Unilateral Feedback Power Amplifier and Method for Realizing the Same

Abstract

A unilateral feedback power amplifier utilizes new feedback techniques and devices to make the amplified high-frequency signal unilateral, let the output power, power gain and impedance matching simultaneously accomplish the optimal values, and enhance the stability of the system. In this feedback amplifier, a generalized multi-port feedback circuit is in shunt with the input terminal and the output terminal of the power transistor. This generalized multi-port feedback circuit receives an amplified high-frequency signal and eliminates the reverse admittance of the amplified high-frequency signal to let the admittance value of the output amplified high-frequency signal approach zero so as to be unilateral. Moreover, the generalized multi-port feedback power amplifier differs from the conventional power amplifier of cascaded architecture in that the ground terminal of the power transistor is directly connected to the system ground. Therefore, the heat-radiating problem of the power transistor can be greatly improved.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawing, in which:

FIG. 1 is a diagram of a conventional power amplifier;

FIG. 2 is a block diagram of the present invention;

FIG. 3 is a diagram of the generalized 4-port feedback circuit of the present invention;

FIG. 4 is a circuit diagram of the generalized 4-port feedback power amplifier of the present invention; and

FIG. 5 is a diagram showing the positions of the power matching points and the conjugate matching points on the Smith chart with and without the feedback amplifier.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention proposes a new unilateral feedback power amplifier, in which a generalized multi-port feedback circuit is used to let the output power, power gain and impedance matching of a power amplifier accomplish the optimum values. Moreover, the high-frequency signal amplified by the power amplifier is made unilateral to enhance the stability of the system. The present invention will be exemplified with generalized 4-port feedback circuits below.

In order to improve the drawbacks of conventional power amplifiers, as shown in FIG. 2, the present invention proposes a new unilateral feedback power amplifier, which comprises a 2-port power transistor 200, a generalized 4-port feedback circuit 205, an output impedance matching circuit 210 and an input impedance matching circuit 215. It should be noted that the generalized 4-port feedback circuit 205 includes all feedback circuits that can be used with 2-port power transistors (a 2- or 3-port feedback circuit can be viewed as a special case of the generalized 4-port feedback circuit). The generalized 4-port feedback circuit 205 in FIG. 2 is further composed of two 2-port circuits and a capacitive shunt component. Through the feedback circuit, in order to let the admittance Y_opt of the output terminal of the power transistor 200 viewed at plane A satisfy Y_1dB,opt, the required load admittance at plane A′ is converted to:

$Y_L=\frac{\left(\begin{array}{c}-Y_{24}^fY_{33}^fY_{41}^fY_{21}^d+Y_{23}^fY_{34}^fY_{41}^fY_{21}^d+\\ Y_{24}^fY_{31}^fY_{43}^fY_{21}^d-Y_{21}^fY_{34}^fY_{43}^fY_{21}^d-Y_{23}^fY_{31}^fY_{44}^fY_{21}^d+\\ Y_{21}^fY_{33}^fY_{44}^fY_{21}^d+Y_{34}^fY_{41}^fY_{12}^dY_{21}^d-Y_{31}^fY_{44}^fY_{12}^dY_{21}^d+\\ Y_{24}^fY_{32}^fY_{41}^fY_{22}^d-Y_{22}^fY_{34}^fY_{41}^fY_{22}^d-Y_{24}^fY_{33}^fY_{42}^fY_{22}^d+\\ Y_{21}^fY_{34}^fY_{42}^fY_{22}^d+Y_{22}^fY_{31}^fY_{44}^fY_{22}^d-Y_{21}^fY_{32}^fY_{44}^fY_{22}^d-\\ Y_{34}^fY_{41}^fY_{11}^dY_{22}^d-Y_{34}^fY_{41}^fY_{11}^dY_{22}^d+Y_{31}^fY_{44}^fY_{11}^dY_{22}^d+\\ Y_{24}^fY_{32}^fY_{41}^fY_{\mathrm{opt}}-Y_{24}^fY_{32}^fY_{42}^fY_{\mathrm{opt}}+Y_{21}^fY_{34}^fY_{42}^fY_{\mathrm{opt}}+\\ Y_{22}^fY_{31}^fY_{44}^fY_{\mathrm{opt}}-Y_{34}^fY_{41}^fY_{11}^dY_{\mathrm{opt}}+Y_{31}^fY_{44}^fY_{11}^dY_{\mathrm{opt}}+\\ Y_{24}^fY_{32}^fY_{21}^dY_{\mathrm{opt}}-Y_{21}^fY_{44}^fY_{21}^dY_{\mathrm{opt}}\end{array}\right)}{\left(\begin{array}{c}{Y}_{23}^fY_{31}^fY_{21}^d-Y_{21}^fY_{33}^fY_{21}^d+Y_{31}^fY_{12}^dY_{21}^d-Y_{22}^fY_{31}^fY_{22}^d+\\ Y_{21}^fY_{32}^fY_{22}^d-Y_{31}^fY_{11}^dY_{22}^d-Y_{22}^fY_{31}^fY_{\mathrm{opt}}-Y_{21}^fY_{32}^fY_{\mathrm{opt}}-\\ Y_{31}^fY_{11}^dY_{\mathrm{opt}}+Y_{21}^fY_{21}^dY_{\mathrm{opt}}\end{array}\right)}$

where Y_mn^f, (m,nεN, 1≦m,n≦4) are 4-port admittance matrix parameters of the generalized 4-port feedback circuit, Y₂₁^d (m,nεN, 1≦m,n≦2) are 2-port admittance matrix parameters of the power transistor. By adjusting the 4-port admittance matrix parameters of the generalized 4-port feedback circuit 205, the power transistor 200 plus the generalized 4-port feedback circuit can first be made unilateral, and conjugate matching of Y_L and the output impedance Y_OUT of the power transistor 200 matched with the 4-port feedback circuit 205 can then be achieved. In this way, the output power, power gain and impedance matching of the power transistor 200 can simultaneously accomplish the optimum values.

FIG. 3 is a diagram of the generalized 4-port feedback circuit 205 of the present invention. The generalized 4-port feedback circuit 205 comprises a capacitive shunt component (jB) 300 and a generalized 2-port circuit (T1) 305 disposed at the input terminal of the power transistor 200 and a generalized 2-port circuit (T2) disposed at the output terminal of the power transistor 200. Moreover, a ground terminal 315 of the power transistor 200 is directly connected to the system ground to greatly improve the heat-radiating problem. The steps of making the power transistor 200 unilateral are as follows: first adjusting T1 (305) and T2 (310) to let the real part of the reverse admittance Y₁₂′ in [Y′] be zero; then using the capacitive shunt component (jB) 300 to eliminate the imaginary part of the reverse admittance Y₁₂′ in [Y′]. Because there are many sets of (T1) 305 and (T2) 310 letting the real part of Y₁₂′ be zero, an arbitrary set can be chosen to accomplish conjugate matching of Y_L and the output impedance Y_OUT of the power transistor 200 matched with the 4-port feedback circuit 205.

FIG. 4 is a circuit diagram of the generalized 4-port feedback power amplifier of the present invention. The power transistor 200 used is of the type HWF1686RA manufactured by Hexawave Inc. Each of the generalized 2-port circuits (T1) 305 and (T2) 310 is realized with a series transmission line and a parallel transmission line. The capacitive shunt component (jB) 300 is realized with a capacitor of 0.1 pF. The output matching circuit 210 and the input matching circuit 215 are realized using the transmission lines as the matching components. Moreover, a bias circuit 320 is responsible for providing a load voltage for the 2-port circuit (T1) 305, and a bias circuit 325 is responsible for providing a load voltage for the 2-port circuit (T2) 310. FIG. 5 is a diagram showing the positions of the power matching points and the conjugate matching points on the Smith chart with and without the feedback amplifier. As can be clearly seen from the figure, two matching points of the conventional power amplifier are far apart from each other, causing the designer to be hard to design an appropriate matching circuit. For a power amplifier added with the generalized 4-port feedback circuit of the present invention, however, the distance between the two matching points are apparently small, hence facilitating the design. It is also demonstrated that the 4-port feedback circuit of the present invention can let the output power, power gain and impedance matching of the power transistor simultaneously accomplish the optimum values. Table 1 shows the differences and improvements in characteristics of the conventional power amplifier without feedback and the power amplifier added with the generalized 4-port feedback circuit of the present invention. As can be clearly seen from Table 1, regardless of simulation or actual measurement, the power amplifier with feedback has apparent improvements in the characteristics such as reflection loss, power gain and reverse gain. Moreover, the output power (P_1dB) can achieve the output power of the conventional power amplifier.

	TABLE 1
		Power amplifier
		added with the
		generalized 4-port
	Conventional power	feedback circuit
	amplifier without	of the present
	feedback	invention	Difference
Characteristics	Simulated	Measured	Simulated	Measured	Simulated	Measured
Power gain (dB)	13.4	12.6	19	18.8	5.6	6.2
Reverse gain (dB)	−28.3	−30	−41.6	−43.1	−13.3	−13.1
Output reflection loss	3	3.8	11	8.6	8	4.8
(dB)
Input reflection loss	30	12.2	23.6	20.4	−6.4	8.2
(dB)
Gain compression (P1 dB)		29		29		0
(dBm) at output power
of 1 dB
Power added efficiency		40		37		−3
(PAE) (%)

Although the present invention has been described with reference to the preferred embodiment thereof exemplified with a generalized 4-port feedback circuit, it will be understood that the invention is not limited to the details thereof. Various substitutions and modifications have been suggested in the foregoing description, and other will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.

Claims

1. A unilateral feedback power amplifier comprising: a signal input terminal for receiving a high-frequency signal to be amplified;a power transistor for receiving said high-frequency signal from said signal input terminal and outputting an amplified high-frequency signal;a multi-port feedback circuit connected to an input terminal and an output terminal of said power transistor, said multi-port feedback circuit receiving said amplified high-frequency signal and eliminating the reverse admittance of said amplified high-frequency signal to let the admittance value of the output amplified high-frequency signal approach zero;a signal output terminal for outputting said amplified high-frequency signal processed by said multi-port feedback circuit; andtwo impedance matching circuits respectively disposed at said signal input terminal and said signal output terminal and used to perform impedance matching to high-frequency signals from said signal input terminal to said signal output terminal.

2. The unilateral feedback power amplifier as claimed in claim 1, wherein said multi-port feedback circuit is a 4-port feedback circuit.

3. The unilateral feedback power amplifier as claimed in claim 2, wherein said unilateral feedback power amplifier utilizes a matrix:

4. The unilateral feedback power amplifier as claimed in claim 3, wherein said 4-port feedback circuit makes said power transistor plus said feedback circuit unilateral by adjusting said 4-port admittance matrix parameters (Ymnf).

5. The unilateral feedback power amplifier as claimed in claim 3, wherein said 4-port feedback circuit achieves conjugate matching with the output impedance of said power transistor plus said feedback circuit by adjusting said admittance value (Yopt) at the output terminal of said power transistor.

6. The unilateral feedback power amplifier as claimed in claim 1, wherein a ground terminal of said power transistor is directly connected to a system ground.

7. The unilateral feedback power amplifier as claimed in claim 1, wherein said multi-port feedback circuit is capable of making a high-frequency signal amplified by said power transistor unilateral.

8. The unilateral feedback power amplifier as claimed in claim 2, wherein said 4-port feedback circuit further comprises: two 2-port circuits respectively disposed at an input terminal and an output terminal of said power transistor; anda capacitive shunt component to let said 2-port circuit at said input terminal of said power transistor and said 2-port circuit at said output terminal of said power transistor be shunted together.

9. The unilateral feedback power amplifier as claimed in claim 8, wherein said capacitive shunt component is used to eliminate the imaginary part of the reverse admittance of said high frequency signal amplified by said power transistor.

10. The unilateral feedback power amplifier as claimed in claim 8, wherein said 2-port circuits are used to eliminate the real part of the reverse admittance of said high frequency signal amplified by said power transistor.

11. A method for realization unilateralization of amplified high-frequency signal comprising the step of: using a multi-port feedback circuit to make an output high-frequency signal amplified by a power transistor unilateral.

12. The method as claimed in claim 11, wherein said multi-port feedback circuit is a 4-port feedback circuit.

13. The method as claimed in claim 11, wherein two impedance matching circuits respectively disposed at a signal input terminal and a signal output terminal are used to achieve impedance matching of said amplified high-frequency signal.

14. The method as claimed in claim 11, wherein said unilateral amplified high-frequency signal has a admittance value that is close to zero.

15. The method as claimed in claim 12, wherein said unilateral feedback power amplifier utilizes a matrix:

16. The method as claimed in claim 12, wherein said 4-port feedback circuit makes said power transistor plus said feedback circuit unilateral by adjusting said 4-port admittance matrix parameters (Ymnf).

17. The method as claimed in claim 15, wherein said 4-port feedback circuit achieves conjugate matching with the output impedance of said power transistor plus said feedback circuit by adjusting said admittance value (Yopt) at the output terminal of said power transistor.

18. The method as claimed in claim 11, wherein a capacitive shunt component of said multi-port feedback circuit is used to eliminate the imaginary part of the reverse admittance of said amplified high frequency signal.

19. The method as claimed in claim 11, wherein two 2-port circuits of said multi-port feedback circuit are used to eliminate the real part of the reverse admittance of said amplified high frequency signal.