CIRCUIT ARRANGEMENT COMPRISING A POWER AMPLIFIER STAGE

Abstract: A circuit arrangement is described comprising: a power amplifier stage located on a forward gain path arranged between a signal input and a signal output, a feedback path, connecting the signal output to the signal input, and 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; a re-combining stage for re-combining a feedback signal from the output of the feedback path with an external input signal, an output of the re-combining stage being coupled to the signal input of the power amplifier stage; a first gain control element in the forward gain path; a second gain control element in the feedback path; and a control circuit which varies the first and second gain control elements inversely, so that the product of their gain factors remains constant, in essence. To improve the operating behavior even further, particularly with respect to noise, the invention provides that the first gain control element is formed by an adjustable attenuator which is preceded in the forward gain path by a low-noise amplifier stage which has a substantially constant gain factor.

Description: Circuit arrangement comprising a power amplifier stage. The invention relates to a circuit arrangement comprising a power amplifier stage located on a forward gain path arranged between a signal input and a signal output, a feedback path, connecting the signal output to the signal input, and 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, a re-combining stage for re-combining a feedback signal from the output of the feedback path with an external input signal, an output of the re-combining stage being coupled to the signal input of the power amplifier stage, a first gain control element in the forward gain path, a second gain control element in the feedback path, and a control circuit which varies the first and second gain control elements 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. 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 overcompen sated 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 overcompen sated 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. An illustrative embodiment is represented in the single Figure of the drawing and will be further described in the following. This Figure shows a section of the Figure of EP 0 638 994 Al 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 44 and 46 for the quadrature components of the signal to be amplified. The output signals of the mixers 44 and 46 are applied according to the present invention to a summing stage 52 via a low-noise amplifier 441, 461 respectively, and additively combined in that stage. From the summing stage 52, the sum signal goes via an adjustable attenuation element 541 to an input 30 of the power amplifier stage 28 and from the amplifier stage output 32 via a coupler 56 partly to an output 24 which can be connected to an antenna and partly to the second gain control element 58. The adjustable attenuation element 541 and the second gain control element 58 are varied inversely by a control circuit 66 in the manner -mown from EP 0 638 994 Al. This control circuit 66 may preferably comprise a microprocessor. In a modification of the illustrative embodiment shown, also the power amplifier stage 28 can be controlled by the control circuit 66. The control circuit varies the gain factors of the delay element 541 (first gain control element), of the second gain control element 58 and of the power amplifier stage 28 in such a way that its product remains substantially constant. Preferably, the control circuit can also make a measurement of the gain factor of the power amplifier stage i.e. an evaluation of the ratio of the signal amplitudes on the output 32 and input 30. The thus established actual value of the gain factor of the power amplifier stage may then be used as a basis for the setting of the gain factor of the two gain control elements.

Claims: CLAIMS: 1. A circuit arrangement comprising a power amplifier stage located on a forward gain path arranged between a signal input and a signal output, a feedback path, connecting the signal output to the signal input, and 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, a re-combining stage for re-combining a feedback signal from the output of the feedback path with an external input signal, an output of the re-combining stage being coupled to the signal input of the power amplifier stage, a first gain control element in the forward gain path, a second gain control element in the feedback path, and a control circuit which varies the first and second gain control elements inversely, so that the product of their gain factors remains constant, in essence, characterized in 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. 2. A circuit arrangement as claimed in Claim 1, characterized in that the control circuit controls the product of the gain factors of the first and second gain control elements and of the power amplifier stage with an essentially constant value. 3. A circuit arrangement as claimed in Claim 1 or 2, characterized by a Cartesian loop architecture. 4. A transmitter power amplifier, characterized iby a circuit arrangement as claimed in Claim 1,2 or 3. 5. A transmitter, characterized by a transmitter power amplifier as claimed in Claim 4. 6. A telecommunication apparatus, characterized by a transmitter as claimed in Claim 5.

Inventors: SPARKS GEOFFREY SIDNEY, SPARKS, GEOFFREY, SIDNEY
Applicants: PHILIPS ELECTRONICS NV, PHILIPS NORDEN AB, PHILIPS PATENTVERWALTUNG, SPARKS GEOFFREY SIDNEY, PHILIPS ELECTRONICS N.V., PHILIPS PATENTVERWALTUNG GMBH, SPARKS, GEOFFREY, SIDNEY
Application year: 1997
Main classification: H03F1
IPC codes: H03F1, H03G3