Abstract:
A method is described for locating a detection microchip that transmits a detection signal, which is received and evaluated by a reader. The current distance between the reader and the detection microchip is determined from a run-time dependent feature of the received detection signal and the propagation speed of electromagnetic waves.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The invention relates to a method for locating a detection microchip.  
         [0002]     Detection microchips that are attached to products and store unique identifying information are being used increasingly for the identification of goods that are kept in stock and being transported. The goods can be identified by reading the identification information via a reader.  
         [0003]     If multiple products are contained in a transport or storage unit of extensive physical space, detection microchips and readers having a sufficiently large detection range are needed for the identification. A method for isolating them must also be implemented. Detection microchips and readers that operate at frequencies in the UHF range and above satisfy the prerequisites for this. In this frequency range, it is possible to achieve both the physical range and a sufficiently high data transmission rate to be able to isolate and read separately all the detection microchips that are located in the desired detection range at the same time, and to do so within an acceptable period of time.  
         [0004]     However, since field propagation in the UHF range can be inhomogeneous due to reflection and absorption, the transmission power and reception sensitivity of the reader must be sufficient to allow the detection microchips to be read reliably even under unfavourable constellations in the desired detection range. As a result, the problem arises that the capture field cannot be restricted in targeted manner to a selected transport or storage unit when there are multiple transport or storage units, but instead also detects adjacent transport or storage units. Thus, in order to be able to distinguish products of a selected transport or storage unit from products of other transport or storage units, the microchips attached to the products must therefore also be located and then selected after they have been read.  
       SUMMARY OF THE INVENTION  
       [0005]     The object of the present invention is to provide a method for locating a detection microchip that enables detection of at least one spatial coordinate.  
         [0006]     The invention is based on a detection microchip that emits a detection signal, which is received and evaluated by a reader. This may be a passive detection microchip, which changes the carrier signal of the reader into cycles of modulation in amplitude and/or phases, or an active detection microchip, whose detection signal includes a carrier that is generated synchronously with the carrier signal of the reader.  
         [0007]     Because of the final propagation speed of electromagnetic waves, run-time-dependent features of the detection signal are altered on the way from the detection microchip to the reader. In this context, the change in the run-time is proportional to the distance between the detection microchip and the reader. Analysing the run-time-dependent characteristic of the detection signal received by the reader in conjunction with the known propagation speed of electromagnetic waves enables the distance to be determined.  
         [0008]     The phase and amplitude of the received detection signal are preferably evaluated as the run-time-dependent characteristic of the detection signal.  
         [0009]     In this case, the run-time-dependent characteristic may be analysed following demodulation, which is necessary anyway for data acquisition, and thus also in a lower frequency range than the frequency of the carrier signal.  
         [0010]     In a first embodiment of the method, at least during a locating period the detection microchip receives a carrier signal from the reader and transmits a detection signal that is modulated with a modulation signal and has the same frequency as the carrier signal. The modulation signal has signal points that may be approximated by a straight line in a signal space diagram. The detection signal received by the reader is demodulated, the difference between the phase angle of the detection signal at a current distance and a reference distance between the detection microchip and the reader is determined, and the current distance between the detection microchip and the reader is determined from the difference in the phase angle, the carrier frequency and the propagation speed of the electromagnetic waves.  
         [0011]     This instruction, that the modulation signal has signal points that are approximable in a signal space diagram by a straight line, enables the phase angle of the detection signal to be reproduced. The transition between the signal points does not have to be approximable by a straight line. Outside of the locating period, other modulation modes may also be used in which the signal points may lie anywhere in a signal space diagram.  
         [0012]     The final propagation speed of electromagnetic waves gives rise to a time difference between the output of the detection signal and its reception at the reader, which in turn results in a difference between the phase angle of the carrier signal produced by the reader and the phase angle of the detection signal of the same frequency that is received by the reader. This difference in the phase angles is a measure of the distance between the detection microchip and the reader.  
         [0013]     Since the difference between the phase angles also depends on the frequency of the carrier signal, short wavelengths in the UHF range yield a large enough value for the difference between the phase angles to make it possible technically to measure a distance having a resolution in the cm range. Signal run times inside the reader and detection microchip may be considered constant and do not affect the difference between phase angle changes when there are changes in distance.  
         [0014]     The following abbreviations are used for the mathematical description of the signals:  
         [0015]     a Distance between detection microchip and reader  
         [0016]     f Carrier frequency of the reader  
         [0017]     c Propagation speed of waves in air  
         [0018]     t Runtime of the signal from the reader to the detection 
        microchip     and back        
 
         [0021]     Wavelength of the carrier frequency; λ=c/f  
         [0022]     λ Oscillation period at f; T=1/f  
         [0023]     πpi  
         [0024]     α Phase angle; α=2π*t/T  
         [0025]     N 0, 1, 2 . . . Ambiguity of the phase angle  
         [0026]     The equation t=2*a/c results for the run-time and, after conversion, the equation a=t*c/2 for the distance. Taking into account the phase angle, it follows that for the run-time t=(α/2π+N)*T and, after conversion, for the distance a=(α/2π+N)*T*c/2 or a=(α/2π+N)*1/f*c/2 or a=α*c/4πf for N=0.  
         [0027]     For a carrier frequency f, the phase angle takes on the same value again after a segment λ/2. Segment λ/2 results from the fact that run-time t of the signal includes both the path from the reader to the detection microchip and the path back from the microchip to the reader. Within a segment &lt;λ/2, the difference of the phase angles between a current distance and a reference distance is unambiguous. For a segment &gt;λ/2, ambiguities N occur that can be resolved by continuous updating of the position of the detection microchip in steps &lt;λ/2.  
         [0028]     Another possibility for eliminating ambiguities with segments &gt;λ/2 is described in a second embodiment of the method. At least during a locating time frame, the detection microchip receives signals of a first frequency and then of at least one second frequency from the reader carrier, and transmits detection signals that are each modulated with a modulation signal, each of which have the same frequency as the carrier signals. The modulation signals have signal points that are approximable by a straight line in a signal space diagram. The detection signals received by the reader are demodulated, the respective phase angle of the detection signal in question is determined and the current distance between the detection microchip and the reader is determined via joint analysis from the phase angles, the carrier frequencies and the propagation speed of the electromagnetic waves.  
         [0029]     Alternatively, the detection microchip may receive carrier signals of a first and simultaneously at least one second frequency from the reader and simultaneously transmit detection signals that are each modulated with a modulation signal. The detection signals received from the reader are separated and demodulated via filters, the respective phase angle of each detection signal is determined at the same time.  
         [0030]     Unlike a staggered emission, simultaneous transmission of detection signals at various frequencies prevents time-variable influences of the reading field and the distance from affecting the analysis result.  
         [0031]     Different phase angles occur at equal distances for different frequencies. Since the phase angles at these different frequencies are proportional to the distance, the difference between the phase angles is also proportional to the distance. Accordingly, the distance is obtained not just for the absolute phase angle at a frequency, but also for the difference between the phase angles when there is a difference between various frequencies.  
         [0032]     Then, a reference distance is not necessary. Sources of interference due to effects that are not constant over the long term are eliminated by the formation of differences. However, greater precision is needed when determining the phase angles.  
         [0033]     The following abbreviations are used for further mathematical description of the signals:  
         [0034]     f 1 , f 2 , Carrier frequencies of the reader  
         [0035]     λ 1 , λ 1 , Wavelength of the carrier frequency; λ 1,2 =c/f 1,2    
         [0036]     α 1 , α 2  Phase angles; α 1 , α 2 =2π*t/T 1,2    
         [0037]     The formula for the distance at two different phase angles and carrier frequencies is then: 
 
 a =(α 1 , α 2 )* c/ 4π( f   1   −f   2 ) 
 
         [0038]     Only at segments |λ 2 −λ 1 ,|&gt;min(λ 1,2 ) do ambiguities again occur.  
         [0039]     By appropriate selection of the carrier frequency, a distance range can be detected without ambiguities in the UHF range within the reachable space of the reading field, which is limited by the typically low transmission power of the reader. In readers having a greater reading range or at higher carrier frequencies, the phase angle may also be measured at more than two carrier frequencies in order to resolve these ambiguities.  
         [0040]     According to a further development, the phase angle may be determined at least twice during the locating period with a time interval, and a change of the phase angle in the time interval may be determined as a relative movement between the reader and the detection microchip, while a correspondence may be determined as a constant distance between the reader and the detection microchip.  
         [0041]     Using time-offset distance measurements, a criterion is determined as to whether the reader and detection microchip are moving in distance relative to each other. One possibility for using this criterion consists in distinguishing products furnished with detection microchips on a movable transport unit, e.g. a pallet on a fork lift, from stationary products furnished with detection microchips, e.g. on pallets on a rack.  
         [0042]     Moreover, the speed and/or directional vector of the movement may be determined from the magnitude of the change in the distance or phase angle within a time interval.  
         [0043]     In a technical implementation of the method, the detection signal is modulated during the locating period with a signal that switches between two states, e.g. A and B. The detection signal received by the reader is split into an in-phase and a quadrature component by multiplying with a signal that is synchronous with the carrier frequency. The in-phase component of the modulation signal is derived from the difference between the signal portions of the at least two states for the in-phase component, and the quadrature component of the modulation signal is derived from the difference between the signal portions of the at least two states for the quadrature component. The phase angle is then determined trigonometrically.  
         [0044]     The following abbreviations are used for the mathematical description of the signals:  
         [0045]     X(t) the amplitude curve of the unmodulated carrier signal  
         [0046]     U IN-A  reception signal in modulator state A  
         [0047]     U IN-B  reception signal in modulator state B  
         [0048]     U A  signal portion A affected by the detection microchip  
         [0049]     U B  signal portion B affected by the detection microchip  
         [0050]     U KI  signal portion of the in-phase component that is affected by the unmodulated carrier signal  
         [0051]     U KQ  signal portion of the quadrature component that is affected by the unmodulated carrier signal  
         [0052]     U AI  signal portion A of the in-phase component that is affected by the detection microchip  
         [0053]     U AQ  signal portion A of the quadrature component that is affected by the detection microchip  
         [0054]     U BI  signal portion B of the in-phase component that is affected by the detection microchip  
         [0055]     U BQ  signal portion B of the quadrature component that is affected by the detection microchip  
         [0056]     U I  in-phase component of the modulation signal  
         [0057]     U Q  quadrature component of the modulation signal  
         [0058]     ψ phase generally  
         [0059]     ψ A  phase of the signal portion A that is affected by the detection microchip  
         [0060]     ψ B  phase of the signal portion B that is affected by the detection microchip  
         [0061]     An unmodulated carrier signal with form X(t)=cos(2πft)=cos(x(t)) is generated by the reader and passed to the detection microchip. A modulator in the detection microchip modulates the carrier signal with a modulation signal that switches between the at least two states A and B. Besides the carrier signal, the reader also receives a portion of the modulated detection signal via direct coupling and reflection. The reception signal in modulator state A is: 
 
 U   IN-A   =U   A *cos ( x+ψ   A )+ U   KI *cos( x )+ U   KQ *sin( x ). 
 
         [0062]     The reception signal in modulator state B is: 
 
 U   IN-B   =U   B *cos( x+ψ   B )+ U   KI *cos( x )+ U   KQ *sin( x ). 
 
         [0063]     In an I/Q demodulator, the input signal is multiplied by a reference signal and a reference signal that is phase-shifted through 90°. The result of the multiplication in the generally standardized form for the I-component reads: 
 
cos( x )*sin( x+ψ   a )=−½*sin(ψ)+½*sin(2 x +ψ) 
 
         [0064]     and for the Q-component: 
 
sin( x )*sin( x+ψ)=+ ½*cos(ψ)−½*cos)2 x +ψ) 
 
         [0065]     In this context the expression sin(x+p) stands for the reception signal and the expressions sin(x) or cos(x) represent the reference signal or its phase-shifted equivalent. The 2x in the last term stands for the signal portions of the doubled carrier frequency, which are then suppressed by low-pass filters.  
         [0066]     For the signal 
 
 U   IN-A =U A *cos( x +ψ A )+ U   KI *cos( x )+ U   KQ *sin( x ) 
 
         [0067]     the following are then produced by multiplication for the I-channel:  
                       cos   ⁡     (   x   )       *     U     IN   -   A         =       ⁢     U   AI                 =       ⁢           U   A     /   2     *     cos   ⁡     (     φ   A     )         +         U   A     /   2     *     cos   ⁡     (       2   ⁢   x     +     φ   A       )         +                     ⁢           U             ⁢   KI       /   2     *     cos   ⁡     (   0   )         +         U             ⁢   KI       /   2     *     cos   ⁡     (     2   ⁢   x     )         -                     ⁢           U             ⁢   KQ       /   2     *     sin   ⁡     (   0   )         +         U             ⁢   KQ       /   2     *     sin   ⁡     (     2   ⁢   x     )                           
 
         [0068]     and for the Q-channel:  
                   sin   ⁡     (   x   )       *     U     IN   -   A         =       ⁢     U   AQ                 =       ⁢           U   A     /   2     *     sin   ⁡     (     φ   A     )         +         U   A     /   2     *     sin   ⁡     (       2   ⁢   x     +     φ   A       )         +                     ⁢           U   KI     /   2     *     sin   ⁡     (   0   )         +         U   KI     /   2     *     sin   ⁡     (     2   ⁢   x     )         +                     ⁢           U   KQ     /   2     *     cos   ⁡     (   0   )         -         U   KQ     /   2     *       cos   ⁡     (     2   ⁢   x     )       .                         
 
         [0069]     For the signal 
 
 U   IN-B   =U   B *cos ( x +ψ B )+U KI *cos( x )+ U   KQ *sin( x ) 
 
         [0070]     the following are then produced by multiplication for the I-channel:  
                   cos   ⁡     (   x   )       *     U     IN   -   B         =       ⁢     U   BI                 =       ⁢           U   B     /   2     *     cos   ⁡     (     φ   B     )         +         U   B     /   2     *     cos   ⁡     (       2   ⁢   x     +     φ   B       )         +                     ⁢           U   KI     /   2     *     cos   ⁡     (   0   )         +         U   KI     /   2     *     cos   ⁡     (     2   ⁢   x     )         -                     ⁢           U   KQ     /   2     *     sin   ⁡     (   0   )         +         U   KQ     /   2     *     sin   ⁡     (     2   ⁢   x     )                           
 
         [0071]     and for the Q-channel:  
                   sin   ⁡     (   x   )       *     U     IN   -   B         =       ⁢     U   BQ                 =       ⁢           U   B     /   2     *     sin   ⁡     (     φ   B     )         +         U   B     /   2     *     sin   ⁡     (       2   ⁢   x     +     φ   B       )         +                     ⁢           U   KI     /   2     *     sin   ⁡     (   0   )         +         U   KI     /   2     *     sin   ⁡     (     2   ⁢   x     )         -                     ⁢           U   KQ     /   2     *     cos   ⁡     (   0   )         +         U   KQ     /   2     *       cos   ⁡     (     2   ⁢   x     )       .                         
 
         [0072]     By separating out the high-frequency portions, the following expressions remain for the I-channel: 
 
U AI   =U   A /2*cos (ψ A )+ U   KI /2 
 
 U   BI   =U   B /2*cos (ψ B )+ U   KI /2 
 
         [0073]     and for the Q-channel: 
 
 U   AQ   =U   A /2*sin (ψ A )+ U   KQ /2 
 
 U   BQ   =U   B /2*sin (ψ A )+ U   KQ /2. 
 
         [0074]     The signal portion U KI  or U KQ  affected by the unmodulated carrier signal is removed by subtraction, and the in-phase component of the modulation signal U I  and the quadrature component of the modulation signal U Q  remain as the only variables that are measured following a low-pass filtering. 
 
 U   I   =U   B /2*cos (ψ B )− U   A /2*cos (ψ A ) 
 
 U   Q   =U   B /2*sin (ψ B )− U   A /2*sin (ψ A ) 
 
         [0075]     The phase angle of the current distance relative to the reference phase angle of a reference distance is then yielded as α=arctan (U Q /U I ).  
         [0076]     Phase shifts are incorporated in the phase angle a due to run times when the signal is processed inside the reader and the detection microchip. However, these phase shifts are compensated by reference to a reference phase at a reference distance.  
         [0077]     Given that modulation states A and B are able to be assigned, a=α*c/4nf for a segment &lt;λ/2. If states A and B are able to be distinguished from one another but not assigned, only an angle range from 0° to 180° is unique for α. Ambiguities then occur at distances as short as λ/4.  
         [0078]     Further, a resulting amplitude value of the detection signal may be determined from the in-phase and quadrature components of the individual measured values via U 2 =U I   2 +U 0   2 .  
         [0079]     In this way, the calculated distance values may be verified additionally. Moreover, a comparative quality test of detection microchips during production and use is possible by analysing the amplitude of the detection signal for a known distance. The amplitudes may be analysed over a large frequency range, for example to gauge resonance frequency and quality.  
         [0080]     According to a further development, in order to make an assignment to the at least two modulation states A and B, the signal portions of the at least two states may be evaluated over at least one evaluation period with at least two evaluation functions that contain an expected signal sequence. An evaluation result that returns a maximum amplitude is evaluated as the amplitude of the signal portions of the at least two states.  
         [0081]     If the received signal sequence corresponds to the expected signal sequence and if the received signal sequence is evaluated phase-synchronously with the evaluation functions that contain the expected signal sequence, e.g. by multiplication, the evaluation result returns a maximum positive value, which corresponds to an amplitude value. Otherwise, the evaluation result supplies a positive value that is smaller than the maximum positive value or even a negative value. If the evaluation is performed with two or more evaluation functions, different evaluation results are thus produced. The probability that the at least two states A and B are correctly assigned is largest for the evaluation result with the maximum amplitude.  
         [0082]     A special case occurs if only two evaluation functions are used and are distinguished only by a constant factor. An evaluation with the second evaluation function then corresponds to a multiplication of the result of evaluation of the first evaluation function by this factor.  
         [0083]     The amplitudes of the signal portions of the at least two states may be averaged over multiple evaluation periods.  
         [0084]     Interference portions are reduced, thereby improving measurement precision, by averaging.  
         [0085]     A reference detection microchip may be disposed at a reference distance from the reader in the vicinity of the detection microchips to be identified. A correction value may be determined by comparing the measured phase angle to a reference phase angle for the reference distance, and the measured phase angle of the detection microchips to be identified may be corrected using the correction value.  
         [0086]     In this way, effects on the phase angle, such as by reflections of the carrier signal and/or the detection signal on objects, may be compensated.  
         [0087]     The reference detection signal of the reference detection microchip may be modulated with a modulation signal that differs from the modulation signal of the detection microchip to be identified, and in the reader the reference detection signal of the reference detection microchip and the detection signal of the detection microchip to be identified may be separated by filters and evaluated simultaneously.  
         [0088]     Temporally changeable effects of the reading field on the analysis result are avoided by simultaneous analysis of the reference detection signal of the reference detection microchip and of the detection signal of the detection microchip to be identified, compared to a staggered analysis.  
         [0089]     According to a further development, multiple distance measurements are carried for no less than two different antenna positions of the reader, and the position of the detection microchip may be determined from the intersection points of the distance position curves of the antenna positions of the reader as determined by distance measurements.  
         [0090]     In this context, the different antenna positions may be controlled by switching between multiple positionally separated antennae of the reader.  
         [0091]     Locating is further improved via the distance measurements with different antenna positions because the direction between reader and detection microchip may be determined as well as the distance.  
         [0092]     In addition, the radiation lobe of an antenna array comprising at least two positionally separated antennae is aligned after the position of the detection microchip has been determined by phase-shifted control of the antennae in the direction of the detection microchip.  
         [0093]     The reading field strength and the noise ratio are increased simultaneously compared to possible interference radiation from other directions by aligning the radiation lobe. In this way, the reading quality of the detection signals is improved, which also has a favourable effect on the accuracy of the distance measurement and any additional directional measurements.  
         [0094]     Furthermore, the detection microchip may be activated by the reader from at least two different antenna positions before the distance measurement. In addition or alternatively thereto, the detection microchip may be activated by the reader on at least two different carrier frequencies before the distance measurement.  
         [0095]     In the UHF range, the reading field strength may exhibit minima due to shadowing or stationary waves caused by reflections. If a detection microchip happens to be located at the position of such a minimum, there is a danger that the detection microchip may not be able to be identified. The distribution of the reading field strength is changed by using different antenna positions and/or carrier frequencies. As a result, the probability of being able to identify detection microchips is increased. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0096]     The invention will described in the following with reference to exemplary embodiments that are depicted in the drawing. In the drawing:  
         [0097]      FIG. 1  shows an arrangement of a reader and a detection microchip with a representation of signal components,  
         [0098]      FIG. 2  shows a phasor diagram of the signal components at the input of the reader, and  
         [0099]      FIG. 3  shows a block diagram of an analysis circuit of the reader.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0100]      FIG. 1  shows an arrangement of a reader  10  and a detection microchip  12  with a representation of signal components. Reader  10  includes a transmitter, which transmits a carrier signal via a transmission antenna  14 , and a receiver having a receiving antenna  16 , a demodulator and an analysis circuit. Detection microchip  12  includes a detection microchip antenna  18 , a control circuit, a memory and a modulator. Detection microchip  12  may be a passive detection microchip supplied with energy from reader  10  or a detection microchip having its own power source.  
         [0101]     The modulator of detection microchip  12  modulates the carrier signal of reader  10  by in-time attenuation of its modulation content. This represents a usable signal component, which travels as a detection signal having run time τ t  from detection microchip  18  to receiving antenna  16  of reader  10 .  
         [0102]     In addition, components of the carrier signal having run time τ r  also arrive at receiving antenna  16  of reader  10  even by direct coupling from transmission antenna  14  and by reflections of the carrier signal having run time τ d2  on objects  20 . Reflections of the detection signal having run time t d1  may also occur on objects  20 , but they are not considered further in the following.  
         [0103]      FIG. 2  shows a phasor diagram of the signal components at the receiving antenna of the reader. In this context, the components of the carrier signal as direct coupling on the reception antennae and the components formed by reflections of the carrier signal on objects are combined in component U K  and are comprised in the complex phasor diagram of an in-phase component U KI  and a quadrature component U KQ . These components are not modulated by the detection microchip.  
         [0104]     In the detection microchip, the carrier signal is modulated with a modulation signal that switches in the exemplary embodiment between two modulation states A and B and is represented by an index U A  for modulation state A and an index U B  for modulation state B. The modulated component formed by the detection signal is shown as component U T , constituted in the complex phasor diagram of an in-phase component U TI  and a quadrature component U TQ . Interference portions of the transmission path affect the position of modulation states A and B in the complex phasor diagram, which is shown by circular areas with several diffusing values.  
         [0105]      FIG. 3  shows a block diagram of an analysis circuit of the reader. The analysis circuit includes a first I/Q demodulator  22 , comprising a first multiplier  24 , a second multiplier  26  and a local oscillator  28 . Both an input signal U RF  and an oscillator signal from local oscillator  28  having the same frequency as the carrier frequency of input signal U RF  arrive at first multiplier  24  and second multiplier  26 .  
         [0106]     The oscillator signal is supplied to first multiplier  24  as U LO *cos(ωt) and to second multiplier  26  phase-shifted through 90° as U LO *sin(ωt). After I/Q demodulator  22 , the signal path is split into an in-phase channel I and a quadrature phase channel Q. Connected thereto are a signal processor  30  for the in-phase channel I and a signal processor  32  for the quadrature phase channel Q. Outputs from signal processor  30  for in-phase channel I and from signal processor  32  for quadrature phase channel Q lead to a computer  34 , which carries out a trigonometric calculation of the phase angle and the amplitude.  
         [0107]     Signal processors  30  and  32  include n multipliers  36 ,  36 ′,  36 ″;  38 ,  38 ′,  38 ″ and summing units  40 ,  40 ′,  40 ″;  42 ,  42 ′,  42 ″ for multiplying and summing the multiplication results of the signals of in-phase channel I and quadrature phase channel Q with evaluation functions f 1 (t), f 2 (t), f n (t), a shared amplitude evaluation unit  44  and one summing unit  48 ;  50  each for averaging over a plurality of evaluation periods.  
         [0108]     Signals U I  of in-phase channel I and signals U Q  of quadrature phase channel Q are supplied to the respective multipliers  36 ,  36 ′,  36 ″;  38 ,  38 ′,  38 ″ and multiplied by various evaluation functions f 1 (t), f 2 (t), f n (t) in the signal processor  30 ;  32 . The evaluation functions each include a signal sequence of the detection microchip that is expected within an evaluation period and are distinguished, e.g. by the phase angle of the expected signal sequence. The multiplication occurs separately for each sampling value within the evaluation period (in digital signal processing, e.g. for each bit cycle). Then the products of multiplication for each sampling value within the evaluation period are summed by summing units  40 ,  40 ′,  40 ″;  42 ,  42 ″,  42 ″.  
         [0109]     Depending on the correspondence of the evaluation functions with the input signals originating from the detection microchips, different values are obtained for the summed multiplication products of the sampling values. The maximum values are evaluated and selected as amplitude values of the signal portions A bI  for the in-phase channel I and A bQ  for the quadrature phase channel Q by the shared amplitude evaluator  44  that comes next in succession. The subsequent summing units  48 ;  50  form average values of the amplitude values of the signal portions over multiple evaluation periods, e.g. via a complete data telegram of the detection microchip. The absolute amplitudes of the signals for in-phase channel I and for quadrature phase Q may also be determined through standardization.  
         [0110]     Both the calculated amplitudes A tI  of the signals for in-phase channel I and the calculated amplitudes A tQ  of the signals for quadrature phase channel Q are fed to the computer  34 , which is connected next. From these, computer  34  calculates phase angle ψ t  and the resulting amplitude A t  trigonometrically.  
         [0111]     In the exemplary embodiment, it is assumed that the modulation states of the detection signal switch between A and B. Then the mathematical description of input signal U RF  for modulator state A reads: 
 
 U   RF-A   =U   A *cos( x+ψ   A )+ U   KI *cos( x )+ U   KQ *sin( x ) 
 
         [0112]     and for modulator state B: 
 
 U   RF-B   =U   B *cos( x+ψ   B )+ U   KI *cos( x )+ U   KQ *sin( x ) 
 
         [0113]     The mathematical description of the product of multiplying modulator state A with the signal of the local oscillator for the I channel is as follows:  
                   cos   ⁡     (   x   )       *     U     RF   -   A         =       ⁢     U   AI                 =       ⁢           U   A     /   2     *     cos   ⁡     (     φ   A     )         +         U   A     /   2     *     cos   ⁡     (       2   ⁢   x     +     φ   A       )         +                     ⁢           U   KI     /   2     *     cos   ⁡     (   0   )         +         U   KI     /   2     *     cos   ⁡     (     2   ⁢   x     )         -                     ⁢           U   KQ     /   2     *     sin   ⁡     (   0   )         +         U   KQ     /   2     *     sin   ⁡     (     2   ⁢   x     )                           
 
         [0114]     and for the Q-channel:  
                   sin   ⁡     (   x   )       *     U     RF   -   A         =       ⁢     U   AQ                 =       ⁢           U   A     /   2     *     sin   ⁡     (     φ   A     )         +         U   A     /   2     *     sin   ⁡     (       2   ⁢   x     +     φ   A       )         +                     ⁢           U   KI     /   2     *     sin   ⁡     (   0   )         +         U   KI     /   2     *     sin   ⁡     (     2   ⁢   x     )         +                     ⁢           U   KQ     /   2     *     cos   ⁡     (   0   )         -         U   KQ     /   2     *     cos   ⁡     (     2   ⁢   x     )                           
 
         [0115]     and of modulator state B for the I-channel:  
                   cos   ⁡     (   x   )       *     U     RF   -   B         =       ⁢     U   BI                 =       ⁢           U   B     /   2     *     cos   ⁡     (     φ   B     )         +         U   B     /   2     *     cos   ⁡     (       2   ⁢   x     +     φ   B       )         +                     ⁢           U   KI     /   2     *     cos   ⁡     (   0   )         +         U   KI     /   2     *     cos   ⁡     (     2   ⁢   x     )         -                     ⁢           U   KQ     /   2     *     sin   ⁡     (   0   )         +         U   KQ     /   2     *     sin   ⁡     (     2   ⁢   x     )                           
 
         [0116]     and for the Q-channel:  
                   sin   ⁡     (   x   )       *     U     RF   -   B         =       ⁢     U   BQ                 =       ⁢           U   B     /   2     *     sin   ⁡     (     φ   B     )         +         U   B     /   2     *     sin   ⁡     (       2   ⁢   x     +     φ   B       )         +                     ⁢           U   KI     /   2     *     sin   ⁡     (   0   )         +         U   KI     /   2     *     sin   ⁡     (     2   ⁢   x     )         +                     ⁢           U   KQ     /   2     *     cos   ⁡     (   0   )         -         U   KQ     /   2     *     cos   ⁡     (     2   ⁢   x     )                           
 
         [0117]     When the high frequency portions are suppressed using a low-pass filter (not shown), the following expressions remain for the I-channel: 
 
 U   AI   =U   A /2*cos(ψ A )+ U   KI /2 
 
 U   BI   =U   B /2*cos(ψ B )+ U   KI /2 
 
         [0118]     and for the Q-channel: 
 
 U   AQ   =U   A /2*sin(ψ A )+U KQ /2 
 
 U   BQ   =U   B /2*sin(ψ B )+ U   KQ /2. 
 
         [0119]     After evaluation and averaging, the I-output returns voltage 
 
 A   tI   =U   I   =U   B /2*cos(ψ B )− U   A /2*cos(ψ A ) 
 
         [0120]     and the Q-output returns the voltage 
 
 A   tQ   =U   Q   =U   B /2*sin(ψ B )− U   A /2*sin(ψ A ) 
 
         [0121]     The phase angle is then 
 
α=arctan ( U   Q   /U   I ),
 
 and the resulting amplitude is 
 
 A   t   2   =U   1   2   +U   Q   2 .