Abstract:
An apparatus for regulation of the signal power of a transmitter includes a control loop. The control loop includes a controlled module, a voltage detector, an evaluation circuit and an input amplification module. A decoupling module decouples the output of the control loop from a downstream electrical load.

Description:
PRIORITY CLAIM 
     This application is a continuation-in-part of International Patent Application No. PCT/DE2005/000843, filed May 4, 2005, which claims the benefit of priority of German Patent Application No. DE 10 2004 023 441.8, filed May 12, 2004, the contents of both of which are incorporated by reference in their entirety herein. 
    
    
     BACKGROUND 
     1. Technical Field 
     The invention relates to a system for regulation of the output power of a transmitter, in particular of a radio-frequency transmitter. 
     2. Background Information 
     Relatively large fluctuations may occur in the process parameters during the process of producing semiconductor components using CMOS technology. This variation may lead to severe fluctuations in the component characteristics of CMOS semiconductor components. For power amplifiers produced using CMOS technology, this leads to considerable variations in the output power. In this case, power differences of several dB typically occur particularly in radio-frequency transmitters, in which a modulated and amplified, radio-frequency transmission signal is produced from a modulation signal. 
     In addition, the characteristics of the semiconductor components vary based on temperature fluctuations, and for amplifiers, this leads to additional fluctuations in the output power. Analog controllers may be used to compensate for the temperature-dependent fluctuations of the component characteristics. However, CMOS semiconductor components have a highly complex temperature response, which necessitates a high degree of complexity to achieve satisfactory results. Furthermore, a controller such as this does not allow compensation for the fluctuations in the component characteristics that are caused by the production process. 
     In addition, a control loop may be provided in which the output power of an amplifier is measured, and its input signal regulated. If the load at the output of the amplifier is formed by a load which is not specified in any more detail, such as an unmatched antenna, then special precautions are required to reduce reaction effects on the power measurement, and these can lead to corrupted measurement results. By way of example, a directional coupler is required for this purpose, which must be arranged externally, that is to say not within the integrated circuit. This type of power measurement thus increases the number of components, which results in an increased space requirement, an increased current drawn by the overall apparatus, and in increased production costs. 
     A further option for compensation for the fluctuations in the component characteristics caused by the production process is to measure each transmission circuit individually after production, and to calibrate it in accordance with the measurement results. This option is not practicable, because of the excessively high costs. 
     BRIEF SUMMARY 
     A cost-effective apparatus and a method which involves little effort for regulation of the signal power of a transmitter is disclosed. In particular, a radio-frequency transmitter, which is able to compensate for signal power fluctuations caused by fluctuations in the component characteristics, is disclosed. 
     The invention makes use of the fact that the signal power can be determined indirectly by means of a voltage measurement, if the voltage is measured decoupled from the load. 
     A control loop includes a controlled module which produces an analog output signal, a voltage detector which produces a detector signal based on the analog output signal, an evaluation circuit which receives the detector signal and produces an evaluation signal, as well as an input amplification element for amplification of the input signal to the controlled system as a function of the evaluation signal. The transmitter includes a decoupling element, which is connected downstream from the control loop and decouples the output of the control loop from a downstream electrical load. 
     The decoupling element, whose output power is controlled by its input voltage, decouples the output of the control loop from the load which is connected downstream from the decoupling element and whose input impedance is in general unknown. The output power of the decoupling element can thus be determined in a simple manner by means of a voltage measurement at its input. The control loop can thus regulate the signal power at the output of the decoupling element on the basis of a single voltage measurement at the input of the decoupling element. There is no need for a complex power measurement of the signal for this purpose. 
     The disclosure may make it possible to readjust fluctuations in the signal power, without any reaction. In particular, fluctuations and scatters of the component characteristics which are caused by the production process and by temperature are readjusted, particularly for components in the controlled system. This makes it possible to effectively and simply counteract even major fluctuations in the component characteristics, such as those which occur, for example, in CMOS semiconductor components. The disclosure reduces the influence of process fluctuations on the output power without any negative influence on the overall current drawn. 
     Other systems, methods, features and advantages of the invention will be, or will become, apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the following claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like referenced numerals designate corresponding parts throughout the different views. 
         FIG. 1  is a schematic block diagram of an apparatus within a radio-frequency transmitter. 
         FIG. 2  illustrates an example voltage peak detector. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a radio-frequency transmitter which converts the I and Q values of a modulation signal to an I and Q-modulated transmission signal, amplifies it, and emits it to an antenna  4 . The radio-frequency transmitter comprises a digital vector modulator  1 , a control loop  2  and a decoupling element  3 , which has a known and essentially constant input impedance. The control loop  2  and the decoupling element  3  are located within one integrated circuit, and are produced using an identical semiconductor technology, for example CMOS technology. Further amplifier elements (not illustrated) can be connected to the decoupling element  3 , and are likewise located on the integrated circuit, or arranged externally to it. 
     The digital vector modulator  1  passes digital I and Q values to the control loop which are converted, by two digital/analog converters  22 ,  22 ′ within the controlled system  21 , to two analog signals. The two analog signals are passed to an analog vector modulator  23 . A local oscillator produces a radio-frequency carrier signal as well as a version of the carrier signal which has been phase-shifted through 90°. In the analog vector modulator  23 , the two radio-frequency signals are multiplied by the two analog signals from the digital/analog converters  22 ,  22 ′, and are mixed to form an I/Q-modulated transmission signal. The transmission signal is amplified in a preamplifier  24 , and is passed to the decoupling element  3 . 
     The decoupling element  3  comprises an amplifier element. In particular, the preamplifier  24  together with the decoupling element  3  forms a multiple-stage amplifier, whose last stage represents the decoupling element  3 . The regulation mechanism comprises a voltage peak detector  31 , an evaluation circuit  32  and an input amplification element  33 . The voltage peak detector  31  determines the magnitude of the voltage peaks in the radio-frequency transmission signal at the input of the decoupling element  3 , and/or in the drive for the last stage of the multiple-stage amplifier  24 ,  3 , and passes the measurement or detector signal to the evaluation circuit  32 . The evaluation circuit  32  produces a digital evaluation signal in the form of an output value  44 , which is passed to the input amplification element  33 . In the input amplification element  33 , the digital input signals to the control loop, the I and Q values of the modulation signal, are multiplied by the digital evaluation signal (that is to say the output value  44 ) in multiplication units  34 ,  34 ′. The output signals from the two digital/analog converters  22 ,  22 ′ are thus amplified uniformly, as a result of which the analog vector modulator  23  emits a correspondingly amplified transmission signal to the preamplifier  24 , and the radio-frequency transmitter emits a correspondingly amplified output signal to the transmission antenna  4 . 
     The frequency at which the voltage peak detector  31  emits a measurement signal to the evaluation circuit  32  is variable. The voltage peak detector  31  may emit only one measurement signal per transmitted data unit, in particular per transmitted data burst. The measurement signal is thus a measure of the transmission power of the overall data burst. Since only one power matching process takes place per transmitted data burst, and the integration time of the voltage peak detector  31  is thus considerably longer than the duration of the power fluctuation which results from amplitude modulation, the transmitter may also be used for power regulation of amplitude-modulated signals. 
     The evaluation circuit  32  comprises a window comparator  41  which receives the measurement signal from the voltage peak detector  31 . The window comparator  41  checks whether the detector signal is within a nominal window, which is defined by an upper and a lower comparison voltage. If the detector signal overshoots or undershoots the nominal window, then the window comparator  41  sends a decrementing or incrementing signal  42 , respectively, to a counter  43 , whose count is thus respectively decremented or incremented. 
     The digital evaluation signal or the output value  44  is determined on the basis of the count of the counter  43 . A new output value  44  is determined such that the signal power is varied in defined steps, for example in steps of 1.5 to 2 dB. The determination of the new output value  44  can include a weighting, which takes account of the last stage  3  (which is located outside the controlled system) of the multiple-stage amplifier  24 ,  3  and of the decoupling element  3 . Furthermore, a self-trimming process can be carried out when an external amplifier is provided downstream from the decoupling element  3 . 
     The output value  44  can be determined on a software or hardware basis by a process controller (not illustrated). In the simplest case, the count is added to an initial output value for this purpose, and the sum itself or a value calculated from it (for example in a suitably weighted form) is emitted as the output value  44 . The initial output value may be stored in a non-volatile memory component, so that it is possible to provide a good estimate of the output value  44 , even at the start. The count at the start may be about zero. Other algorithms for determination of the output value may also be provided. For example, the output value can also be determined based on the multiplication of the count by a predetermined weighting factor. 
     In one example system, the possible output values  44  are stored in a non-volatile memory component (not illustrated). The non-volatile memory component may comprise a ROM table. The stored output values  44  are then already weighted with respect to the decoupling element  3 , which is located outside the controlled system, as well as possibly further amplifier modules which are connected downstream from the decoupling module  3 , and/or are matched to them. The current count of the counter  43  determines which entry is selected from the ROM table. When the count is decremented or incremented, then the next-lower or the next-higher output value  44  is selected from the non-volatile memory component (such as, for example, the ROM table), and is emitted to the input amplification element  33 . The determination of the output value  44  based on the ROM table can also be combined with software-based control. 
     In another system, the output value  44  and/or the information on which output value  44  was most recently used and which output value should be used at the start are/is stored in a non-volatile memory component, to provide an estimate of the output power for restarting. 
       FIG. 2  shows an example voltage peak detector  31  with cross-coupled CMOS transistors T 1 , T 2 . The differential, analog output signal from the controlled system is injected via the connections RFIN, RFINX into the voltage peak detector  31 . During the respective positive and negative half-cycles of the radio-frequency signal, the drain-source paths through the two transistors T 1 , T 2  are switched on alternately, as a result of which the capacitor C 1  is charged, and the peak voltage U peak  can then be tapped off. Furthermore, the common-mode signal U rms  is required for voltage measurement in the case of differential radio-frequency signals. This is done by the low-pass filter R 1  or R 2  and C 2 . The measurement or detector signal which the voltage peak detector  31  emits to the evaluation circuit  32  may comprise the two measurement values U peak  and U rms . 
     It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this invention.