JP2009130897A - Power amplifier of mf/hf band transmitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem in a power amplifier of MF/HF bands that optimal capacitors have to be used respectively for frequencies since the effect of characteristic improvement is small in low bands and middle bands owing to frequency characteristics of the capacitors although efficiency, etc. of high bands is particularly improved by inserting a capacitor to a secondary side of an output transformer and adjusting impedance matching. <P>SOLUTION: A plurality of capacitors for frequency matching are provided in the secondary side of the output transformer of the power amplifier. A switching circuit for selecting the capacitors is provided. A current detecting circuit which detects the current that flows to the power amplifier and a power detecting circuit which detects the power from the power amplifier are provided. A SW control circuit which controls the switching circuit so that the detected output of the current detecting circuit is minimum and the detected output from the power detecting circuit is maximum is provided. Thus, the capacitors that maximize efficiency is selected. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a high-frequency power amplifier having a wide frequency range, such as used in a transmitter of a radio device used in the MF / HF band (1.6 MHz to 30.0 MHz).

When the high frequency power amplifier is operated in a non-linear region where high efficiency can be obtained, the distortion characteristics deteriorate, and conversely, when operated in a linear region where the distortion characteristics are good, the efficiency deteriorates. As shown in Non-Patent Document 1, the efficiency varies greatly depending on the drive class of the transistor used for amplification, how to select the load impedance, and harmonic processing.

As a technique for improving the efficiency of a high-frequency power amplifier, as disclosed in Patent Document 1, a Doherty amplifier that improves the efficiency at the time of back-off operation, or a LINC (Linear Amplifying Usage Nonlinear) that always operates the amplifier in saturation Components). However, these methods are realized by using a quarter wavelength transmission line in the amplifier.

The quarter wavelength transmission line is configured by a pattern formed on a substrate, and the pattern length and pattern width differ depending on the frequency. Assuming that this amplifier is used in a frequency band with a wide operating frequency range and a long wavelength, providing a transmission line for each frequency or providing a quarter wavelength transmission line makes the circuit large and complicated. Therefore, realization is difficult.

Yasuyuki Ito, Nao Takagi, “Basics and Applications of MMIC Technology”, Realize, May 1996, p29-31 JP 2006-33981 A

Most of the compensation circuits using the quarter wavelength transmission lines as described above are mainly used in the VHF band and the UHF band. However, use in the MF / HF band cannot be used because the circuit becomes large and difficult to implement.

The basic circuit diagram of the MF / HF band power amplifier is as shown in FIG. 1. By inserting capacitors C101 and C102 on the primary side and secondary side of the output transformer T101 and adjusting impedance matching, In particular, it is improving the efficiency of high frequencies. However, the operating frequency band is wide, and the effect of improving the characteristics in the low and middle ranges is small due to the frequency characteristics of the capacitors. For this reason, it is necessary to use an optimum capacitor for each frequency.
An object of the present invention is to provide a circuit having a simple circuit configuration and improving efficiency.

The present invention is configured as follows to achieve the above-described object.

That is, in the MF / HF band power amplifier, a plurality of capacitors for frequency matching are provided on the secondary side of the output transformer, a switch circuit for selecting these capacitors is provided, and current detection for detecting an inflow current to the power amplifier. A power detection circuit for detecting power from the circuit and the power amplifier, and a SW control circuit for controlling the switch circuit so that the detection output of the current detection circuit is minimum and the detection output from the power detection circuit is maximum. The capacitor that maximizes efficiency can be selected.

According to the present invention, it is possible to expect an effect that the efficiency is improved in the entire low, middle, and high frequencies.

As shown in FIG. 2, a plurality of capacitors C1 to Cn are prepared in the matching circuit 302 on the secondary side of the output transformer T101 of the power amplifier circuit 301 of the power amplifier, and a plurality of switches SW1 to SW1 are changed so that the capacitance can be changed according to the frequency. SWn is provided.

Next, a method of selecting the capacitors C1 to Cn for achieving the best efficiency is shown in FIG.

As shown in FIG. 3, the current flowing into the power amplifier circuit 301 is detected by the current detection circuit 303 and a signal Ic proportional to the amount of current is supplied to the SW control circuit 305. In addition, the power from the power amplifier circuit 301 is detected by the power detection circuit 304 and a signal Vf proportional to the amount of power is supplied to the SW control circuit 305.

The SW control circuit 305 controls the SW circuit 306 so as to select capacitors C1 to Cn such that the detection output Ic from the current detection circuit 303 is minimized and the detection output Vf from the power detection circuit 304 is maximized. In this way, the power amplifier can achieve maximum efficiency.

Next, an example of a current detection circuit of the current detection circuit 303 is shown in FIG. As shown in FIG. 4, the current detection uses the current detection shunt resistor Rs to detect a voltage drop due to the shunt resistor Rs based on Vout of the IC.

Next, an example of the power detection circuit of the power detection circuit 304 is shown in FIG. As shown in FIG. 5, the current Ip is detected by the current transformer, the divided voltage Vp of the capacitors Cp1 and Cp2 is detected, and Vf is detected using the difference between the values.

As shown in FIG. 6, the SW control circuit 305 reads the values of Vf and Ic when the capacitors C1 to Cn are switched by the A / D of the CPU, and compares these values to obtain an optimum value. The circuit 306 is controlled.
Thus, the present invention can be used with improved efficiency in the entire low, middle, and high frequencies.

It is a basic circuit diagram of a power amplifier in the MF / HF band. FIG. 3 is a basic circuit diagram of a proposed MF / HF band power amplifier. FIG. 4 is a control system diagram of a proposed MF / HF band power amplifier. It is an example of a current detection circuit. It is an example of a power detection circuit. In this example, the SW circuit is controlled by the SW control circuit.

Explanation of symbols

T101 Output transformers C101 and C102 Capacitors C1 to Cn Capacitors SW1 to SWn Switch 301 Power amplification circuit 302 Matching circuit 303 Current detection circuit 304 Power detection circuit 305 SW control circuit 306 SW circuit

Claims (1)

In the MF / HF band power amplifier, a current detection circuit including a plurality of capacitors for frequency matching on the secondary side of the output transformer, a switch circuit for selecting the capacitors, and detecting an inflow current to the power amplifier; Efficiency is provided by including a power detection circuit that detects power from the power amplifier, and a SW control circuit that controls the switch circuit so that the detection output of the current detection circuit is minimized and the detection output from the power detection circuit is maximized. Power amplifier that can select the capacitor that maximizes.