CN112953419A - Nonlinear cancellation power amplifier based on cascode structure - Google Patents

Abstract

The invention belongs to the technical field of wireless communication, and provides a cascode-structure-based nonlinear cancellation power amplifier, which is used for solving the problems of poor linearity and poor return loss performance of an output end of the conventional cascode-structure-based power amplifier. The single-ended cascode structure circuit and the nonlinear cancellation circuit are formed, the common-gate tube M3 is added at the middle node of the single-ended cascode structure, the output resistance of the power amplifier is changed to be approximately equal to the optimal load resistance, and the output return loss performance of the device is greatly improved; meanwhile, the non-linear currents of the common-gate tube M3 and the common-source tube M1 in the common-source common-gate structure are mutually offset, so that the linearity of the power amplifier is improved; in addition, the common-gate transistor M3 does not introduce extra power consumption by itself, nor does it degrade the output power of the power amplifier. In conclusion, the nonlinear cancellation power amplifier provided by the invention has higher linearity and better output return loss performance.

Description

A Nonlinear Cancelling Power Amplifier Based on Cascode Structure

technical field

The invention belongs to the technical field of wireless communication, relates to a power amplifier in a transmitter of a communication system, and specifically provides a nonlinear cancellation power amplifier based on a cascode structure.

Background technique

With the rapid development of wireless communication technology, people have put forward a series of requirements for radio frequency transceivers, such as higher frequency, smaller size, lower power consumption, and higher reliability. As the core module in the RF transceiver, the performance of the power amplifier (PA) directly affects the quality of signal transmission, and its linearity and return loss at the output are two key performance indicators. A cascode structure is a common structure of a power amplifier (PA), and its circuit diagram is shown in Figure 1. The cascode structure has the advantages of high output power and high gain, but it also has many problems: First, the cascode transistor superimposed on the cascode will introduce additional nonlinearity, deteriorating the overall linearity of the cascode Second, the output resistance of the power amplifier of the cascode structure is too large, and the resistance value of the optimal load resistance connected to its output end is greatly different, so it has poor output return loss; third Third, the internal nodes of the cascode structure have impedance mismatches, which will reduce the overall gain.

In response to the above problems, the researchers improved the traditional cascode structure. An improved method is to add an inductance connected in parallel to the ground where the cascode transistor and the cascode transistor are connected, so that the parasitic capacitance of the node can be The inductor forms a parallel resonant cavity, which avoids the leakage of the signal at this node, thereby improving the gain, as shown in Figure 2; another improvement method is to insert a series inductor at the connection between the common gate tube and the common source tube, so that the common gate tube and the common source tube are connected. The load impedance seen by the source tube changes from capacitive to inductive, which achieves the matching between the common gate tube and the common source tube, and finally improves the gain, as shown in Figure 3.

However, the above two improvement methods both introduce inductance, which occupies a large layout area, is not conducive to layout, and introduces additional losses. In addition, the above-mentioned improved structure only improves the gain of the cascode structure power amplifier, and does not solve the problems of the linearity and poor return loss at the output end of the cascode structure power amplifier. The linearity of the power amplifier directly affects the communication quality. The lower the linearity, the greater the distortion of the transmitted signal and the worse the communication quality; the return loss at the output of the power amplifier limits its reliability, and the greater the return loss, The greater the reflected energy between the power amplifier and the load, the less reliable it is. Based on this, the present invention provides a new type of power amplifier with improved cascode structure.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a new type of cascode structure power amplifier in view of many problems existing in the above-mentioned traditional and improved cascode structure power amplifiers; the present invention adopts a linearized cascode structure without inductance, without The inductance structure greatly reduces the area of the circuit, and the linearization technology is realized by using an additional common gate transistor, which effectively changes the output impedance of the cascode and the flow of the internal nonlinear current, so that the power amplifier can achieve higher linearity and good return loss at the output.

To achieve the above object, the technical scheme adopted in the present invention is:

A nonlinear cancellation power amplifier based on a cascode structure, comprising: a single-ended cascode structure circuit, the single-ended cascode structure circuit comprising: a cascode transistor M1 and a cascode transistor M2; the The power amplifier further includes: a nonlinear cancellation circuit, which is composed of a common gate transistor M3, a high-frequency bypass capacitor C and an isolation resistor R, wherein the source of the common gate transistor M3 and the common source transistor M1 are connected. The drain is connected, the gate is connected to the control voltage V _ctrl after the isolation resistor R, the drain is connected to the supply voltage V _x , one end of the high-frequency bypass capacitor C is connected to the gate of the common gate transistor M3, and the other end is grounded.

Further, in the single-ended cascode structure, the source of the cascode transistor M1 is grounded, the drain is connected to the source of the cascode transistor M2, and the power supply voltage VDD is connected to the drain of the cascode transistor M2 through a choke inductor. The input signal is input from the gate of the common source transistor M1, amplified by the common source transistor M1 and the common gate transistor M2, and then output from the drain of the common gate transistor M2.

The beneficial effects of the present invention are:

The present invention provides a nonlinear cancellation power amplifier based on a cascode structure, which is composed of a single-ended cascode structure circuit and a nonlinear cancellation circuit. The connection point with the common gate tube) adds the common gate tube M3 (non-linear cancellation circuit) to change the output resistance of the power amplifier to make it almost equal to the optimal load resistance, thereby greatly improving the output return loss performance of the power amplifier; At the same time, the non-linear current of the cascode transistor M3 is opposite to the non-linear current of the cascode structure (M1), which can cancel each other out, thereby significantly improving the linearity of the power amplifier; , since no current flows through the common gate transistor M3, that is, it will not introduce additional power consumption itself, nor will it deteriorate the output power of the power amplifier, and there is no inductive structure in the nonlinear cancellation circuit, so that the layout area of the circuit is large. reduce;

To sum up, compared with the traditional power amplifier based on the cascode structure, the nonlinear cancellation power amplifier based on the cascode structure provided by the present invention has higher linearity and better output return. wave loss performance.

Description of drawings

FIG. 1 is a schematic circuit diagram of a conventional power amplifier based on a cascode structure.

FIG. 2 is a schematic circuit diagram of a power amplifier based on a cascode structure with an inductor in parallel at an intermediate node.

FIG. 3 is a schematic circuit diagram of a power amplifier based on a cascode structure with a series inductor at an intermediate node.

FIG. 4 is a schematic circuit diagram of a nonlinear cancellation power amplifier based on a cascode structure in the present invention.

FIG. 5 is a schematic diagram of the flow of nonlinear current of the nonlinear cancellation power amplifier based on the cascode structure in the present invention.

FIG. 6 is a comparison diagram of the output return loss of the nonlinear cancellation power amplifier based on the cascode structure and the power amplifier of the traditional cascode structure according to the embodiment of the present invention.

FIG. 7 is a comparison diagram of IMD3 between a non-linear cancellation power amplifier based on a cascode structure and a power amplifier with a traditional cascode structure according to an embodiment of the present invention.

Detailed ways

The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

This embodiment provides a non-linear cancellation power amplifier based on a cascode structure, the circuit structure of which is shown in Figure 4, and the linearization technology not only effectively improves the linearity of the traditional cascode structure, but also greatly improves the traditional cascode structure. The return loss of the structure, thereby significantly improving the reliability of the cascode power amplifier.

The present invention is mainly composed of two parts, the first part is a traditional single-ended cascode structure, including: a common source tube M1 and a common gate tube M2, wherein the source of the M1 tube is grounded, and its drain is connected to the source of the M2 tube, The power supply voltage VDD supplies power to the drain of M2 through the choke inductor, the signal is input from the gate of M1 tube, and is amplified by M1 and M2 and then output from the drain of M2; the second part is the common gate tube M3, high-frequency bypass A nonlinear cancellation circuit composed of capacitor C and isolation resistor R, in which the source of M3 tube is connected to the drain of M1 tube, the gate of M3 tube is connected to the control voltage V _ctrl after isolation resistor R, and the drain of M3 tube is connected to the control voltage V ctrl. The pole is connected to the power supply voltage V _x , one end of the high-frequency bypass capacitor C is connected to the gate of the M3 tube, and the other end is grounded; the specific circuit diagram is shown in Figure 4, the common source tube M1, the common gate tube M2 and the common gate tube M3 all use NMOS transistors .

The working principle of the present invention is:

1. Improvement of the return loss at the output of the power amplifier;

Due to the non-linear cancellation circuit, the output resistance of the power amplifier is reduced from g _m2 · r _O1 · r _O2 in the traditional structure to g _m2 · (r _O1 //r ₃ ) · r _O2 , where g _m2 is the value of M2 Transconductance, r _O1 is the output resistance of M1, r _O2 is the output resistance of M2, r ₃ is the drain-source resistance of M3; and the optimal load resistance of the cascode structure PA is equal to VDD/(2I _DC ), where VDD is the power supply The voltage and I _DC are the drain quiescent current of the common source transistor M1. For a general CMOS process, the value of VDD/(2I _DC ) is about several tens of ohms, the value of g _m2 ·r _O1 ·r _O2 is between several hundred and several thousand ohms, g _m2 ·(r _O1 // r ₃ ) The value of r _O2 is between tens to hundreds of ohms; to achieve the maximum power of the power amplifier (PA), the PA output must be connected to the optimal load resistance, and the return loss of the output is determined by the output resistance and the load. The value of the resistor determines, the closer the two are, the better the return loss.

It can be seen that in the traditional power amplifier based on the cascode structure, there is an order of magnitude difference between the optimal load resistance VDD/(2I _DC ) and the output resistance g _m2 · r _O1 · r _O2 ; and in the present invention, the optimal load resistance The resistance VDD/(2I _DC ) is very close to the output resistance g _m2 · (r _O1 //r ₃ ) · r _O2 , and by adjusting the size of M3 and V _ctrl , r ₃ can be further changed, so that the output resistance and the most The optimal load resistances are nearly equal; therefore, the present invention has better return loss than the traditional cascode structure. In addition, since there is no voltage difference between the source and drain of M3, no current will flow through this transistor, so it will not introduce additional power consumption by itself, nor will it deteriorate the output power of the PA.

2. For the improvement of the linearity of the power amplifier;

其中，g₃为M1管的三阶跨导、A为输入电压的幅度，流过M3的三阶非线性电流幅度为：

其中，

是M3管的三阶跨导，

为X点的电压幅度。通过调节M1和M3的尺寸，可以使得流过二者的三阶非线性电流的幅度相等，从而使得流过M2的三阶非线性电流为0，也就没有非线性电流会输出到负载；因此，本发明相较于传统的cascode结构提升了线性度。In this embodiment, the flow direction of the nonlinear current of the nonlinear cancellation power amplifier based on the cascode structure is shown in FIG. 5 ; the magnitude of the third-order nonlinear current flowing through M1 is:

Among them, g ₃ is the third-order transconductance of the M1 tube, A is the amplitude of the input voltage, and the third-order nonlinear current amplitude flowing through M3 is:

in,

is the third-order transconductance of the M3 tube,

is the voltage amplitude at point X. By adjusting the size of M1 and M3, the amplitude of the third-order nonlinear current flowing through them can be made equal, so that the third-order nonlinear current flowing through M2 is 0, and no nonlinear current will be output to the load; therefore , compared with the traditional cascode structure, the present invention improves the linearity.

To sum up, the present invention adopts the nonlinear cancellation technology, compared with the power amplifier of the traditional cascode structure, the return loss and linearity of the output end have been significantly improved; under the condition that the main circuit parameters are kept the same, the In the embodiment, the nonlinear cancellation power amplifier based on the cascode structure and the traditional cascode structure power amplifier (FIG. 1) are simulated and tested, and the test results are shown in FIG. 6 and FIG. 7, respectively. As shown in FIG. 6 , compared with the traditional cascode structure power amplifier, the return loss ( S22 ) of the output end of the power amplifier provided in this embodiment is increased by 6-8 dB in the entire operating frequency band; as shown in FIG. 7 , compared with For the traditional cascode structure power amplifier, the IMD3 of the power amplifier provided in this embodiment is increased by at most 20dB; it can be seen that, compared with the traditional cascode structure power amplifier, the present invention has better output return loss characteristics and higher linearity Spend.

The above descriptions are only specific embodiments of the present invention, and any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes; all the disclosed features, or All steps in a method or process, except mutually exclusive features and/or steps, may be combined in any way.

Claims (2)

1. A nonlinear cancellation power amplifier based on a cascode structure, comprising: a single-ended cascode structure circuit, the single-ended cascode structure circuit comprising: a cascode transistor M1 and a cascode transistor M2; The power amplifier further includes: a nonlinear cancellation circuit, which is composed of a common gate transistor M3, a high-frequency bypass capacitor C and an isolation resistor R, wherein the source of the common gate transistor M3 and the common source transistor The drain of M1 is connected, the gate is connected to the control voltage V _ctrl after the isolation resistor R, and the drain is connected to the supply voltage V _x . One end of the high-frequency bypass capacitor C is connected to the gate of the common gate transistor M3 and the other end is grounded. 2. The nonlinear cancellation power amplifier based on the cascode structure according to claim 1, characterized in that, in the single-ended cascode structure, the source of the cascode M1 is grounded, and the drain and the common source are grounded. The source of the gate transistor M2 is connected, the power supply voltage VDD is connected to the drain of the common gate transistor M2 through the choke inductance, the input signal is input from the gate of the common source transistor M1, amplified by the common source transistor M1 and the common gate transistor M2, The drain output of gate transistor M2.

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