Power amplifier

A power amplifier includes a plurality of power amplification modules, each of which includes an input terminal and an output terminal. Equivalent input impedances seen respectively into the power amplification modules from the input terminals thereof are the same, and equivalent output impedances seen respectively into the power amplification modules from the output terminals thereof are the same. The input terminals of the power amplification modules are coupled together for receiving an input signal. The output terminals of the power amplification modules are coupled together for outputting an output signal. Each of the power amplification modules amplifies a portion of a power of the input signal to obtain a portion of a power of the output signal.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of Taiwanese Application No. 103129194, filed on Aug. 25, 2014.

FIELD OF THE INVENTION

The invention relates to an amplifier, and more particularly to a power amplifier.

BACKGROUND OF THE INVENTION

Referring toFIG. 1, a conventional radio frequency (RF) power amplifier includes a Wilkinson power divider81, two power amplifier modules82and a Wilkinson power combiner83.

The Wilkinson power divider81includes an input terminal811and two output terminals812,813. An equivalent impedance (Z91) seen into the Wilkinson power divider81from the input terminal811thereof is 50 ohms. Equivalent impedances (Z94, Z95) seen into the Wilkinson power divider81respectively from the output terminals812,813thereof are both 50 ohms. The Wilkinson power divider81receives a radio frequency input signal with a power of P1 at the input terminal811thereof, divides the radio frequency input signal into two first radio frequency signals, each with a power of P2, and outputs the first radio frequency signals respectively at the output terminals812,813thereof.

Each power amplifier module82is coupled to a respective output terminal812,813of the Wilkinson power divider81for receiving a respective first radio frequency signal therefrom, and amplifies the power of the respective first radio frequency signal by a predetermined amplification factor to obtain a respective second radio frequency signal with a power of P3.

The Wilkinson power combiner83includes two input terminals831,832coupled respectively to the power amplifier modules82, and an output terminal833. Equivalent input impedances (Z92, Z93) seen into the Wilkinson power combiner83respectively from the input terminals831,832thereof are both 50 ohms. An equivalent output impedance (Z96) seen into the Wilkinson power combiner83from the output terminal833thereof is 50 ohms. The Wilkinson power combiner83receives the second radio frequency signals respectively from the power amplifier modules82, combines the second radio frequency signals to obtain a radio frequency output signal with a power of P4, and outputs the radio frequency output signal at the output terminal833thereof.

The Wilkinson power divider81achieves a high degree of isolation between the output terminals812,813thereof (i.e., a scattering parameter therebetween is zero) when the equivalent impedances seen into the Wilkinson power divider81respectively from the input and output terminals811,812,813thereof are matched. The Wilkinson power combiner83achieves a high degree of isolation between the input terminals831,832thereof (i.e., a scattering parameter therebetween is zero) when the equivalent impedances seen into the Wilkinson power combiner83respectively from the input and output terminals831,832,833thereof are matched. In order to achieve impedance matching, the Wilkinson power divider81has to include a resistive element coupled between the output terminals812,813thereof, and the Wilkinson power combiner83has to include a resistive element coupled between the input terminals831,832thereof. With the inclusion of the resistive elements, the Wilkinson power divider81and the Wilkinson power combiner83are lossy (i.e., 2×P2<P1, and P4<2×P3), and a power gain of the conventional radio frequency power amplifier (i.e., a ratio of the power of the radio frequency output signal to the power of the radio frequency input signal) is decreased (i.e., smaller than the predetermined amplification factor). Therefore, the conventional radio frequency power amplifier cannot achieve both the high degree of isolation and the high power gain.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a power amplifier that can overcome the aforesaid drawback associated with the prior art.

According to this invention, a power amplifier is adapted for amplifying an input signal to generate an output signal. The power amplifier includes a number (N) of power amplification modules, each of which includes an input terminal and an output terminal, where N is a positive integer greater than one.

Equivalent input impedances seen respectively into the power amplification modules from the input terminals thereof are the same, and equivalent output impedances seen respectively into the power amplification modules from the output terminals thereof are the same.

The input terminals of the power amplification modules are coupled together for receiving the input signal. The output terminals of the power amplification modules are coupled together for outputting the output signal, and each of the power amplification modules amplifies a portion of a power of the input signal to obtain a portion of a power of the output signal.

DETAILED DESCRIPTION OF THE EMBODIMENT

Referring toFIG. 2, an embodiment of a power amplifier according to this invention is adapted to be coupled to a signal source (not shown) and an end terminal circuit (not shown). The power amplifier receives an input signal from the signal source, amplifies the input signal to generate an output signal, and outputs the output signal to the end terminal circuit. In an example, the power amplifier may be used in a transceiver of a communication system, the signal source may be a mixer or another power amplifier of the transceiver, and the end terminal circuit may be an antenna of the transceiver. Moreover, each of the input and output signals may be a signal of radio or other frequency.

The power amplifier includes a number (N) of power amplification modules1, each of which includes an input terminal11and an output terminal12, where N is a positive integer greater than one. Equivalent input impedances (Z1) seen respectively into the power amplification modules1from the input terminals11are the same, and equivalent output impedances (Z2) seen respectively into the power amplification modules1from the output terminals12are the same. The input terminals11of the power amplification modules1are coupled together for receiving the input signal, the output terminals12of the power amplification modules1are coupled together for outputting the output signal, and each of the power amplification modules1amplifies a portion of a power of the input signal to obtain a portion of a power of the output signal.

In one embodiment, the equivalent input impedance (Z1) seen into each of the power amplification modules1from the input terminal11thereof is N times an equivalent output impedance seen into the signal source, and the equivalent output impedance (Z2) seen into each of the power amplification modules1from the output terminal12thereof is N times an equivalent input impedance seen into the end terminal circuit. In this embodiment, the equivalent output impedance seen into the signal source and the equivalent input impedance seen into the end terminal circuit are both, for example, 50 ohms (i.e., pure resistive), each equivalent input impedance (Z1) is, for example, N×50 ohms, and each equivalent output impedance (Z2) is, for example, N×50 ohms. It is noted that, in other embodiments, the equivalent output impedance seen into the signal source, the equivalent input impedance seen into the end terminal circuit, the equivalent input impedances (Z1) and the equivalent output impedances (Z2) may be complex.

In this embodiment, each of the power amplification modules1further includes a first impedance matching unit13, a second impedance matching unit15, a third impedance matching unit16, a fourth impedance matching unit17and an amplification unit14. The first impedance matching unit13is coupled to the input terminal11. The second impedance matching unit15is coupled to the output terminal12. The amplification unit14is coupled between the first and second impedance matching units13,15for amplifying the portion of the power of the input signal to obtain the portion of the power of the output signal. The third impedance matching unit16is coupled between the amplification unit14and a power supply (not shown) that supplies a voltage (VDD). The fourth impedance matching unit17is coupled between ground and the amplification unit14. The third and fourth impedance matching units16,17cooperate with the first impedance matching unit13to determine the equivalent input impedance (Z1) seen into the power amplification module1from the input terminal11. The third and fourth impedance matching units16,17cooperate with the second impedance matching unit15to determine the equivalent output impedance (Z2) seen into the power amplification module1from the output terminal12.

FIG. 3illustrates an example of this embodiment in which N=2. In this example, the amplification unit14of each of the power amplification modules1includes a transistor (M1), e.g., an N-type metal oxide semiconductor field effect transistor. The transistor (M1) has a first terminal coupled to the second and third impedance matching units15,16, a second terminal coupled to the fourth impedance matching unit17, and a control terminal coupled to the first impedance matching unit13. Alternatively, the amplification unit14of each of the power amplification modules1may include multiple transistors (M1) that are, for example, cascoded or cascaded.

The first impedance matching unit13of each of the power amplification modules1includes a first transmission line (TL1) coupled between the input terminal11and the control terminal of the transistor (M1) of the amplification unit14.

The second impedance matching unit15of each of the power amplification modules1includes a second transmission line (TL2) coupled between the output terminal12and the first terminal of the transistor (M1) of the amplification unit14.

The third impedance matching unit16of each of the power amplification modules1includes a third transmission line (TL3) and a bypass capacitor (Cby). The third transmission line (TL3) is coupled between the power supply and the first terminal of the transistor (M1) of the amplification unit14. The bypass capacitor (Cby) is coupled between ground and a common node between the third transmission line (TL3) and the power supply, and has a capacitance of, for example, 1.23 pF. Alternatively, the bypass capacitor (Cby) may be omitted.

The fourth impedance matching unit17of each of the power amplification modules1includes a fourth transmission line (TL4) coupled between ground and the second terminal of the transistor (M1) of the amplification unit14.

The first to fourth transmission lines (TL1-TL4) of each power amplification module1are configured such that the equivalent input impedance (Z1) seen into the power amplification module1from the input terminal11is 2×50=100 ohms and such that the equivalent output impedance (Z2) seen into the power amplification module1from the output terminal12is 2×50=100 ohms. As a result, the equivalent input impedance seen into the power amplifier is 100//100=50 ohms, and matches the equivalent output impedance seen into the signal source, and the equivalent output impedance seen into the power amplifier is 100//100=50 ohms, and matches the equivalent input impedance seen into the end terminal circuit.

Since the equivalent input impedances (Z1) seen respectively into the power amplification modules1from the input terminals11thereof are the same, the amplification unit14of each power amplification module1receives half of the power of the input signal from the input terminal11through the first impedance matching unit13, and amplifies the received power of the input signal to obtain half of the power of the output signal that is outputted to the output terminal12thereof through the second impedance matching unit15. Then, the two halves of the power of the output signal outputted respectively by the power amplification modules1are summed at a common node between the output terminals12of the power amplification modules1.

In view of the above, since the power amplification modules1are coupled in parallel and have the same equivalent input impedances (Z1) and the same equivalent output impedances (Z2) in this embodiment, no resistive element is required to be coupled between any two of the power amplification modules1to achieve impedance matching, thereby attaining both a high degree of isolation and a high power gain. In addition, since a transmission line is nearly lossless, the power gain can be further increased when each of the first to fourth impedance matching units13,15,16,17is implemented by a transmission line.