A transmission line compensated bias circuit

Abstract

This invention belongs to the field of solid-state microwave power amplifiers, specifically relating to a transmission line compensated bias circuit. This transmission line compensated bias circuit has a symmetrical structure, mainly composed of transmission line 1, transmission line 2, and a bias line. Transmission line 1 has a characteristic impedance of Z and an electrical length of θ; transmission line 2 has a characteristic impedance of Z and an electrical length of θ; and the bias line has a characteristic impedance of Z0. b / 2, Electric length is θ b When the characteristic impedance Z of the bias line b / 2, Electrical length θ b When determined, the optimal values ​​for Z and θ are: the parasitic inductance of the transmission line compensated bias circuit of this invention is smaller than that of existing bias circuits, resulting in less voltage overshoot when applied to high-power pulse power amplifiers, thus improving the reliability and safety of high-power pulse power amplifiers. Simultaneously, the matching bandwidth of the transmission line compensated bias circuit is more than twice that of existing bias circuits, making it more suitable for broadband power amplifiers. This invention has high application value in the field of high-power broadband pulse power amplifiers.

Description

Technical Field

[0001] This invention belongs to the field of solid-state microwave power amplifiers, specifically relating to a transmission line compensated bias circuit. Background Technology

[0002] Pulsed microwave systems have a wide range of applications, including pulsed radar and burst communication systems. These systems require power amplifier circuits to operate in pulse modulation mode. Pulse modulation includes gate bias voltage modulation and drain bias voltage modulation. Hyo-Jong Kim et al., in their 2017 article "An X-Band 100W GaNHEMT PowerAmplifier Using a Hybrid Switching Method for Fast Pulse Switching" (published in Progress In Electromagnetics Research B, Vol. 78), pointed out that drain bias voltage modulation can achieve higher efficiency and greater output power than gate bias voltage modulation. Therefore, pulsed power amplifiers mainly use drain bias voltage modulation. When a pulsed power amplifier uses drain bias modulation, the drain supply current is a dynamic current Id within the microwave excitation pulse and a static current Iq outside the microwave excitation pulse. Therefore, at the instant the microwave excitation signal is turned off, a drain voltage overshoot V occurs. s :

[0003]

[0004] In the formula, L is the parasitic inductance of the drain power supply path, and t f The falling edge time of the excitation signal. Reduce drain voltage overshoot V. s With L, I d I q t f Related. With the increasing maturity of GaN technology, a third-generation semiconductor material, the output power of power amplifiers has been continuously improving, currently exceeding the kW level. For example, in the 2007 paper by E. Mitani et al., "A kW-class AlGaN / GaN HEMT Pallet Amplifier for S-band High Power Application" (published in Proceedings of the 2nd European Microwave Integrated Circuits Conference), the current I... d I q The value and difference increase significantly, and at the same time, in order to improve the waveform quality, tf Only at the nanosecond level, these factors cause a small inductance L to result in a large voltage overshoot V. s When the drain voltage overshoots V s If the value is too high, it will cause the drain voltage amplitude to be too large, affecting the safety of the power amplifier.

[0005] To reduce drain voltage overshoot and improve the safety and reliability of power amplifiers, it is necessary to reduce the drain parasitic inductance L. The bias circuit of the power amplifier is a crucial factor affecting the drain parasitic inductance. By reducing the size of the bias circuit, the parasitic inductance of the bias circuit can be reduced, thereby reducing the drain parasitic inductance.

[0006] Existing technology:

[0007] Figure 1 This is a schematic diagram of an existing bias circuit, consisting of transmission line 1, transmission line 2, and a bias line. Transmission line 1 has a characteristic impedance of 50Ω and an electrical length of λ / 4, transmission line 2 has a characteristic impedance of 50Ω and an electrical length of λ / 4, and the bias line has a characteristic impedance of Zc and an electrical length of λ / 4. The power amplifier outputs microwaves at frequency f, which are input through port 1, pass through transmission lines 1 and 2, and are output through port 2. The bias line is equivalent to an open circuit for microwaves at frequency f, so it does not affect microwave transmission. The drain current is input through the power supply port, passes through the bias line and transmission line 1, and provides a pulse voltage to the drain of the power amplifier. The parasitic inductance of the bias circuit is determined by the dimensions of transmission lines 1 and the bias line; the smaller the width and the larger the length of transmission lines 1 and the bias line, the larger the parasitic inductance of the bias circuit.

[0008] Problems with existing technology:

[0009] The bias lines and transmission lines of existing bias circuits are relatively large, resulting in a large parasitic inductance. When applied to high-power pulse power amplifiers, this can lead to significant voltage overshoot, affecting the reliability and safety of the power amplifier. Summary of the Invention

[0010] In view of the above-mentioned technical problems, the present invention proposes a transmission line compensation type bias circuit, which can reduce the size of the bias line, thereby reducing the parasitic inductance of the bias circuit, reducing voltage overshoot when applied to high-power pulse power amplifiers, and improving the reliability and safety of high-power pulse power amplifiers.

[0011] The technical solution of the present invention is as follows:

[0012] Figure 2This is a schematic diagram of the transmission line compensation bias circuit proposed in this invention. The transmission line compensation bias circuit has a symmetrical structure and mainly consists of transmission line 1, transmission line 2, and a bias line. Transmission line 1 has a characteristic impedance of Z and an electrical length of θ; transmission line 2 has a characteristic impedance of Z and an electrical length of θ; and the bias line has a characteristic impedance of Z0. b / 2, Electric length is θ b The power amplifier outputs microwaves at frequency f, which are input through port 1, pass through transmission lines 1 and 2, and are output through port 2. The drain supply current is input through the power supply port, passes through the bias line and transmission line 1, and provides a pulse voltage to the drain of the power amplifier. The parasitic inductance of the bias circuit is determined by the dimensions of transmission line 1 and the bias line; the smaller the width and the longer the length of transmission line 1 and the bias line, the larger the parasitic inductance of the bias circuit.

[0013] The following proves that the bias line is equivalent to an open circuit for microwaves at frequency f, and that the bias line does not affect microwave transmission. Figure 3 This is a schematic diagram of the equivalent circuit of the transmission line compensation bias circuit proposed in this invention. The characteristic impedance is Z. b / 2, Electric length is θ b The bias line is split into two characteristic impedances Z. b The electric length is θ b The offset line. Y in the diagram. A Y is the admittance of the right-hand transmission line end when viewed from the right side. B For the admittance looking toward the bias line, Y CR Y CL These are the admittances when viewed from the middle end towards the right and left, respectively.

[0014] According to transmission line theory, we can obtain:

[0015]

[0016]

[0017] Y CR =Y A +Y B

[0018] Because the left and right sides are perfectly symmetrical, therefore Y CR Y CL equal:

[0019] Y CR =Y CL

[0020] To achieve impedance matching between the load and the power amplifier using the bias network, Y CR Y CL Conjugate matching is required, that is:

[0021]

[0022] We can obtain:

[0023] img(Y CR ) = 0

[0024] By combining the above equations, we can obtain Z, θ, and Zo. b θ b The relationship between them:

[0025]

[0026] In the formula, Z L For load, the value is 50 ohms.

[0027] This equation is a quadratic equation in tanθ, in Z. b θ b Given that the equation has a solution, the condition is:

[0028]

[0029] Z must meet one of the following two conditions:

[0030]

[0031]

[0032] For Z that satisfies the above conditions, the transmission line electrical length θ has the following corresponding solutions:

[0033]

[0034]

[0035] Because the matching bandwidth of the bias circuit is related to Y CR The slope of the phase change with frequency They are negatively correlated, so The smaller the value, the wider the matching bandwidth of the bias circuit. When Z has only one root, The minimum value is obtained by widening the matching bandwidth of the bias circuit, i.e., the optimal solution for Z is:

[0036]

[0037] At this point, θ1 and θ2 are equal, and the optimal solution for the transmission line electrical length θ is:

[0038]

[0039] The beneficial effects of this invention are:

[0040] The transmission line compensated bias circuit proposed in this invention can reduce the parasitic inductance of the bias circuit by more than 2 / 5 compared with existing bias circuits. Therefore, when applied to high-power pulse power amplifiers, the transmission line compensated bias circuit exhibits less voltage overshoot, thus improving the reliability and safety of the high-power pulse power amplifier. Simultaneously, the matching bandwidth of the transmission line compensated bias circuit is more than twice that of existing bias circuits, making it more suitable for broadband power amplifiers. This invention has high application value in the field of high-power broadband pulse power amplifiers. Attached image description:

[0041] Figure 1 Schematic diagram of a traditional bias circuit;

[0042] Figure 2 : Schematic diagram of the transmission line compensation bias circuit proposed in this invention;

[0043] Figure 3 : Equivalent circuit diagram of the transmission line compensation bias circuit proposed in this invention;

[0044] Figure 4 : Compensate for the characteristic impedance and electrical length of the transmission line;

[0045] Figure 5 Phase slope at 8 GHz;

[0046] Figure 6 Different Z0 correspond to different phases;

[0047] Figure 7 Simulation results of reflection coefficients of transmission line compensated bias circuits and existing bias circuits;

[0048] Figure 8 Simulation results of insertion loss of transmission line compensated bias circuit and existing bias circuit. Detailed implementation method:

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0050] Operating at 8GHz, Z b θ b Simulations were conducted with the current set to 100Ω and 30° respectively. Figure 4The text explains the acceptable characteristic impedance and electrical length of the transmission line: when the characteristic impedance is less than 30Ω, there are two electrical lengths to choose from; when the characteristic impedance is 30Ω, there is only one electrical length to choose from, 53°; when the characteristic impedance is greater than 30Ω, it is impossible to ideally compensate for the bias line.

[0051] Figure 5 Y was calculated CR The curve showing the phase slope as a function of characteristic impedance shows that at 30Ω, Y... CR The phase slope is the smallest. Figure 6 The figure shows Y under three characteristic impedances. CR The phase further confirms this view.

[0052] Based on the above analysis, the transmission line compensated bias circuit achieves the widest matching bandwidth when the characteristic impedance and electrical length are selected to be 30Ω and 53°, respectively. Simulation comparisons of the reflection coefficient and insertion loss between the transmission line compensated bias circuit and existing bias circuits are shown in [the table below]. Figure 7 , Figure 8 S11 and S12 represent the reflection coefficient and insertion loss of the transmission line compensated bias circuit, with a loss of 0dB at 8GHz and a relative bandwidth (matching bandwidth) of 89.1% for the -15dB reflection coefficient. S33 and S34 represent the reflection coefficient and insertion loss of the existing bias circuit, with a loss of 0dB at 8GHz and a relative bandwidth (matching bandwidth) of 44.2% for the -15dB reflection coefficient. Simulation results demonstrate that the matching bandwidth of the transmission line compensated bias circuit is more than twice that of the existing bias circuit.

[0053] The bias line length of the transmission line compensation type bias circuit proposed in this invention is 30°, which is only 1 / 3 of the bias line length of existing bias circuits, and the corresponding parasitic inductance is also only 1 / 3. The characteristic impedance of transmission line 1 in the transmission line compensation type bias circuit proposed in this invention is 30Ω, which is only 3 / 5 of the bias line length of existing bias circuits, and the corresponding parasitic inductance is also only 3 / 5. Considering the changes in parasitic inductance of the bias line and the transmission line, the parasitic inductance of the transmission line compensation type bias circuit proposed in this invention is reduced by more than 2 / 5 compared with the parasitic inductance of existing bias circuits.

[0054] Theoretical and simulation results show that selecting the correct transmission line impedance and length can effectively reduce the parasitic inductance of the transmission line compensated bias circuit proposed in this invention. When applied to high-power pulse power amplifiers, the transmission line compensated bias circuit exhibits less voltage overshoot, thus improving the reliability and safety of the amplifiers. Furthermore, the matching bandwidth of the transmission line compensated bias circuit is more than twice that of existing bias circuits, making it more suitable for broadband power amplifiers.

Claims

1. A transmission line compensation type bias circuit, which is a symmetrical structure and mainly consists of a transmission line 1, a transmission line 2 and a bias line, the transmission line 1 has a characteristic impedance of Z and an electrical length of θ, the transmission line 2 has a characteristic impedance of Z and an electrical length of θ, and the bias line has a characteristic impedance of Z / 2 and an electrical length of θ. b b A microwave with a power amplifier output frequency of f is input from a port 1, output from a port 2 after passing through the transmission line 1 and the transmission line 2, and a drain supply current is input from a power supply port, and a pulse voltage is provided for the drain of the power amplifier after passing through the bias line and the transmission line 1; characterized in that:​ In the formula, Z L is a load, the value of which is 50 ohms.

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