JP2000068754A - Distortion compensating circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distortion compensating circuit omitting time and labor for adjustment for removing the distortion of a high frequency amplifier and reducing the number of parts. SOLUTION: A balance amplifier provided with a hybrid power distributor 22, two amplifier circuits 23, 24 and a hybrid power synthesizer 25 is used as a high frequency amplifier circuit. Distortion detected by utilizing one output port 26b of the synthesizer 25 as a port for detecting the distortion of the circuits 23 and 24 is fed back to a normal amplifying signal through an adjusting circuit 28 and a directional coupler 32 to remove distortion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a distortion compensating circuit for compensating for nonlinear distortion of a power amplifier.

[0002]

2. Description of the Related Art In recent years, in the field of communication devices such as mobile phones, weight reduction and miniaturization have progressed, and with this, the power supply voltage has decreased, and further lower power consumption has been required. When the power supply voltage (operating voltage) decreases, the power amplifier tends to saturate and the noise tends to increase, but in order to meet the demanding requirements of users, good calls are always ensured even in a low power consumption environment. There must be.

Therefore, it is important to compensate for the nonlinear distortion of the high-frequency power amplifier in order to ensure the communication quality. Japanese Patent Application Laid-Open No. 6-375 discloses a nonlinear distortion compensating circuit for a power amplifier.
No. 51.

FIG. 5A is a diagram showing more specifically the main part of the distortion compensating circuit described in JP-A-6-37551.
FIG. 5B is a diagram illustrating nonlinear distortion of the high-frequency power amplifier.

In FIG. 5A, reference numeral 6 denotes a high-frequency power amplifier (power amplifier). In FIG. 5A,
Although only one power amplifier is illustrated for simplicity, the high-frequency power amplifier 6 is actually configured using a plurality of balance amplifiers configured using a hybrid power divider or a hybrid power combiner.

The input / output characteristics of the high-frequency power amplifier 6 are as follows:
As shown by a characteristic “b” shown by a solid line in FIG. 5B, saturation occurs in a high input range, and nonlinear distortion is likely to occur. FIG. 5 (b)
In the graph, the characteristic a indicated by the dotted line indicates an ideal characteristic.

Therefore, in the circuit of FIG. 5A, a directional coupler (consisting of juxtaposed microstrip lines) is used.
A distortion extracting means comprising a first adjusting circuit 2 for adjusting the signal level and phase, and a second adjusting circuit (compensating amplifier) 9 for adjusting the level and phase of the extracted distortion signal; , And the output of the second adjustment circuit (compensation amplifier) 9 is fed back to the output signal of the power amplifier 6 via the directional coupler 13 (specifically, the negative-phase addition is performed). Non-linear distortion is removed.

As shown, the first adjustment circuit 2 includes a variable attenuator 3, a phase shifter 4, and an amplifier 5. Similarly, the second adjustment circuit (compensation amplifier) 9 includes a variable attenuator 10, a phase shifter 11, and an amplifier 12.

The operation of removing nonlinear distortion will be briefly described with reference to the frequency spectrum (1) shown in FIG.

It is assumed that two signals (regular signals) S1 and S2 having different frequencies as shown in FIG.

When the input signal passes through the high-frequency power amplifier 6, distortion components N1 and N2 are generated as shown in FIG. The distortion components N1 and N2 cause the power amplifier 6 to perform a mixer-like operation with the characteristic deterioration of the high-frequency power amplifier 6,
This is a third-order distortion generated by mixing the normal signals S1 and S2.

On the other hand, the normal input signals S1 and S2 are also input to the first adjustment circuit 2 via the directional coupler 1, and are subjected to attenuation, phase shift, and amplification processes as required, and are subjected to level adjustment. Is adjusted.

The output of the first adjustment circuit 2 is added to the output of the power amplifier 6 (indicated by (1)) in opposite phases via the directional couplers 7 and 8, so that the directional coupler 8 After passing, only the distortion components N1 and N2 are extracted as shown in the figure. This extracted distortion component N
1 and N2 are input to a second adjustment circuit 9 and subjected to processes such as attenuation, phase shift, and amplification, as needed, to adjust the level and the like.

The signal (noise component signal) whose level or the like has been adjusted is added to the output signal of the high-frequency power amplifier 6 through the directional coupler 13 in reverse phase. As a result, the distortion is removed as shown in the figure, and normal signals S1 and S2 are obtained.

[0015]

However, in the above-described distortion compensation circuit, a circuit for obtaining a difference between an input signal and an output signal of a power amplifier for extracting a distortion component (ie, a directional coupler). (A distortion extraction circuit including the first, second, and seventh adjustment circuits 2) is particularly required, and a large number of circuits are required, which limits the miniaturization of the apparatus.

The first adjusting circuit 2 has a variable attenuator 3, a phase shifter 4, and an amplifier 5, and it is necessary to precisely adjust each of them in advance. Therefore, adjustment for distortion detection is troublesome.

The present invention has been made based on the above considerations, and has eliminated the trouble of adjustment for removing distortion, and
An object of the present invention is to provide a distortion compensation circuit that can reduce the number of components.

[0018]

According to the present invention, a balanced amplifier using a hybrid power divider and a hybrid power combiner is used as power amplification, and one port (terminal) of the normally terminated hybrid power combiner is used. ) Is actively used as a port (terminal) for distortion detection, thereby extracting distortion of the power amplifier without using a special configuration.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first aspect of the present invention comprises a hybrid power divider, a hybrid power combiner, and an amplifier provided between the hybrid power divider and the hybrid power combiner. In the balanced amplifier circuit, a distortion compensation circuit that uses an output port other than a normal signal output port of the hybrid power combiner as a distortion detection port generated by the amplifier, and is obtained from the distortion detection port. The present invention employs a configuration including adjusting means for performing desired processing on the distortion signal, and feedback means for feeding an output of the adjusting circuit back to a regular signal output from the regular signal output port of the hybrid power combiner.

Conventionally, the output ports other than the normal signal output port in the balanced amplifier circuit are terminated by connecting a terminating resistor. However, the distortion component generated in the amplifier is reduced to the normal signal in this port. It has the characteristic that it is output without being suppressed. Paying attention to this point, it is possible to extract distortion without using a special circuit by using a port that has been terminated as a port for distortion detection. Distortion can be removed by making a desired adjustment to the output of this port and feeding it back to the output of the power amplifier.

According to a second aspect of the present invention, in the first aspect, the adjusting means includes a variable attenuation circuit, a phase shift circuit, and an amplifier circuit.

With this configuration, the level and phase shift of the signal (distortion signal) fed back to the output of the power amplifier can be adjusted as appropriate, thereby increasing the effect of removing distortion.

According to a third aspect of the present invention, in the first aspect or the second aspect, the hybrid power splitter comprises:
A first input port to which an input signal is supplied, a second input port to which a terminating resistor is connected, and first and second output ports; and wherein the hybrid power combiner includes first and second output ports. A second output port functioning as a distortion detection port, a first output port functioning as a distortion detection port, and a second output port functioning as a normal signal output port; and a first output port of the hybrid power distributor. A first amplifier circuit is connected between the output port of the hybrid power combiner and the second output port of the hybrid power combiner and the second output port of the hybrid power combiner. In which the second amplifier circuit is connected between the input ports.

Thus, a balanced hybrid amplifier is formed.

According to a fourth aspect of the present invention, there are provided the first to third aspects.
A transmitter comprising the distortion compensation circuit according to any one of the above aspects.

According to this configuration, it is possible to obtain a small transmitter capable of performing high quality transmission.

According to a fifth aspect of the present invention, there are provided the first to third aspects.
A receiver comprising the distortion compensation circuit according to any one of the aspects.

According to this configuration, it is possible to obtain a small-sized receiver capable of high-sensitivity reception.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1) FIG. 1 is a diagram showing a configuration of a distortion compensation circuit according to the present embodiment. As shown in the figure, the distortion compensating circuit is established on the premise that a two-input two-output balanced amplifier is used, and the output port 26b that is normally terminated is distorted by the amplifying circuits 23 and 24. The output port 26
b, a level and phase adjustment circuit 28 is connected to the circuit, and the output of the adjustment circuit 28 is fed back to a normal signal (obtained from the output port 27b) via the directional coupler 32 to remove distortion. Has become.

Before describing the details of the distortion compensating circuit of FIG. 1, the configuration of the balanced amplifier and the general usage (conventional usage) will be described with reference to FIGS. 2 (a) and 2 (b). explain.

FIG. 2A is a diagram showing a basic configuration of the balance amplifier, and FIG. 2B is an equivalent circuit diagram of the balance amplifier.

As shown in FIG. 2B, the balance amplifier divides the signal (IN) input to the input terminal 20 into two systems by the power divider 22 and divides each of the two divided signals into two. The signal is amplified by two amplifier circuits (amplifiers) 23 and 24, and then the two amplified signals are combined by a power combiner 25 to obtain an amplified output signal (OUT).

According to such a configuration, each of the amplifiers 23,
Since the power of the signal assigned to 24 is １ ／,
The load on each amplifier is reduced as compared with the case where amplification is performed by one amplifier, and saturation is less likely to occur, so that it is easy to secure linearity. Further, since the load on one amplifier is reduced, there is an advantage that desired performance can be obtained even if a low-priced amplifier is used.

Specifically, the balance amplifier is shown in FIG.
The power distributor 22 and the power combiner 25 both have a two-input two-output hybrid configuration. Here, the “hybrid configuration”
It means "a configuration having four terminal (port) pairs used for the purpose of distributing an input signal to two systems or combining two signals into one signal".

In FIG. 2A, an input signal (IN) is applied to one input port 20a of the hybrid power distributor 22.
Is input to A 50Ω termination resistor R1 is connected to the other input terminal 21a of the power distributor 22 to adjust the impedance.

The signal (I) input to the input port 20a
N) is divided into two, and the divided signals are routed through two routes "A" and "B" to output port 20 respectively.
b, 21b. At this time, the phase of the signal output from the output port 20b via the route “A” is
The phase of the signal output from the output port 21b via the route “B” is shifted by 90 ° with respect to the phase of the input signal (IN). I have.

Each output port 20b, 2 of the power distributor 22
1b output from an amplifier circuit (amplifier) 2
Amplified at 3,24. The output of each amplifier is connected to the input ports 26a and 27a of the hybrid power combiner 25.
Is input to

The hybrid power combiner 25 combines the two input signals and outputs an amplified signal (normal signal OUT) from the output port 27b. A termination resistor R2 of 50Ω is connected to the other output port 26b, so that a normal signal is not output from this output port.

That is, in the hybrid power combiner 25, the signal input to the input port 26a is transmitted to the two output ports 26 via the route "C" and the route "E".
b, 27b. Similarly, a signal input to the input port 27a is distributed to two output ports 26b and 27b via a route "D" and a route "F". At this time, the phase of the signal output via route “C” and route “D” is shifted by 90 ° with respect to the phase of the input signal, and output via route “E” and “F”. The phase of the signal is the same as the phase of the input signal.

Here, focusing on the output port 26b,
The signal appearing at this port is a signal that has passed through the route “A” of the power divider 22 and the route “D” of the amplifier 24 and the power combiner 25 (the total phase of the input signal IN is 180 ° (= 90 °). {+90}), the route "A" of the power distributor 22, the amplifier 23, and the power combiner 25.
(The signal having the same phase as the input signal IN) that has passed through the route “E”. That is, since signals whose phases are shifted by 180 ° are added, each signal is canceled and suppressed, and the normal signal is output from the output port 26.
No signal is output from b.

On the other hand, the output port 27b of the power combiner 25
Paying attention to this, the signal appearing at this port is a signal that has passed through the route “B” of the power distributor 22 and the route “F” of the amplifier 24 and the power combiner 25 (the phase is shifted by 90 ° with respect to the input signal IN). And a signal that has passed through the route “A” of the power divider 22, the amplifier 23, and the route “C” of the power combiner 25 (a signal having a 90 ° phase shift with respect to the input signal IN). Signal. That is, signals having phases shifted by 90 ° with respect to the input signal (IN) are added (that is, signals having the same phase are added). Therefore, the amplified normal signal (OUT) is output from the output port 27b.
Is output.

The above is the basic operation of the balance amplifier. As described above, in the present embodiment, the output port 26b (FIG.
Since (a)) is characterized in that it is used as a distortion detection port of the amplifiers 23 and 24, this point will be described below.

In FIG. 2A, an amplifying circuit (amplifier)
23 and 24 are output ports 20b and 21 of the power distributor 22.
As a matter of course, there is no distortion (non-linear distortion) due to the amplifiers 23 and 24 in the signal path before the output ports 20b and 21b of the power distributor 22 because the signal path is connected to the signal path b. Therefore, regarding the influence of noise generated in the amplifiers 23 and 24, it is sufficient to consider the circuits after the output stages of the amplifiers 23 and 24.

Here, how the signal distortion generated in the amplifiers 23 and 24 appears at the output port 26b of the power combiner 25 will be considered. The signal distortion (noise) generated by the amplifier 23 reaches the output port 26b via the input port 26a and the route "E" of the power combiner 25 without undergoing a phase shift. On the other hand, amplifier 2
The distortion (noise) generated at 4 passes through the input port 27a of the power combiner 25 and the route “D”, reaches the output port 26b with a phase shift of 90 °, and passes through the route “E”. Combined with the signal.

As described above, in the case of a normal signal (main signal), since signals having a phase difference of 180 ° are combined by the operation of the balance circuit, the signal is strongly suppressed and is not output from the output port 26b. However, the amplifier 23,
In the case of the noise generated at 24, since the phase difference between the distorted signals to be synthesized is only 90 °, the signal is not suppressed as much as a normal signal (main signal), and the distorted signal (distortion component) is output from the output port 26b. Only signal) is output.

That is, in FIG. 2A, the output port 26b of the power combiner 25, which has been conventionally terminated, has a function as a port for detecting distortion signals of the amplifiers 23 and 24. In the present embodiment, this new knowledge is used to perform distortion detection without providing a special configuration, thereby simplifying the configuration of the distortion detection circuit, and eliminating the need for advance adjustment for distortion detection. It is.

Hereinafter, the specific configuration and operation of the distortion compensating circuit according to this embodiment will be described with reference to FIG.

The balance amplifier shown in the preceding stage of FIG.
This is the same as that described in FIG. 2A, and the same reference numerals are used. The output port 26b of the power combiner 25 constituting the balance amplifier is connected to a variable attenuator 29, a phase shift circuit 30, and an adjustment circuit 28 including an amplification circuit (amplifier) 31.

The adjustment circuit 28 adjusts the level and phase of the distortion signal output from the output port 26b of the power combiner 25 (ie, the distortion detection ports of the amplifiers 23 and 24) appropriately.

The distortion signal whose amplitude and phase have been adjusted via the adjustment circuit 28 is transmitted via the directional coupler 32 to a normal signal (output port 26b and output port 27b) output from the output port 27b of the power combiner 25. (An equivalent distortion signal is superimposed), thereby removing (or suppressing) distortion.

The above operation is described in FIG.
This will be described using the frequency spectrum of FIG. That is,
Two signals of different frequencies (regular signal,
It is assumed that the main signals S1 and S2 are input to the high-frequency power amplifier 6. When this input signal passes through the balance amplifier, distortion components N1 and N2 are generated as shown in (1) due to the nonlinearity of the amplifier circuits (amplifiers) 23 and 24.
The distortion components N1 and N2 perform a mixer-like operation with the characteristic deterioration of the amplifiers 23 and 24, and generate normal signals S1 and S2.
Is the third-order distortion generated by mixing.

On the other hand, the output port 26b of the power combiner 25
The distortion components (N1, N2) output from are subjected to various processes such as attenuation, phase shift, and amplification, as needed, to adjust the level and the like (frequency spectrum in FIG. 1). The distortion signals (N1 and N2) are added via the directional coupler 32 to the output signal of the port 27b of the power combiner 25 (the signal shown in (2)) in opposite phases. As a result, distortion is removed as shown in the figure, and normal signals (main signals) S1 and S2 are obtained.

The distortion compensating circuit of the present embodiment is similar to that of FIG.
No special circuit is required for detecting the distortion signal as in the conventional circuit shown in FIG. 5A (that is, the directional couplers 1, 7, 8 and the adjustment circuit 2 in FIG. 5A are not required). Is). Therefore, the configuration is simple and suitable for miniaturization of a communication device such as a mobile phone.

Further, with respect to the noise generated by the amplifier, the noise is effectively and reliably detected by utilizing the inherent characteristic of the balance amplifier that the suppression by the balance circuit does not work as well as the normal signal. Therefore, the adjustment circuit 2 required in the conventional circuit of FIG.
No prior adjustment of the characteristics is required, and the adjustment work of the circuit is also simplified.

(Embodiment 2) FIG. 3 is a diagram showing a configuration of a transmitting apparatus according to Embodiment 2 of the present invention.

This transmitting apparatus includes a local oscillation circuit 40, a quadrature modulation circuit 43, a preamplifier circuit (preamplifier) 44
And a distortion compensation circuit 45 using the balance amplifier described in the first embodiment (the reference numerals of the respective units are the same as those in FIG. 1), and an antenna 46. Quadrature modulation circuit 43
, Two signals (I signal and Q signal) having a phase difference of 90 ° are input via two signal input terminals 41 and 42.

The distortion compensation circuit 45 is constructed by utilizing the characteristics of the balance amplifier, and is therefore suitable for reducing the size and cost of the transmitter. The distortion compensating circuit 45 has a feed-forward configuration (the amplifiers 23 and 2).
4 is fed back to a circuit after the amplifiers 23 and 24 to cancel the distortion). For this reason, the signal amplified by the balance amplifier is directly output to the antenna 46, which is advantageous for realizing high efficiency and low distortion.

(Embodiment 3) FIG. 3 is a diagram showing a configuration of a receiving apparatus according to Embodiment 3 of the present invention.

This receiving apparatus includes an antenna 50, a low-noise amplifier 51, a distortion compensating circuit 52 using a balanced amplifier described in the first embodiment (the same reference numerals as in FIG. 1), and a down-converter. It includes a converter 54 and a local oscillation circuit 53.

A receiving amplifier directly connected to the antenna 50 is required to have low noise (low distortion) and low power consumption in order to amplify a received high-power signal, but these are basically contradictory characteristics. Under strict demands for low cost and miniaturization, realization is difficult. However, in the present embodiment, since the distortion compensation circuit is mounted,
A low distortion balance amplifier is realized. In addition, since distortion is canceled by using the characteristics of the balance amplifier, the configuration is simple and suitable for miniaturization and cost reduction.

In this embodiment, the distortion compensating circuit (balance amplifier) 52 is arranged before the down-converter 54, so that a normal received signal can be amplified in a portion where the received power is large, and the noise is reduced. Is suppressed, so S
There is also a merit that it is easy to improve / N.

[0063]

As described above, according to the present invention, one port of a power combiner in a hybrid balance amplifier (high-frequency amplifier) is used for detecting distortion generated in an amplifier circuit, thereby reducing the size and cost. Thus, a distortion compensation circuit suitable for the above can be realized. In addition, there is no need for prior adjustment for distortion detection.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a distortion compensation circuit according to a first embodiment of the present invention.

FIG. 2A is a circuit diagram showing a configuration of a hybrid balance amplifier. FIG. 2B is an equivalent circuit diagram of the hybrid balance amplifier.

FIG. 3 is a circuit diagram showing a configuration of a transmitter according to a second embodiment;

FIG. 4 is a circuit diagram showing a configuration of a receiver according to a third embodiment;

5A is a circuit diagram showing a configuration of a conventional example of a distortion compensating circuit. FIG. 5B is a characteristic diagram for explaining nonlinear distortion of an amplifier circuit.

[Explanation of symbols]

20a, 21a, 26a, 27a Input port (input terminal) 20b, 21b, 26b, 27b Output port (output terminal) 22 Hybrid power distributor 23, 24 Amplifying circuit 25 Hybrid power combiner 28 Adjustment circuit 29 Variable attenuator 30 Transfer Phaser 31 Amplifying circuit 32 Directional coupler R1 Terminating resistor (50Ω)

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 5J090 AA01 AA21 AA41 CA26 CA27 CA92 FA08 FA19 GN02 GN05 GN07 HA26 HN03 HN14 KA16 KA26 KA68 MA14 MA20 SA14 TA01 TA03

Claims (5)

[Claims] 1. A hybrid power combiner in a balanced amplifier circuit comprising a hybrid power divider, a hybrid power combiner, and an amplifier provided between the hybrid power divider and the hybrid power combiner. A distortion compensation circuit that uses an output port other than the output port of the normal signal as a distortion detection port generated by the amplifier, and an adjustment unit that performs a desired process on a distortion signal obtained from the distortion detection port. Feedback means for feeding back the output of the adjustment circuit to a regular signal output from the regular signal output port of the hybrid power combiner. 2. The distortion compensation circuit according to claim 1, wherein said adjustment means includes a variable attenuation circuit, a phase shift circuit, and an amplification circuit. 3. The hybrid power divider includes a first input port to which an input signal is supplied, a second input port to which a terminating resistor is connected, and first and second output ports. Further, the hybrid power combiner includes:
A first output port functioning as a distortion detection port, a second output port functioning as a normal signal output port, and a second output port functioning as a normal signal output port; A first amplifier circuit is connected between the first output port and the first input port of the hybrid power combiner, and a second output port of the hybrid power divider and a hybrid power combiner of the hybrid power combiner. 3. The distortion compensation circuit according to claim 1, wherein a second amplifier circuit is connected between the second input ports. 4. A transmitter comprising the distortion compensation circuit according to claim 1. 5. A receiver comprising the distortion compensation circuit according to claim 1.