and the change in the parameters of the transistor causes the static operating point of the transistor to change with the temperature. Therefore, solving the temperature drift of the transistor has always been a key issue in transistor circuit design.

[0005] Traditionally, of course, there are also occasions where a current bias circuit that does not change with temperature is required. Therefore, there are many compensation technologies currently under study, that is, the positive and negative temperature coefficients are compensated through a certain structure to achieve a zero temperature coefficient. At present, the so-called zero temperature coefficient current bias circuits all use two different types of resistors, such as well resistors and high-resistance polycrystalline resistors, and use their opposite temperature coefficients to compensate. However, the temperature characteristics of these two types of resistors are not exactly the same, that is, as the temperature changes, the resistance change characteristics of the two types of resistors are different, so temperature compensation cannot be truly achieved. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a bias circuit that is insensitive to temperature, thereby solving the problem of being unable to perform temperature compensation.

[0007] The present invention is achieved in this way.

[0008] A bias circuit that is insensitive to temperature includes a first transistor, a second transistor, a third transistor, and a fourth transistor, a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, and a seventh resistor, and a first DC power supply and a second DC power supply, wherein the positive electrode of the first DC power supply is connected to the collector of the third transistor through the sixth resistor, the emitter of the third transistor is grounded, the base of the third transistor is connected to the base of the first transistor through the second resistor and the first resistor, the emitter of the first transistor is grounded, and the collector of the first transistor is connected to an external circuit; the emitter of the second transistor is connected to the common end between the second resistor and the first resistor, the base of the second transistor is connected to the collector of the third transistor, and the collector of the second transistor is connected to the positive electrode of the second current source; the collector of the fourth transistor is connected to the positive electrode of the second current source through the seventh resistor, the base of the fourth transistor is connected to the collector of the third transistor through the fifth resistor, and the emitter of the fourth transistor is grounded through the fourth resistor and the third resistor, and the first transistor, the second transistor, and the third transistor form an adaptive bias feedback loop. The third, fourth, fifth, and seventh resistors form a thermal feedback circuit with the fourth transistor.

[0009] Further, the first transistor is a power transistor unit, and the third transistor is a thermal sensor transistor.

[0010] Furthermore, based on a bias circuit that is insensitive to temperature as a core, a first capacitor is connected to the base of the fourth transistor, and the other end of the first capacitor is grounded.

[0011] Furthermore, the temperature of the third transistor changes with the temperature of the first transistor, and different thermal coupling strengths are achieved by adjusting the distance between the third transistor and the first transistor.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] 1. The present invention provides a HBT bias circuit including an adaptive bias feedback loop and a thermal feedback circuit, which can simultaneously realize temperature compensation and linearity compensation for the power tube.

[0014] 2. In the present invention, when the first transistor needs to amplify a signal, the second transistor and the third transistor form a feedback loop to automatically increase the bias current in the base region of the first transistor, thereby improving the linearity of the first transistor.

[0015] 3. The third, fourth, fifth and seventh resistors of the present invention form a feedback network with the fourth transistor that can adjust the temperature compensation coefficient. By adjusting the specific resistance values ​​of the third and fourth resistors, temperature compensation coefficients of different strengths can be achieved. When the temperature rises, the junction voltage of the third transistor decreases and the collector current decreases, thereby causing the base current flowing through the fourth transistor to increase, so that the emitter current of the fourth transistor increases. The increased current falls on the third resistor and the fourth resistor, so that the voltage of the third resistor increases, so that the junction voltage of the third transistor rises back, so that the bias current in the first transistor drifts very little with temperature.

[0016] 4. The temperature of the third transistor of the present invention changes with the temperature of the first transistor, so that different thermal coupling strengths can be achieved by adjusting the distance between the third transistor and the first transistor.

[0017] 5. In order to further reduce the influence of the thermal feedback loop on the linearization feedback loop, a capacitor is added to the base region of the fourth transistor to further reduce the influence on the linearization feedback loop.

[0018] Additional aspects and advantages of the invention will become apparent from the following description, or may be learned by practice of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic diagram of a bias circuit that is insensitive to temperature according to the present invention is shown;

[0020] Figure 2 A schematic diagram of an improved model of a bias circuit that is insensitive to temperature according to the present invention is shown;

[0021] Figure 3 A curve diagram showing the current of the first power transistor in the temperature-insensitive bias circuit of the present invention changes with temperature;

[0022] Figure 4 A Pout and Pin curve diagram of a temperature-insensitive bias circuit according to the present invention is shown. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0025] Figure 1 A bias circuit that is not sensitive to temperature is shown, which includes a first transistor, a second transistor, a third transistor and a fourth transistor, a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor and a seventh resistor, and a first DC power supply and a second DC power supply.

[0026] The first transistor is a power transistor unit, whose collector is connected to an external circuit, whose emitter is grounded, and whose base is connected to a first resistor. The collector of the second transistor is connected to a 5V DC power supply, whose emitter is connected to a second resistor, whose base is connected to a sixth resistor, and whose sixth resistor is connected to a 3.3V first DC power supply. The third transistor is a thermal sensor transistor, whose emitter is grounded, whose collector is connected to a sixth resistor, whose base is respectively connected to a fourth resistor, a third resistor, and a second resistor. The temperature of the third transistor changes with the temperature of the first transistor, thereby achieving thermal coupling. The first transistor, the second transistor, and the third transistor form a feedback loop for adaptive biasing of the HBT transistor. The emitter of the fourth transistor is connected to the fourth resistor, then to the third resistor, and finally to the ground, and the collector is connected to the seventh resistor, and the base is connected to the fifth resistor. The right end of the first resistor is connected to the base of the first transistor, and the left end is connected to the second resistor. The left end of the second resistor is connected to the base of the third transistor, and the right end is connected to the first resistor. The lower end of the third resistor is grounded, and the upper end is connected to the fourth resistor. The lower end of the fourth resistor is connected to the third resistor, and the upper end is connected to the emitter of the fourth transistor. The left end of the fifth resistor is connected to the sixth resistor and the collector of the third transistor. The upper end of the sixth resistor is connected to the first 3.3V DC power supply, and the lower end is respectively connected to the base region of the second transistor, the fifth resistor and the collector of the third transistor. The lower end of the seventh resistor is connected to the collector of the fourth transistor, and the upper end is connected to the second 5V DC power supply. The current in the first transistor is determined by the area ratio of the first transistor to the third transistor, the first resistor, the second resistor and the sixth resistor.

[0027] The third resistance value and the fourth resistance value are 10kΩ, the fifth resistance value and the seventh resistance value are 1kΩ, the first DC power supply is 3.3V, and the second DC power supply is 5.0V.

[0028] Figure 2An improved version based on the above structure provided for another embodiment, in order to make the fourth transistor not cause other effects on the circuit, a capacitor can be added to the base region of the fourth transistor. It is made to not cause other effects on the circuit, and further reduce the influence of the thermal feedback loop on the linearization feedback loop. Specifically, the first transistor is a power transistor unit, whose collector is connected to the external circuit, the emitter is grounded, and the base is connected to the first resistor. The collector of the second transistor is connected to a 5V DC power supply, the emitter is connected to the second resistor, the base is connected to the sixth resistor, and the sixth resistor is connected to a 3.3V DC power supply. The third transistor is a thermal sensor transistor, whose emitter is grounded, the collector is connected to the sixth resistor, and the base is connected to the fourth, third and second resistors respectively. The temperature of the third transistor changes with the temperature of the first transistor, thereby achieving thermal coupling. The first transistor, the second transistor and the third transistor form a feedback loop of the adaptive bias of the HBT transistor. The emitter of the fourth transistor is connected to the fourth resistor, then to the third resistor, and finally to the ground, the collector is connected to the seventh resistor, and the base is connected to the fifth resistor and the first capacitor. The right end of the first resistor is connected to the base of the first transistor, and the left end is connected to the second resistor. The left end of the second resistor is connected to the base of the third transistor, and the right end is connected to the first resistor. The lower end of the third resistor is grounded, and the upper end is connected to the fourth resistor. The lower end of the fourth resistor is connected to the third resistor, and the upper end is connected to the emitter of the fourth transistor. The left end of the fifth resistor is connected to the sixth resistor and the collector of the third transistor. The upper end of the sixth resistor is connected to a 3.3V DC power supply, and the lower end is respectively connected to the base of the second transistor, the fifth resistor and the collector of the third transistor. The lower end of the seventh resistor is connected to the collector of the fourth transistor, and the upper end is connected to a 5V DC power supply. The current in the first transistor is determined by the area ratio of the first transistor to the third transistor, and the first, second and sixth resistors. The improvement is that the resistor in the base of the fourth transistor is changed to a large resistor, and a capacitor is added.

[0029] The third resistance value and the fourth resistance value are 10kΩ, the fifth resistance value is 5kΩ, and the seventh resistance value is 1kΩ. The first DC power supply is 3.3V, and the second DC power supply is 5.0V.

[0030] The temperature of the third transistor changes as the temperature of the first transistor changes, and different thermal coupling strengths are achieved by adjusting the distance between the third transistor and the first transistor.

[0031] Figure 3 Figure 4 A curve graph of the current of the first transistor in a temperature-insensitive bias circuit described in the present invention varying with temperature and a curve graph of input power and output power are respectively shown. It can be seen that the current does not change much in the range of -40 degrees Celsius to +90 degrees Celsius, and the input power and output power show a very good approximate linear relationship.

[0032] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A temperature-insensitive bias circuit, characterized in that: The invention comprises a first transistor, a second transistor, a third transistor and a fourth transistor, a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor and a seventh resistor, and a first direct current power supply and a second direct current power supply, wherein the positive electrode of the first direct current power supply is connected to the collector of the third transistor through the sixth resistor, the emitter of the third transistor is grounded, the base of the third transistor is connected to the base of the first transistor through the second resistor and the first resistor, the emitter of the first transistor is grounded, and the collector of the first transistor is connected to an external circuit; the emitter of the second transistor is connected to a common end between the second resistor and the first resistor, the base of the second transistor is connected to the collector of the third transistor, and the collector of the second transistor is connected to the positive electrode of the second current source; the collector of the fourth transistor is connected to the positive electrode of the second current source through the seventh resistor, the base of the fourth transistor is connected to the collector of the third transistor through the fifth resistor, and the emitter of the fourth transistor is grounded through the fourth resistor and the third resistor, the first transistor, the second transistor and the third transistor form an adaptive bias feedback loop, and the third, fourth, fifth and seventh resistors form a thermal feedback circuit with the fourth transistor.

2. The temperature-insensitive bias circuit according to claim 1, characterized in that The first transistor is a power transistor unit and the third transistor is a thermal sensor transistor.

3. The temperature-insensitive bias circuit according to claim 1, characterized in that The base of the fourth transistor is connected to the first capacitor, and the other end of the first capacitor is grounded.

4. The temperature-insensitive bias circuit according to claim 1 or 3, characterized in that: The temperature of the third transistor changes as the temperature of the first transistor changes, and different thermal coupling strengths are achieved by adjusting the distance between the third transistor and the first transistor.

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