Power amplifier

Abstract

A power amplifier includes a transistor, a temperature sensor, and a filter. The transistor is configured to receive a bias signal and amplify a radio frequency signal. The temperature sensor is disposed proximate to the transistor and is configured to detect a temperature of the transistor and provide a voltage signal at a control node in response thereto. The filter is coupled to the temperature sensor and is configured to filter the voltage signal to generate a filtered voltage. The bias signal is adjusted in response to the filtered voltage.

Description

Technical Field

[0001] This invention relates to power amplifiers, particularly power amplifiers with temperature compensation that maintain substantially constant gain when temperature changes. Background Technology

[0002] Almost all electronic devices use power amplifiers, especially radio frequency (RF) devices such as smartphones, Wi-Fi hotspots, and other wireless devices. Power amplifiers convert low-power RF signals into high-power RF signals. During operation, the power amplifier continuously heats up due to the current flowing through it. The heat generated by the power amplifier reduces its gain, thus decreasing its linearity and signal quality. Because heat can accumulate over time, the degradation in linearity and signal quality is particularly noticeable during the transmission of long frames of data.

[0003] Therefore, there is a need for a power amplifier that can maintain a substantially constant gain even when heat is generated inside and / or outside the power amplifier. Summary of the Invention

[0004] This invention provides a power amplifier comprising a transistor, a temperature sensor, and a filter. The transistor receives a bias signal and amplifies a radio frequency signal. The temperature sensor is located near the transistor to detect its temperature and provide a voltage signal at a control node accordingly. The filter is coupled to the temperature sensor to filter the voltage signal to generate a filtered voltage. The bias signal is adjusted based on the filtered voltage. Attached Figure Description

[0005] Figure 1 This is a block diagram of a power amplifier according to an embodiment of the present invention.

[0006] Figure 2 This is the waveform of the voltage signal in Figure 1.

[0007] Figure 3 This is the waveform of the filtered signal in Figure 1.

[0008] Figure 4 This is the circuit diagram of the filter in Figure 1.

[0009] Figure 5 This is the circuit diagram of the bias circuit in Figure 1.

[0010] Figure 6 The waveform of the power amplifier is shown in Figure 1.

[0011] Figure 7 This is a block diagram of another power amplifier in an embodiment of the present invention.

[0012] Figure 8 This is a block diagram of another power amplifier in an embodiment of the present invention.

[0013] Figure 9 This is a module diagram of another power amplifier section in an embodiment of the present invention.

[0014] Figure 10 This is a block diagram of another power amplifier in an embodiment of the present invention.

[0015] Symbol Explanation

[0016] 1,7,8,9,100: Power amplifiers

[0017] 10: Scale-up stage

[0018] 11,13: Reference End

[0019] 12: Temperature sensor

[0020] 14,80: Filter

[0021] 16: Bias circuit

[0022] 18: Current Source

[0023] 20, 30: Envelope

[0024] 22: Carrier

[0025] 32: Filtered carrier

[0026] 140: Variable Impedance Component

[0027] 160: Current source

[0028] 60: Gain

[0029] 70: Adder

[0030] 90: Second chip

[0031] 92: First Chip

[0032] 920: Sample and Hold Circuit

[0033] 921: Buffer

[0034] 922: Sampling Circuit

[0035] 924: Holding Circuit

[0036] 925: Differential Amplifier

[0037] 926: Voltage-to-current converter

[0038] C,Cgnd,923: Capacitor

[0039] Cs: Shunt capacitor

[0040] D1: Diode

[0041] GaAs: Gallium arsenide

[0042] I: Current

[0043] N1: Control Node

[0044] Nref: Reference node

[0045] R, R1, R2: Resistors

[0046] Sb: Bias signal

[0047] Sc: Control signal

[0048] SOI: Silicon-coated Insulator

[0049] Srfi: RF input signal

[0050] Srfo: RF output signal

[0051] SW1, SW2: Switches

[0052] t, t0, t1: Time

[0053] T1 to T4: Transistors

[0054] V+: Initial voltage

[0055] V-: Update voltage

[0056] Vb1: Bias voltage

[0057] Vcc: Supply voltage

[0058] Vf: Filter voltage

[0059] Vss: Ground voltage or common voltage

[0060] VTD: Voltage signal Detailed Implementation

[0061] This document will describe exemplary embodiments in detail with reference to the accompanying drawings to facilitate understanding of the disclosure. This disclosure is for illustrative purposes only and is not intended to be limiting.

[0062] Figure 1This is a block diagram of a power amplifier 1 according to an embodiment of the present invention. By offsetting the temperature change caused by the self-heating of the power amplifier 1, the power amplifier 1 can maintain a substantially constant gain over time. In addition, the power amplifier 1 can preprocess the temperature detection signal representing the temperature of the power amplifier 1 to improve the accuracy and speed of temperature compensation, thereby improving the linearity and signal quality of the power amplifier 1.

[0063] Power amplifier 1 may include an amplification stage 10, a temperature sensor 12, a filter 14, a bias circuit 16, and a current source 18. The amplification stage 10 may include a transistor T1. The temperature sensor 12 may be located near the amplification stage 10, specifically near the transistor T1. The transistor T1 may be a bipolar junction transistor (BJT), such as a heterojunction bipolar transistor (HBT). In some embodiments, the temperature sensor 12 may be located immediately adjacent to the transistor T1. The temperature sensor 12 is coupled to the filter 14, which is coupled to the bias circuit 16, which is coupled to the transistor T1. The temperature sensor 12 may include a diode D1. The diode D1 includes a first terminal and a second terminal coupled to a reference terminal 13. The first terminal of the diode D1 may be the anode, and the second terminal may be the cathode. The current source 18 includes a first terminal coupled to a reference terminal 11 and a second terminal coupled to the first terminal of the diode D1. Transistor T1 includes a first terminal coupled to reference terminal 11, a second terminal coupled to reference terminal 13, and a control terminal coupled to bias circuit 16. Transistor T1 is used to receive bias signal Sb and radio frequency (RF) input signal Srfi. Reference terminal 11 can provide a power supply voltage Vcc, for example, 3.3V, and reference terminal 13 can provide a ground voltage or common voltage Vss, for example, 0V.

[0064] Transistor T1 receives an RF input signal Srfi and a bias signal Sb, and amplifies the power of the RF input signal Srfi to generate an RF output signal Srfo. The bias signal Sb can be a current signal or a voltage signal. For example, in some embodiments, the bias signal Sb can be a current signal. Temperature sensor 12 detects the temperature of transistor T1 to provide a voltage signal VTD at control node N1 accordingly. Current source 18 provides a constant current to diode D1. Diode D1, operating at a constant current, can be used as a complementary to absolute temperature (CTAT) component; the voltage across diode D1 decreases as the temperature increases, causing the voltage signal VTD to decrease. Therefore, the voltage signal VTD can be used to represent the temperature of power amplifier 1. In some embodiments, at a predetermined temperature, diode D1 can set the voltage signal VTD to a default level. For example, at a predetermined temperature of 25 degrees Celsius, the default level of the voltage signal VTD can be 1.2V; at a temperature of 100 degrees Celsius, the level of the voltage signal VTD can be 1.1V; and at a temperature of -50 degrees Celsius, the level of the voltage signal VTD can be 1.3V. In some embodiments, diode D1 can be replaced by a bipolar junction transistor (BJT), such as a heterojunction bipolar transistor (HBT). The BJT can be connected in diode form or biased to be set to the operating region, such as the saturation region. Filter 14 can be a low-pass filter that filters the voltage signal VTD to generate a filtered voltage Vf. Bias circuit 16 can generate a bias signal Sb based on the filtered voltage Vf and provide the bias signal Sb to transistor T1. When the power amplifier 1 is transmitting data, the bias signal Sb can be adjusted to maintain the gain at a substantially constant level. For example, the bias signal Sb can increase with increasing temperature to maintain a substantially constant gain. In addition, current source 18 can also provide current to bias circuit 16.

[0065] To obtain an accurate temperature value for transistor T1, temperature sensor 12 can be placed near transistor T1. However, the short distance between transistor T1 and temperature sensor 12 increases signal coupling from transistor T1 to temperature sensor 12, introducing high-frequency noise into the voltage signal VTD. This high-frequency noise corresponds to the frequency of the RF output signal Srfo. For example, when the RF output signal Srfo is a WiFi signal, the high-frequency noise could be 5 GHz. Furthermore, due to signal coupling from transistor T1, diode D1 can conduct, thus generating a voltage clipping of the voltage signal VTD. This voltage clipping, via the bias signal Sb, can introduce low-frequency noise into the RF output signal Srfo. For example, the low-frequency noise could be 80 MHz and / or 160 MHz. Both high-frequency and low-frequency noise can lead to inaccurate or even erroneous temperature compensation and can degrade the error vector magnitude (EVM) or dynamic error vector magnitude (DEVM) of the RF output signal Srfo.

[0066] Filter 14 can thoroughly and quickly filter out noise in the voltage signal VTD to reduce the impact of noise on the bias signal Sb. Figure 2 and Figure 3 The waveforms of the voltage signal VTD and the filter voltage Vf from power amplifier 1 are displayed respectively. The voltage signal VTD is input to filter 14, and the filter voltage Vf is output from filter 14. Figure 2 The voltage signal VTD is displayed as an envelope 20 and a carrier wave 22, and Figure 3 The filtered voltage Vf contains envelope 30 and filtered carrier 32. Envelope 20 and envelope 30 are essentially the same. The noise level and frequency components of filtered carrier 32 are both lower than those of carrier 22. That is, the higher frequency components of carrier 22 are attenuated or removed to produce filtered carrier 32 in filtered voltage Vf.

[0067] Filter 14 may include Figure 4 The circuit diagram shows an RC circuit. Filter 14 may include a variable impedance component 140 and a capacitor C coupled to each other. Variable impedance component 140 may include a resistor R coupled to capacitor C. Variable impedance component 140 may include a first terminal for receiving a voltage signal VTD and a second terminal for outputting a filtered voltage Vf. Capacitor C includes a first terminal coupled to the second terminal of variable impedance component 140 and a second terminal coupled to reference terminal 13.

[0068] The variable impedance component 140 can be adjusted according to the control signal Sc to provide a first impedance at least in a first interval and a second impedance in a second interval. For example, the second impedance may be greater than the first impedance. (Reference) Figure 4The variable impedance component 140 may include a switch SW1 and a resistor R coupled in parallel with the switch SW1.

[0069] When switch SW1 is on, variable impedance component 140 provides a first impedance; when switch SW1 is off, variable impedance component 140 provides a second impedance. The first impedance can be substantially equal to 0 ohms, and the second impedance can be substantially equal to the resistance value of resistor R. The product of the resistance value of resistor R and the capacitance value of capacitor C is called the time constant. A larger time constant can remove more low-frequency components and delay the circuit response. The resistance value of resistor R and / or the capacitance value of capacitor C can be set relatively large to filter out low-frequency and high-frequency noise in the voltage signal VTD. Switch SW1 can be on in the first interval to accelerate the circuit response of filter 14 and quickly set the filter voltage Vf to the operating level. The operating level of filter voltage Vf can be 1.2V. In the second interval, switch SW1 can be off to suppress low-frequency noise. The first interval can be a short time interval after the start of data transmission. For example, the first interval can be 0 to 400 ns of data transmission. The second interval can be a longer time interval that begins immediately after the first interval. For example, the second interval can be from 400 ns to the end of data transmission. In this way, filter 14 can quickly set the filter voltage Vf to the operating level, while also transmitting an accurate temperature signal.

[0070] In some embodiments, the resistor R in the variable impedance component 140 can be replaced by an inductor. Similar to the RC filter 14, in the LC filter, the product of the inductance of the inductor and the capacitance of the capacitor C is called the time constant. The operation of the LC filter is similar to that of the RC filter 14, and will not be described again here.

[0071] Figure 5This is a circuit diagram of bias circuit 16. Bias circuit 16 may include current source 160, transistors T2 to T4, resistors R1 and R2, and capacitor Cgnd. Current source 160 may be a BJT or a field-effect transistor (FET). Current source 160 includes a first terminal for receiving the supply voltage Vcc, a second terminal for receiving the filter voltage Vf, and a control terminal. Transistor T2 includes a first terminal for receiving the supply voltage Vcc, a second terminal for receiving the supply voltage Vcc, and a control terminal. Resistor R2 includes a first terminal and a second terminal, wherein the first terminal is coupled to the control terminal of transistor T2 and the second terminal of current source 160. Transistor T3 includes a first terminal and a second terminal coupled to the second terminal of resistor R2, and a control terminal coupled to the first terminal of transistor T3. Transistor T4 includes a first terminal coupled to the second terminal of transistor T3, a second terminal coupled to reference terminal 13, and a control terminal coupled to the first terminal of transistor T4. Resistor R1 includes a first terminal and a second terminal, wherein the first terminal is coupled to the second terminal of transistor T2. The capacitor Cgnd, which can be a grounding capacitor, includes a first end coupled to the second end of the resistor R1 and a second end coupled to the reference terminal 13.

[0072] Current source 160 can generate a variable current based on the filter voltage Vf. The magnitude of the variable current is negatively correlated with the magnitude of the filter voltage Vf. When the temperature of power amplifier 1 increases, the filter voltage Vf decreases, and the variable current increases accordingly, thereby increasing the bias signal Sb. When the temperature of power amplifier 1 decreases, the filter voltage Vf increases, and the variable current decreases accordingly, thereby decreasing the bias signal Sb.

[0073] Figure 6 The waveforms of the bias signal Sb and gain 60 of power amplifier 1 are displayed, where the horizontal axis represents time t and the vertical axis represents current I. At time t0, power amplifier 1 begins data transmission, and the bias signal Sb drives the gain to the predetermined level from the initial current level. Between times t0 and t1, power amplifier 1 continues to heat up, and the bias signal Sb increases to maintain the gain 60 at the predetermined level. After time t1, data transmission is complete, and both the bias signal Sb and gain 60 drop to a low level. Figure 6 The temperature compensation can produce a relatively stable gain of 60 throughout the data transmission period, thereby increasing the linearity and signal quality of power amplifier 1.

[0074] Figure 7This is a schematic diagram of another power amplifier module 7 in an embodiment of the present invention. The power amplifier 7 differs from the power amplifier 1 in that it further includes a shunt capacitor Cs. The shunt capacitor Cs is disposed between the control node N1 and the reference terminal 13. The shunt capacitor Cs includes a first end coupled to the first terminal of the diode D1 and a second end coupled to the reference terminal 13. The shunt capacitor Cs is connected in parallel to the temperature sensor 12 and can be disposed near the transistor T1, the temperature sensor 12, and the through silicon via (TSV). The TSV serves as a ground connection. The shunt capacitor Cs can be placed close to the transistor T1, the temperature sensor 12, and the TSV to guide high-frequency noise to ground, further reducing noise in the voltage signal VTD.

[0075] The power amplifier 7 can further remove high-frequency noise in the voltage signal VTD by using the shunt capacitor Cs located near the transistor T1, temperature sensor 12 and through-silicon via, thereby improving the accuracy of temperature compensation, the linearity of the power amplifier 7 and the signal quality.

[0076] Figure 8 This is a block diagram of another power amplifier 8 in an embodiment of the present invention. The power amplifier 8 differs from the power amplifier 7 in that it utilizes transistor T4 for temperature sensing, omits diode D1, and includes an adder 70. The bias circuit 16 includes a temperature sensor 12 and can generate a bias signal Sb based on the variable current generated by the current source 160. The first terminal and control terminal of transistor T4 are further coupled to the first terminal of the shunt capacitor Cs and the filter 14. The adder 70 includes a first input terminal for receiving the bias voltage Vb1, a second input terminal coupled to the filter 14 and for receiving the filter voltage Vf, and an output terminal coupled to the control terminal of the current source 160. The bias voltage Vb1 can be adjusted according to the power and / or frequency of the RF input signal Srfi. The filter voltage Vf can correspond to the temperature of the power amplifier 8. The adder 70 can add the bias voltage Vb1 and the filter voltage Vf to generate a control voltage, which represents the change in the power and / or frequency of the RF input signal Srfi and the temperature change of the power amplifier 8. Therefore, current source 160 can receive a control voltage to generate a variable current, thereby controlling transistor T2 to generate a bias signal Sb. In this way, the bias signal Sb can be adjusted according to the power and / or frequency of the RF input signal Srfi and the temperature of power amplifier 8, so as to keep the gain of power amplifier 8 substantially constant. In some embodiments, adder 70 can be removed from power amplifier 8, and filter 14 can be directly coupled to current source 160. Transistor T4 can be placed near transistor T1 to detect its temperature. The configuration and operation of other components in power amplifier 8 are similar to those in power amplifier 7, and will not be described again here.

[0077] Compared to power amplifier 7, power amplifier 8 uses transistor T4 connected in a diode manner in bias circuit 16 to sense temperature, saving circuit area, while maintaining a substantially constant gain level over time.

[0078] Figure 9 This is a block diagram of a selected circuit of a power amplifier 9 according to an embodiment of the present invention. The power amplifier 9 differs from the power amplifier 1 in that it additionally includes a filter 80 and a reference node Nref. The reference node Nref is coupled to a current source 18. In some embodiments, the current source 18 can be replaced by a voltage source. The filter 80 is coupled between the reference node Nref and the control node N1, and can filter out noise in the voltage signal VTD to prevent noise from affecting the current source 18. The configuration and operation of other components in the power amplifier 9 are similar to those in the power amplifier 1, and will not be described again here.

[0079] The power amplifier 9 uses a filter 80 to isolate the current source 18 from unwanted noise.

[0080] Figure 10 This is a block diagram of another power amplifier 100 in an embodiment of the present invention. The power amplifier 100 differs from power amplifier 1 in that it further includes a sample-and-hold circuit 920. The sample-and-hold circuit 920 may include a buffer 921, a sampling circuit 922, a switch SW2, a capacitor 923, a holding circuit 924, a differential amplifier 925, and a voltage-to-current (V2I) converter 926. The buffer 921 is coupled to a filter 14. The sampling circuit 922 and the switch SW2 are coupled to the buffer 921. The capacitor 923 and the holding circuit 924 are coupled to the switch SW2. The differential amplifier 925 includes a first input terminal coupled to the sampling circuit 922, a second input terminal coupled to the holding circuit 924, and an output terminal coupled to the voltage-to-current (V2I) converter 926. The first input terminal may be an inverting input, and the second input terminal may be a non-inverting input. The voltage-to-current converter 926 may be coupled to a bias circuit 16.

[0081] Buffer 921 can be a buffer amplifier to hold the filtered voltage Vf. Sampling circuit 922 samples the filtered voltage Vf at regular intervals to generate an updated voltage V-. Switch SW2 is connected to switch SW1 of filter 14 (e.g., Figure 4(As shown) can operate according to different timing sequences. Capacitor 923 can be used to store the initial voltage V+. Holding circuit 924 can maintain the initial voltage V+ at capacitor 923. In some embodiments, holding circuit 924 can periodically recharge (refresh) and maintain the initial voltage V+ at capacitor 923. Differential amplifier 925 can generate a difference voltage Vdf based on the difference between the initial voltage V+ and the refresh voltage V-, and output the difference voltage Vdf to voltage-to-current converter 926. Voltage-to-current converter 926 can convert the difference voltage Vdf into a difference current, and bias circuit 16 can generate a bias signal Sb based on the difference current.

[0082] Switch SW2 can be turned on for a predetermined period of time when power amplifier 100 is powered on, and then turned off. The predetermined period of time can be 10 microseconds or less. During the predetermined period of time after power-on, the temperature of power amplifier 100 can remain almost unchanged or change very little, such that the temperature remains substantially stable. For example, switch SW2 can be turned on for 4ms when powered on, and then turned off. When switch SW2 is turned on, capacitor 923 can be charged to an initial voltage V+ equal to the filter voltage Vf within the predetermined period of time. For example, the initial voltage V+ can be 1.12V. Holding circuit 924 can transmit the initial voltage V+ to the second input terminal of differential amplifier 925. At the same time, sampling circuit 922 can sample the filter voltage Vf to generate an updated voltage V-. Since the initial voltage V+ is equal to the updated voltage V-, the difference voltage Vdf generated by differential amplifier 925 can be substantially equal to 0V. That is, power amplifier 100 does not perform temperature compensation during this stage.

[0083] Subsequently, as the power amplifier 100 begins to heat up, when the preset time period ends, switch SW2 can be turned off. The initial voltage V+ remains unchanged (e.g., 1.12V). Due to the increased temperature, the update voltage V- generated by the sampling circuit 922 can decrease (e.g., 1.1V), and the difference voltage Vdf may not be zero. Since the difference between the initial voltage V+ and the update voltage V- may be small, the differential amplifier 925 can amplify the difference between the initial voltage V+ and the update voltage V- to produce a difference voltage Vdf with a significant amplitude. For example, the initial voltage V+ may correspond to 25 degrees Celsius, the update voltage V- may correspond to 85 degrees Celsius, the difference between the initial voltage V+ and the update voltage V- may be 10mV, the differential amplifier 925 may be set to a gain of 20, and the differential voltage Vdf output by the differential amplifier 925 may be 200mV.

[0084] The bias signal Sb is positively correlated with the differential current. The bias signal Sb is then transmitted to the amplification stage 10 to bias the amplification stage 10. The configuration and operation of other components in the power amplifier 100 are similar to those in the power amplifier 1, and will not be described again here.

[0085] Initially, when amplification stage 10 is not operating, the initial voltage V+ and the update voltage V- are sampled, so the initial voltage V+ equals the update voltage V-. During data transmission, the voltage signal VTD decreases as amplification stage 10 begins to heat up, and the update voltage V- is less than the initial voltage V+, thus increasing the difference voltage Vdf. The increased difference voltage Vdf is converted into an increased bias signal Sb, which is used to bias transistor T1, thereby maintaining a substantially constant gain.

[0086] The current source 18, filters 14 and 80, sample-and-hold circuit 920, and bias circuit 16 can be fabricated on the first chip 92, such as on a silicon-on-insulator (SOI) chip, and the amplification stage 10 and temperature sensor 12 can be fabricated on the second chip 90, such as on a gallium arsenide (GaAs) chip, thereby reducing manufacturing costs, maintaining substantially constant gain, and improving the signal quality of the power amplifier 100. In some embodiments, the voltage-to-current converter 926 may include a first circuit portion and a second circuit portion. The first circuit portion may be disposed on the first chip 92, and the second circuit portion may be disposed on the second chip 90. The second circuit portion may include a resistor. Since gallium arsenide technology can provide high-precision resistors, the resistor in the second circuit portion can be a high-precision resistor. The first circuit portion can be coupled to the resistor in the second circuit portion via connection pads on the first chip 92 and the second chip 90.

[0087] Although Figure 1 , 7 Figures 8 and 10 show a single amplification stage 10. In some embodiments, multiple amplification stages can be used instead of a single amplification stage 10. One or more temperature sensors can be located near the selective amplification stage, and the corresponding bias signal can be adjusted to compensate for the self-heating effect. For example, the temperature sensor can be located near the final amplification stage, and the bias signal can be adjusted to compensate for the self-heating effect.

[0088] The above are merely preferred embodiments of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be considered within the scope of the present invention.

Claims

1. A power amplifier, characterized in that, Include: A first transistor is configured to receive a bias signal and amplify a radio frequency signal; A temperature sensor is disposed near the first transistor and is used to detect a temperature of the first transistor in order to provide a first voltage signal at a control node accordingly. and A first filter is coupled to the temperature sensor and used to filter the first voltage signal to generate a filtered voltage. The first filter includes a variable impedance component, which is used to adjust an impedance according to a control signal to provide a first impedance in a first interval and a second impedance in a second interval after the first interval, wherein the second impedance is greater than the first impedance. The bias signal is adjusted based on the filter voltage.

2. The power amplifier as described in claim 1, characterized in that, It also includes a bias circuit coupled to the first filter to generate the bias signal based on the filter voltage.

3. The power amplifier as described in claim 2, characterized in that, The bias circuit includes: A second transistor includes a first terminal coupled to a first reference terminal, a second terminal, and a control terminal; A third transistor includes a first terminal, a second terminal, and a control terminal coupled to the first terminal of the third transistor; and A fourth transistor includes a first terminal coupled to the second terminal of the third transistor, a second terminal coupled to a second reference terminal, and a control terminal coupled to the first terminal of the fourth transistor.

4. The power amplifier as described in claim 3, characterized in that, in, The bias circuit further includes a first resistor, which includes a first terminal and a second terminal coupled to the second terminal of the second transistor.

5. The power amplifier as described in claim 4, characterized in that, in, The bias circuit further includes a grounding capacitor, which includes a first end coupled to the second terminal of the first resistor and a second end coupled to the second reference terminal.

6. The power amplifier as described in claim 3, characterized in that, The bias circuit further includes a second resistor, which includes a first terminal coupled to the control terminal of the second transistor and a second terminal coupled to the first terminal of the third transistor.

7. The power amplifier as claimed in claim 1, characterized in that, It also includes a shunt capacitor, which is disposed between the control node and a first reference terminal.

8. The power amplifier as described in claim 7, characterized in that, in, The shunt capacitor and the temperature sensor are connected in parallel.

9. The power amplifier as described in claim 7, characterized in that, in, The shunt capacitor is located near the first transistor.

10. The power amplifier as claimed in claim 1, characterized in that, It also includes a bias circuit that includes the temperature sensor and is used to generate the bias signal based on a variable current.

11. The power amplifier as claimed in claim 1, characterized in that, The first filter further includes: A first capacitor includes a first terminal coupled to the variable impedance component and a second terminal coupled to a second reference terminal.

12. The power amplifier as claimed in claim 1, characterized in that, in, The variable impedance component includes a first switch that is coupled in parallel with a resistor.

13. The power amplifier as claimed in claim 1, characterized in that, in, The variable impedance component includes a first switch that is coupled in parallel with an inductor.

14. The power amplifier as claimed in claim 1, characterized in that, Also includes: A reference node, coupled to a current source or a voltage source; and A second filter is coupled between the reference node and the control node and is used to filter the first voltage signal.

15. The power amplifier as claimed in claim 14, characterized in that, in, The second filter is used to filter out noise from the first voltage signal to prevent the noise from affecting the current source or the voltage source.

16. The power amplifier as claimed in claim 15, characterized in that, The noise originates from an RF signal coupled to the temperature sensor.

17. The power amplifier as claimed in claim 1, characterized in that, in, The first voltage signal contains noise from the temperature sensor, and the first filter is used to filter out the noise to prevent it from affecting the bias signal.

18. A power amplifier, characterized in that, Include: A first transistor is configured to receive a bias signal and amplify a radio frequency signal; A temperature sensor is disposed near the first transistor and is used to detect a temperature of the first transistor in order to provide a first voltage signal at a control node accordingly. and A first filter is coupled to the temperature sensor and is used to filter the first voltage signal to generate a filtered voltage. A buffer, coupled to the first filter; A sampling circuit, coupled to the buffer, is used to sample the filter voltage to generate an update voltage; A second switch includes a first terminal and a second terminal coupled to the buffer; A capacitor is coupled to the second terminal of the second switch and is used to store an initial voltage; A holding circuit is coupled to the second terminal of the second switch; A differential amplifier is coupled to the sampling circuit and the holding circuit, the differential amplifier being used to generate a differential voltage based on a difference between the initial voltage and the updated voltage; and A voltage-to-current converter is coupled between the differential amplifier and a bias circuit to convert the differential voltage into a differential current. The bias signal is adjusted based on the filter voltage.

19. The power amplifier as claimed in claim 18, characterized in that, The sampling circuit, the capacitor, the differential amplifier, and the bias circuit are fabricated on a first chip, and the first transistor is fabricated on a second chip.

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