Telecommunications Device Comprising an Electrical Balance Duplexer and Method for Balancing the Electrical Balance Duplexer

Abstract

The present disclosure relates to a telecommunications device. The telecommunications device includes an electrical balance duplexer connected to an output node of a transmission path, an input node of a receive path, an antenna, and a tunable impedance. The electrical balance duplexer is configured to isolate the transmission path from the receive path by tuning the tunable impedance. The telecommunications device also includes a tuning circuit for tuning the tunable impedance. The tuning circuit includes amplitude detectors for measuring voltage amplitudes, phase detectors for measuring voltage phase differences, an impedance sensor for measuring an input impedance of the electrical balance duplexer, and a processing unit operatively connected to the detectors, the impedance sensor, and the tunable impedance. The processing unit is configured to calculate an optimized impedance value. The processing unit is also configured to tune the tunable impedance towards the optimized impedance value.

Claims

1. A telecommunications device comprising: an electrical balance duplexer connected to an output node of a transmission path, an input node of a receive path, an antenna, and a tunable impedance, wherein the electrical balance duplexer is configured to isolate the transmission path from the receive path by tuning the tunable impedance; and a tuning circuit for tuning the tunable impedance, wherein the tuning circuit comprises: amplitude detectors for measuring voltage amplitudes at each of the connections between the electrical balance duplexer and the transmission path, between the electrical balance duplexer and the receive path, and between the electrical balance duplexer and the tunable impedance; phase detectors for measuring voltage phase differences between each of the connections between the electrical balance duplexer and the transmission path, between the electrical balance duplexer and the receive path, and between the electrical balance duplexer and the tunable impedance; an impedance sensor for measuring an input impedance of the electrical balance duplexer at the connection between the electrical balance duplexer and the tunable impedance; and a processing unit operatively connected to the amplitude detectors, the phase detectors, the impedance sensor, and the tunable impedance, wherein the processing unit is configured to: calculate an optimized impedance value from the voltage amplitudes, the voltage phase differences, and the input impedance of the electrical balance duplexer; and tune the tunable impedance towards the optimized impedance value.

2. The telecommunications device according to claim 1, wherein the processing unit is further configured to calculate the optimized impedance value from at least four scattering parameters between any two of the transmission path, the receive path, and the tunable impedance, wherein the scattering parameters are calculated from the voltage amplitudes, the voltage phase differences, and the input impedance.

3. The telecommunications device according to claim 1, wherein the processing unit is further configured to iteratively calculate the optimized impedance value and tune the tunable impedance towards the optimized impedance value.

4. The telecommunications device according to claim 1, wherein at least one of the detectors is implemented using a root mean square (rms) voltage detector.

5. The telecommunications device according to claim 1, wherein the impedance sensor is implemented using the amplitude detector at the connection between the electrical balance duplexer and the tunable impedance.

6. The telecommunications device according to claim 1, wherein the tuning circuit further comprises an analog-to-digital converter configured to digitize the voltage amplitudes, the voltage phase differences, and the input impedance.

7. A method for tuning a tunable impedance of a telecommunications device comprising an electrical balance duplexer connected to an output node of a transmission path, an input node of a receive path, an antenna, and the tunable impedance, wherein the electrical balance duplexer is configured to isolate the transmission path from the receive path by tuning the tunable impedance, the method comprising: measuring voltage amplitudes at each of the connections between the electrical balance duplexer and the transmission path, between the electrical balance duplexer and the receive path, and between the electrical balance duplexer and the tunable impedance; measuring voltage phase differences between each of the connections between the electrical balance duplexer and the transmission path, between the electrical balance duplexer and the receive path, and between the electrical balance duplexer and the tunable impedance; measuring an input impedance of the electrical balance duplexer at the connection between the electrical balance duplexer and the tunable impedance; calculating an optimized impedance value from the measured voltage amplitudes, the voltage phase differences, and the input impedance; and tuning the tunable impedance towards the optimized impedance value.

8. The method according to claim 7, wherein the optimized impedance value is calculated from at least four scattering parameters between any two of the transmission path, the receive path, and the tunable impedance, and wherein the scattering parameters are calculated from the measured voltage amplitudes, the measured voltage phase differences, and the input impedance.

9. The method according to claim 7, wherein the steps of the method are iteratively repeated until a scattering parameter from the transmission path to the receive path is below a predetermined threshold value.

10. The method according to claim 7, wherein calculating an optimized impedance value from the measured voltage amplitudes, the voltage phase differences, and the input impedance, and tuning the tunable impedance towards the optimized impedance value are performed iteratively.

11. The method according to claim 7, wherein measuring the voltage amplitudes or measuring the voltage phase differences is performed using a root mean square (rms) voltage detector.

12. The method according to claim 7, wherein measuring the input impedance is performed using an amplitude detector at the connection between the electrical balance duplexer and the tunable impedance.

13. The method according to claim 7, further comprising digitizing the voltage amplitudes, the voltage phase differences, and the input impedance.

14. A tuned impedance for a telecommunications device comprising an electrical balance duplexer connected to an output node of a transmission path, an input node of a receive path, an antenna, and the tuned impedance, wherein the electrical balance duplexer is configured to isolate the transmission path from the receive path by tuning the tuned impedance, and wherein the tuned impedance is tuned according to a method comprising: measuring voltage amplitudes at each of the connections between the electrical balance duplexer and the transmission path, between the electrical balance duplexer and the receive path, and between the electrical balance duplexer and the tuned impedance; measuring voltage phase differences between each of the connections between the electrical balance duplexer and the transmission path, between the electrical balance duplexer and the receive path, and between the electrical balance duplexer and the tuned impedance; measuring an input impedance of the electrical balance duplexer at the connection between the electrical balance duplexer and the tuned impedance; calculating an optimized impedance value from the measured voltage amplitudes, the voltage phase differences, and the input impedance; and tuning the tuned impedance towards the optimized impedance value.

15. The tuned impedance according to claim 14, wherein the optimized impedance value is calculated from at least four scattering parameters between any two of the transmission path, the receive path, and the tuned impedance, and wherein the scattering parameters are calculated from the measured voltage amplitudes, the measured voltage phase differences, and the input impedance.

16. The tuned impedance according to claim 14, wherein the steps of the method are iteratively repeated until a scattering parameter from the transmission path to the receive path is below a predetermined threshold value.

17. The tuned impedance according to claim 14, wherein calculating an optimized impedance value from the measured voltage amplitudes, the voltage phase differences, and the input impedance, and tuning the tuned impedance towards the optimized impedance value are performed iteratively.

18. The tuned impedance according to claim 14, wherein measuring the voltage amplitudes or measuring the voltage phase differences is performed using a root mean square (rms) voltage detector.

19. The tuned impedance according to claim 14, wherein measuring the input impedance is performed using an amplitude detector at the connection between the electrical balance duplexer and the tuned impedance.

20. The tuned impedance according to claim 14, wherein the method further comprises digitizing the voltage amplitudes, the voltage phase differences, and the input impedance.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0034] The disclosure will be further elucidated by means of the following description and the appended figures.

[0035] FIG. 1 shows an electrical balance duplexer.

[0036] FIG. 2 shows a prior art tuning circuit for tuning the tunable impedance of an electrical balance duplexer of the state of the art.

[0037] FIG. 3 shows an electrical balance duplexer assumed as a 3-port network.

[0038] FIG. 4 shows a schematic representation of the electronics communication device, according to example embodiments.

[0039] FIG. 5 shows a schematic representation of the tuning circuit of the electronic communication device, according to example embodiments.

[0040] FIG. 6 shows an impedance detector of the electronics communication device, according to example embodiments.

[0041] FIG. 7 shows an example implementation of an amplitude detector of the electronics communication device, according to example embodiments.

[0042] FIG. 8 shows an example implementation of a phase detector of the electronics communication device, according to example embodiments.

DETAILED DESCRIPTION

[0043] The present disclosure will be described with respect to particular embodiments and with reference to certain drawings but the disclosure is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not necessarily correspond to actual reductions to practice of the disclosure.

[0044] Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. The terms are interchangeable under appropriate circumstances and the embodiments of the disclosure can operate in other sequences than described or illustrated herein.

[0045] Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. The terms so used are interchangeable under appropriate circumstances and the embodiments of the disclosure described herein can operate in other orientations than described or illustrated herein.

[0046] The term comprising, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It should be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression a device comprising means A and B should not be limited to devices consisting only of components A and B. It means that with respect to the present disclosure, the only relevant components of the device are A and B.

[0047] FIG. 3 shows the electrical balance duplexer 1 when assuming that it is a 3-port network with the antenna 4 included in the S-parameter representation of the electrical balance duplexer 1. The reason for the inclusion of the antenna 4 is that we assume the antenna 4 to be an unknown impedance that also varies over time. In that case, the S-parameters describing all the transfer paths throughout the 3-port network are given as:

[00002]$\left[\begin{array}{c}{b}_1\\ b_2\\ b_3\end{array}\right]=\left[\begin{array}{ccc}{S}_{11}& S_{12}& S_{13}\\ S_{21}& S_{22}& S_{23}\\ S_{31}& S_{32}& S_{33}\end{array}\right]\left[\begin{array}{c}{a}_1\\ a_2\\ a_3\end{array}\right],$

where the first port (PA/TX port) is the connection to the transmission path 2, the second port is the connection to the tunable impedance 5 (balance network Z.sub.bal), and the third port (LNA/RX port) is the connection to the receive path 3.

[0048] The disclosure provides a tuning circuit 6 with a sensing method that derives the equations in order to calculate Z.sub.bal in real-time and provide automated tuning, using minimal hardware, for any antenna condition.

[0049] As also already mentioned, considering the problem in a 3-port fashion helps to simplify the problem, and allows the use of less hardware. FIG. 4 shows the same 3-port network with a tuning circuit 6, of which more detail is shown in FIG. 5, connected to the three ports (in a schematic sense), and provides a closed-loop that tunes Z.sub.bal to achieve isolation. The embodiment assumes a test signal is available from the transmitter TX, and that an optimized Z.sub.bal exists for any signal frequency at which the transmitter TX is active.

[0050] In the case where all 9 S-parameters (the full matrix) would be known, it would be possible to calculate the associated Z.sub.bal for achieving isolation in the duplexer 1 in a single step. However, we solve the problem of finding Z.sub.bal in an iterative manner, with practically implementable (cheap, low-power, low-area, etc.) sensors on as little nodes as possible.

[0051] In particular, the algorithm uses the sensed information using detectors or sensors 7, 8, 9 at just the TX, RX and BAL ports, thus respectively the connections between the electrical balance duplexer 1 on the one hand and the transmission path 2, the receive path 3 and the tunable impedance 5 on the other hand, to solve the following equations derived from the S-parameter matrix to arrive at Z.sub.bal, using only S.sub.13, S.sub.12, S.sub.23 and S.sub.22 (4 out of 9 parameters):

[00003]$S_{13}+\frac{{}_2.Math.S_{12}.Math.S_{23}}{1+S_{22}.Math.{}_2}=0.Math.{}_2=\frac{-S_{13}}{S_{12}.Math.S_{23}+S_{13}.Math.S_{22}}.Math.{}_2=\frac{Z_{\mathrm{bal}}-Z_0}{Z_{\mathrm{bal}}+Z_0}{Z}_{\mathrm{bal}}=Z_0.Math.\frac{1+{}_2}{1-{}_2}$

where S.sub.ij is the S-parameter that describes the transfer from port i to j, and .sub.i describes the so-called reflection coefficient, which is calculated from a limited amount of S-parameters (not all 9 are used). This directly limits the associated hardware to solve the equation.

[0052] Note that, although a first approximation of Z.sub.bal may already be calculated from the 4 S-parameters in a first calculation based on a single measurement from the detectors 7, 8, 9, the calculated Z.sub.bal may still not be optimized due to a number of assumptions on, for example, what the input and load impedances are on all ports. The provided equations are thus not always able to give a fully accurate answer for Z.sub.bal in a single calculation based on the detected information. Therefore, the algorithm is further optimized by iterating a number of times to improve upon possible differences or deviations caused by the assumptions in the equations.

[0053] In an example practical embodiment, amplitude sensors 7 can be used to observe amplitude or magnitude information at all nodes, and phase detectors 8 could be used to observe the phase information. Then, from that information, the set of 4 S-parameters can be derived, with simpler hardware.

[0054] In that case, the following equations may be solved first, before finally solving the equation for Z.sub.bal (as shown above).

[00004]$S_{12}=\frac{\sqrt{.Math.\left(Z_1\right)}}{\sqrt{.Math.\left(Z_2\right)}}.Math.\frac{1}{2}.Math.\left(1+\frac{Z_2^{*}}{Z_{\mathrm{bal}}}\right).Math.\frac{.Math.V_2.Math.}{.Math.V_1.Math.}.Math.e^{\left({}_2-{}_1\right).Math.j}$$S_{13}=\frac{\sqrt{.Math.\left(Z_1\right)}}{\sqrt{.Math.\left(Z_3\right)}}.Math.\frac{.Math.V_3.Math.}{.Math.V_1.Math.}.Math.e^{\left({}_3-{}_1\right).Math.j}$$S_{32}=\frac{\sqrt{.Math.\left(Z_3\right)}}{\sqrt{.Math.\left(Z_2\right)}}.Math.\frac{1}{2}.Math.\left(1-\frac{Z_2}{Z_{\mathrm{bal}}}\right).Math.\frac{.Math.V_2.Math.}{.Math.V_3.Math.}.Math.e^{\left({}_2-{}_3\right).Math.j}$$S_{22}=\frac{Z_2-Z_{\mathrm{bal}}^{*}}{Z_2+Z_{\mathrm{bal}}}$

[0055] Where j is the imaginary number operator, Z.sub.i is the impedance looking into the electrical balance duplexer, in this case a hybrid transformer, at port i, |V.sub.i| is the voltage amplitude detected at port i, (Z.sub.i) is the real part of impedance Z.sub.i and .sub.i is the phase of the voltage at port i. Note that S.sub.22 relates to Z.sub.2 and Z.sub.2*, which is the input impedance of the electrical balance duplexer 1 at the connection between the electrical balance duplexer 1 and the tunable impedance 5, and thus the impedance seen when looking into the hybrid transformer 5 from the balance network port.

[0056] To arrive at these equations, it is assumed that the antenna impedance negligibly influences Z.sub.2. It is also assumed that the tunable impedance Z.sub.bal is known or can be measured. It is also assumed that the impedance of the transmission path 2 is matched to the impedance of the electrical balance duplexer 1 at the connection between both, and that the impedance of the receive path 3 is matched to the impedance of the electrical balance duplexer 1 at the connection between both. Thus, the PA and LNA are matched to their respective ports. For example, if PA output impedance=25, then Z.sub.1=25. And if LNA input impedance=100, then Z.sub.3=100. It is also assumed that the network is reciprocal network. i.e. S.sub.ij=S.sub.ji. It is also assumed that the S-parameters between ports (e.g. S.sub.ij between port i and j) are simplified to be the transfer function of the output over the input signal. For example, S.sub.31=b.sub.3/a.sub.1.

[0057] From these equations, it becomes clear that a necessary condition is that the impedance Z.sub.2 should be known. With Z.sub.2 being the input impedance looking into the electrical balance duplexer 1 at the BAL-port interface, i.e. the connection between the electrical balance duplexer 1 and the tunable impedance 5.

[0058] FIG. 5 shows block level diagram of a tuning circuit of an electronic communication device according to an embodiment of the present disclosure. In this embodiment, analog voltages and phases at the ports of the EBD are measured by means of amplitude detectors 7, phase detectors 8 and an impedance detector 9 partially implemented by means of an amplitude detector 9 as shown in FIG. 6. The measured data is digitized by means of analog-to-digital converters ADC, and forwarded to the processing unit 10 where it is used for tuning the tunable impedance 5 according to an embodiment of the method of the present disclosure.

[0059] FIG. 6 shows an example impedance detector or sensor 9 that could be used to sense both Z.sub.2 as well as provide a calibration engine for Z.sub.bal (a-priori to live operation), using a three-way switch and two voltage sensors (connected to terminals V.sub.2 and V.sub.2). V.sub.ref is an RF voltage that could be derived from the transmitter, and operation for this test could be performed at low-power, i.e. tapped from prior to the PA.

[0060] For each port, an amplitude (RMS) detector 7 (magnitude sensor) would be required. An implementation of one such magnitude sensor which could be used in the example diode-connected FET device shown in FIG. 7. Between two ports, a phase detector 8, such as for example shown in FIG. 8, could be used to measure the voltage phase difference .sub.i.sub.j. It should however be clear that shown amplitude detectors 7 and phase detectors 8 are only example implementations, and different types of suitable detectors may be used.

[0061] Various mathematical assumptions and simplifications can be applied for the implementation of an algorithm that can arrive at a value for Z.sub.bal for any antenna impedance Z.sub.ant within 1.5:1 VSWR even when the detectors/sensors 7, 8, 9 exhibit up to 20% voltage error, 10 degrees phase error, and 20% error in Z.sub.2. This is true even for a hybrid transformer 1 that is not symmetric, i.e. Z.sub.BALZ.sub.ANT. For example, typical hybrid transformer implementations use skewing to favor TX over RX loss, and have capacitive coupling which means that single-ended EBDs (FIG. 1) can have asymmetric values (by nature).

[0062] The algorithm, in pseudocode, operates as follows:

TABLE-US-00001 1: put Z.sub.bal(0) = 50 2: evaluate .sub.2(0) 3: [00005]$\mathrm{evaluate}.Math..Math.Z_c\left(0\right)=Z_0.Math.\frac{1-{}_2\left(0\right)}{1-{}_2\left(0\right)}$ 4: put Z.sub.bal(1) = Z.sub.c(0) 5: i = 1 6: while S.sub.13 < Threshold do Ex.: Threshold = 50 dB 7: evaluate .sub.2(i) 8: evaluate Z.sub.c(i) 9: Corr = 50 Z.sub.c(i) 10: put Z.sub.bal(i + 1) = Z.sub.bal(i) K * Corr K = attenuation factor 11: i++
In optimization, Z.sub.0, the Threshold factor and attenuation factor K are found such that the algorithm finds Z.sub.bal in as low as possible iterations.

[0063] The method according to a further embodiment of the present disclosure thus comprises the steps of: setting the tunable impedance 5 to a predetermined initial value, e.g. 50, calculating a reflection coefficient .sub.2 at the side of the electrical balance duplexer 1 connected to the tunable impedance 5 from values measured by the detectors 7, 8, 9 of the tuning circuit 6, calculating a first estimate of the optimized impedance value from the predetermined initial value of the tunable impedance 5 and the calculated reflection coefficient .sub.2, and setting the tunable impedance 5 to the first estimate of the optimized impedance value.

[0064] In some embodiments, the method further comprises the steps of: recalculating the reflection coefficient .sub.2, calculating an intermediate value of the optimized impedance value from the previous estimate of the optimized impedance value and the recalculated reflection coefficient .sub.2, calculating a correction term Corr by subtracting the calculated intermediate value from the predetermined initial value, calculating a further estimate of the optimized impedance value by subtracting the correction term Corr from the predetermined initial value, optionally after multiplying the correction term with an attenuation factor K, and setting the tunable impedance to the further estimate of the optimized impedance value. In some embodiments, these steps are iteratively repeated until the value of the scattering parameter S.sub.13 from transmission path 2 to the receive path 3, which scattering parameter S.sub.13 is calculated from measurements of the detectors 7, 8, 9 at the connections between the electrical balance duplexer 1 on the one hand and the transmission path 2 and the receive path 3 on the other hand, is smaller than a predetermined threshold value, below which threshold value the transmission path 2 is substantially isolated from the receive path 3.