JPH06164267A - Power amplifier - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a power amplifier that improves efficiency regardless of changes in load impedance. [Structure] A series connection circuit of a high-pass filter 16 and a terminating resistor 15, which serves as a cutoff region for a fundamental wave of an output signal and a passband for a second harmonic wave or more of the fundamental wave, is connected to a harmonic filter 13 A low-pass filter 17, which is connected in parallel to the output side and serves as a pass band for the fundamental wave of the output signal and a cut-off region for the second harmonic wave or more of the fundamental wave, is provided on the output side of the harmonic filter 13. Connected in series to the low-pass filter 17
Is connected to the output terminal OUT.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly efficient and highly linear power amplifier used in the microwave band.

[0002]

2. Description of the Related Art Microwave power amplifiers used in digital mobile communications are required to have high efficiency and high linearity.

For example, one of the items representing the transmission quality in digital mobile communication is the adjacent channel leakage power characteristic. The adjacent channel leakage power characteristic is greatly affected by the linearity of the amplification element that constitutes the power amplifier.

Therefore, in order to improve the linearity of the amplification element, for example, there is a method of giving a margin to the saturation output of the amplification element. However, if the saturation output of the amplifying element has a margin, the current consumption of the amplifying element increases, and high efficiency cannot be expected.

Further, as a method of improving the efficiency of the power amplifier, there is a structure in which a harmonic filter having a short-circuit or open characteristic with respect to a harmonic is used and the harmonic filter is connected to the output side of the amplifying element.

Now, a conventional power amplifier using a harmonic filter will be described with reference to FIG.

IN is an input terminal of the power amplifier, and the input terminal IN
Signal is input from. The input terminal IN is an input matching circuit 31.
Connected to.

The input matching circuit 31 is connected to an amplifying element, for example, the gate G of the field effect transistor 32.
The field effect transistor 32 has a drain D and a source S electrode in addition to the gate G.

A harmonic filter 33 is connected to the drain D of the field effect transistor 32. The harmonic filter 33 has characteristics of being short-circuited for even-order harmonics and open for odd-order harmonics when viewed from the end face of the drain D, and is a cut-off band characteristic that does not pass so-called a second harmonic wave or more of the fundamental wave. Has become.

An output matching circuit 34 is connected to the harmonic filter 33, and the output matching circuit 34 is connected to the output terminal OUT.

The output terminal OUT of this power amplifier is connected to a load such as an antenna 36 via an isolator 35.

[0012]

In the above power amplifier, since the harmonic filter 33 is connected to the output side of the amplifying element 32, the efficiency is improved without deteriorating the adjacent channel leakage power characteristic of the amplifier. There is.

By the way, the power amplifier is connected to a load such as an antenna 36 via an isolator 35 as shown in FIG.

Even if the impedance of the antenna 36 changes, the isolator 35 prevents the change from affecting the power amplifier. By connecting the isolator 35, the isolator 35 changes its fundamental wave. The impact is almost gone.

However, since the isolator has a limited band in which it exhibits an irreversible characteristic, it does not exhibit a sufficient irreversible characteristic when it becomes a higher harmonic of the second or higher order.

Accordingly, even if an isolator is connected between the antenna and
The harmonic filter 33 is affected by the load impedance.

As a result, the characteristics of the harmonic filter deviate from the designed values, and the efficiency of the power amplifier does not necessarily improve.

An object of the present invention is to solve the above problems and to provide a power amplifier which can improve the efficiency regardless of the fluctuation of the load impedance.

[0019]

According to the present invention, an amplifying element for amplifying an input signal and an output side of the amplifying element are connected,
Of the output signals amplified by the amplifying element, 2 of the fundamental wave
A power amplifier comprising: a harmonic filter that serves as a cutoff band for harmonics and higher, and a first band that serves as a cutoff band for the fundamental wave of the output signal and a passband for more than the second harmonic of the fundamental wave. A serial connection circuit of the filter and the terminating resistor is connected in parallel to the output side of the harmonic filter, and the pass band and the fundamental wave of the fundamental wave of the output signal are
A second filter, which serves as a cutoff region for harmonics or higher, is connected in series to the output side of the harmonic filter, and the second filter is connected to the output terminal.

[0020]

As described above, the series connection circuit of the first filter and the terminating resistor, which serves as a cutoff region for the fundamental wave of the output signal and a passband for the second harmonic wave or more of the fundamental wave, is It is connected in parallel to the output side of the filter.

A second filter, which is a pass band for the fundamental wave of the output signal and a cut-off region for the second harmonic wave or more of the fundamental wave, is connected in series to the output side of the harmonic filter, And it is connected to the output terminal.

According to this structure, the fundamental wave of the amplified signal is output to the output terminal through the second filter. In addition, second and higher harmonics such as the amplified signal are terminated by the series connection circuit of the terminating resistor and the first filter.

As a result, the influence of load impedance fluctuations on the power amplifier is eliminated, and the efficiency of the power amplifier can be improved.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIG.

IN is an input terminal of the power amplifier, and the input terminal IN
Signal is input from. The signal input from the input terminal IN passes through the input matching circuit 11 and is input to the amplifying element, for example, the gate G of the field effect transistor 12.

The source S of the field effect transistor 12 is grounded, and the signal amplified by the field effect transistor 12 is output from the drain D.

A harmonic filter 13 is connected to the drain D of the field effect transistor 12.

The harmonic filter 13 has characteristics of short-circuiting with respect to even-order harmonics and opening with respect to odd-order harmonics, and has a characteristic of cutting off at least the second harmonic of the fundamental wave.

An output matching circuit 14 is connected to the harmonic filter 13.

On the output side of the output matching circuit 14, a series connection circuit of a terminating resistor 15 of 50Ω and a high-pass filter 16 that passes a second harmonic wave or more is connected in parallel.

A low pass filter 17 is connected in series to the output side of the output matching circuit 14. The low-pass filter 17 is open to the second harmonic wave or more, and has a characteristic of not passing the second harmonic wave or more. The low-pass filter 1
7 is connected to the output terminal OUT of the power amplifier.

Therefore, of the signals amplified by the field effect transistor 12, the fundamental wave is the low pass filter 17
And is output to the output terminal OUT. And the output end O
The load is supplied from the UT to the load, for example, the antenna 19 via the isolator 18.

The higher harmonics of the second order and higher in the amplified signal are terminated by the series connection circuit of the terminating resistor 15 and the high pass filter 16.

In this case, the second and higher harmonics are represented by an equivalent circuit as shown in FIG. 2. Among the output of the power amplifier 21, the second and higher harmonics are terminated by the terminating resistor R. To be done. Therefore, the power amplifier 21 is not affected by the impedance of the antenna as shown by the dotted line.

As described above, according to the power amplifier of the present invention, the leakage power to the adjacent channel can be reduced, and
The efficiency is improved.

In the above embodiment, the high pass filter 16 and the low pass filter 17 are used. However, instead of the high-pass filter 16, a band-pass filter having a sufficiently large input impedance with respect to the fundamental wave and a cut-off band characteristic and a pass band with respect to frequencies of at least a second harmonic can be used.

Further, instead of the low pass filter 17, it is possible to use a band pass filter having a pass band for the fundamental wave and having a sufficiently large input impedance and a cut-off band characteristic at least at a second harmonic or more.

[0038]

According to the present invention, it is possible to realize a power amplifier which can reduce the leakage power to the adjacent channel regardless of the fluctuation of the load impedance and can improve the efficiency.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention.

FIG. 2 is a circuit configuration diagram illustrating the present invention.

FIG. 3 is a circuit configuration diagram illustrating a conventional technique.

[Explanation of symbols]

 11 ... Input matching circuit 12 ... Field effect transistor 13 ... Harmonic filter 14 ... Output matching circuit 15 ... Termination resistor 16 ... High pass filter 17 ... Low pass filter 18 ... Isolator 19 ... Antenna IN ... Input terminal OUT ... Output terminal

Claims (1)

[Claims] 1. An amplifying element for amplifying an input signal, and an output signal of the amplifying element, which is connected to an output side of the amplifying element and serves as a cutoff region for a second harmonic wave or more of a fundamental wave among output signals amplified by the amplifying element In a power amplifier equipped with a harmonic filter,
A series connection circuit of a first filter and a terminating resistor, which serves as a cutoff band for the fundamental wave of the output signal and a pass band for the second harmonic wave or more of the fundamental wave, is connected in parallel to the output side of the harmonic filter. A second filter connected in series to the output side of the harmonic filter, the second filter being a pass band for the fundamental wave of the output signal and a cutoff region for the second harmonic wave or more of the fundamental wave. And the second filter is connected to the output terminal.