RU2542879C1 - Key power amplifier - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: in key power amplifier the high-frequency signal from the output of the pre-amplifier operating in the mode of amplification of "A" class is converted by a pulse-width modulator in a row of rectangular impulses which being added result in the input signal on a new power level is reproduced. The amplifier has considerably lower level of even harmonics in comparison with known key amplifiers at keeping the requirements to suppression of odd harmonics.

EFFECT: improvement of linearity of amplification of key power amplifiers due to significant decrease in level of even harmonicas in the spectrum of the amplified signal.

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Description

The present invention relates to the field of electrical engineering, in particular to key high-frequency amplifiers, and can be used in radio transmitters.

One of the main parameters of radio transmitters is gain linearity, which fully applies to transmitters with key power amplifiers.

Key amplifiers with improved gain linearity are known, for example A.S. USSR No. 1104647, H03F 3/217, 1984, a.s. USSR No. 1314438, a.s. USSR No. 1490704, H03F 3/217, 1989.

A key power amplifier is also known: RF patent No. 2400923, H03F 3/217 from 04/07/2008. "KEY POWER AMPLIFIER" (prototype), Trouble S.I., Muravchenko V.L., Katanovich A.A., Hotuleva N.V., containing a pulse-width modulator, high-frequency splitter, push-pull output stage, amplifiers of the same type ( transistors), adder and output filter.

The disadvantage of both analogues and the prototype is the presence of even-order harmonics in the spectrum of the amplified signal (in this case, as practice has shown, the use of push-pull amplification schemes does not solve the problem of attenuating even harmonics to levels that meet the ever-increasing requirements for modern high-power amplifiers frequency).

The aim of the invention is to improve the linearity of amplification of key power amplifiers by significantly reducing the level of harmonics of even orders in the spectrum of the amplified signal.

This goal is achieved by the fact that in the key power amplifier containing a pulse-width modulator, a high-frequency splitter, an output amplifier containing N of the same type of amplifying elements, an adder and an output filter, a pre-amplifier with a Class “A” gain mode is additionally included, and the output of the pre-amplifier connected to the input of a pulse-width modulator, the output of which is connected to the input of a high-frequency splitter, N outputs of which are connected to the inputs of N amplifying elements output stage, N outputs of which are connected to N inputs of the adder, the output of which is connected to the input of the output filter.

The structural diagram of the proposed key power amplifier is shown in figure 1.

A key power amplifier consists of the following functional blocks:

1 - pre-amplifier;

2 - pulse width modulator;

3 - high-frequency splitter;

4 - output stage;

4 ₁ ... 4 _N - the same type of amplifying elements (transistors);

5 - adder;

6 - output filter.

The operation of the device is as follows.

An amplified harmonic signal is fed to the input of the preamplifier. The preamplifier is set to class “A” gain mode, which provides the highest gain linearity compared to other classes of signal amplification mode.

From the output of the pre-amplifier, a working frequency signal of the form

i (t) = I _m (1 + cosωt)

fed to the input of a pulse-width modulator.

In a pulse-width modulator, each period of the harmonic signal is converted into a summed sequence of N rectangular-shaped pulses of the same amplitude. The number N is determined by the requirements for the higher harmonics levels specific to the amplifier being developed. The larger N, the lower the amplitudes of the summed pulses, the more accurately the harmonic oscillation is reproduced and the lower the level of higher harmonics.

The current shape at the output of the adder is shown in Fig.2.

I ₁ - the total amplitude of the first harmonic of N pulses having the same amplitude 2I _m / N at the outputs of N amplifying elements.

The maximum current value i (t) = I _m (1 + cosωt) is 2I _m .

The value of I ₁ is determined using the Fourier expansion:

The amplitudes of the higher harmonics are determined by the following relationships:

The duration of the pulses corresponds to the requirements of the generators of harmonic oscillations by the method of adding rectangular pulses, described, for example, in the literature: Dmitrikov V.F. and others. Highly efficient harmonic oscillators. Moscow, Radio and Communications, 1988.

The whole set of N rectangular pulses is fed to the adder, for example, a.s. 527008. Device for adding the capacities of electric oscillation generators. S.E. London, C.V. Tomashevich, publ. 1976.

From the output of the adder, the summed signal is fed to the input of the output filter, which selects the oscillations of the operating frequency.

Figure 3 shows a graph of the degree of suppression of G (k) dB harmonics of various orders of k (from 1 to 21) for the case of the number of splits of the signal amplitude into N = 200 summed rectangular pulses. The value of t _{n is} normalized to the value of the period of harmonic oscillation T, taken equal to 1. The value of I _{m is} also taken equal to 1.

The value of G (k) dB was calculated by the formula:

From the graph presented in Figure 3, it is seen that the level of even harmonics is suppressed by at least 200 dB relative to the level of suppression of harmonics of odd orders.

The proposed scheme of the utility model of the key amplifier in comparison with other types of key power amplifiers allows to provide the required suppression of odd harmonics of the operating frequency while significantly suppressing harmonics of even orders, improving the linear properties of such power amplifiers.

Claims (1)

A key power amplifier containing a pulse-width modulator, a high-frequency splitter, an output amplifier containing N of the same type of amplifying elements, an adder and an output filter, characterized in that the pre-amplifier with class “A” amplification mode is additionally turned on, and the output of the pre-amplifier is connected to the input pulse-width modulator, the output of which is connected to the input of a high-frequency splitter, N outputs of which are connected to the inputs of N amplifying elements of the output stage, N outputs of which are connected to N inputs of the adder, the output of which is connected to the input of the output filter.

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