Amplifiers – With pilot frequency control means
Reexamination Certificate
2001-09-17
2003-04-22
Lam, Tuan T. (Department: 2816)
Amplifiers
With pilot frequency control means
C330S151000
Reexamination Certificate
active
06552608
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a linear amplifier for amplifying power of a radio-frequency signal whose level varies widely, based on feed-forward technique.
2. Description of the Related Art
In recent years, a CDMA (Code Division Multiple Access) has been applied to many mobile communication systems since it has characteristics that it has a high ability of keeping confidentiality and is not easily influenced by selective fading and other interference/jamming in a radio transmission path and also since technology of realizing transmitting power control which is indispensable for solving a near-far problem which is peculiar to it has been established.
Wireless zones of these mobile communication systems are formed, via redundantly structured power amplifiers and directional antennas, as a plurality of sector cells having the following advantages.
to be able to reduce interferences of the same channel and improve utilization efficiency of radio frequencies based on directivity of the antennas
to be able to have a large number of co-callers (number of subscribers) per unit frequency compared with that in omni-zones
to be able to perform channel control (including transmitting power control) independently for each sector
Feed-forward technique is also applied to many of the power amplifiers described above.
FIG. 16
is a diagram showing a structure example of the power amplifier to which the feed-forward technique is applied.
In the drawing, an input of a variable attenuator
41
is given an input signal whose power is to be amplified (hereinafter referred to as a ‘principal signal’) and an output of the variable attenuator
41
is connected to inputs of a variable attenuator
42
and a delaying part
43
. An output of the variable attenuator
42
is connected to an input of a main amplifier
45
via a variable phase-shifter
44
and an output of the main amplifier
45
is connected to an input of the attenuator
46
. Outputs of the delaying part
43
and the attenuator
46
are connected to an input of a variable attenuator
47
and an output of the variable attenuator
47
, as well as the output of the main amplifier
45
, is connected to an input of a pilot signal detecting part
51
via a variable phase-shifter
48
, an auxiliary amplifier
49
, and a detector
50
. To the input of the variable attenuator
42
, an output of a pilot signal generating part
52
is connected via a variable attenuator
53
and to control inputs of the variable attenuators
41
,
42
,
47
and the variable phase-shifters
44
,
48
as well as control inputs of the pilot signal generating part
52
and the variable attenuator
53
, corresponding output ports of a controlling part
54
are connected. Monitor outputs of the detector
50
and the pilot signal detecting part
51
are connected to corresponding input ports of the controlling part
54
and in an output of the pilot signal detecting part
51
, the principal signal to be transmitted as a transmission wave is obtained.
Note that a loop-shaped circuit which is formed between the output of the variable attenuator
41
and the input of the variable attenuator
47
is hereinafter referred to as an ‘error detection loop’ (a principal-signal cancellation loop) and a loop-shaped circuit which is formed between the output of the main amplifier
45
and the input of the pilot signal detecting part
51
is referred to as an ‘error elimination loop’ (a distortion cancellation loop).
Operations of the power amplifier as structured above in its steady state are explained below.
The variable attenuator
41
is given by the controlling part
54
attenuation which is determined under the channel control (may include the transmitting power control) and applies to each of the variable attenuator
42
and the delaying part
43
the principal signal at a level at which predetermined transmitting power is achieved.
The pilot signal generating part
52
constantly generates a sine wave signal (hereinafter referred to as a ‘pilot signal’) with a known frequency outside an occupied bandwidth of the principal signal and applies the pilot signal at a predetermined level to the input of the variable attenuator
42
via the variable attenuator
53
whose attenuation is set by the controlling part
54
.
The main amplifier
45
gives to the attenuator
46
a signal obtained by amplifying the principal signal and the pilot signal which are applied via the variable attenuator
42
and the variable phase-shifter
44
(hereinafter referred to as a ‘provisional output-signal’). The attenuator
46
has attenuation equal to an inverse number of a nominal value of a total gain of the variable attenuator
42
, the variable attenuator
44
, and the main amplifier
45
which are cascaded and generates a signal corresponding to the sum of the principal signal inputted to the variable attenuator
42
and the pilot signal (hereinafter referred to as a ‘reduced input-signal’).
Delay time of the delaying part
43
is set in advance at a value equal to a sum (difference) of a nominal value of total propagation delay time of the variable attenuator
42
, the variable phase-shifter
44
, the main amplifier
45
, and the attenuator
46
which are cascaded and time corresponding to a half of a cycle of the principal signal.
The delaying part
43
delays the principal signal outputted by the variable attenuator
41
over this delay time to output a signal whose phase is 180 degrees ahead of (delayed behind) the reduced input-signal which is obtained in the output of the attenuator
46
(hereinafter referred to as a ‘principal-signal cancellation signal’).
The variable attenuator
47
, the variable phase-shifter
48
, the auxiliary amplifier
49
, and the detector
50
vary a level and a phase of a signal which is given as a sum string of instantaneous values of the reduced input-signal and the principal-signal cancellation signal under control of the controlling part
54
to generate a ‘distortion cancellation signal’.
The detector
50
extracts and detects a component of the principal signal included in the distortion cancellation signal to detect a level of the component of the principal signal.
Furthermore, the pilot signal detecting part
51
outputs a signal which is given as a sum of the provisional output-signal and the distortion cancellation signal and detects a level of a component of the pilot signal included in the signal.
Meanwhile, the controlling part
54
sets at a starting time a level of the pilot signal which is applied to the variable attenuator
42
by setting the aforesaid attenuation for the variable attenuator
53
(FIG.
17
(
1
)) and supplies driving power to the main amplifier
45
via a power controlling part which is not shown (FIG.
17
(
2
)).
The controlling part
54
also performs processing (hereinafter referred to as ‘initialization processing’) of setting attenuation ATT
ed
, ATT
es
of the variable attenuators
42
,
47
and phase-shift &PHgr;
ed
, &PHgr;
es
of the variable phase-shifters
44
,
48
at predetermined initial values (here to simplify the explanation, supposed to be a digital value X (a positive pure binary number) at which the attenuation/the phase-shift become a mean value) (FIG.
17
(
3
)).
After finishing the initialization processing, the controlling part
54
updates the attenuation ATT
es
of the variable attenuator
47
and the phase-shift &PHgr;
es
of the variable phase-shifter
48
at a predetermined frequency based on an adaptive algorithm for minimizing the level of the pilot signal which is detected by the pilot signal detecting part
51
(FIG.
17
(
4
)). Note that processing of updating the attenuation ATT
es
of the variable attenuator
47
and the phase-shift &PHgr;
es
of the variable phase-shifter
48
in this way is hereinafter referred to simply as ‘distortion cancellation processing’.
Furthermore, after finishing the distortion cancellation processing, the controlling part
54
discriminates whether or not the level of the principal signal detected by a principa
Matsuda Ayanori
Saito Yutaka
Fujitsu Limited
Katten Muchin Zavis & Rosenman
Lam Tuan T.
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