Abstract:
In a controller-assisted device for determining a characteristic of a compensation element in a level control circuit, the compensation element is serially mounted inside the level control circuit for a high-frequency signal (S&lt;SB&gt;HF&lt;/SB&gt;) in a signal channel with respect to said signal channel. The characteristic of the compensation element has a characteristic which the inverse of the non-linear transmission characteristic of the signal channel in the event of ideal compensation. In the controller-assisted method for the determination of a characteristic of the compensation element in a level control circuit, each ordinate value of the characteristic of the compensation element arises, in the event of a bridged compensation element, from the corrective signal value (P astel ) which is adjusted at a signal level of the level reference signal (P ref ) in the adjusted level control circuit, corresponding to the associated abscissa value of the characteristic of the compensation element.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a controller-assisted method and a controller-assisted device for determining the characteristic of a compensation element in a level-control circuit. 
   2. Related Technology 
   According to the prior art, the signal level of high-frequency signals, for example, in transmitter output modules, receiver input modules or signal generators, is compensated to an adjustable level-reference value in automatic-gain control (AGC) circuits. EP 0 451 277 B1 discloses an automatic level-control circuit of this kind in a receiver input module. In this context, the amplification and/or attenuation factor of an amplification and/or attenuation element integrated in the signal channel is automatically adjusted via an adjustment signal, which is generated in a controller unit on the basis of the control difference between the level-reference value and the signal level of the high-frequency signal registered via a detector unit at the output of the signal channel. 
   Non-linearities in the signal channel, for example, in the amplification and/or attenuation element, cause instability in the level-control circuit and impair the dynamics of the level-control circuit. 
   In the case of DE 36 36 865 A1, an exact inverse adjustment of the transmission characteristic of the attenuation element to the transmission characteristic of the transmitter output module is implemented offline within the framework of an adjustment or calibration procedure by parameterization of the attenuation factor for all level values of the high-frequency signal. Since the course of the transmission characteristic of the transmission output module and, corresponding to this, of the transmission characteristic of the attenuation element, is dependent upon a series of parameters—such as the frequency of the high-frequency signal and the ambient t emperature—a plurality of characteristic courses must be determined for the attenuation element. Once again, within the framework of individual calibration procedures, a plurality of characteristic value pairs must be determined for each individual characteristic. This increases the adjustment cost to a considerable extent before the use of the transmitter, receiver or signal generator. 
   GENERAL DESCRIPTION OF THE INVENTION 
   The invention significantly reduces the cost of adjustment or calibration in determining the transmission characteristics of a compensation or attenuation element within a level-control circuit. 
   The invention provides a controller-assisted method for determining the characteristic of a compensation element and a controller-assisted device for determining the characteristic of a compensation element. 
   According to the invention, a method of determining characteristic value pairs of a compensation element in a level-control circuit includes the steps of: 
   connecting a compensation element in series with a signal channel that provides a high-frequency signal to a level control circuit, wherein the signal channel produces a non-linear transmission characteristic; 
   bridging a compensation element that, in the event of an ideal compensation, provides a characteristic inverse to the non-linear transmission characteristic of the signal channel; and 
   generating a characteristic value pair using the bridged compensation element, wherein an abscissa value of the pair indicates a level of the level-reference signal and an ordinate value of the pair indicates a value of an adjustment signal generated from the level of the level-reference signal. 
   The invention also provides a device for determining the characteristic of a compensation element including: 
   a signal channel that provides a non-linear transmission characteristic; 
   a level-control circuit that operates on a high-frequency signal of the signal channel, the level-control circuit including a controller for forming an adjustment signal dependent upon a control difference between a signal level of a level-reference signal and an actual-level value of the high-frequency signal; 
   a compensation element that, in the event of an ideal compensation, provides a characteristic inverse to the non-linear transmission characteristic of the signal channel and generates a non-linear distorted adjustment signal; 
   an adjustment element-integrated in the signal channel with an amplification factor that is adjustable based on the non-linear distorted adjustment signal 
   wherein the compensation element is adapted to be bridged and further adapted to determine each characteristic value pair, including an ordinate and abscissa value, of the characteristic of the compensation element. 
   Determining the individual characteristic value pairs of the compensation element, exploits the property of the level-control circuit that, with a bridged compensation element and with a signal level of the level-reference signal at the magnitude of the abscissa value of the characteristic of the compensation element in the compensated level-control circuit, a value occurs as the adjustment signal, which corresponds to the associated ordinate value of the characteristic of the compensation element with an ideal compensation of the transmission characteristic in the signal channel. 
   With a fixed frequency of the high-frequency signal at the input of the signal channel and by variation of the signal level of the level-reference signal in the compensated condition of the level-control circuit, it is therefore possible to register at the adjustment-signal terminal the ordinate values of the characteristic of the compensation element associated with the abscissa values present at the level-reference terminal, and accordingly to determine the characteristic of the compensation-element characteristic for a given frequency of the high-frequency signal in a comparatively low-cost manner. In the same manner, all the characteristics of the compensation element associated with the respective frequencies of the high-frequency signal can be determined by varying the frequency of the high-frequency signal within a given frequency raster. 
   By comparison with the adjustment and/or calibration methods of the prior art, no high-cost adjustment procedures are required for defined adjustment signals, no high-cost measurement procedures are required for determining the corresponding high-frequency signals at the output of the signal channel and, building upon this, comprehensive mathematical calculation procedures are not required for determining the characteristic value pairs for the individual characteristics of the compensation element. On the contrary, with the method according to the invention and with the device according to the invention, the adjustment of the individual abscissa values at the level-reference terminal and of the individual frequencies at the signal source of the high-frequency signal and the reading out of the ordinate values at the adjustment-signal terminal of the level-control circuit can be automated. Without high-cost mathematical calculations, the ordinate values of the frequency-dependent characteristics of the compensation element associated with the individual abscissa values can be written to the individual memory cells of the digitally-realized compensation element directly after reading out. 
   The temperature dependence of the transmission characteristic of the signal channel, which is only associated with a vertical displacement of the transmission characteristic, is determined in an exactly analogous manner by measuring the adjustment-signal change of the level-control circuit at a given ambient temperature relative to a reference ambient temperature with a fixed frequency of the high-frequency signal and a fixed signal level of the level-reference signal. By variation of the ambient temperature relative to a reference ambient temperature, the respective adjustment-signal change and/or the change in the respective actual level value of the high-frequency signal can be determined for use as a compensation signal in a unit for temperature compensation. 
   Since the temperature dependence of the transmission characteristic of the signal channel provides both a linear dependence—caused by the adjustment element of the signal channel—and also a logarithmic dependence—caused by the isolation amplifier of the signal channel, the corresponding temperature-dependent adjustment-signal changes must be measured for this purpose in separate measurement sequences in the case of a linear dependence; and the temperature-dependent changes of the actual level value of the high-frequency signal must be measured in separate measurement sequences in the case of a logarithmic dependence. In the case of a logarithmic dependence, the correspondingly-determined compensation values should be stored with the level reference signal in a first unit for temperature compensation for additive superimposition. In the case of a logarithmic dependence, the correspondingly-determined compensation values should be stored with the adjustment signal in a third unit for temperature compensation for additive superimposition. Finally, compensation values for compensating temperature-determined changes in the amplification factor of the measurement amplifier should be stored with the adjustment signal in a second unit for temperature compensation for additive superimposition. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An exemplary embodiment of exemplifying the controller-assisted method and the controller-assisted device for determining the characteristic of the compensation element in a level-control circuit is explained in greater detail below with reference to the drawings. The drawings are as follows: 
       FIG. 1  shows a block circuit diagram of the controller-assisted device according to the invention for determining the characteristic of a compensation element in a level-control circuit; 
       FIG. 2  shows a block circuit diagram of the compensation element in the controller-assisted device according to the invention for determining the characteristic of a compensation element in a level-control circuit; 
       FIG. 3  shows a detail from the characteristic of the compensation element in the controller-assisted device according to the invention for determining the characteristic of a compensation element in a level-control circuit; 
       FIG. 4  shows a flow chart of the controller-assisted method according to the invention for determining the characteristic of a compensation element in a level-control circuit; 
       FIG. 5  shows a flow chart for determining the compensation values in the case of a temperature-dependent displacement of the isolation-amplifier transmission characteristic in the signal channel; 
       FIG. 6  shows a flow chart for determining the compensation values in the case of a temperature-determined displacement of the adjustment-element transmission characteristic in the signal channel and 
       FIG. 7  shows a flow chart for determining the compensation values in the case of a temperature-dependent change of the amplification factor of the measurement amplifier in the level-control circuit. 
   

   DETAILED DESCRIPTION 
   The device according to the invention for determining the characteristic of a compensation element in a level-control circuit is used in a signal generator as shown in  FIG. 1 . Alternatively, the device according to the invention can also be used in other high-frequency technical equipment and systems, for example, in transmitter output modules or in receiver input modules, in which the level of a high-frequency signal is automatically adjusted with a level-control circuit. 
   The level-control circuit  1  includes a signal channel  2 , in which a high-frequency signal, which is generated by a signal source  3 , is guided and subjected to various message-processing functions. The frequency f Sig  of the high-frequency signal S HF  is adjusted in the signal source  3 . The signal level of the high-frequency signal S HF  is adjusted in an adjustment element  4  of the signal channel  2  adjacent to the signal source  3 . For this purpose, the adjustment element  4  is controlled by a compensated adjustment signal P adjusted     —     compensated  proportional to the level re-adjustment of the high-frequency signal S HF . 
   The high-frequency signal S HF  re-adjusted with regard to its signal level in the adjustment element  4  is then supplied via a calibration line  5  with defined impedance values to an isolation amplifier  6 . In the isolation amplifier  6 , a galvanic decoupling is implemented via two amplification stages  7  and  8  between the signal source of the signal generator and the input/output module  9  of the signal channel  2  of the signal generator. Between the two amplifier stages  7  and  8 , the isolation amplifier  6  additionally contains a low-pass filter  10  for the attenuation of injected higher-frequency interference signals. A detection device  11 , which is designed as a directional coupler in the signal generator shown in  FIG. 1 , is connected between the isolation amplifier  6  and the input/output module  9 . For the measurement, the high-frequency signal S HF  is registered and decoupled in the directional coupler  11  at the end of the signal channel  2 . 
   The decoupled high-frequency signal S HF  is mixed down in the adjacent down mixer  12  by means of the mixer signal LO 1  into the intermediate-frequency signal S IF . The adjacent measurement amplifier  13 , which provides a controllable amplification factor, implements an adaptation of the level of the intermediate-frequency signal S IF  to the predominant level of the digital signal processing range  14  of the level-control circuit  1 . The adjacent antialiasing low-pass filter  15  suppresses the generation of higher-transient spectral components caused by the adjacent analog/digital conversion. 
   The analog/digital conversion in the analog/digital converter  16  leads to the digitized intermediate-frequency signal S IFD , which is transferred in the adjacent down mixer  17  by means of the mixer signal LO 2  into the corresponding digitized baseband signal S BBD . The digitized baseband signal S BBD  is logged in the log unit  18  to form the logarithmic actual-level value P Actual  so that it is present in the same scale as the logged level-reference signal P Ref  thereby allowing a meaningful formation of the control difference in the adjacent control-difference-forming unit  19 . 
   A compensation signal Comp 1  is additively superimposed over the logarithmic level-reference signal P Ref  upstream of the control-difference forming unit in a summation element  20 . This compensation signal Comp 1  is generated in a first temperature-compensation unit  21 . The compensation signal Comp 1  is used to compensate the temperature-determined logarithmic displacements of the transmission characteristic of the signal channel  2 , which occur focally in the isolation amplifier  6 . 
   The control-difference signal ΔP from the control-difference forming unit  19  is supplied to the digitally-realized controller  22 , which provides, for example, a proportionally-integrating control dynamic realized in the form of a digital filter. The adjustment signal P Adj  generated by the controller  22  is subjected to an adjustment-signal limitation in a signal limiter  23 . An additional additive injection of a pre-control signal P Pre     —     ctrl  to the limited adjustment signal P Adj  of the controller  22  is implemented in a further summation element  24 . This pre-control signal P Pre     —     ctrl  is not absolutely essential, but significantly accelerates the transient process of the level-control circuit  1 . The pre-control signal P Pre     —     ctrl , which is determined dependent upon the signal value of the level-reference signal P Ref , is connected directly to the adjustment element  4  without feedback and leads to a level adjustment of the high-frequency signal S HF  in the proximity of the adjusted signal level of the level-reference signal P Ref . The pre-control signal P Pre     —     ctrl  therefore has the transient dynamic of the pre-control branch of the level-control circuit  1  reduced by comparison with a closed control circuit. 
   Accordingly, the controller  22  now still only controls the residual control-difference ΔP between the adjusted signal level of the level-reference signal P Ref  and the actual level value P Actual  of the high-frequency signal S HF  achieved by the pre-control signal P Pre     —     ctrl , which are caused, for example, by superimposed interference signals or by parameter fluctuations in the functional units of the pre-control branch of the level-control circuit  1 . 
   An additional additive injection of an additional compensation signal Comp 2  to the summation signal derived from the pre-control signal P Pre     —     ctrl  and the limited adjustment signal P Adj  of the controller  22  is implemented in the subsequent summation element  25 . This compensation signal Comp 2  is generated in a second temperature-compensation unit  26 . The temperature-compensation signal Comp 2  is used to compensate temperature-determined changes of the amplification factor of the measurement amplifier  13 . 
   In the adjacent compensation element  27 , of which the non-linear characteristic in the event of an ideal compensation is exactly inverse to the non-linear transmission characteristic of the signal channel  2 , the un-compensated summation adjustment signal P Adj     —     Uncomp  at the input of the compensation element  27 , formed from the pre-control signal P Pre     —     ctrl , the amplitude-limited adjustment signal P Adj  of the controller  22  and the compensation signal Comp 2 , is distorted in a nonlinear manner, which leads to a non-linear-distorted summation-adjustment signal P Adj     —     Comp  compensated by the compensation element  27  at the output of the compensation element  27 . Since the transmission characteristic of the signal channel  2  is dependent upon the frequency f Sig  of the high-frequency signal S HF , the compensation element  27  also provides corresponding inverse, non-linear characteristics dependent upon the respective frequency f Sig . The correct characteristic dependent upon the frequency f Sig  of the high-frequency signal S HF  is selected in the compensation element  27  via the frequency signal f Sig  of the high-frequency signal S HF  present at the input of the compensation element  27 . 
   The compensated summation-adjustment signal P Adj     —     Comp  at the output of the compensation element  27  is locked in the phase of the determination of the characteristic of the compensation element  27  with the downstream switch  28  for the further control of the adjustment element  4  open and conveyed forward in the phase of the normal level-control mode with the downstream switch  28  for the further control of the adjustment element  4  closed. In the adjacent digital/analog converter  29 , the compensated summation-adjustment signal P Adj     —     Comp  is converted from the digital format of the digital signal-processing region  14  of the level-control circuit  1  into the analog format. 
   The adjustment signal P Adj  generated by the controller  22  is conveyed forward in the phase of the determination of the characteristic of the compensation element  27  with the downstream switch  31  for the further control of the adjustment element  4  closed and locked in the phase of the normal level-control mode with downstream switch  31  for the further control of the adjustment element  4  open. The adjustment signal P Adj  of the controller  22  conveyed forward via the closed switch  31  in the phase of the determination of the characteristic of the compensation element  27  is converted by the digital/analog converter  32  from the digital format of the digital signal-processing region  14  of the level-control circuit into the analog format. Dependent upon the operating phase, the summation element  30  connects either the compensated summation-adjustment signal P Adj     —     Comp  of the compensation element  27  or the adjustment signal P Adj  of the controller  22  in order to control the adjustment element  4 . As an alternative to the two switches  28  and  31  of the summation element  30  and the two digital/analog converters  29  and  32 , a multiplexer and an adjacent digital/analog converter can also be used, wherein, dependent upon the operating phase, the multiplexer, connects either the compensated summation-adjustment signal P Adj     —     Comp  of the compensation element  27  or the adjustment signal P Adj  of the controller  22  in order to control the adjustment element  4 . 
   In a further summation element  33 , an additive superimposition of an additional compensation signal Comp 3  on the compensated summation-adjustment signal P Adj     —     Comp  is implemented in the phase of the normal level-control mode. This additional compensation signal Comp 3  is generated in a third temperature-compensation unit  34 . The compensation signal Comp 3  is used for the compensation of temperature-determined, linear displacements of the transmission characteristic of the signal channel  2 , which occur focally within the adjustment element  4 . The compensated summation-adjustment signal P Adj     —     Comp  with the addition of the compensation signal Comp 3  is provided at the output of the summation element  34  and conveyed as a completely level-compensated summation-adjustment signal P Adj     —     Comp′ to the adjustment signal  4  in order to re-adjust the signal level of the high-frequency signal S HF . 
   The realization of the compensation element  27 , which is designed in a digital manner, is presented in detail in  FIG. 2 . The ordinate values associated with the respective abscissa values of the non-linear characteristic are stored in the individual memory cells of a memory (RAM)  35 . However, in this context, only the coarse ordinate values associated with a coarse raster of abscissa values of the non-linear characteristic are stored in this manner. The coarse-raster abscissa values of the non-linear characteristic correspond to the higher-value bits of the digitized, uncompensated adjustment signal highBits(P Adj     —     Uncomp ). The higher value bits of the digitized un-compensated adjustment signal P Adj     —     Uncomp  are used in order to address the associated coarse ordinate values of the non-linear characteristic. The frequency signal f Sig  of the signal source  3  is used because of the frequency dependence of the characteristic. After addressing, the corresponding coarse ordinate value P Adj     —     Uncomp     —     coarse  of the non-linear characteristic is provided at the output of the memory (RAM)  35 . 
   In addition to the coarse ordinate value P Adj     —     Uncomp     —     coarse  of the nonlinear characteristic, an additional fine ordinate value P Adj     —     Comp     —     fine  is generated in an interpolator  36 . This fine ordinate value of the non-linear characteristic corresponds to the correction or incremental value at the coarse ordinate value with a finer rastering of the abscissa values of the non-linear characteristic. The finer rastering of the respective abscissa values of the non-linear characteristic is obtained from the lower-value bits of the digitized uncompensated adjustment signal lowBits(P Adj     —     Uncomp ). The fine ordinate value P Adj     —     Comp     —     fine  is determined in the interpolator  36  by linear interpolation from the coarse ordinate value P Adj     —     Comp     —     coarse     —     i  disposed at the output of the memory  35  and the adjacent ordinate value P Adj     —     Comp     —     coarse     —     i+1  of the non-linear characteristic, the coarse-abscissa-value raster highBits(P Adj     —     Uncomp     —     i+1 )−highBits(P Adj     —     Uncomp     —     i ) and the fine abscissa value of the lower-value bits of the digitized un-compensated adjustment signal lowBits(P Adj     —     Uncomp ) as shown in equation (1) and the nomenclature of in  FIG. 3 . 
   
     
       
         
           
             
               
                 
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   In the subsequent summation element  37 , the coarse ordinate value P Adj     —     Comp     —     coarse     —     i  at the output of the memory  35  and the fine ordinate value P Adj     —     Comp     —     fine     —     i  at the output of the interpolator  36  are added to the exact ordinate value P Adj     —     Comp     —     i  of the non-linear characteristic, which represents the compensated adjustment signal P Adj     —     Comp . 
   The flow chart in  FIG. 4  shows the controller-assisted method according to the invention for determining the characteristic of a compensation element  27  in a level-control circuit  1 . 
   In procedural stage S 10 , the frequency f Sig  of the high-frequency signal S HF  is adjusted at the signal source  3 . 
   In the subsequent procedural stage S 20 , the signal level of the level-reference signal P Ref  in the level-control circuit  1  is adjusted to correspond to the abscissa value of the respective characteristic value pair of the characteristic of the compensation element  27 . 
   The switch  31  is closed, while the switch  28  is opened. The temperature compensation unit  34  is inactive at the current time, so that after switching on the controller  22  of the level-control circuit  1  and waiting for the transient procedure of the level-control circuit  1  at the control input of the adjustment element  4 , the adjustment signal P Adj  generated by the controller  22  and converted into an analog signal is present as a stationary signal. In procedural stage S 30 , the value of the adjustment signal P Adj  of the controller  22  occurring as a stationary signal can be read out in a digital format before the digital input of the digital/analog converter  32  at the terminal point  38  as an ordinate value of the characteristic of the compensation element  27 , and can be written as a coarse ordinate value P Adj     —     Comp     —     coarse     —     i  to the memory cell of the memory component  35  of the compensation element  27  addressed by the associated abscissa value, which corresponds to the adjusted signal level of the level-reference signal P Ref . 
   Procedural stages S 10 , S 20  and S 30  are then implemented repetitively in order to determine all of the characteristic value pairs of the characteristic of the compensation element  27 . 
   In procedural stage S 40 , after the determination of all characteristic value pairs of the characteristic of the compensation element  27  in the preceding procedural stages S 10 , S 20  and S 30 , the compensation values Comp 1i  of the first compensation signal Comp 1  for the temperature compensation in the first temperature-compensation unit  21 , which compensate a logarithmic temperature-determined displacement of the non-linear transmission characteristic of the signal channel  2  caused, in particular, by the isolation amplifier  6 , are determined. 
   Procedural stage S 40  for determining the compensation values Comp 1i  of the first compensation signal Comp 1  is subdivided into the sub-procedural stages S 41  to S 44  as shown in  FIG. 5 . 
   In the sub-procedural stage S 41 , the frequency f Sig  of the high-frequency signal S HF  is adjusted at the signal source  3 , and a given signal level of the level-reference signal P Ref  is specified at the level-reference input of the level-control circuit  1 . 
   In sub-procedural stage S 42 , the adjustment element  4  is bridged in order to avoid the temperature-determined displacement of the transmission characteristic of the signal channel  2  on the linear scale, which is caused, in particular, by the adjustment element  4 . Since the temperature-determined displacement of the transmission characteristic of the signal channel  2  is implemented on the logarithmic scale, a corresponding temperature compensation must also be implemented on the logarithmic scale and must accordingly be realized within the range of the control-difference formation of the level-control circuit  1  implemented on a logarithmic scale. For this reason, the level-control circuit  1  is open in the range of the actual level-value input of the control-difference-forming unit  19 . In sub-procedural stage S 42 , the actual level value P Actual     —     T0  occurring at a reference ambient temperature T 0  and at a specified signal level of the level-reference signal P Ref  is measured with a given reference ambient temperature T 0  at the terminal  39  of the level-control circuit  1  immediately before the open position of the level-control circuit  1  in the proximity of the actual level-value input of the control-difference forming unit  19 . 
   In the subsequent sub-procedural stage S 43 , the ambient temperature T i  is varied and, with the same signal level of the level-reference signal P Ref , the actual level value P Actual     —     Ti  changing in a temperature-determined manner relative to the ambient temperature T i  is measured. 
   Finally, in the last sub-procedural stage S 44 , the actual-level-value change ΔP Actual     —     i =P Actual     —     Ti −P Actual     —     T0  determined by the temperature change between the ambient temperature T i  and the reference ambient temperature T 0  is calculated from the previously-measured actual-level values P Actual     —     Ti  and P Actual     —     T0  and stored in the first temperature compensation unit  21  as a compensation value Comp 1i  of the first compensation signal Comp 1  with a temperature change from the reference ambient temperature T 0  the ambient temperature T i . 
   The sub-procedural stages S 43  and S 44  are implemented in a given temperature raster for different ambient-temperature values T i  in an analogous manner to the determination of corresponding compensation values Comp 1i  of the first compensation signal Comp 1 . 
   In the next main procedural stage S 50 , the compensation values Comp 3i  of the third compensation signal Comp 3  for the compensation of the temperature-determined displacement of the transmission characteristic of the signal channel  2  on the linear scale, which is caused, in particular, by the temperature-determined displacement of the pinch-off voltage of the GaAs-field-effect transistors in the adjustment element  4 , are determined. 
   The determination of the compensation values Comp 3i  of the third compensation signal Comp 3  of the main procedural stage S 50  is broken down into the sub-procedural stages S 51  to S 54  as shown in  FIG. 6 . This takes place by analogy with the determination of the characteristic value pairs of the compensation element  27  in the procedural stages S 10  to S 30 . 
   In sub-procedural stage S 51 , by analogy with sub-procedural stage S 41  for a signal source  3 , the frequency f Sig  of the high-frequency signal S HF  is adjusted, and a given signal level for the level-reference signal P Ref  is applied to the level-reference input of the level-control circuit  1 . 
   In determining the compensation values Comp 3i  of the third compensation signal Comp 3  in sub-procedural stage S 52 , the isolation amplifier  6  is bridged in order to avoid additional temperature-determined displacements of the non-linear transmission characteristic of the signal channel  2  on a logarithmic scale caused by the isolation amplifier  6 . In sub-procedural stage S 52 , the adjustment signal value P Adj     —     Comp     —     T0  occurring at the input of the adjustment element  4  is determined with a reference ambient temperature T 0  and a compensated level-control circuit. 
   In the next sub-procedural stage S 53 , the ambient temperature T i  is varied and the new adjustment signal value P Adj     —     Comp     —     Ti  occurring at the new ambient temperature T i  as a result of the temperature-increase-determined displacement of the non-linear transmission characteristic of the signal channel  2  is measured. 
   In the final sub-procedural stage S 54 , the calculation of the compensation values Comp 3i  of the third compensation signal Comp 3  is implemented for a temperature compensation of the temperature-determined displacement of the transmission characteristic of the signal channel  2  on the linear scale with a temperature change ΔT i =T i −T 0  by forming the adjustment-signal change ΔP Adj     —     Comp     —     i  as the difference between the adjustment signal value P Adj     —     Comp     —     Ti  occurring at the ambient temperature T i  and the adjustment signal value P Adj     —     Comp     —     T0  occurring at the reference ambient temperature T 0  and entering this in the third temperature-compensation unit  34  as the compensation value Comp 3i  of the third compensation signal Comp 3  with a temperature increase ΔT i . 
   By analogy, the sub-procedural stages S 53  and S 54  are implemented within a given temperature raster for different ambient temperature values T i , and the corresponding compensation values Comp 3i  of the third compensation signal Comp 3  are stored in the third temperature compensation unit  34 . 
   Finally, it should be noted that the influence of the characteristic of the compensation element  27  on the adjustment-signal change ΔP Adj     —     Comp     —     i  and therefore on the compensation values Comp 3i  of the third compensation signal Comp 3  no longer occurs as a result of the difference formation, so that the determination of the individual adjustment signals P Adj     —     Comp     —     Ti  occurring at the ambient temperatures T i  can be implemented either with switch  28  closed or with switch  31  closed. 
   Finally, in the last main procedural stage S 60 , the compensation values Comp 2i  of the second compensation signal Comp 2  for the temperature compensation of the temperature-determined change of the transmission behavior, especially the amplification factor, of the measurement amplifier  13  are determined. For this purpose, the main procedural stage S 60  is broken down into the sub-procedural stages S 61  to S 64  as shown in  FIG. 7 . 
   Sub-procedural stages S 61  to S 64  for determining the compensation values Comp 2i  of the second compensation signal Comp 2  for the temperature compensation of the temperature-determined change of the transmission behavior of the measurement amplifier  13  correspond to sub-procedural stages S 51  to S 54  for determining the compensation values Comp 3i  of the third compensation signal Comp 3  for the temperature compensation of the temperature-determined displacement of the transmission characteristic of the signal channel  2  on the linear scale. Accordingly, reference will be made only to the differences between the two main procedural stages S 50  and S 60 . 
   In order to avoid additional temperature-determined changes of the transmission characteristic of the signal channel  2 , which undesirably falsify the adjustment signal P Adj     —     Comp     —     Ti  to be determined at the ambient temperatures T i , the adjustment element  4  and the isolation amplifier  6  are bridged in sub-procedural stage S 62 . 
   By analogy with the main procedural stage S 50 , in order to determine the compensation values Comp 2i  of the second compensation signal Comp 2  for the temperature compensation of the temperature-determined change of the transmission behavior of the measurement amplifier  13 , the characteristic of the compensation element  27  does not influence the adjustment-signal change ΔP Adj     —     Comp     —     i  and therefore the compensation values Comp 2i  of the second compensation signal Comp 2  as a result of the difference formation, so that either switch  28  or switch  31  can be closed for the determination of the adjustment signals P Adj     —     Comp     —     Ti  occurring at the ambient temperature T i . 
   The compensation values Comp 2i  of the second compensation signal Comp 2  for the temperature compensation of the temperature-determined change of the transmission behavior of the measurement amplifier  13  are stored in the second temperature-compensation unit  26 . 
   The invention is not restricted to the embodiment presented. In particular, other regulation and control structures for forming the level-control circuit  1  and also for implementing the controller-assisted method and the controller-assisted device for determining the characteristic of the compensation element of a level-control circuit can be used and are covered by the invention. Finally, it should also be noted, that instead of the digital realization of the signal-processing region  14  of the level-control circuit  1 , an analog realization of the invention is also covered.