Amplifiers – With pilot frequency control means
Reexamination Certificate
2000-11-02
2002-05-14
Shingleton, Michael B (Department: 2817)
Amplifiers
With pilot frequency control means
C330S151000
Reexamination Certificate
active
06388515
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a feedforward amplifier in which distortion occurring when a multifrequency multiplexed signal of a high frequency band is amplified is suppressed to produce only a main amplified signal.
DESCRIPTION OF THE PRIOR ART
For feedforward amplifiers, various circuit configurations have been proposed, but the configurations become complex, which has soared the production cost of the amplifier.
FIG. 12
shows a circuit layout example of a feedforward amplifier of the prior art.
The feedforward amplifier of
FIG. 12
includes a distortion detecting loop A and a distortion removing loop B. In the loop A, an input signal from an input terminal
301
is a multifrequency multiplexed signal of a high frequency band. The input signal is simultaneously amplified by a main amplifier
304
. A nonlinear distorted signal component resultant from the amplification by the main amplifier
304
is detected by canceling the amplified input signal components. In the distortion removing loop B, the distorted signal component detected by the loop A is amplified by a subordinate amplifier
315
. The amplified signal is mixed with an output signal which includes a distorted signal component and which is outputted from the main amplifier
304
. This cancels the distorted signal component in the output signal from the main amplifier
304
to obtain only the amplified input signal component.
The distortion detecting loop A includes a directional coupler
319
, a two-output distributor
302
, a vector adjuster
303
, a main amplifier
304
, a delay line
306
, a controller
309
, and a detector circuit
322
. The loop A further includes couplers
307
and
308
, which are shared between the loops A and B.
Operation of the distortion detecting loop A will be described. The directional coupler
319
mixes the multifrequency multiplexed signal received from the input terminal
301
with a single-frequency pilot signal. The mixed signal is distributed by the two-output distributor
302
as a first output and a second output. The first output is delivered via the vector adjuster
303
to the main amplifier
304
, which resultantly produces an output signal. The coupler
308
mixes a part of the output signal with the second output signal which is outputted from the two-output distributor
302
and which has passed the delay line
306
. These signals having mutually opposite phases.
The detector circuit
322
detects the pilot signal in the mixed signal. To minimize a signal level of the pilot signal component from the detector circuit
322
, the controller
309
controls the vector adjuster
303
to adjust quantity or values of attenuation and phase. When the controller
309
appropriately controls the vector adjuster
303
, the coupler
308
outputs only the distorted signal resultant from the amplification of the main amplifier
304
.
Description will now be given of operation of the distortion removing loop B. In the coupler
312
, the distorted signal detected by the distortion detecting loop A is received as a first input via the vector adjuster
313
and the subordinate amplifier
315
. The coupler
312
receives as a second input the output signal from the main amplifier
304
delayed through the delay line for a propagation delay time of the vector adjuster
313
and the subordinate amplifier
315
. The first and second input signals have opposite phases.
The coupler
912
mixes these signals with each other and feeds a resultant mixed signal to a coupler
316
. The coupler
316
delivers a part of the mixed signal to a detector circuit
323
. The detector circuit
323
detects a pilot signal component of the input signal and outputs the pilot signal component to a controller
314
. To minimize a level of the pilot signal component, the controller
314
controls the vector adjuster
313
to adjust quantity of attenuation and phase. Therefore, when the controller
314
controls the vector adjuster
313
in an appropriate manner, the coupler
316
outputs only the input signal component amplified by the main amplifier
304
.
To implement the function, each of the distortion detecting loop A and the distortion removing loop B of the feedforward amplifier of the prior art includes a pilot oscillator (
318
,
320
) a controller (
309
,
314
) and a detector circuit (
322
,
323
).
However, the feedforward amplifier of this configuration requires a large number of elements and hence a high production cost. Consequently, various feedforward amplifiers of a simplified circuit configuration have been proposed.
Japanese Patent Laid-Open Publication No. Heisei 6-244647 describes an example of a feedforward amplifier of the prior art. As shown in
FIG. 13
, the feedforward amplifier includes a switching unit S at an output terminal of a spread spectrum (SS) pilot signal oscillator
401
to deliver pilot signals to couplers
408
and
409
. Namely, the pilot signal oscillator
401
is shared between a distortion detecting loop and a distortion removing loop.
The feedforward amplifier further includes a controller
407
to receive output signals respectively from couplers
411
and
410
. The controller
407
receives a pilot signal component in a mixed signal from the coupler
411
and a pilot signal component in a mixed signal from the coupler
410
. To minimize a reception level of each of the pilot signal components, the controller
407
controls a distortion detecting vector adjuster
404
and a distortion removing vector adjuster to adjust magnitude of amplitude and phase.
In the feedforward amplifier of the prior art, the distortion detecting loop and the distortion removing loop share the pilot signal oscillator
401
and the controller
407
. To achieve the function of the feedforward amplifier shown in
FIG. 13
, this amplifier is more simplified in the circuit configuration when compared with that of FIG.
12
.
In the feedforward amplifier configured as shown in
FIG. 13
, the pilot signal oscillator and the controller are shared between the distortion detecting loop and the distortion removing loop. Therefore, the feedforward amplifier includes two output terminals to deliver pilot signals from the pilot signal oscillator, and the controller includes two input terminals to receive mixed signals.
When the pilot signal oscillator
401
outputs a pilot signal from a first output terminal, a leakage signal of the pilot signal appears on a second output terminal of the oscillator
401
. When a mixed signal is delivered to a first input terminal of the controller
407
, a leakage signal of the mixed signal takes place on a second input terminal of the controller
407
.
Consequently, the mixed signal propagating through the circuit includes an inherent pilot signal component and a leakage pilot signal component having a frequency equal to that of the inherent pilot signal component. The controller detects both of these signals to control the vector adjusters
404
and
405
. This naturally leads to a control error.
In this connection, the feedforward amplifier of the prior art shown in
FIG. 13
includes a spread spectrum (SS) pilot signal. Therefore, the control error due to the signal leakage between two output terminals and between two in t terminals is small enough for the controller
407
to appropriately control the distortion detecting vector adjuster
404
and the distortion removing vector adjuster
405
.
However, when the single frequency pilot signal described in conjunction with
FIG. 12
is applied in place of the spectrum spread pilot signal to the feedforward amplifier in which the distortion detecting loop and the distortion removing loop share the pilot signal oscillator and the controller as shown in
FIG. 13
, the control error in the adjustment of the quantity of attenuation and phase in the vector adjusters becomes greater when compared with a case in which the spectrum spread (SS) pilot signal is employed. Consequently, there arises a problem of insufficient improvement in the removal of the distorted signal. This problem is not tak
NEC Corporation
Shingleton Michael B
Sughrue & Mion, PLLC
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