JPH0746049A - High-frequency linear power amplifier - Google Patents

Abstract

PURPOSE:To obtain a high-frequency linear power amplifier improving its linearity by detecting the beat frequency (DELTAf), for instance, of an input signal in a bias device and generating the distortion components controlled according to frequencies in a distortion compensating device. CONSTITUTION:In a high-frequency linear power amplifier, an f/V conversion circuit 21 detecting the changed amt. of voltage due to frequency is provided on a bias device. The signal detected in this f/V conversion circuit 21 is applied to a controller 19 and the distortion components controlled by frequency are generated in a distortion compensating device 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency linear power amplifier used in digital communication systems such as satellite communication systems, mobile phone systems and digital cordless systems.

[0002]

2. Description of the Related Art A high frequency linear power amplifier used in a digital communication system has strict linearity and efficiency. Power devices used in high frequency linear power amplifiers, eg field effect transistors (hereinafter F
(ET) may require performance that exceeds linearity and efficiency of a single unit. When there is such a demand, in order to reduce the distortion generated in the power element, a distortion compensator (linearizer) is provided to improve the linearity.

However, the distortion characteristics of the power element change depending on the usage conditions such as the input signal level and the temperature. For this reason,
When the usage conditions change, the distortion generated in the power element also changes. Therefore, in order to reduce the distortion generated in the power element, it is necessary to adjust the distortion component for compensation generated in the distortion compensator according to the usage conditions.

The distortion component of the distortion compensator is obtained by generating a distortion signal in the distortion generating circuit and controlling the magnitude and phase of the distortion signal. Therefore, in order to obtain the optimum distortion component for distortion compensation, for example, a method is used in which the control condition for the distortion signal generated in the distortion generating circuit is measured in advance according to the use condition and the control condition is stored in the memory. To be Then, the usage condition when the power element is actually operating is monitored, and the distortion signal is controlled under the control condition corresponding to the usage condition.

In addition to the input level and the temperature, a frequency difference (a beat frequency: a beat frequency) when simultaneously amplifying a large number of signal waves is used as an operating condition affecting the distortion generated in the power element.
There is Δf).

When a large number of signal waves are simultaneously input to the power element, the output power of the power element changes depending on the beat frequency (Δf) of the input signal. The power element is usually biased to class AB or class B to improve efficiency. Therefore, when the output power changes, the average value of the current (drain current in the case of FET) changes.
When the average value of the current changes, it is necessary to supply the charge from the bias device to the terminals of the power element at a speed that follows the beat frequency (Δf).

However, since the bias device includes an inductance component, the charge supplied from the bias power source to the power device cannot follow the beat frequency (Δf).
In such a case, the bias voltage is lowered and the linearity of the power element is deteriorated. When the frequency band used is narrow and therefore the beat frequency (Δf) is small, the linearity deterioration is small.

However, the frequency band used becomes wider,
As the beat frequency (Δf) increases, the linearity of the power element deteriorates, and the influence of the beat frequency (Δf) on the distortion of the power element cannot be ignored.

Not only the beat frequency (Δf) when a large number of signal waves are amplified at the same time, the same phenomenon occurs depending on the modulation method even when a single signal wave is amplified. In the case of a single signal wave, its modulation speed has the same effect as the beat frequency (Δf) in the case of multiple signal waves.

When the distortion signal generated by the distortion generating circuit of the distortion compensator is to be controlled by the frequency of the input signal, a detection circuit for detecting the frequency is provided on the transmission line in order to monitor the frequency of the input signal. Is inserted. However, when the detection circuit is inserted in the transmission line, the signal transmitted by the detection circuit is attenuated.

Further, when the frequency of the input signal is monitored, an f / V conversion circuit is used to obtain an output proportional to the frequency. However, as the frequency increases, such as in the microwave band, the f / V conversion circuit becomes complicated and large. Therefore, the method of controlling the distortion signal generated by the distortion generation circuit of the distortion compensator by frequency has not been used so far.

Now, a conventional high frequency linear power amplifier will be described with reference to FIG. FIG. 3 shows an example using a predistorter type distortion compensator.

IN is an input terminal, and the distortion compensator 31 shown by the dotted line is connected to the input terminal IN. The distortion compensator 31 generates an antiphase distortion component that cancels the distortion generated in the power element 32 connected in the subsequent stage.

The signal input to the distortion compensating device 31 is divided into two by the distributor 33, and one of them is fed from the distortion generating circuit 34 to the attenuator 3.
5, added to the combiner 37 through the phase shifter 36. The other is added to the combiner 37 through the transmission line 38. The input signal combined by the combiner 37 is amplified by the power element 32 and output from the output terminal OUT.

In the distortion generating circuit 34, the power element 32
A distortion signal for compensating for the distortion generated at is generated. The magnitude and phase of the distortion signal are controlled by the attenuator 35 and the phase shifter 36, and the distortion signal has a phase opposite to that of the distortion generated in the power element 32 and is added to the combiner 37 as a distortion component for compensation. The magnitude and phase shift amount of the distortion signal controlled by the attenuator 35 and the phase shifter 36 are controlled by the control circuit 39.

Further, the temperature sensor 4 is provided near the power element 32.
0 is provided and the ambient temperature is measured. Temperature sensor 4
The temperature information measured at 0 is sent to the control circuit 39. In the control circuit 39, control conditions for the attenuator 35 and the phase shifter 36 are stored in a memory according to temperature conditions. Then, based on the temperature information sent from the temperature sensor 40,
The attenuator 35 and the phase shifter 36 are controlled under the control conditions stored in the memory so that the distortion of the signal output from the power element 32 is minimized. In the example of FIG. 3, the attenuator 35 and the phase shifter 36 are controlled by temperature information, and are not controlled by the input level. Here, a bias device that supplies a bias voltage to the power device will be described with reference to FIG.
Will be described with reference to. IN is an input terminal of the power element, and the FET 41 is used as the power element. The FET 41 has drain D, source S, and gate G terminals, the source S is grounded, and the drain D is connected to the output terminal OUT. A bias voltage is supplied to the drain D and the gate G from the bias power sources B1 and B2 through the inductance elements L1 and L2. The capacitors C1 and C
2 prevents the bias power sources B1 and B2 from affecting the high frequency signal.

[0017]

Power element such as FET
In a bias device that applies a bias voltage to the device, its inductance affects the distortion generated in the power device. Up to now, the location and length of the inductance element have been devised to minimize the inductance component. However, when the frequency band used becomes wider, the effect of inductance cannot be ignored. Further, the distortion generated in the power element changes with the beat frequency (Δf) when a large number of signal waves are input, for example.

By the way, the distortion component generated by the distortion compensator is set to have an opposite phase with respect to the distortion generated in the power element at a specific beat frequency (Δf). Therefore, it does not necessarily have an opposite phase with respect to other beat frequencies (Δf). Therefore, multiple beat frequencies (Δf)
On the other hand, in order to compensate the distortion generated in the power element,
The distortion component generated by the distortion compensator is set to the beat frequency (Δf)
Need to be controlled accordingly. However, since it is difficult to control by the frequency as described above, the control for each beat frequency (Δf) is not performed. Up to now, control has been performed so that all beat frequencies (Δf) in the used frequency band have an average compensation effect.

Therefore, in the conventional high frequency linear power amplifier, when the used frequency band becomes wide, the distortion generated in the power element cannot be sufficiently compensated.

The present invention solves the above-mentioned drawbacks by detecting, for example, the beat frequency (Δf) of an input signal with a bias device, and generating a distortion component controlled according to the frequency with a distortion compensating device. An object of the present invention is to provide a high frequency linear power amplifier that improves linearity.

[0021]

According to the present invention, there is provided a power element for amplifying a high frequency signal, a bias device for supplying a bias voltage to a terminal of the power element, and a distortion for compensating for distortion caused by non-linearity of the power element. In a high-frequency linear power amplifier including a distortion compensator that generates a component and a controller that controls the distortion component generated by the distortion compensator, a detection device that detects a change in voltage due to frequency is used as the bias device. A signal detected by the detection device is provided to the control device to control the distortion component generated by the distortion compensation device.

[0022]

According to the above construction, the bias device is provided with the detecting device for detecting the change amount of the frequency, and the distortion compensating device generates the distortion component controlled by the change amount of the frequency. Therefore, it is possible to compensate for a change in distortion due to a change in output of the power element, and improve the linearity of the high frequency linear power amplifier. Further, since the bias device is provided with the detection device for detecting the change in frequency, the detection device does not attenuate the input signal.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the circuit configuration diagram of FIG. The embodiment of FIG. 1 is an example using a predistorter type distortion compensator as in FIG. IN is an input terminal, and the distortion compensator 11 shown by the dotted line is connected to the input terminal IN. The signal input to the distortion compensator 11 is divided into two by the distributor 12, one of which is passed through the distortion generating circuit 13, the attenuator 14, and the phase shifter 15 to combiner 1
Added to 6. The other is through the transmission line 17 and the synthesizer 1
Added to 6. The signal combined by the combiner 16 is amplified by the power element 18, for example, FET, and output from the output terminal OUT.

In the distortion generating circuit 13, the power element 18
A distortion signal for compensating for the distortion generated at is generated. The magnitude and phase of the distortion signal are controlled by the attenuator 14 and the phase shifter 15, and the distortion signal is added to the combiner 16 as a distortion component for compensating for the phase opposite to the distortion generated in the power element 18. The attenuator 1
4 and the amount of phase shift of the distortion signal controlled by the phase shifter 15 are controlled by the control circuit 19.

Further, the distortion component for compensation applied to the combiner 16 is applied to the power element 18 together with the input signal as the output of the distortion compensator 11. At this time, the power element 18
The distortion generated in 1 is compensated by the distortion component sent from the distortion compensating circuit 11.

A temperature sensor 20 is provided near the power element 18 to measure the ambient temperature. Further, an f / V conversion circuit 21 is provided in, for example, a bias device of the power element 18, and frequency information such as a beat frequency (Δf) is detected. Then, the temperature information measured by the temperature sensor 20 and the frequency information detected by the f / V conversion circuit 21 are sent to the control device 19. The control device 19 stores control conditions for the attenuator 14 and the phase shifter 15 in the distortion compensating device 11 in a memory according to usage conditions such as temperature and frequency, and temperature information sent from the temperature sensor 20 and f
The attenuator 14 and the phase shifter 15 are controlled based on the frequency information sent from the / V conversion circuit 21.

Here, f / constructed in the bias device
The V conversion circuit will be described with reference to FIG. IN is an input terminal of the power element, and for the power element, for example, FET25
Is used. The FET 25 has drain D, source S, and gate G terminals, and the source S is grounded. Also,
The drain D is connected to the output terminal OUT. A bias voltage is supplied to the drain D and the gate G from the bias power sources B1 and B2 through the inductance elements L1 and L2. The capacitors C1 and C2 prevent the influence of the bias power supplies B1 and B2 on the high frequency signal. Then, the f / V conversion circuit 26 is connected to both ends of the capacitor C1.

In the above configuration, when a large number of signal waves are simultaneously input to the power element 25, the voltage value of the capacitor C1 changes at the beat frequency (Δf) of the input signal due to the influence of the inductance element L1. To do. The frequency of this voltage change is detected by the f / V conversion circuit 26 and detected by the control circuit 19.
(Fig. 1). Then, the distortion signal generated by the distortion generation circuit 13 is controlled by the frequency information detected by the f / V conversion circuit 21.

In this configuration, since the f / V conversion circuit for detecting the beat frequency (Δf) is inserted in the bias device, the input signal is not attenuated. Also,
The beat frequency (Δf) is about several tens of MHz, which is lower than that of the input signal in the microwave band. Therefore, the configuration of the f / V conversion circuit is simpler than that in the case of directly detecting the input signal.

When the beat frequency (Δf) has a small influence on the distortion of the power element, the accuracy of the frequency detected by the f / V conversion circuit is not so required. in this case,
The f / V conversion circuit can be configured by an LC resonance circuit or an amplifier whose gain changes. Further, since the beat frequency (Δf) is proportional to the voltage amplitude, the f / V conversion circuit can be configured by a circuit that monitors the voltage amplitude. In this case, the f / V conversion circuit becomes simpler.

According to the above-described structure of the present invention, for example, the beat frequency of the input signal is detected in the bias device, and the distortion component is controlled by the detected frequency. Therefore, there is no attenuation of the input signal and The distortion generated in the power element can also be reduced.

[0032]

According to the present invention, it is possible to realize a high frequency linear power amplifier which does not attenuate an input signal and has a small distortion generated in a power element.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram illustrating an embodiment of the present invention.

FIG. 3 is a circuit configuration diagram showing a conventional example.

FIG. 4 is a circuit diagram illustrating a conventional example.

[Explanation of symbols]

 11 ... Distortion compensator 12 ... Distributor 13 ... Distortion generating circuit 14 ... Attenuator 15 ... Phase shifter 16 ... Synthesizer 17 ... Transmission line 18 ... Power element 19 ... Control circuit 20 ... Temperature sensor 21 ... F / V conversion circuit IN ... Input terminal OUT ... Output terminal

Claims (1)

[Claims] 1. A power element for amplifying a high frequency signal, a bias device for supplying a bias voltage to a terminal of the power element, and a distortion compensating device for generating a distortion component for compensating for distortion caused by non-linearity of the power element. In a high frequency linear power amplifier including a control device that controls a distortion component generated by this distortion compensation device, a detection device that detects a change in voltage due to frequency is provided in the bias device, and is detected by the detection device. A high frequency linear power amplifier, wherein the distortion component generated by the distortion compensator is controlled by applying the generated signal to the controller.