Description Detector circuit The present invention relates to detector circuits, e.g. for impedance measurement systems of mobile communication

devices .

Technical background

Impedance measurement systems can be used to determine the impedance of a signal path in a mobile communication device where the signal path's impedance depends on its external conditions. In other words: where the signal path has a variable load impedance.

In the case of mobile communication devices with an antenna, the variable load impedance can be due to the antenna's changing environment.

In order to optimize the transmission coefficient of Tx or Rx signals propagating in the signal path, the signal path's actual impedance must be known. Conventional impedance measurement systems, e.g. known from patent publication US 6,822,433, uses a phase detector and two additional RSSI-chains as level detectors to determine a variable load impedance. It is an object of the present invention to provide an alternative detector circuit without the need for a level detector, e.g. an RSSI-chain. Therefore, a detector circuit according to claim 1 is provided. Dependent claims provide preferred embodiments of the invention. Features of the detector circuit shown hereinafter do not exclude each other. The phase detector can comprise each feature in combination with other features in order to provide an individually optimized detector circuit. Summary of the invention

A detector circuit is provided that comprises a first signal input determined to receive a first signal Si, a second signal input determined to receive a second signal S ₂ having a phase difference a relative to the first signal Si and a third signal input determined to receive a third signal S ₃ having a phase difference β relative to the first signal Si. The detector circuit further comprises a phase detector determined to derive the phase differences a and β. Further, the detector circuit comprises a calculation circuit

determined to derive a ratio selected from | Si | / | S ₃ 1 ,

I S ₃ 1 / I S ₂ 1 , and I S ₂ 1 / I Si | and the respective inverse ratios. Derivation of the ratio is achieved by evaluating the two phase differences a and β obtained from the phase detector. Further, the detector circuit comprises a signal output determined to provide the ratio.

Such a detector circuit may be used in an impedance

measurement system for a signal path shown in FIG. 2. The signal path SP may be connected to an antenna having a variable load impedance. Such an antenna and its load impedance is represented by an impedance Z _x . Further, the signal path SP comprises a sensing impedance Z _sense which may be an inductive element IE. V2 ₀ denotes the voltage drop across the load impedance Z _x . V ₁ 2 denotes the voltage drop across the impedance Z _senS e- ₁ 0 is the sum of the voltages V ₂ o and V ₁ 2 : V ₁ 0 = V20 + V ₁ 2. Thus, the impedance of the signal path SP equals the load impedance Z _x plus the sensing

impedance Z _sense which may be a known impedance. From FIG. 2, it is clear that Z = Z _sens V ₁ 0/V ₁ 2 where V ₁ 0 and Vi ₂ are voltages representable as complex numbers. In one embodiment, the first signal Si, the second signal S2, and the third signal S ₃ are voltage or current signals.

Accordingly, in one embodiment of the detector circuit, the first signal Si is the voltage V ₁₀ . The second signal S2 is the voltage V20. The third signal S3 is the voltage V ₁ 2.

However, the above relations between Si, S2, and S ₃ on one hand and V ₁₀ , V2 ₀ , and V ₁ 2 on the other hand are only examples. In particular it is possible that Si, S2, and S ₃ are chosen arbitrarily. In other words: From three input signals two arbitrarily chosen different phase differences are needed to determine the last phase difference and to obtain full information about impedances and impedance matching.

Further, it is clear that the situation shown in FIG. 2 can be described with parameters other than voltages V ₁₀ , V ₁ 2, and V2 ₀ . The central idea of the present invention does not depend on details of parameters used as signal inputs for the detector circuit. Other parameters are also possible. It was found that the problem of deriving the unknown

impedance Z can be reduced to determining the ratio V ₁₀ /V ₁ 2. V ₁ 0 may be written as V ₁ 0 = I Vio l exp (jcot) . Then, Vi ₂ may be written as Vi ₂ = I ₁₂ | exp ( (jcot) +(p) , i.e. V ₁₀ and Vi ₂ are signals of the same frequency with a phase difference of φ between Vio and V _i2 . Accordingly, the ratio V ₁₀ /V ₁ 2 can be written as V ₁ 0/V ₁ 2 = I Vio I / I V ₁ 2 I exp (j(p) . The correlations between Vio, V ₁ 2, and V2 ₀ are visualized in a complex plane view in FIG. 9. Then, a can be ψ, β can be φ and the phase difference between the second signal S2 and the third signal S ₃ Y, i.e. the difference χ = 180° - ψ - β, can be the difference γ = 180° - β - a. In particular, it is possible that Si = S ₂ + S ₃ .

The problem of deriving the ratio V ₁₀ /V ₁ 2 can, thus, be reduced to derive the ratio of the absolute values I Vi01 / I _i2 1 and by measuring the phase difference φ . The circuit known from US 6,822,433 uses two RSSI-chains to obtain the ratio of the absolute values. A further phase detector is needed to obtain phase information.

The central idea of the present invention is based on the fact that knowing the values of phase differences φ and ψ intrinsically also comprise information about the ratio of the absolute values I Vi0 I / I V ₁₂ I - Generally: by knowing two phase differences between two sets of the three input signals Si, S2 and S ₃ , one can calculate any ratio between two

absolute levels from the set of Si, S2 and S ₃ . One important aspect of the invention is that circuitry is provided that allows direct access to phase information by processing the three signals Vio, V _i2 , and V ₂ o- Especially, the invention is based on the fact that the inventors have found a geometric correlation between signal levels and phase information on one hand and electric circuitry that allows to make use of this correlation on the other hand.

It was found that the following identity (sine rule) :

I Vio I / I Vi2 I = sin (x) / sin (ψ) = sin (ψ + φ) / sin (ψ) allows to directly obtain the ratio of the absolute values of signals Vio and Vi ₂ as the three input signals can be

interpreted according to FIG. 9. It is clear that with the same geometric correlation, respective other ratios of inputs of the absolute values of input signals can be obtained and utilized for impedance measurement systems in which the detector circuit can be integrated.

The phase detector of the detector circuit provides the phase differences φ and ψ. The third phase difference χ can either be measured as the phase difference between the second signal S ₂ and the third signal S3. However, it is possible to calculate the value for X as (p + i|r + X = 180°. Further, the respective ratios of the complex numbers can be obtained also .

In one embodiment, the phase detector works in the analog domain or in the digital domain. If the phase detector works in the digital domain, then the detector circuit comprises an analog/digital-converter. The analog/digital-converter can digitalize the values of a and β. Calculation of the ratios and of the third phase difference χ, respectively, can be performed via conventional integrated circuits, e.g. of an ASIC (ASIC = Application-Specific Integrated Circuit) . In one embodiment, the calculation circuit works in the digital domain and the phase detector comprises an

analog/digital-converter. Then, signals encoding phase difference information can be obtained via an analog circuit and digitalized via the analog/digital-converter. However, it is also possible that the phase detector itself works in the digital domain and comprises the analog/digital-converter at its signal input. In one embodiment, the calculation circuit determines the three ratios: S ₁ /S3, S3/S2, and S2/S ₁ .

Each of the three ratios can be expressed as a ratio of the other two ratios or the respective inverse ratio. Thus, the respective measured third ratio can be utilized to improve the accuracy of the other two ratios by comparison with the to be expected third ratio.

In one embodiment, the calculation circuit determines the phase difference of the second signal S2 relative to the third signal S3. In other words: the calculation circuit determines the value for the third angle, χ . By summing all three phase differences, the correctness of the measured phase differences can easily be determined as the sum of the phase differences should equal 180°.

In one embodiment, the calculation circuit utilizes a lookup table. Via a lookup table, a digitalized value representing the phase difference can easily be converted into the direct digital representation of the angle's value.

In one embodiment, the detector circuit provides information about a positive ratio selected from: I Si | / | S31 , I S31 / | S ₂ 1 , I S ₂ I / I S i I . The detector circuit provides information about the phase difference α , β, and/or γ. It is possible that the detector circuit is an impedance detector. The phase detector can be implemented using limiter

amplifiers. Limiter amplifiers create square wave signals which can be processed by conventional phase detector

circuits. The use of limiter amplifiers before the

conventional phase detectors eliminate amplitude information and ensures that the phase detector circuits work properly.

It is possible that a first phase detector circuit determines β while at the same time a second phase detector circuit determines a . However, it is possible that one and the same phase detector circuit provides β and a one after another. Then, a switching circuit can be utilized to provide the single phase detector circuit with different input signals. Only one absolute ratio and one angle is sufficient to provide a ratio S _x /S _y (x, y = 1, 2, or 3) with which the impedance Z can be determined when the impedance Z _sense is known.

However, measuring and determining alternative ratios and phase differences can be used to improve the accuracy of the detector circuit.

Examples of the detector circuit, its basic principles and ideas are shown in the schematic figures.

Brief description of the figures

FIG. 1 schematically shows the basic concept of the

detector circuit, shows an equivalent circuit diagram of a signal path comprising an unknown load impedance Z _x and a sensing impedance Z _senS e , shows an embodiment of the detector circuit with the calculation circuit CC between the phase detector PD and an analog/digital-converter ADC, shows an embodiment of the detector circuit with an analog/digital-converter ADC between the phase detector PD and the calculation circuit CC, shows an embodiment of the detector circuit with the phase detector PD between an analog/digital- converter ADC and the calculation circuit CC, shows an embodiment of the detector circuit with a combination of phase detectors PD and

analog/digital-converters ADC, shows an embodiment of the detector circuit with the calculation circuit CC between two phase detector circuits PD and an analog/digital- converter ADC, shows an embodiment of the detector circuit with a switching circuit SW before the phase detector PD, shows fundamental correlations between the different input signals and their respective phase differences .

Detailed description FIG. 1 schematically shows an embodiment of the detector circuit DC comprising three signal inputs SIi, SI ₂ , SI ₃ . Each signal input SI is determined to receive a respective input signal Si, S ₂ , and S ₃ . A phase detector PD derives at least two out of three phase differences, e. g. the phase

differences β between the first input signal Si and the third input signal S ₃ and the phase difference a between the second signal S2 and the first signal Si. The derived phase

differences a and β are fed into a calculation circuit CC which derives at least one of the ratios I Si | / | S ₃ | , I S ₃ | / | S ₂ | , and I S ₂ I / I Si I or the respective inverse ratio. The ratio or ratios, possibly in combination with the measured phase differences, is provided at a signal output SO which can then be utilized by other circuits, e.g. of a mobile communication device .

Thus, only a phase detector PD and a calculation circuit CC are needed to provide a detector circuit for an impedance measurement system. No additional RSSI-chains providing direct level information are needed.

FIG. 2 schematically shows a signal path SP in which radio frequency signals may propagate. A potentially variable load impedance is denoted as Z _x . Further, the signal path SP comprises a sensing element Z _sense needed for determining phase information. The sensing impedance Z _sense could be established by an inductive element IE. V ₁₀ , V2 ₀ , and Vi ₂ could be the differences between the potentials Po, Pi, and P ₂ ,

respectively.

In the circuit shown in FIG. 2, when the signals V ₁₀ , Vi ₂ , and V ₂ o are voltages, then V ₁ 0 = V _i2 + V ₂ o- FIG. 3 shows an embodiment of the detector circuit further comprising an analog/digital-converter ADC. The

analog/digital-converter ADC is connected between the

calculation circuit CC and the signal output SO. The phase detector PD and the calculation circuit CC can work in the analog domain and the signal output of the calculation circuit can be digitalized by the analog/digital-converter ADC which provides digital information about the actual load impedance Z _x at the signal output SO.

FIG. 4 shows an embodiment of the detector circuit where the analog/digital-converter ADC is connected between the phase detector PD and the calculation circuit CC . Thus, the phase detector PD can work in the analog domain while the

calculation circuit CC can work in the digital domain.

FIG. 5 shows an embodiment of the detector circuit where the signal inputs SI are directly connected to an analog/digital- converter ADC. Then, the phase detector PD and the

calculation circuit CC can work in the digital domain. The input signals are digitalized by the analog/digital-converter and the derivation of phase differences and the calculation of the signal ratios are performed by integrated circuits, which may be comprised by an ASIC (Application-Specific

Integrated Circuit) .

FIG. 6 shows an embodiment of the detector circuit DC

comprising amplifiers AMP for preprocessing the input signals before they are fit to the phase detector. The amplifiers AMP may be limiter amplifiers which provide square wave signals to the phase detector PD. The phase detector PD can comprise two phase detector circuits PDCi, PDC ₂ . Each of the two phase detector circuits derives a phase difference and transmits the phase difference to an analog/digital-converter ADC. The first phase detector circuit PDCl derives the phase

difference between the first input signal S i and the second input signal S ₂ . The second phase detector circuit PDC2 derives the phase difference between the third input signal S3 and the first input signal S i . The respective phase difference is transmitted to a second analog/digital- converter ADC. It is, however, possible that both phase detector circuits transmit the respective phase difference one after the other to one and the same analog/digital- converter ADC. The digitalized information is transferred to the calculation circuit CC which provides phase information, ratio information, or impedance information at the signal output SO.

The input signals S i , S ₂ , S3 can arbitrarily be chosen from the available input signals, e.g. from the input signals a circuit as shown in figure 2 provides.

FIG. 7 shows an embodiment of the detector circuit DC where the derived phase information is directly transferred to the calculation circuit CC . The output of the calculation circuit CC is digitalized by the analog/digital-converter ADC.

FIG. 8 shows an embodiment of the detector circuit where a switching circuit SW is connected between the signal inputs and the phase detector PD. The switching circuit SW can be utilized to connect different signal inputs with the phase detector PD. Such a switching circuit SW allows to provide a phase detector PD or an analog/digital-converter ADC with only a single signal path as the input signals can be

connected to the phase detector PD one after the other. Thus, phase detectors PD, analog/digital-converters ADC and

calculation circuits CC having a less complex inner

construction, which are cheaper to produce, are possible. FIG. 9 shows a possible correlation between the input signals Si, S2 and S3 and voltages obtained from a type of circuits as shown in figure 2 V ₁ 0, V ₁ 2, and V20. V ₁ 2 could be the voltage drop across the sensing element Z _sense , which may be an inductive element. V ₁₀ may be the voltage between the input of the signal path and the ground potential. V2 ₀ is the voltage drop across the unknown load impedance Z _x . I. e., V ₁₀ is the sum of the voltages V ₁ 2 and V2 ₀ . Accordingly, the three voltages establish a triangle defined by the length of the vectors and the respective angles. When from this triangle two values from the set of six values (three angles, three ratios of side lengths) are known, the other four can be calculated .

As a result of the inventors' findings, an alternative detector circuit is provided that makes the use of RSSI- chains or any other circuitry for level ratio detection dispensable .

The detector circuit is not limited to the embodiments described in the specification or shown in the figures.

Detector circuits comprising further elements such as further phase detectors, calculation circuits, analog/digital- converters and further switches or impedance elements or combinations thereof are also comprised by the present invention.

The features shown above do not exclude each other. The detector circuit can comprise each feature in combination with other features to obtain an especially optimized detector circuit.

List of reference symbols α, β, γ: phase differences between input signals Si

S2 , S3

ADC: analog/digital -converter

AMP: amp1i fier

CC calculation circuit

DC: detector circuit

IE inductive element

Po,i, ₂ : potentials

PD: phase detector

PDCi, PDC ₂ : first, second phase detector circuit

9 X Ψ: phase differences between voltages V ₁₀ , V _i2

Si, S ₂ , S3: first, second, third input signal

SIi,2, ₃ : first, second, third signal input

SO signal output

SP signal path

SW switching circuit

V10, V12, V20 voltages

Zsense · sensing impedance

load impedance