JP3037584B2 - Feed forward amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feed-forward amplifier which is used as a base station or a relay device of a mobile communication system such as a car telephone and is a kind of a highly linear amplifier for simultaneously amplifying multi-frequency signals. is there.

[0002]

2. Description of the Related Art A base station and a wireless relay device in an 800 MHz band mobile telephone system and the like are provided with a multi-frequency common amplifier for simultaneously amplifying multi-frequency signals. In this multi-frequency common amplifier, it is necessary to sufficiently improve the linearity in order to minimize the intermodulation distortion, and a small and high linearity amplifier is used. One of them is a self-adjustable feedforward amplifier (SAFF-A: Self-Ad).
justifying Feed-Forward Ampl
and a common amplifier that compensates for all intermodulation distortion and noise by self-adjustment. This feed-forward amplifier is composed of a distortion detection circuit and a distortion removal circuit. A distortion detection circuit including a main amplifier which is a compensation target amplifier detects a distortion component other than an input signal, and detects the detected distortion component (error component). Is input to a distortion removal circuit including an auxiliary amplifier (error amplifier) to amplify the distortion component, and then, is combined with the multi-frequency amplified signal amplified by the main amplifier in reverse phase to cancel the distortion component. .

FIG. 1 is a block diagram of a self-adjusting feedforward amplifier to which the present invention is applied. In the figure, 1 is a power divider for distributing an input signal, 2 is a variable attenuator, 3 is a variable phase shifter, 4 is a main amplifier, 5 is a delay line,
6 is a pilot oscillator, 7 is a power combiner, 8 is a variable attenuator, 9 is a variable phase shifter, 10 is an auxiliary amplifier, 11 is a delay line, 12 is a power combiner, 13 is a power divider, and 14 is a selection level meter. , 15 are control circuits. Reference numeral 20 enclosed by a broken line denotes a distortion detection circuit, and reference numeral 30 denotes a distortion removal circuit. Reference numeral 16 denotes an input level detector, which may or may not be provided in the present invention, as described later. The multi-frequency input signal is input to the power divider 1, and one of the two multi-frequency signals is amplified by the main amplifier 4 via the variable attenuator 2 and the variable phase shifter 3. The output is input to the power combiner 7 as a multi-frequency amplified signal including a distortion (error) component generated at the time of amplification, branched and output by the power distributor 1, and input to the power combiner 7 via the delay line 5. The multi-frequency input signal is subjected to reverse phase synthesis and a distortion component is detected.

The control by the control circuit 15 of the distortion detection circuit 20 is performed so that the multi-frequency input signal component contained in the distortion component output of the power combiner 7 is sufficiently canceled, that is, the distortion component output level is minimized. The variable attenuator 2 and the variable phase shifter 3 are controlled. The multi-frequency amplified signal including one distortion component output from the power combiner 7 passes through the delay line 11 to the power combiner 12
Is input to The other distortion component output from the power combiner 7 passes through the variable attenuator 8 and the variable phase shifter 9 to the auxiliary amplifier 1
The signal is amplified by 0 and is input to the power combiner 12 to invert the polarity, and is subjected to reverse phase synthesis with the multi-frequency amplification signal including the distortion component input through the delay line 11 to cancel the distortion component, and to reduce the multi-frequency with little distortion. A common amplified signal is output. As a method of detecting the distortion component of the distortion removing circuit 30, for example, a distortion generated when a tone is injected from the pilot oscillator 6 to amplify the pilot signal without directly detecting the distortion component of the multi-frequency amplified signal is detected by the main amplifier. 4. Under the assumption that the distortion is equivalent to the distortion of the multi-frequency amplification signal generated in step 4, the pilot signal is extracted from the power distributor 13, and its level is monitored by the selection level meter 14 to detect the pilot signal. The variable attenuator 2, the variable phase shifter 3, and the variable attenuator 8, the variable phase shifter 9 are controlled by the control circuit 15.
Is generally controlled to suppress the distortion component.

[0005]

In such a self-adjusting feedforward amplifier, the level of a multi-frequency input signal may fluctuate rapidly in a short time. For example,
TDMA used in digital car phone systems, etc.
(Time Division MultipleAc
In the ESS (time division multiple access) system, three channels are frequency-division multiplexed per one frequency of the downlink, and one frame of 20 ms is composed of three slots with about 6.7 ms as one slot. Transmission power control is being performed. When such a transmission wave is received and amplified, when the multi-frequency input signal level changes every 6.7 ms, the distortion component output level obtained from the distortion detection circuit 20 also changes. Therefore, when the control circuit 15 controls the variable attenuator 2 and the variable phase shifter 3 so that the distortion component output level is always minimized, the multi-frequency input signal component included in the distortion component output is sufficiently canceled. If the multi-frequency input signal of the next slot changes during the control operation, the distortion component output level changes irrespective of the control, causing a problem that the control malfunctions.

An object of the present invention is to solve the problem that the self-adjustment control of the feedforward amplifier in the TDMA system malfunctions because the input level of the multi-frequency signal changes due to power control and burst control for each slot on the transmission side. It is another object of the present invention to provide a feedforward amplifier capable of performing stable self-adjustment even when the input level changes for each slot.

[0007]

A feedforward amplifier according to the present invention branches and outputs a multi-frequency input signal by a power divider, and outputs one of the signals via a first variable attenuator and a first variable phase shifter. The signal amplified by the main amplifier and the signal obtained by adjusting the timing of the other signal by the first delay line are subjected to reverse-phase synthesis by a first power combiner to detect a distortion component generated in the main amplifier. A distortion detection circuit;
A signal obtained by amplifying the distortion component output from the power combiner through a second variable attenuator and a second variable phase shifter with an auxiliary amplifier, and a main amplifier output from the first power combiner. A second power combiner reversely combines the amplified signal with a signal whose timing is adjusted by a second delay line to cancel a distortion component generated in the main amplifier and output a multi-frequency amplified signal. A feed-forward amplifier comprising: a removal circuit; and a control circuit that controls the first variable attenuator and the first variable phase shifter to minimize a distortion level detected by a distortion detection circuit. When the level of the signal is different for each slot in the TDMA frame, the control circuit sets the level of the multi-frequency input signal in the frame to a maximum value by an input level detector provided on the input side of the power divider. And detecting the first variable attenuator and the first variable phase shifter of the frame using a distortion detection level obtained from the distortion detection circuit of the slot. Is what you do. Furthermore, the control circuit uses the average value of the data of the slot indicating the maximum value in the frame of the level of the distortion detection signal obtained from the distortion detection circuit, or the data of several slots from the slot indicating the maximum value. The apparatus is characterized in that the first variable attenuator and the first variable phase shifter of a frame are controlled.

The main purpose of the distortion detection circuit 20 is to include the distortion output from the main amplifier 4 because the distortion component generated when the multi-frequency input signal is amplified by the main amplifier 4 is canceled by the distortion removal circuit 30. It is to output a distortion component by canceling out the multi-frequency signal components of the multi-frequency signal. Therefore, the residual multi-frequency signal component after the cancellation has low new distortion generated in the distortion removal circuit 30, and the multi-frequency output signal component due to the residual multi-frequency signal when the distortion is canceled at the output portion of the distortion removal circuit 30. The level may be set so that the offset amount of is reduced.

[0009]

2A and 2B are diagrams for explaining the operation of the present invention. FIG. 2A shows the signal level of each slot of a multi-frequency input signal, and FIG. 2B shows the signal output from the corresponding distortion detecting circuit 20. This shows the distortion component output level. In the feed-forward amplifier shown in FIG. 1, when a multi-frequency signal as shown in FIG.
When the period is divided into three slots, and the signal level in each slot is different, the distortion detection signal a of the distortion detection circuit 20 output from the power combiner 7 is shown in FIG.
Assume that the level is as shown in FIG. (1) When the input level detector 16 is provided and the level change shown in FIG. 2A can be detected, the distortion detection level at the timing of the slot with the highest input level in one frame is used for control. For example, the input level is sampled at least once every about 6.7 ms, and the distortion detection level is sampled at the timing when the highest level slot is detected within 20 ms to obtain a distortion detection value. In general, the higher the input level, the higher the amount of distortion. Therefore, the variable attenuator 2 and the variable phase shifter 3 are controlled so that the detected value is minimized. (2) When the input level detector 16 is not used, the maximum value in one frame of the distortion detection signal a of the distortion detection circuit 20 or the average value of several data from the maximum is used for control. For example, the level of the distortion detection signal a is sampled at least once every about 6.7 ms, and the maximum value during 20 ms is taken out as a distortion detection value, and the variable attenuator 2 and the variable phase shifter are set so that this detection value becomes minimum. 3 is controlled.

Each of the above (1) and (2) is to optimize the distortion detection circuit 20 for the slot having the maximum distortion level in one frame. Data sampling does not need to be synchronized with the frame, and at least one circuit is sampled in one slot, so that a synchronization signal is unnecessary. In this method, since the distortion detection value is obtained in one frame period, in the above example, the variable attenuator 2 and the variable phase shifter 3 are controlled once every 20 ms.

[0011]

By implementing the present invention, in digital communication that will be increasingly used in the future, stable feedforward control is performed even when the multi-frequency input signal changes, so that the practical effect is extremely small. large.

[Brief description of the drawings]

FIG. 1 is a block diagram of a self-adjusting feedforward amplifier to which the present invention is applied.

FIG. 2 is a diagram illustrating the operation of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power splitter 2,8 Variable attenuator 3,9 Variable phase shifter 4 Main amplifier 5,11 Delay line 6 Pilot signal generator 7,12 Power combiner 10 Auxiliary amplifier 13 Power splitter 14 Selection level meter 15 Control circuit 16 Input level detector

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Nobuyasu Shimada 3-14-20 Higashinakano, Nakano-ku, Tokyo International Electric Company (72) Inventor Eiji Hirota 3-14-20 Higashinakano, Nakano-ku, Tokyo Country (58) Field surveyed (Int.Cl. ⁷ , DB name) H03F 1/30-1/40 H04J 3/00

Claims (2)

(57) [Claims] A multi-frequency input signal is branched and output by a power divider, and one of the signals is amplified by a main amplifier via a first variable attenuator and a first variable phase shifter, and the other signal is amplified by a main amplifier. A first power combiner for detecting a distortion component generated in the main amplifier by synthesizing a signal whose timing is adjusted by a first delay line with a first power combiner; and a first power combiner. The distortion component output from
The signal amplified by the auxiliary amplifier via the variable attenuator and the second variable phase shifter and the signal amplified by the main amplifier output from the first power combiner are matched in timing by a second delay line. A second power combiner for synthesizing a signal and a second power combiner to cancel a distortion component generated in the main amplifier and output a multi-frequency amplified signal; and a first variable attenuator and a first variable attenuator. And a control circuit that controls the variable phase shifter so that the distortion level detected by the distortion detection circuit is minimized, when the level of the multi-frequency input signal is different for each slot in the TDMA frame, The control circuit detects, by an input level detector provided on the input side of the power divider, a slot in which the level of a multi-frequency input signal in a frame has a maximum value, and detects the distortion of the slot. Use distortion detection level obtained from the output circuit and the first variable attenuator and a first feedforward amplifier, characterized in that the the to control the variable phase shifter of the frame. 2. The control circuit uses data of a slot indicating a maximum value in a frame of a level of a distortion detection signal obtained from the distortion detection circuit or an average value of data of several slots from the slot indicating the maximum value. 2. The feedforward amplifier according to claim 1, wherein the first variable attenuator and the first variable phase shifter of the frame are controlled.