Amplifiers – With control of power supply or bias voltage – With control of input electrode or gain control electrode bias
Reexamination Certificate
2003-02-19
2004-09-14
Mottola, Steven J. (Department: 2817)
Amplifiers
With control of power supply or bias voltage
With control of input electrode or gain control electrode bias
C330S132000, C330S140000
Reexamination Certificate
active
06791406
ABSTRACT:
The present invention relates to the field of transmitting radio frequency (RF) signals, and it relates more particularly to a power servo-loop, in particular for controlling a power amplifier.
BACKGROUND OF THE INVENTION
In known manner, in a telecommunications system in which an RF signal transmitter is sending to a receiver of such signals, it is necessary to ensure maximum quality of service. For example, when transmitting digital signals, this condition requires the binary error rate to remain at all times below a specified rate. To satisfy this condition on reception, it is necessary to ensure that the received signal-to-noise ratio is at all times above a predetermined value.
In order to make it possible to raise the power of the RF signals for transmission, the transmitter is provided with a power amplifier. By way of example, for a call between a mobile terminal and a base station in a cellular network of the GSM (global system for mobile communications) type, the purpose of the power amplifier is to transmit at a power that is sufficient to enable the corresponding base station to receive properly in compliance with the specifications in force. Thus, when the base station is far away from the terminal so that it receives the communications information from the terminal poorly or not at all, the base station sends an instruction to the terminal to transmit at a higher power level as determined by the base station.
In a transmitter, it is known for the amplifier to be servo-controlled by means of a power servo-loop that regulates the power of the RF signals for transmission at the output of the amplifier.
More precisely, an RF signal generated by the transmitter is supplied to the input of the amplifier. The power loop includes a detection circuit having coupling means for taking off a fraction of the output signal from the power amplifier. This RF signal as taken off represents the output signal and it is rectified on passing through a diode of a detection unit so as to constitute a “detection” direct current (DC) voltage level. This detection voltage is then compared with a reference voltage by means of a comparator unit placed at the outlet from the detection circuit. Until the reference voltage has been reached, the comparator unit acts on the power amplifier to increment the power level of the output signal.
Unfortunately, it can happen that an interference RF signal travels through the transmitter in the direction opposite to the propagation direction of the output signal. For example, this may be power reflected from a mismatched antenna of the transmitter, i.e. an antenna having a high standing wave ratio (SWR). This interference signal also has a fraction of its power taken off via the coupling means of the detection circuit, which fraction is added to the taken-off fraction of the output signal and leads to distortion such that the detection voltage is no longer a true image of the output signal. This poor detection degrades the servo-control of the amplifier. This can lead either to the transmitter consuming too much power or to deterioration in the transmission performance of the signal for transmission.
In the prior art, certain transmitters have been fitted with a circulator located upstream from the power loop relative to the propagation direction of the reflected power. The circulator is a one-way device: it allows the signal for transmission to pass through while eliminating the reflected signal that is propagating in the opposite direction.
Such a circulator is an expensive component. In addition, because of its large size, it is difficult to integrate in certain transmitters that are of small dimensions, such as portable radio telephone stations, for example.
OBJECT AND SUMMARY OF THE INVENTION
The object of the invention is to provide a servo-loop having a detection circuit that includes detection control means and that is of lower cost.
To this end, the present invention provides a power servo-loop in particular for controlling a power amplifier, the servo-loop including a detection circuit, which comprises:
coupling means for taking off RF signals; and
a detection unit for delivering a detection signal partially representative of a first RF signal taken off by the coupling means;
wherein the detection circuit further comprises, between the coupling means and the detection unit, detection control means for substantially eliminating an “interfering” second RF signal also taken off by the coupling means so that the detection signal is entirely representative of the first RF signal.
The control means of the invention are integrated in the detection circuit. It is no longer necessary to use a circulator upstream from the loop as in the prior art.
In a preferred embodiment of the invention, the detection circuit comprises, at the output from the coupling means, first and second “output” branches interconnected on a “detection” branch including the detection unit, each output branch serving to convey a respective component of the interference signal as taken off. The detection control means comprise first phase shifter means inserted in the first output branch, and second phase shifter means inserted in the second output branch, the first and second phase shifter means being suitable for inducing substantially opposite phase shifts to said components.
The phase shifter means of the invention cause the components of the interfering signal that are taken off to be in phase opposition so that they cancel at the detection branch.
Preferably, each of the first and second phase shifter means comprises an inductor coupled with a capacitor.
Thus, the control means of the invention include low cost discrete components that are easy to integrate in portable equipment and that can easily be added to loops that already exist.
In this particular embodiment, the first output branch may comprise a main branch leading to the detection branch and including a first one of said inductors, together with a secondary branch including a first one of said capacitors, which is connected between a ground plane and a connection point with the associated main branch. The second output branch may also comprise a main branch leading to the detection branch and including the other one of said capacitors, which is substantially identical to the first capacitor, and a secondary branch including the other one of said inductors, which is substantially identical to the first inductor, and which is connected between a ground plane and a connection point with the associated main branch.
Advantageously, the detection control means comprise an attenuator disposed in one of the output branches so as to make it easier to equalize the amplitudes of the two interference signal components that are to be eliminated.
Preferably, the coupling means comprise phase shifter means suitable for phase shifting the taken-off RF signals.
The present invention also provides an RF signal amplification circuit comprising a power amplifier and a power servo-loop for said amplifier as defined above.
The present invention also provides an RF signal transmitter having RF signal transmitter means fitted with an amplification circuit as defined above.
The transmitter of the invention is preferably selected from the group comprising: portable radio telephone stations; personal digital assistants; and portable computers.
A portable radio telephone station of the invention may be a cellular telephone of the GSM type, of the digital communication system (DCS) type, or of the universal mobile telecommunications system (UMTS) type, or it may be a telephone of the digital European cordless telecommunications (DECT) type.
REFERENCES:
patent: 4122400 (1978-10-01), Medendorp et al.
patent: 4353037 (1982-10-01), Miller
patent: 4729129 (1988-03-01), Koerner
patent: 6549068 (2003-04-01), Bollenbeck
Kolodziej Pierre
Pouliquen Mikaël
Alcatel
Mottola Steven J.
LandOfFree
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