Amplifiers – With semiconductor amplifying device – Including gain control means
Patent
1998-02-27
1999-12-28
Pascal, Robert
Amplifiers
With semiconductor amplifying device
Including gain control means
330129, 455126, H03G 330
Patent
active
060086971
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a circuit arrangement comprising signal input and a signal output, comprising an extraction stage for extracting part of a signal from the output of the power amplifier stage to the feedback path, and comprising a feedback function stage, the feedback path with an external input signal, an output of the recombining stage being coupled to the signal input of the power amplifier stage, inversely, so that the product of their gain factors remains constant, in essence.
From European Patent Application 0 638 994, to whose overall disclosure content is expressly referred hereby, is known such a circuit arrangement of the type disclosed in the first claim. This circuit arrangement is to achieve a linearization of the transmission characteristic of the power amplifier stage. Since the gain factors of the gain control elements are varied inversely, so that their product remains substantially constant, there is additionally achieved that the feedback loop (formed by forward gain path, feedback path and re-combining stage) formed by the circuit arrangement is also operated with different powers transmitted via the power amplifier stage with constant signal levels on the signal input and is thus capable of operating at a signal level to which it is optimally designed.
SUMMARY OF THE INVENTION
It is an object of the invention to arrange the circuit arrangement described above so that a further improvement of the operating behavior is achieved, particularly with respect to noise.
According to the invention, a solution to this objective is that the first gain control element is formed by an adjustable delay element which is preceded in the forward gain path by a low-noise amplifier stage which has a substantially constant gain factor. Losses in downstream elements in the forward gain path are overcompensated for by the gain factor of the low-noise amplifier stage. The low-noise increase of the signal level in the low-noise amplifier stage provides an improvement of the signal-to-noise ratio in this part of the forward gain path.
The invention is particularly advantageous if the circuit arrangement is embodied as a Cartesian loop. As shown in the publication EP 0 638 994, a summing stage is inserted into the forward gain path between the up-converters for the Cartesian components of the signal to be amplified and the power amplifier stage. Losses occurring in this summing stage are overcompensated for according to the invention in that between the mixers for the quadrature components of the signal to be amplified and the summing stage, low-noise amplifiers are inserted which form the low-noise amplifier stage in the forward gain path. This improves the noise characteristic in the range of the summing stage.
According to a further embodiment of the invention, the control circuit does not only maintain the product of the gain factors of the first and second gain control elements at a constant level, but also the gain factor of the power amplifier stage is incorporated in this product which is maintained at a constant level. As a result, variations in the gain of the power amplifier stage, caused, for example, by temperature variations or ageing, can be compensated for, so that the overall transmission behavior of the circuit arrangement becomes more constant.
Preferably, a circuit arrangement according to the invention is used within a transmitter power amplifier of a transmitter apparatus. Such a transmitter can advantageously be used in a telecommunication apparatus.
BRIEF DESCRIPTION OF THE DRAWING
An illustrative embodiment is represented in the single FIGURE of the drawing and will be further described in the following.
DESCRIPTION OF THE PREFERRED EMBODIMENT
This FIGURE shows a section of the FIGURE of EP 0 638 994 A1 in which the elements known from that document are referenced by the characters used there. Only the section of the FIGURE in which the modifications according to this invention are used are shown. The forward gain path comprises the mixers
REFERENCES:
patent: 5212814 (1993-05-01), Iwane
patent: 5469105 (1995-11-01), Sparks
patent: 5507017 (1996-04-01), Whitmarsh et al.
Halajian Dicran
Nguyen Khanh Van
Pascal Robert
U.S. Philips Corporation
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