RU2625019C1 - Microwave power amplifier - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: microwave power amplifier comprises a main amplifier module comprising a controlled attenuator and a microwave power amplifier, an input envelope detector, an output envelope detector, a reflected power peak detector, a falling power peak detector, an antenna power sensor, a reflected power sensor, a subtractor, a linear adder, a nonlinear adder, two operational amplifiers, a reflector of a reflected power, an incident power generator, a harmonic filter.

EFFECT: linearizating the amplitude characteristic and protecting the output stage of the amplifier from exceeding the peak power, stabilizing the power of the output cascade.

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Description

The invention relates to radio engineering and allows you to build radio transmitters with increased linearity of the amplitude characteristics, while protecting the output stages from exceeding the peak power and protecting them when working at an unmatched load. The invention can be effectively used in radio communication systems using various types of amplitude or multi-frequency modulation.

When constructing radio transmitters, the following requirements are often imposed on a power amplifier:

- ensuring sufficient linearity of the amplitude characteristic,

- ensuring the maintenance of constant peak power supplied to the output load when it changes during operation,

- protection of the output stage of the amplifier from exceeding the peak power,

- protection of the amplifier output stage from load mismatch.

The above list is usually supplemented by the requirement to ensure the level of harmonics of the carrier frequencies below the maximum permissible values.

In the practical implementation of amplifiers, the task of constructing microwave power amplifiers that fulfill a set of set requirements is relevant.

There is a known [1] method for reducing intermodulation products, in which, in a microwave amplifier with transistors, a low-frequency correcting envelope signal from the output of the modulator or from the output of the detector is fed to the input of the transistor through circuits defining the operating point.

The disadvantage of the proposed method of increasing the linearity of the microwave amplifier is the dependence of the degree of suppression of intermodulation products on the following factors:

- the level of harmonics in the spectrum of the output signal,

- amplifier gain

- input signal level.

As a result, a sufficient suppression of intermodulation products of 3, 5, and higher orders is difficult to achieve in the frequency range.

In addition, the proposed scheme

- difficult to set up a compensating circuit in the range of frequencies and temperatures,

- does not provide protection for the amplifier when the load mismatch and when the peak level of the output signal is exceeded.

There is a known [2] scheme for constructing a radio transmitter power amplifier, which provides stabilization of the output power and provides an increase in linearity when the amplifier operates on an inconsistent load.

The circuit [2] is focused on tube output stages. When transistors are used in the output stages, protection is not provided in it in cases of exceeding the permissible level of reflected power and protection against exceeding the peak output power. In addition, the level of intermodulation products at the output of the amplifier according to the scheme [2] will depend on the level of harmonics of the carrier frequencies at the output of the amplifier.

Scheme [2] is a prototype of the scheme proposed in this application for invention.

The objective of the invention is to reduce the level of intermodulation products during multi-frequency modulation and to reduce non-linear distortion of the signal with different types of amplitude modulation, as well as protecting the amplifier from exceeding peak power and stabilizing it during operation, protecting the amplifier during operation for a mismatched load.

The problem is achieved in that the microwave power amplifier contains a linearizable amplifier module, detectors and a signal processing circuit. According to the invention, the signal from the modulator is fed to the linearizable amplifier module and simultaneously to the input envelope detector, the linearizable amplifier is made in the form of a microwave input connected to a controlled attenuator and microwave power amplifier connected in series, the detectors are included as a detector of the first (input) envelope, the detector of the second (output) envelope, the peak detector of the reflected power, the peak detector transmitted to the antenna (incident) power, and supplement the microwave power amplifier no introduced subtracter, adder linear and non-linear adder, the first and second operational amplifiers, the sensor (directional coupler) reflected power, harmonic filter, a sensor (directional coupler), the power supplied to the antenna setting elements reflected and incident power.

The detector output of the first (input) envelope of the amplifier is connected to the first input of the subtractor, the second input of the subtractor is connected to the detector output of the second (output) envelope, and the output of the subtractor is connected to the first input of the linear adder, the second input of which is connected to the output of the nonlinear adder, the output the linear adder is connected to the control input of the controlled attenuator included in the main amplifier module, the output of the main amplifier is connected to the sensor input of the power reflected from the antenna and, the output of which is connected to the harmonic filter input, the harmonic filter output is connected to the sensor input of the power transmitted to the antenna, the first output of which is connected to the antenna, and the second output is connected to the detector input of the second (output) envelope, the output of which is connected to the first input of the second operating amplifier, the output of the reflected power sensor is connected to the input of the peak reflected power detector, the output of which is connected to the first input of the first operational amplifier, the second input of the first operational amplifier is connected the output of the reflected power master, and the output of the first operational amplifier is connected to the first input of the nonlinear adder, the second input of which is connected to the output of the peak detector of the power transmitted to the antenna, the input of which is connected to the output of the second operational amplifier, the second input of the second operational amplifier is connected to the master supplied to the antenna (falling) power.

Achievable technical result is the linearization of the amplitude characteristics and the protection of the amplifier output stage from exceeding the peak power, the protection of the output stage during antenna mismatch, as well as the stabilization of the power supplied to the antenna.

Figure 1 presents the structural diagram of the proposed device, the input of which from the modulator 1 is fed to the amplified signal, and this signal is divided and fed

- on the linearized power amplifier of the radio transmitter 2, consisting of an input device 2-1, a controlled attenuator 2-2 and a microwave power amplifier 2-3,

- to the envelope detector No. 1 (envelope of the input signal).

A directional coupler - reflected power sensor 3 is connected to the output of the linearized microwave power amplifier 2, a harmonic filter 4 is connected to one output of it, which reduces the level of higher harmonics in the output signal of the linearized amplifier 2. A peak detector is connected to the other output of the reflected power sensor (directional coupler) 3 reflected power 8, at the output of which the signal is proportional to the power reflected from the antenna path.

A directional coupler is connected to the output of the harmonic filter 4 — a sensor of power 5 supplied to the antenna, from one output of which the signal enters the antenna path, and a part of the output signal proportional to the power supplied to the antenna branches off and enters the envelope detector No. 2 of the output signal 9.

From the output of the peak reflected power detector 8 and from the output of the envelope detector No. 2 of the output signal 9, the signals are fed to the inputs of the operational amplifiers 13 and 12. The other voltages of the operational amplifiers 13 and 12 are supplied with reference voltages E1 and E2, respectively. The signal from the output of the operational amplifier 12 is fed to a peak detector of incident power 14.

The signal from the peak detector of incident power 14 is fed to the input M of the nonlinear adder 15, the signal from the peak detector of reflected power 8, passed through the operational amplifier 13, is fed to the input D of the nonlinear adder 15. The larger of the two signals present at the inputs of the nonlinear adder 15 from its output to the input E of the linear adder 16.

The signals from the outputs of the envelope detectors 6 and 9 are fed to a subtractor 7, the output of which through the separation capacitance C, the variable component of the error signal between the envelopes y is proportional to the difference between the instantaneous amplitudes of the envelopes at the input and output of the linearized amplifier 2.

From the output of the subtracting device 7 through a separation capacitor, removing the constant component of the error signal between the envelopes of the signals at the input and output of the microwave power amplifier. This signal is proportional to the signal G [U _BX (t)] described by formula (4), that is, proportional to the error between the envelopes of the RF signals at the input and output of the linearized amplifier 2. It is fed to the second input of the linear adder 16. At the output of the linear adder 16, the sum two signals:

- the signal received from the nonlinear adder 15, which supports the peak level of either the incident or reflected power at the output,

- an error signal between the envelopes at the input and output. This component of the signal at the output of the linear adder changes the instantaneous gain value of the microwave power amplifier 2 in such a way that increases the linearity of its amplitude characteristic.

The signal from the linear adder 16 is fed to the control input of the controlled attenuator 2-2.

As a result, the signal at the control input of the controlled attenuator provides simultaneously

- maintaining the peak level of the signal at the output of the power amplifier 2 proportional to the value specified by the incident power setter 11, if the value of the reflected power signal is less than the value set by the reflected power setter 10;

- maintaining the signal at the output of the power amplifier 2, reflected from the antenna path, not exceeding the value specified by the signal from the setpoint unit of the reflected power 10, regardless of what the set value of the incident power,

- reducing the deviation of the amplitude characteristic of the microwave power amplifier 2 from linear at any peak power.

It should be noted that in an amplifier having the described circuit, linearization of the amplitude characteristic occurs both with a single-frequency analog input signal with amplitude modulation, for example, with SSB modulation, and with multi-frequency modulation, for example, OFDM.

The operation of the device can be described as follows. The nonlinear amplitude characteristic of the power amplifier, which is the dependence of the amplitude of the output signal U _OUT (t) on the amplitude of the input U _IN (t) and described by some function

It can be expanded in Maclaurin series in powers of the signal U _BX near some small value of U _BX ≈0. Taking a limited number of members of the series, we obtain a polynomial describing the nonlinear amplitude characteristic in the form

описывается выражением, которое на основании (1) должно иметь видAmplitude response of a linear amplifier

is described by the expression, which on the basis of (1) should have the form

Comparing (1) and (2), we can state that the amplitude characteristic of a nonlinear amplifier can be represented by the sum

Where

It is the terms in (4) that form the products of intermodulation of different orders. In addition, the components included in (4) give frequencies at and near the harmonics of the input signal, as well as a signal at zero frequency, that is, a constant component.

Based on the expressions (1) ... (4), it is possible to select a value proportional to G [U _BX (t)]. For this, it is necessary to isolate the envelopes at the input of non-linear amplifier 2 and its output. This selection is carried out using the envelope detectors 6 and 9, connected to the input and output of the power amplifier 2. But the envelope of the input signal in the gain of the amplifier is less than the envelope of the output signal. Therefore, it is necessary to select such transmission coefficients of the signals to the inputs of the envelope detectors so that the terms proportional to A _L [U _BX (t)] at the outputs of the envelope detectors at points of circuit A and B are equal. Then, having fed the signals from the envelope detectors 6 and 9 to the subtractor 7, we obtain at its output a signal proportional only to G [U _BX (t)].

Further, to reduce the component G [U _BX (t)] at the amplifier output, negative feedback should be introduced into the microwave power amplifier so that the extracted error signal received after the subtractor 7 reduces the component G [U _BX (t)].

Since the components of even degrees of expression (4) will give a constant component at the output of the envelope detectors 6 and 9, the error signal should be introduced into the feedback circuit of the envelope through a circuit that does not pass the constant component. Such a circuit may simply be a separation tank C shown in FIG. 1, or a high-pass filter.

In order to exclude the influence on the envelope of the signal of those components (4) that give the envelope at frequencies that are harmonics of the input signal or at frequencies close to them, between the envelope detector 9 and the output of the microwave power amplifier 2 a harmonic filter should be included 4. Harmonic filter often at the output of power amplifiers, radio transmitters are turned on to fulfill the requirements for out-of-band emissions, therefore, a harmonic filter 4 can simultaneously perform both of these functions:

- reduction of harmonic components to the required standard values,

- reduce envelope distortion at the output of the power amplifier.

To maintain a constant peak power at the transmitter output, a peak detector is connected in series with the envelope detector, and the signal from the peak detector is compared with the signal of the peak level setter.

In order for the auto power control ring at the output of the linearizable amplifier 2 to support either incident or reflected power, a non-linear adder 15 is included in the circuit, which only allows one of the two signals at its inputs to pass through to the output.

The normal operating conditions of a linearized microwave power amplifier as part of a radio transmitter will be when the value of the reflected power from the antenna side does not exceed a predetermined value. This value is determined by the setpoint reflected power 10.

If the power reflected from the antenna side is small, then thanks to the non-linear adder 15, the signal from the operational amplifier 14 will be the only signal at its output.

If the power reflected from the antenna is large, then the signal at point D of the circuit will be greater than at point M, and only the signal determining the reflected power will be at the output of the nonlinear adder. In this case, the auto-control ring will keep the reflected power, not the incident power, constant, no matter what the power is falling.

Thus, the component of the signal at the output of the linear adder 16, which changes together with the change in the value of the envelope, keeps the level of intermodulation products low.

The microwave component at the input of the linear adder slowly changing with changing operating conditions of the power amplifier, received from the output of the nonlinear adder 15 (it changes with changing the temperature, frequency or load of the amplifier, other destabilizing effects), passing the linear adder 16, slowly changes the transmission coefficient of the controlled attenuator 2 -2, maintaining a constant incident or reflected power.

Information sources

1. Patent RU 2487464, H03F 3/00, publ. 12/10/2012.

2. USSR Author's Certificate No. 733082, H03F 1/34, publ. 05/05/1980.

Claims (1)

Microwave power amplifier, the input signal of which comes from the modulator, and its output is connected to the antenna, containing the main amplifier module, detectors and an auto power control ring, characterized in that the main amplifier module contains a microwave input connected to the input of the controlled attenuator, the output of which is connected with the input of the microwave power amplifier, the detectors are made in the form of a first envelope detector, a second envelope detector, a peak detector reflected from the power output, a peak detector applied to the power output In addition, a subtractor, a linear adder and a nonlinear adder, first and second operational amplifiers, a reflected power sensor, a harmonic filter, an incident power sensor, a reflected power sensor and an incident power sensor are additionally introduced, the modulator output connected to the microwave input of the main amplifier module and with the input of the detector of the first envelope, the output of which is connected to the first input of the subtractor, and the signal from the detector of the second envelope is fed to its second input, the output of the subtractor is connected with the first input of the linear adder, the second input of which is connected to the output of the nonlinear adder, and the output of the linear adder is connected to the control input of the controlled attenuator connected to the input of the main amplifier module, the output of which is connected to the input of the reflected wave sensor, one output of which is connected to the input of the harmonic filter whose output is connected to the input of the incident wave sensor, the first output of which is connected to the antenna, and the second output is connected to the input of the second envelope detector, the output of which is connected to the first m is the input of the second operational amplifier, the output of the reflected wave sensor is connected to the input of the peak detector of the reflected wave, the output of which is connected to the first input of the first operational amplifier, the second input of which is connected to the output of the reflected power setter, and the output of the first operational amplifier is connected to the first input of the nonlinear adder, the second input of which is connected to the output of the peak incident wave detector, the input of which is connected to the output of the second operational amplifier, the second input of which is connected to the rear by a falling power meter.

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