Radio frequency amplifier bandwidth expansion circuit based on resistor-capacitor series feedback

Abstract

The invention belongs to the technical field of integrated circuits, and particularly relates to a radio frequency amplifier bandwidth expansion circuit based on resistor-capacitor series feedback. The bandwidth expansion circuit comprises a first-stage common-gate amplifier, a second-stage common-source amplifier, a transformer-based inter-stage matching network between the two stages of amplifiers, and two resistor-capacitor series feedback paths, and a resistor-capacitor series feedback path is bridged at two sides of the interstage matching network, and feedback is introduced from the output end of the common source amplifier to the output end of the common gate amplifier, so that the quality factors of two resonant cavities of the interstage matching transformer are adjusted, and the targets of adjusting the gain of the amplifier and expanding the bandwidth of the radio frequency amplifier are further realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of integrated circuits, and in particular relates to a radio frequency amplifier bandwidth extension circuit based on resistor and capacitor series feedback. Background Art

[0002] In recent years, modern wireless communication technology has dramatically transformed people's lives. Smartphones and laptops supporting 2G / 3G / 4G mobile communication networks (GSM / WCDMA / LTE) have long become essential components of daily life. The advent of the 5G era has further improved the data transmission efficiency of modern communication systems. The 6G communication protocol, which promises comprehensive coverage of 5G millimeter-wave frequency bands and low-Earth orbit (LEO) satellite communication bands, further enables the utilization of a wider range of frequency resources. Achieving communication over such a wide frequency range requires radio frequency transceivers. RF transceivers are at the forefront of wireless communication terminals, and their structure and performance directly impact the entire communication system. To meet the broadband communication requirements of the 5G / 6G protocols, RF transceivers must also possess broadband transmission and reception capabilities.

[0003] Bandwidth extension technology is often used in broadband amplifier design and has extensive and important applications in RF transceivers and phased array circuits. Since the amplitude-frequency response characteristic curve of the transistor itself decreases with increasing frequency, designing an RF amplifier with a stable gain-frequency response curve over a wide frequency range requires the use of some special technical means or circuit topology. In theory, the voltage gain of the amplifier is equal to the transconductance of the transistor multiplied by the transresistance seen by its load end, that is, Therefore, common bandwidth extension technologies can be divided into two aspects. One is to adjust the frequency response of the transistor itself by introducing feedback, such as the gate-drain negative feedback resistor or source degeneration inductor of the common-source amplifier; the other is to adjust the passive load of the amplifier to adjust the frequency response of the transimpedance, such as broadband transformer matching technology.

[0004] Traditional techniques for adjusting amplifier transimpedance typically focus on adjusting the parameters of the amplifier load's inductor, transformer, or capacitor. For example, the classic broadband transformer matching technique utilizes the fourth-order system formed by the transformer and capacitor to produce two pairs of conjugate poles in the frequency response, transforming the transimpedance frequency response curve from a single-peak to a double-peak curve, thereby expanding the bandwidth. Building on this foundation, multi-stage amplifier designs can incorporate additional transformers, allowing for greater freedom in adjusting the gain curves of each amplifier stage, ultimately achieving a flat gain curve over a wide frequency range. However, the voltage gain frequency response of a single-stage amplifier often exhibits a significantly higher gain at low frequencies than at high frequencies. Achieving flat gain across the entire amplifier often requires adding additional resistors in parallel with the load resonant cavity to reduce the gain at low frequencies, but this introduces additional noise and gain loss. While flat gain can also be achieved through multi-stage gain staggering, this approach generally requires designing a cascaded amplifier with three or more stages, which increases design complexity.

[0005] In recent years, some unique methods for adjusting the transimpedance frequency response curve have emerged, such as the common-source amplifier over-neutralization technique. In a system consisting of a first-stage common-gate amplifier and a second-stage common-source amplifier, by increasing the neutralization capacitance of the second-stage common-source amplifier to form capacitive feedback from the drain to the source, the low-frequency value of the first-stage amplifier's load transimpedance frequency response can be reduced while increasing its high-frequency value, thereby reducing the fluctuation between the first-stage amplifier's low-frequency and high-frequency gains and expanding the bandwidth. However, the specific impact of this technique on the transimpedance curve is affected by the parameters of the second-stage common-source amplifier's load transformer, so careful design and adjustment of the passive transformer system is still required. Summary of the Invention

[0006] The purpose of the present invention is to provide a radio frequency amplifier bandwidth extension circuit based on resistor and capacitor series feedback to solve the long-standing problem in radio frequency amplifier design where the low-frequency gain is significantly higher than the high-frequency gain, and to provide a new solution to the bandwidth extension problem encountered in the design of broadband amplifiers, especially commonly used two-stage amplifiers.

[0007] The RF amplifier bandwidth extension circuit based on resistor-capacitor series feedback, provided by this invention, is implemented by introducing an additional resistor-capacitor series feedback path based on a two-stage cascade amplifier and a bandwidth transformer. Specifically, it includes a first-stage common-gate amplifier A, a second-stage common-source amplifier B, a transformer-based interstage matching network between the two amplifier stages, and two resistor-capacitor series feedback paths.

[0008] The amplifier circuit included in the present invention is a differential circuit, so the two-stage amplifier and the inter-stage matching network have differential symmetry, and the series resistor and capacitor feedback path also has differential symmetry.

[0009] In the present invention, two amplifier stages are cascaded via a two-port differential transformer. Each resistor-capacitor series feedback path consists of a resistor and a capacitor connected in series. The order of the series connections has little effect on circuit performance, so the order of the series connections can be reversed. One end of the first resistor-capacitor series path is connected to the negative drain output of the second-stage common-source amplifier, and the other end is connected back to the positive drain output of the first-stage common-gate amplifier. Conversely, one end of the second series path is connected to the positive drain output of the second-stage common-source amplifier, and the other end is connected to the negative drain output of the first-stage common-gate amplifier. The two feedback paths form negative feedback.

[0010] In the present invention, if resistor-capacitor feedback is not implemented, the quality factor of the resonant cavity on both sides of the transformer-based interstage matching network is generally determined by the equivalent parallel resistance of the transistor without an additional parallel resistor. The drain of the first-stage common-gate amplifier is connected to the first coil of the transformer, and its equivalent parallel resistance is generally hundreds of ohms, while the gate of the second-stage common-source amplifier is connected to the second coil of the transformer, and its equivalent parallel resistance is generally thousands of ohms. Therefore, the quality factor of the resonant cavity on the second-stage side of the interstage matching network is significantly higher than that on the first-stage side. This is reflected in the Z21 frequency response curve as a significantly higher low-frequency gain than a significantly higher high-frequency gain. Since the transconductance gain of the transistor itself also gradually decreases from low frequency to high frequency, the voltage gain of the first-stage common-gate amplifier further shows a situation where the low frequency is higher than the high frequency. In a two-stage amplifier, the second-stage voltage gain is generally lower, and the gain of the entire amplifier is mainly determined by the first stage. Therefore, the final amplifier gain is affected by the gain imbalance of the first stage, and the low frequency is significantly higher than the high frequency.

[0011] In the present invention, after introducing the series feedback of resistors and capacitors, the quality factor of the resonant cavity on the common source side of the second stage of the inter-stage matching network will be reduced, while the quality factor of the resonant cavity on the common gate side of the first stage will be improved. Therefore, the difference in the quality factors of the two resonant cavities can be narrowed, thereby reducing the difference between the low-frequency gain and the high-frequency gain of the amplifier.

[0012] In this invention, the specific quality factors of the two resonant cavities are affected by the size of the feedback resistors. Smaller feedback resistors increase the quality factor of the common-gate resonant cavity, while smaller quality factors of the common-source resonant cavity result in lower low-frequency gain and higher high-frequency gain for the first-stage amplifier. By appropriately selecting the feedback resistor values, a relatively stable gain-frequency response curve can be achieved for the entire amplifier.

[0013] In the present invention, the bandwidth extension circuit of the present invention is not only applicable to two-stage amplifiers, but also to multi-stage amplifiers. It can be manufactured under CMOS process, BiCMOS process, GeSi process, and GaAs process, including but not limited to the listed processes, and other processes are also acceptable.

[0014] The present invention is based on a RF amplifier bandwidth extension circuit with resistor and capacitor series feedback. On the basis of broadband matching of the differential amplifier transformer, by introducing additional resistor and capacitor series feedback, the load transimpedance frequency response curve of the common-gate amplifier is adjusted, which can solve the gain frequency response imbalance problem that is widely present in differential amplifiers, and provide a new solution for expanding the bandwidth of RF amplifiers.

[0015] Compared with the prior art, the present invention has the following significant advantages: In traditional broadband amplifier designs, additional resistors are often connected in parallel in the resonant cavity to reduce the gain of the low-frequency peak and thus increase the 3dB bandwidth of the amplifier. However, this approach is equivalent to introducing additional losses in the amplifier, which will reduce the efficiency of the amplifier in the power amplifier design and may also cause a significant deterioration of its noise figure in the low-noise amplifier. In addition, the use of multi-stage amplifier staggered matching requires the cascade of three or more amplifiers, which is more complex in circuit structure and has a large chip area overhead. The resistor-capacitor series feedback adopted in the present invention provides a new dimension for the gain adjustment of the RF amplifier, which can greatly balance the gain of low and high frequencies while introducing losses far lower than the direct parallel resistor solution. The technology of the present invention is widely applicable to the design of two-stage and more amplifiers, with high design freedom and a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the block diagram of the bandwidth expansion circuit structure based on resistor and capacitor series feedback.

[0017] Figure 2 This is a bandwidth expansion circuit diagram based on resistor and capacitor series feedback.

[0018] Figure 3 The frequency response diagram of the first-stage amplifier load transimpedance under different feedback resistor values ​​is shown.

[0019] Figure 4 The frequency response diagram of the first-stage amplifier voltage gain at different feedback resistor values ​​is shown. DETAILED DESCRIPTION

[0020] The present invention is further described below through embodiments in conjunction with the accompanying drawings.

[0021] The bandwidth expansion circuit provided by the present invention has a structure as follows Figure 1 As shown, it specifically includes a first-stage common-gate amplifier A100, a second-stage common-source amplifier B101, a transformer-based inter-stage matching network 102 between the two amplifiers, and two groups of resistor-capacitor series feedback paths, one group is composed of a resistor 103 and a capacitor 104 in series on one side, and the other group is composed of a resistor 105 and a capacitor 106 in series on the other side.

[0022] The amplifier circuit included in the present invention is a differential circuit, so the two-stage amplifier and the inter-stage matching network have differential symmetry, and the series resistor and capacitor feedback path also has differential symmetry, such as Figure 2 As shown. The first-stage amplifier is a common-gate amplifier 110, and the second-stage amplifier is a common-source amplifier 111. The two-stage amplifiers are cascaded via a two-port differential transformer 112. There are two groups of series resistor-capacitor feedback, and each group of resistor-capacitor series feedback paths consists of a resistor and a capacitor in series. The first resistor-capacitor series path consists of resistors 113 and 114, one end of which is connected to the negative drain output terminal 115 of the second-stage common-source amplifier and the other end is connected back to the positive drain output terminal 116 of the first-stage common-gate amplifier. In contrast, the second series path consists of resistors 117 and capacitors 118 in series, one end of which is connected to the positive drain output terminal 119 of the second-stage common-source amplifier and the other end is connected to the negative drain output terminal 1110 of the first-stage common-gate amplifier.

[0023] In the present invention, if resistor-capacitor feedback is not implemented and no additional parallel resistors are connected, the quality factor of the resonant cavities on both sides of the transformer-based interstage matching network is generally determined by the equivalent parallel resistance of the transistors. The drain of the first-stage common-gate amplifier is connected to the first coil 1111 of the transformer, and its equivalent parallel resistance is generally hundreds of ohms. The gate of the second-stage common-source amplifier is connected to the second coil 1112 of the transformer, and its equivalent parallel resistance is generally thousands of ohms. Therefore, the quality factor of the resonant cavity on the second-stage side of the interstage matching network is significantly higher than that on the first-stage side. This is reflected in the Z21 frequency response double-peak curve as the low-frequency peak gain is significantly higher than the high-frequency peak gain. As a result, the voltage gain of the first-stage common-gate amplifier shows a higher voltage gain at low frequencies than at high frequencies.

[0024] In the present invention, after introducing the resistor-capacitor series feedback, the specific quality factors of the two resonant cavities will be affected by the size of the feedback resistance. The smaller the feedback resistance, the higher the quality factor of the common gate side resonant cavity, and the smaller the quality factor of the common source side resonant cavity. Therefore, the gain of the low-frequency peak of the first-stage amplifier is lower, and the gain of the high-frequency peak is higher. Figure 3 The figure shows the Z21 frequency response of the inter-stage matching network under different feedback resistor values. As the resistance gradually decreases from 1000 ohms to 200 ohms, the low-frequency peak of Z21 of the inter-stage matching network gradually decreases, and the high-frequency peak gradually increases. Figure 4 The following is the corresponding voltage gain of the first-stage common-gate amplifier. As the voltage gain decreases, the low-frequency peak gain also gradually decreases, while the high-frequency peak gain gradually increases. By selecting the appropriate feedback resistor value, the gain of the entire RF amplifier can be kept stable over a wide frequency band.

[0025] In addition, during the specific layout implementation of the feedback technology involved in the present invention, it should be noted that since the resistor and capacitor series feedback traces must cross the interstage transformer, their trace length is relatively long, and low-layer metal needs to be used to control the trace width to be small, so as to avoid affecting the coupling coefficient and other parameters of the interstage transformer.

[0026] In summary, the present invention solves the problem of unbalanced gain frequency response curve that is common in two-stage amplifiers, and also solves the problem of large loss and high design complexity introduced by traditional band widening technology. It improves the freedom of gain adjustment of RF amplifiers and can meet the requirements for gain flatness of broadband amplifiers in different processes and scenarios.

Claims

1. A radio frequency amplifier bandwidth extension circuit based on resistor and capacitor series feedback, characterized in that: It includes a first-stage common-gate amplifier, a second-stage common-source amplifier, a transformer-based inter-stage matching network between the two amplifiers, and two resistor-capacitor series feedback paths; The amplifier circuit is a differential circuit, the two-stage amplifier and the inter-stage matching network have differential symmetry, and the series resistor and capacitor feedback path also has differential symmetry; The two-stage amplifiers are cascaded via a two-port differential transformer; each resistor-capacitor series feedback path is composed of a resistor and a capacitor in series; one end of the first resistor-capacitor series path is connected to the negative drain output of the second-stage common-source amplifier, and the other end is connected back to the positive drain output of the first-stage common-gate amplifier; in contrast, one end of the second series path is connected to the positive drain output of the second-stage common-source amplifier, and the other end is connected to the negative drain output of the first-stage common-gate amplifier, and the two feedback paths form negative feedback.

2. The radio frequency amplifier bandwidth extension circuit according to claim 1, wherein: The two resistor-capacitor series feedback paths reduce the quality factor of the resonant cavity on the common source side of the second stage of the inter-stage matching network and increase the quality factor of the resonant cavity on the common gate side of the first stage, thereby narrowing the difference in the quality factors of the two resonant cavities and reducing the difference between the low-frequency gain and the high-frequency gain of the amplifier.

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