Amplifiers – With amplifier bypass means
Reexamination Certificate
2002-07-18
2004-09-14
Nguyen, Linh M. (Department: 2816)
Amplifiers
With amplifier bypass means
C330S149000
Reexamination Certificate
active
06791409
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a feedforward amplifier and a feedforward amplification method used for mobile communication base station equipment and so on.
2. Related Art of the Invention
In recent years, a power amplifier of high efficiency and high linearity is required for a transmitter of a mobile communication base station in order to amplify a large number of signaling channels by one operation, and improvement in the linearity is implemented by performing distortion compensation by a feedforward method. Moreover, a feedforward amplifier will not be described in detail here since it is also described in John L. B. Walker, “High-Power GaAs FET Amplifiers,” Artech House, 1993, pp. 332 to 333 and so on, for instance.
And in recent years, a CDMA (Code Division Multiple Access) method is adopted as a modulation method of a portable telephone, so that the base station requires switching of output power such as high-speed power control and burst transmission, and high-speed distortion compensation control is also required for feedforward distortion compensation. Moreover, the CDMA method will not be described in detail here since it is also described in Tero Ojanpera et al., “Wideband CDMA For Third Generation Mobile Communications,” Artech House, 1998, pp. 58 to 62 and so on, for instance.
Here, configuration of a feedforward amplifier in the past will be described by referring to
FIG. 5
which is a block diagram thereof (for instance, a feedforward nonlinear distortion compensation amplifier described in Japanese Patent Laid-Open No. 2000-196366).
In
FIG. 5
, reference character IN represents an input terminal, Zo represents a terminating resistor, HYB
1
represents a first hybrid, ATT
1
represents a first variable attenuator, PS
1
represents a first variable phase shifter, A
1
represents a main amplifier, D
1
represents a first delay element, HYB
2
represents a second hybrid, D
2
represents a second delay element, ATT
2
represents a second variable attenuator, PS
2
represents a second variable phase shifter, A
2
represents an error amplifier, HYB
3
represents a third hybrid, DC
3
represents a first coupler, DC
2
represents a second coupler, DC
4
represents a third coupler, DC
9
represents a fourth coupler, D
3
represents a third delay element, D
4
represents a fourth delay element, BPF
3
represents a band pass filter, OSC
2
represents a local oscillator, reference numeral
28
denotes an in-phase divider,
36
denotes a first synchronous detector,
38
denotes a second synchronous detector, and
40
denotes an ALC (auto level control) circuit.
Next, operation of the feedforward amplifier in the past will be described.
As for distortion cancellation loop (L
2
) control, a pilot signal generated by the local oscillator OSC
2
is divided by the in-phase power divider
28
, and one of the divided pilot signal is injected from the first coupler DC
3
to the main amplifier A
1
. In addition, a suppressed signal of a distortion cancellation loop is taken out of the third coupler DC
4
and is added to the second synchronous detector
38
together with the other output of the in-phase divider
28
via the band pass filter BPF
3
so as to acquire an amplitude error and a phase error. And the errors thus acquired are added to a control terminal of the second variable attenuator ATT
2
and that of the second variable phase shifter PS
2
so as to exert control.
As for distortion detection loop (L
1
) control, a transmitting carrier taken out of the fourth coupler DC
9
as a combined output is added to the synchronous detector
36
via the third delay element D
3
and the auto level control circuit
40
, and the blocked signal of a distortion detection loop taken out of the second coupler DC
2
as a combined output is added to the synchronous detector
36
via the fourth delay element D
4
. And the amplitude error and the phase error are outputted therefrom, and the outputted errors are added to the control terminal of the first variable attenuator ATT
1
and that of the first variable phase shifter PS
1
so as to exert control.
When the carrier level goes down in such a configuration, distortion detection loop control is stabilized by keeping a level of a reference transmitting carrier constant. For this reason, the auto level control circuit
40
was essential in order to cope with the cases where an output level is significantly changed by a method of a wide dynamic range.
As for such an auto level control circuit, however, an accuracy of distortion compensation is apt to be influenced by a temperature change and so on, and so it may be difficult to obtain stable distortion compensation.
In addition, in the case of performing the burst transmission, there was a limit to speedup of the control since it takes time before the level of the transmitting carrier becomes constant due to use of a feedback circuit as the auto level control circuit.
SUMMARY OF THE INVENTION
An object of the present invention is, in consideration of the above problems in the past, to provide the feedforward amplifier and the feedforward amplification method capable of performing high-speed distortion compensation control without using the auto level control circuit.
One aspect of the present invention is a feedforward amplifier comprising:
a first coupler of dividing an input signal into two outputs;
a first vector adjuster connected to one of the outputs of said first coupler, of adjusting an amplitude and a phase of a passing signal;
a main amplifier connected to the output of said first vector adjuster;
a first delay element connected to the other output of said first coupler;
a second coupler connected to the output of said main amplifier and the output of said first delay element, of outputting the output of said main amplifier as it is as a first output and outputting as a second output a component in which the output of said main amplifier and the output of said first delay element are combined in an opposite phase;
a second delay element connected to the first output of said second coupler;
a second vector adjuster connected to the second output of said second coupler, of adjusting the amplitude and the phase of the passing signal;
an error amplifier connected to the output of said second vector adjuster;
a third coupler connected to the output of said second delay element and the output of said error amplifier, of outputting a component in which the output of said second delay element and the output of said error amplifier are combined in the opposite phase;
a fourth coupler inserted into at least one location between the output of said first vector adjuster and the output of said main amplifier;
a fifth coupler inserted between the output of said main amplifier and said second coupler;
a sixth coupler inserted between the second output of said second coupler and the input of said second vector adjuster;
a seventh coupler connected to the output of said third coupler;
a distortion cancellation loop control circuit of dividing in two the output of at least one predetermined local oscillator, connecting one of the outputs to a combined input of said fourth coupler, inputting the other output and a combined output of said seventh coupler, and comparing an output signal of said at least one local oscillator to a combined output signal of said seventh coupler to acquire an error in the amplitude and an error in the phase so as to provide a control voltage to two control terminals of said second vector adjuster;
an in-phase power dividing circuit connected to the combined output of said fifth coupler;
a 90-degree power dividing circuit connected to the combined output of said sixth coupler;
a first log amplifier connected to one of the outputs of said in-phase power dividing circuit;
a second log amplifier connected to one of the outputs of said 90-degree power dividing circuit;
a first mixer connected to the output of said first log amplifier and the output of said second log amplifier;
a subtraction circuit connected to the output
Ishida Kaoru
Takachi Naoki
Takeuchi Rie
Nguyen Linh M.
RatnerPrestia
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