A high linearity GaN HEMT RF power amplifier circuit

Abstract

This invention discloses a high-linearity GaN HEMT RF power amplifier circuit. It employs multiple GaN HEMT dies, with the drains of each die connected together as the output terminal and the gates of each die connected together as the input terminal. The source of each die is grounded. A resonant network is connected in parallel to the output terminal, and a first inductor L1 and a second inductor L2 are connected in parallel to the gate of each die. By using this invention, the GaN HEMT dies are connected in parallel, a resonant network is connected in parallel to ground at the drain terminals, and two inductors to ground are connected in parallel at the gate terminals of each die. This optimized circuit structure eliminates the influence of parasitic capacitance, effectively improving the linearity of the circuit.

Description

Technical Field

[0001] This invention relates to the field of radio frequency power amplifier technology, and more particularly to a high linearity GaN HEMT radio frequency power amplifier circuit. Background Technology

[0002] With the introduction and development of fifth-generation wireless communication technology, wireless communication systems require higher spectrum utilization. High linearity and radio frequency power amplifiers are widely used. However, modulation signals with varying envelopes will be distorted after passing through nonlinear radio frequency power amplifiers, causing serious inter-symbol interference and adjacent channel interference. This places higher demands on the linearity of radio frequency power amplifiers.

[0003] GaN HEMT RF power devices are widely used in various high-linearity communication systems due to their high breakdown voltage, high saturation speed, and outstanding thermal properties. (See also...) Figure 1 The image shows a cross-sectional view of a prior art GaN HEMT RF power device. The device includes the drain port, gate port, source port, Si3N4 dielectric material between the gate, drain, and source, GaN cap as the device protective layer, AlGaN barrier layer as a barrier layer confining free electrons to move on a two-dimensional electron gas, GaN channel as a channel layer with high free electron concentration, GaN buffer as a buffer layer, and substrate as the device substrate. Its basic working principle is that when a suitable voltage is applied to the drain, gate, and source, free electrons are transmitted from the source port to the drain port through the two-dimensional electron gas. The signal enters from the gate port and exits from the drain port, achieving signal amplification. The distortion during signal amplification is considered the linearity performance of the device.

[0004] For GaN HEMT RF power devices, the metal on the Gate port and the metal on the Source port are located close to each other in the horizontal direction, and the space between them is filled with Si3N4 dielectric. This results in the existence of gate-source parasitic capacitance Cgs, which increases quadratically with increasing Pout. Consequently, Δ deviates further and further from zero as the output power increases, leading to a significant deterioration in linearity. This is one of the main reasons for the significant linearity defects in GaN HEMT RF power devices.

[0005] Therefore, given the shortcomings of existing technologies, it is necessary to propose a technical solution to address the technical problems existing in the current technologies. Summary of the Invention

[0006] In view of this, it is indeed necessary to provide a high linearity GaN HEMT RF power amplifier circuit, which connects GaN HEMT dies in parallel, connects a resonant network in parallel to ground at the drain port of the parallel connection, and connects two inductors to ground in parallel at the gate port of each GaN HEMT die, thereby eliminating the influence of parasitic capacitance by optimizing the circuit structure and effectively improving the linearity of the circuit.

[0007] In order to solve the technical problems existing in the prior art, the technical solution of the present invention is as follows:

[0008] A high linearity GaN HEMT RF power amplifier circuit is provided, which includes multiple GaN HEMT dies. The drains of each GaN HEMT die are connected together as the output terminal, the gates of each GaN HEMT die are connected together as the input terminal, and the source of each GaN HEMT die is grounded. The output terminal is connected in parallel with a resonant network, and the gate of each GaN HEMT die is connected in parallel with a first inductor L1 and a second inductor L2.

[0009] As a further improvement, the resonant network includes a first capacitor C1 and a third inductor L3, wherein one end of the first capacitor C1 is connected to the output terminal, the other end of the first capacitor C1 is connected to one end of the third inductor L3, and the other end of the third inductor L3 is grounded.

[0010] As a further improvement, the circuit is integrated into one unit.

[0011] As a further improvement, the GaN HEMT die includes a substrate layer, a buffer layer, a channel layer, a barrier layer, and a protective layer arranged sequentially, with a source, a gate, and a drain disposed above the protective layer; wherein the protective layer forms an L-shaped groove, and the source is disposed at the top of the L-shaped groove so that the source port and the gate port are horizontally offset from each other.

[0012] As a further improvement, the top of the drain port is flush with the top of the gate port, and the bottom of the source port is flush with the top of the gate port.

[0013] As a further improvement, the channel layer uses GaN material.

[0014] As a further improvement, the barrier layer uses AlGaN material.

[0015] As a further improvement, the substrate layer uses SiC material.

[0016] As a further improvement, the buffer layer uses GaN material.

[0017] As a further improvement, Si3N4 dielectric material is filled between the source, gate, and drain. Internal ports of semiconductor devices require dielectric filling for isolation. Si3N4 has strong oxidation resistance, can withstand thermal shock, has high insulation performance, and is relatively inexpensive to manufacture, making it very suitable for use as an isolation dielectric in semiconductor devices. All GaN HEMT devices use this dielectric.

[0018] Compared with existing technologies, this invention adds inductors and capacitors to the power amplifier circuit to eliminate the influence of parasitic capacitance. Specifically, the two inductors to ground at the gate port of the GaN HEMT die are mainly used to cancel Cgs under high output power. When Pout is very small, Cgs cannot be canceled by these two inductors. As Pout increases, Cgs gradually increases. When it increases to a certain value, Cgs is just canceled by these two inductors. This means that as the output power increases, the influence of Cgs on the Δ value becomes weaker and gradually disappears. Therefore, the trend of the Δ value moving away from 0 is also greatly alleviated, effectively improving the circuit linearity. In addition, the inductor-capacitor resonant network connected in parallel at the drain port can suppress the high-order harmonic energy of the output signal, further improving the linearity of the circuit. Attached Figure Description

[0019] Figure 1 This is a cross-sectional view of a current GaN HEMT RF power device.

[0020] Figure 2 This is a circuit topology diagram of the high linearity GaN HEMT RF power amplifier of the present invention.

[0021] Figure 3 This is a structural block diagram of a preferred embodiment of the GaN HEMT die in this invention.

[0022] In the figure, Drain is the drain port, Gate is the gate port, Source is the source port, Si3N4 is the dielectric material between the gate, drain, and source, GaN cap is the device protective layer with an L-shaped trench structure, AlGaN barrier layer is the barrier layer that confines free electrons to move on a two-dimensional electron gas, GaN channel is the channel layer with a high free electron concentration, GaN buffer is the buffer layer, and Substrate is the device substrate.

[0023] Figure 4 This is a structural block diagram of another preferred embodiment of the GaN HEMT die in this invention.

[0024] In the figure, the AlGaN barrier layer and AlGaN extra layer are barrier layers that confine free electrons to move on a two-dimensional electron gas, and are referred to as the first barrier layer and the second barrier layer, respectively; the original first two-dimensional electron gas is between the AlGaN barrier layer and the GaN channel, and the newly formed second two-dimensional electron gas is between the GaN channel and the AlGaN extra layer.

[0025] The following specific embodiments will further illustrate the present invention in conjunction with the above-described accompanying drawings. Detailed Implementation

[0026] The technical solution provided by the present invention will be further described below with reference to the accompanying drawings.

[0027] To overcome the technical deficiencies of existing technologies, the applicant derived the following from the circuit level: the linearity performance of GaN HEMT RF power devices can also be expressed as the change in gain with output power, Δ. The closer Δ is to 0, the better the linearity performance; the further Δ is from 0, the worse the linearity performance. Δ can be expressed by the following formula:

[0028]

[0029] Where K is a constant, gm is the transconductance of the power device, Cgs is the parasitic capacitance from the Gate to the Source, s is the frequency response (S is a constant once the operating frequency is determined), and Pout is the output power of the power device.

[0030] Based on the above theoretical analysis, the applicant proposes a technical solution to eliminate parasitic capacitance through circuit structure optimization. See [link / reference]. Figure 2 The diagram shows the topology of the high-linearity GaN HEMT RF power amplifier circuit of the present invention. Multiple GaN HEMT dies are used, with the drains of each die connected together as the output terminal and the gates of each die connected together as the input terminal. The source of each die is grounded. A resonant network is connected in parallel to the output terminal, and the gate of each die is connected in parallel to a first inductor L1 and a second inductor L2. This resonant network includes a first capacitor C1 and a third inductor L3. One end of the first capacitor C1 is connected to the output terminal, and the other end is connected to one end of the third inductor L3, which is grounded.

[0031] like Figure 2 In, a1-a mThe circuit consists of a GaN HEMT die, with L1, L2, and L3 as inductors and C1 as a capacitor. Input and Output represent the input and output ports of the RF power amplifier circuit, respectively. The high-linearity GaN HEMT RF power amplifier circuit structure of this invention mainly comprises m GaN HEMT dies connected in parallel. The gates of all GaN HEMT dies are connected together and then connected to the Input port to form the input port. All drains are connected together and then connected to the Output port to form the output port. Each GaN HEMT die has two inductors, L1 and L2, connected in parallel to ground at its gate. When Cgs increases with Pout to a certain value, Cgs will completely cancel out these two inductors, thus mitigating the tendency for the Δ value to deviate from 0. Furthermore, a resonant network formed by an inductor L3 and a capacitor C1 connected in parallel to ground at the drain is used. Selecting appropriate values ​​for C1 and L2 can suppress high-order harmonic energy in the output signal, ultimately ensuring the linearity of the overall circuit.

[0032] The applicant also discovered in their research that for GaN HEMT RF power devices, the metal on the Gate port and the metal on the Source port are located close to each other in the horizontal direction, and the space between them is filled with Si3N4 dielectric. This leads to the existence of gate-source parasitic capacitance Cgs, which increases quadratically with increasing Pout. Consequently, Δ deviates further and further from zero as the output power increases, resulting in a significant deterioration in linearity performance. This is one of the main reasons for the significant linearity defects in GaN HEMT RF power devices.

[0033] Therefore, this invention improves the internal structure of GaN HEMT RF power devices, see [link to relevant documentation]. Figure 3 The diagram shows the structural block diagram of the GaN HEMT RF power device. The GaN HEMT die includes a substrate layer, a buffer layer, a channel layer, a barrier layer, and a protective layer arranged sequentially. A source, a gate, and a drain are arranged above the protective layer. The protective layer forms an L-shaped groove, and the source is arranged at the top of the L-shaped groove so that the source end and the gate end are staggered in horizontal space.

[0034] The above technical solution etches the GaN cap layer into an L-shaped groove structure, and then performs metallization on the top of the L-shaped groove to form the Source port. The bottom of the Source port is flush with the top of the Gate port. At this time, the metal on the Gate and the metal on the Source are completely staggered, which further eliminates the influence of Cgs, thereby alleviating the tendency of Δ to move away from 0 as the output power increases, and effectively improving the linearity of the device.

[0035] Furthermore, the applicant also discovered the variation law of the transconductance gm of the power device in the research, as shown in the following formula (2).

[0036]

[0037] As the output power increases from a small signal level to saturation power, the voltage swing across the gate and drain continuously increases. This means that |VGS| + |VDS| will continuously increase. Furthermore, the increase in |VGS| causes electrons from the two-dimensional electron gas to be continuously drawn onto the gate, resulting in a decrease in N(x). Ultimately, this manifests as gm decreasing with increasing output power, causing Δ to move further away from 0 with increasing output power, leading to a significant deterioration in linearity performance. This is one of the main reasons for the significant linearity defects in GaN HEMT RF power devices.

[0038] Therefore, based on the above technical solution, the applicant has made further improvements to the internal structure of the GaN HEMT RF power device. See [link / reference] Figure 4 The diagram shows a structural block diagram of another preferred embodiment of the device. The GaN HEMT RF power device includes a substrate layer, a buffer layer, a second barrier layer (AlGaN extra layer), a channel layer (GaN channel layer), a first barrier layer (AlGaN barrier layer), and a protective layer arranged sequentially. The protective layer forms an L-shaped groove to offset the source end and the gate end in horizontal space. A first two-dimensional electron gas and a second two-dimensional electron gas are formed between the channel layer and the first and second barrier layers. The source, gate, and drain are used to receive external control signals to control the electron movement of the first and second two-dimensional electron gases formed by the channel layer.

[0039] In the above technical solution, applying electricity to the gate generates an electric field perpendicular to the two-dimensional electron gas. As the electric field on the gate gradually strengthens, electrons in the first two-dimensional electron gas will detach from the two-dimensional electron gas and reach the gate, resulting in electron loss. When the electric field increases to a certain level, electrons in the original two-dimensional electron gas will no longer be lost. After introducing the AlGaN extra layer, electrons in the newly formed second two-dimensional electron gas will also move towards the gate under the influence of the electric field. During this process, some electrons will move into the original first two-dimensional electron gas, thereby compensating for the loss of electrons in the original two-dimensional electron gas. That is, under large signals, electrons in the second two-dimensional electron gas will flow into the first two-dimensional electron gas.

[0040] Compared to traditional structures, this invention adds an AlGaN extra layer below the GaN channel layer, ultimately forming a GaN channel layer, an AlGaN extra layer, and an AlGaN barrier layer. The thickness of the AlGaNextra layer and the AlGaN barrier layer are kept the same. The GaN channel layer cannot be too thick, otherwise the second two-dimensional electron gas cannot enter the first two-dimensional electron gas. Typically, the thickness is around 100 nanometers. At this time, the electrons in the second two-dimensional electron gas formed by the GaN channel layer and the AlGaN extra layer can effectively compensate for the loss of electrons in the original two-dimensional electron gas, alleviate the decrease of gm, and thus alleviate the trend of Δ value moving away from 0, effectively improving the linearity of the device.

[0041] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0042] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A high linearity GaN HEMT RF power amplifier circuit, characterized in that, This circuit is integrated into one unit, with multiple GaN HEMT dies. The drains of each GaN HEMT die are connected together as the output terminal, and the gates of each GaN HEMT die are connected together as the input terminal. The source of each GaN HEMT die is grounded. The output terminal is connected to a resonant network in parallel. The gate of each GaN HEMT die is connected in parallel to one end of the first inductor L1 and the second inductor L2, and the other end of the first inductor L1 and the second inductor L2 is grounded. The resonant network includes a first capacitor C1 and a third inductor L3, wherein one end of the first capacitor C1 is connected to the output terminal, the other end of the first capacitor C1 is connected to one end of the third inductor L3, and the other end of the third inductor L3 is grounded. GaN HEMT die includes a substrate layer, a buffer layer, a channel layer, a barrier layer, and a protective layer arranged sequentially. A source, a gate, and a drain are disposed above the protective layer. The protective layer forms an L-shaped groove, and the source is disposed at the top of the L-shaped groove so that the source port and the gate port are horizontally offset from each other.

2. The high linearity GaN HEMT RF power amplifier circuit according to claim 1, characterized in that, The top of the drain port is flush with the top of the gate port, and the bottom of the source port is flush with the top of the gate port.

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