CN102723917A - Power amplifier - Google Patents

Abstract

A power amplifier, comprising: a common-source transistor, a common-gate transistor and a capacitor, the source of the common-source transistor is connected to a ground signal, and the gate of the common-source transistor is used to connect to a first bias voltage; the common-gate The source of the transistor is connected to the drain of the common-source transistor, the gate of the common-gate transistor is used to connect to the second bias voltage, the drain of the common-gate transistor is coupled to a DC voltage source, and the capacitor is connected to the common The gate and drain of a gate transistor. Since a capacitance is connected between the gate and the drain of the common-gate transistor, a high-pass path is formed between the gate and the drain, so that the voltage difference between the gate and the drain is reduced, so that the drain has a Larger signal swings without reaching gate and drain breakdown voltages.

Description

a power amplifier

technical field

The invention relates to the field of power devices, in particular to a power amplifier.

Background technique

In prior art MOS power amplifiers, the drain-gate voltage is often three times higher than the supply voltage, which limits the maximum supply voltage that can be used in such amplifiers to prevent drain-gate breakdown. One way to improve this problem is to use a cascode structure in the power amplifier, which generally uses two transistors: a common source transistor and a common gate transistor. However, in this commonly used cascode structure, the drain-gate voltage of the common-gate transistor is often twice as high as the power supply voltage. When the power supply voltage is high, the drain-gate voltage of the common-gate transistor is generally also higher than Will exceed the pressure range of the tube.

FIG. 1 shows a standard cascode structure of two transistors, the transistor M1 is a common source transistor, the transistor M2 is a common gate transistor, and the drain of the transistor M1 and the source of the transistor M2 are connected together. For the convenience of description, the letters D, G, and S are used hereinafter to refer to the drain, gate, and source of a given transistor, for example, G1 refers to the gate of transistor M1, D2 refers to the drain of transistor M2, etc. wait. FIG. 2 shows a conventional power amplifier with a cascode structure, the transistor M1 is a cascode transistor, and the transistor M2 is a cascode transistor. The DC voltage Vgg1 is supplied to the gate G1 through a resistor Rg1 to provide a DC bias for the transistor M1, and the DC bias can be selected according to actual needs; the DC voltage Vgg2 is supplied to the gate G2 through a resistor Rg2 to provide a DC bias for the transistor M2. The value can also be selected according to actual needs; RF input signal RFin is coupled to G1 through capacitor Cin, G2 is connected to RF ground through resistor Rg2, but it is not RF ground itself, so the voltage at G2 can have RF swing, as long as The RF signal at D2 has a full swing, and the power amplifier can provide high output power; if the source voltage is high, the drain-gate voltage of the common-gate tube will generally exceed the withstand voltage range of the tube.

Contents of the invention

The invention aims to solve the problem that the drain-gate voltage of the common grid tube of the power amplifier in the prior art will exceed the withstand voltage range of the tube.

In order to solve the above technical problems, the present invention provides the following technical solutions:

A power amplifier, comprising: a common-source transistor, a common-gate transistor and a capacitor, the source of the common-source transistor is connected to a ground signal, and the gate of the common-source transistor is used to connect to a first bias voltage; the common-gate The source of the transistor is connected to the drain of the common-source transistor, the gate of the common-gate transistor is used for connecting the second bias voltage, the drain of the common-gate transistor is used for connecting a DC voltage source, and the capacitor is connected to the The gate and drain of the common gate transistor.

Compared with the prior art, the present invention has the following beneficial effects: in a power amplifier provided by the present invention, since a capacitance is connected between the gate and the drain of the common-gate transistor, a capacitor is formed between the gate and the drain. The high-pass path reduces the voltage difference between the gate and the drain, which enables the drain to have a larger signal swing without reaching the breakdown voltage of the gate and drain.

Description of drawings

FIG. 1 is a schematic diagram of a cascode structure of two transistors.

Fig. 2 is a power amplifier with cascode structure in the prior art.

FIG. 3 is a schematic diagram of a cascode structure of two transistors according to an embodiment of the present invention.

FIG. 4 is a power amplifier with cascode structure according to the first embodiment of the present invention.

FIG. 5 is a power amplifier with cascode structure according to the second embodiment of the present invention.

Detailed ways

In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

3 is a schematic diagram of a cascode structure of two transistors in an embodiment of the present invention; the cascode structure includes a common source transistor M1, a common gate transistor M2, and a capacitor Cb, and the source S2 of the common gate transistor M2 is connected to the common source The drain D1 of the transistor M1 is connected, and the capacitor Cb is connected to the gate G2 and the drain D2 of the common-gate transistor M2; since a capacitor is connected between the gate G2 and the drain D2 of the common-gate transistor M2, the gate A high-pass path is formed between the gate G2 and the drain D2, so that the voltage difference between the gate G2 and the drain D2 is reduced, so that the drain has a larger signal swing without reaching the gap between the gate and the drain. breakdown voltage.

FIG. 4 is a power amplifier with a cascode structure according to the first embodiment of the present invention; on the basis of the cascode structure in FIG. 3 , the gate G1 of the common source transistor M1 is provided with a first bias voltage Vgg1; The gate G2 of the common-gate transistor M2 is provided with a second bias voltage Vgg2, the drain D2 of the common-gate transistor M2 is coupled to a DC voltage source VDD, and the capacitor Cb is connected to the gate G2 of the common-gate transistor M2 and the drain D2; the source S1 of the common source transistor M1 is connected to the ground signal. Since a capacitance Cb is connected between the gate G2 and the drain D2 of the common-gate transistor M2, a high-pass path is formed between the gate G2 and the drain D2, so that the voltage difference between the gate G2 and the drain D2 is reduced , which enables a larger signal swing at the drain without reaching the breakdown voltage of the gate and drain.

In this embodiment, both the common-source transistor M1 and the common-gate M2 transistor are NMOS transistors, and may be other transistors in other embodiments, which will not be repeated here. In this embodiment, the gate G1 electrode of the common source transistor M1 is coupled to the radio frequency signal input terminal RFin through a coupling capacitor Cin; the gate G1 of the common source transistor M1 is connected to the first bias voltage Vgg1 through the first bias resistor Rg1 The drain D2 of the common-gate transistor M2 is connected to the DC voltage source VDD through a drain inductance Ldc; the gate G2 of the common-gate transistor M2 is connected to the second bias voltage Vgg2 through the second bias resistor Rb.

The working principle will be described in detail below. Since the first bias voltage Vgg1 and the second bias voltage Vgg2 are DC bias voltages, the corresponding input RF signal is also RF ground. Since the gate G2-drain D2 of the common-gate transistor M2 is connected to the capacitor Cb; so for DC, the DC bias voltage Vgg2 of the gate G2 of the common-gate transistor M2 is an arbitrary value independently applied through an external pin, The DC voltage of the drain D2 of the common-gate transistor M2 is VDD, and there is no connection between the two. For the radio frequency, the radio frequency swing at the drain D2 of the common gate transistor M2 is weakened by the high-pass characteristic of the Cb-Rb series connection, and the values of Cb and Rb can be reasonably selected according to the needs, so that the common gate transistor M2 A radio frequency swing is obtained at the gate G2 terminal, so that the voltage difference between the gate G2-drain D2 of the common-gate transistor M2 is reduced, which enables a larger signal swing at the drain D2 of the common-gate transistor M2 , without reaching the breakdown voltage of the gate G2-drain D2 of the common-gate transistor M2. As the voltage at the drain D2 of the common-gate transistor M2 increases, the voltage at the gate G2 of the transistor also increases by an amount determined by the values of the capacitor Cb and the second bias resistor Rb; and the source of the common-gate transistor M2 The voltage at terminal S2 is also increased so that the amount of voltage drop across each gate-drain of common-source transistor M1 and common-gate transistor M2 can be balanced. When the values of the second bias voltage Vgg2, the capacitor Cb and the second bias resistor Rb are selected reasonably, the gate-drain voltage difference between the common-source transistor M1 and the common-gate transistor M2 can be equal, and the best performance and the maximum signal swing. Since the value of the resistor and capacitor hardly changes with the voltage applied across it, the output impedance of the power amplifier will not change no matter how much the swing of the radio frequency signal is.

Fig. 5 is a power amplifier with a cascode structure in the second embodiment of the present invention; the first bias voltage Vgg1 and the second bias voltage Vgg2 are DC bias voltages, so they are also radio frequency grounds, but in practice, they are power supplies that provide DC voltages Or the output impedance of the circuit is not zero, so the two places are not ideal radio frequency grounds, so the radio frequency ground capabilities of the two places can be enhanced. In order to strengthen the RF ground at the gate G1 of the common source transistor M1, a first inductor L1 and a first capacitor C1 are also included on the basis of FIG. 4 , the first bias resistor Rg1, the first inductor L1 and the first capacitor C1 Connect to the ground signal after series connection. In order to strengthen the RF ground at the gate G2 of the common-gate transistor M2, a second inductor L2 and a second capacitor C2 are also included on the basis of FIG. Connect to the ground signal after series connection. In this embodiment, the radio frequency grounds at the gate G1 of the common source transistor M1 and the gate G2 of the common gate transistor M2 are strengthened, and the first inductor L1, the first capacitor C1, the second inductor L2, and the second capacitor C2 are all resonated at at the frequency of the radio frequency signal.

In this embodiment, the output of the amplifier is coupled to a load RL through a matching network 100, and the matching network 100 can transform the impedance of the load RL to the conjugate impedance of the output impedance of the amplifier to achieve the maximum power output. The embodiment of the present invention solves the problem of drain-gate withstand voltage faced by power amplifiers (especially class E power amplifiers) by coupling the radio frequency swing between the gate and the drain of the common-gate transistor. In an embodiment of the present invention, the optimum situation is when both transistors experience the same maximum drain-gate voltage, which means that a larger supply voltage can be used, resulting in higher output power.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (8)

1. A power amplifier, characterized in that it comprises: a common source transistor, a common gate transistor and a capacitor, the source of the common source transistor is connected to the ground signal, and the gate of the common source transistor is used to connect the first bias Voltage; the source of the common gate transistor is connected to the drain of the common source transistor, the gate of the common gate transistor is used to connect the second bias voltage, and the drain of the common gate transistor is used to connect a DC voltage source , the capacitor is connected to the gate and the drain of the common-gate transistor. 2. The power amplifier according to claim 1, wherein the common-source transistor and the common-gate transistor are both NMOS transistors. 3. The power amplifier according to claim 1, wherein the gate electrode of the common source transistor is coupled to the radio frequency signal input terminal through a coupling capacitor. 4. The power amplifier according to claim 1, wherein the gate of the common source transistor is connected to a first bias voltage through a first bias resistor. 5. The power amplifier according to claim 4, further comprising a first inductor and a first capacitor, the first bias resistor, the first inductor and the first capacitor are connected in series to the ground signal. 6. The power amplifier according to claim 1, wherein the drain of the common-gate transistor is connected to the DC voltage source through a drain inductance. 7. The power amplifier according to claim 1, wherein the gate of the common-gate transistor is connected to the second bias voltage through a second bias resistor. 8. The power amplifier according to claim 7, further comprising a second inductor and a second capacitor, the second bias resistor, the second inductor and the second capacitor are connected in series to the ground signal.

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