Methods for characterizing and calibrating RF measuring fixtures

Abstract

Method for calibrating and / or characterizing a multi-port, in particular a measuring holder (4), characterized in that no through connection and / or no thru standard is used, wherein a match-open standard and / or an open-short standard and / or a short-open standard is used and wherein a sign of a calibration parameter is determined via knowledge of a mechanical length of a lead.

Description

TECHNICAL FIELD

[0001] The invention relates to a method for calibrating a multi-port device according to the preamble of claim 1 as well as to a computer program, a computer program product, a data carrier and a device according to the independent claims. STATE OF THE ART

[0002] In laboratory and test environments, measurement fixtures are often used when working with electrical components. These fixtures are used to connect test objects to suitable measurement systems. To eliminate the influence of such fixtures on the measurement results, calibrations are typically required prior to measurements. In addition to calibration, the characterization of such fixtures is also of interest in order to evaluate their electrical properties.

[0003] A variety of methods are known for calibrating measurement fixtures. However, calibration methods that also aim to evaluate crosstalk all have the disadvantage that they require the use of a through connection between the test ports of the measurement fixtures, which must either be known or assumed to be perfect or reflection-free. In measurement situations such as those encountered in industrial tests, however, these conditions are extremely difficult or even impossible to achieve due to geometric boundary conditions. Furthermore, taking crosstalk terms into account is very complex in the calibration methods known from the state of the art. Further problems that are only unsatisfactorily solved by the previously known calibration methods for measurement fixtures are the calibration of measurement fixtures with fixed lengths, especially for measurement fixtures without coaxial connections.The possibility of using the calibration methods known from the state of the art in measurement arrangements with differential wiring is also very limited.

[0004] The direct measurement method is often used to characterize the electrical properties of measurement fixtures. This method allows the transmission properties of the measurement fixture and the crosstalk between the individual connection pins of the measurement fixture to be recorded. However, the disadvantages of this method are the high mechanical complexity, the fact that subsequently inserted electronic circuit boards (PCBs) cannot be recorded, that the influence of the DUT package is also not captured, and that multi-port measurements are difficult to implement. Furthermore, it is possible to use methods for characterizing measurement fixtures that are based on the well-known calibration methods for measurement fixtures.The disadvantage of using such methods, however, is that it is not possible to detect crosstalk and that usually not all pin configurations can be taken into account. In this context, the following publications should be noted:

[0005] DE 10 2007 028 725 A1 discloses a calibration method for a vector network analyzer. The goal of the calibration method is to be able to determine a phase difference between an excitation frequency and a measurement frequency. The necessary measurement frequency is generated by the nonlinear device under test itself as soon as it is stimulated with the excitation frequency.

[0006] US 2009 / 0 322 347 A1 presents a measuring device configured to be connected to an analysis unit (including a network analyzer). The measuring device comprises a measuring unit and a calibration and control unit connected to and integrated with the measuring unit.

[0007] In: Chen Z. et al.: Two-port calibration of test fixtures with OSL method. Proceedings IEEE 3rd International Conference on Microwave and Millimeter Wave Technology, 2002, pp. 138–141. IEEE Xplore [online]. DOI: 10.1109 / ICMMT.2002.1187654, an open-short-load (OSL) method for the calibration of one-port test fixtures is presented. The calibration is performed on test fixtures with two ports.

[0008] Finally, reference should be made to DE 43 32 273 A1. This document discloses a method for calibrating a network analyzer, which involves calibrating a network analyzer with two measurement ports by successively measuring the transmission and reflection parameters on several calibration standards in any order, from which correction values ​​are calculated and taken into account in subsequent object measurements. DISCLOSURE OF THE INVENTION

[0009] It is the object of the invention to eliminate or at least reduce the disadvantages of the above-mentioned prior art, in particular it is the object of the invention to provide a method which enables optimal calibration and characterization of measuring fixtures.

[0010] The invention is achieved by a method according to claim 1. Independent subjects of the invention are a computer program, a computer program product, a data carrier and a device according to the independent claims.

[0011] The invention has the advantage over the prior art that it enables a simple calibration procedure for calibrating measurement fixtures. This procedure does not require a through connection, enables differential calibration, and offers the possibility of de-embedding crosstalk or eliminating measurement errors caused by crosstalk. The method also has the advantage of enabling characterization that can be used to detect crosstalk, the influence of PCBs, and the influence of DUT packages. Furthermore, when characterizing a measurement fixture using the method according to the invention, multi-port applications, arbitrary pin configurations, and life cycle monitoring are possible. Compared to known methods, the mechanical complexity of the method according to the invention is significantly reduced.

[0012] According to the invention, a method, in particular a high-frequency method, is provided for calibrating and / or characterizing a multi-port device, in particular a measurement fixture, wherein no through connection or thru standard is used in the method. Typically, the method comprises at least the steps of "measuring the measurement fixture with a match-open standard," "measuring the measurement fixture with an open-short standard," "measuring the measurement fixture with a short-open standard," and "calculating calibration equations based on the measurement results."

[0013] An advantageous method for calibrating and / or characterizing a multi-port device, in particular a measurement fixture, is characterized in that a maximum of three, preferably exactly three, calibration standards are used. In other typical methods according to the invention, more than three calibration standards are used. It is particularly advantageous if, preferably exclusively, a match-open standard, an open-short standard, and a short-open standard are used.

[0014] In a particularly advantageous method, the sign of a calibration parameter is determined based on the mechanical length of a supply line. Various options are available for this. One option is to utilize a continuous phase and the knowledge of the mechanical length of the supply line. From this, the expected phase value can be calculated at low frequencies. Based on this value, the sign selection is carried out in such a way that a continuous phase is maintained.

[0015] A computer program according to the invention advantageously carries out at least parts of the method according to the invention.

[0016] A computer program product according to the invention is typically characterized in that it comprises and / or implements a computer program according to the invention.

[0017] A computer program according to the invention and / or a computer program product according to the invention is advantageously stored or installed on a data carrier according to the invention.

[0018] A hardware component according to the invention preferably comprises an electronic circuit suitable for carrying out the method according to the invention. The data processing required for the method can be implemented, for example, in an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit), or in another suitable hardware component.

[0019] A device according to the invention for calibrating and / or characterizing a multi-port device, in particular a measurement mount, comprising a network analyzer, at least one supply line, and at least one connection port typically does not include a thru standard or through connection. It is particularly advantageous if the device includes a maximum of three calibration standards, preferably exactly three calibration standards.

[0020] In a preferred embodiment, the device comprises exactly three calibration standards, namely a match-open standard, an open-short standard, and a short-open standard; however, the use of other calibration standards is also possible. Furthermore, it is possible to provide or use more than three calibration standards.

[0021] It is particularly advantageous if the multiport is a two-port system. However, the multiport can also comprise more than two ports, which then makes it possible to implement multiport calibration methods, which then allow, for example, differential measurements to be performed.

[0022] In particularly advantageous embodiments, the multi-port or two-port is a measuring holder and / or a measuring base.

[0023] A particularly advantageous device is characterized by the fact that the measurement fixture has a fixed length. In typical embodiments, the measurement fixture does not have a fixed length, but merely meets certain requirements: The reflection factors at the inputs of the measurement fixture must be sufficiently similar or essentially the same; the reflection factors in one plane of the DUT must be sufficiently similar or essentially the same; the transmission properties of the connections must be sufficiently similar or essentially the same; and reciprocity must be ensured. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In the following, the invention is briefly explained with the help of drawings, which show: Fig. 1: schematic view of a device according to the invention with a match-open standard, Fig. 2: schematic view of a device according to the invention with an open-short standard, Fig. 3: schematic view of a device according to the invention with a short-open standard and Fig. 4: Signal flow graph to visualize the simplifications made in the method according to the invention. DESCRIPTION OF A PREFERRED EMBODIMENT

[0025] Fig. 1 shows a schematic view of a device V.1 according to the invention for calibrating and / or characterizing a measurement fixture 4. The measurement fixture 4 to be calibrated or characterized is connected to a network analyzer (not shown in detail) via two supply lines (not shown in detail) using two connection ports 1.1 and 1.2. The device V.1 further comprises a Match-Open Standard, which is modularly constructed from a Match Standard 2 and an Open Standard 3.

[0026] The Fig. 2 and Fig. 3 show the devices V.2 and V.3 according to the invention. The devices V.2 and V.3 essentially correspond to the Fig. 1, but the device V.2 comprises an Open-Short Standard instead of the Match-Open Standard, which is modularly constructed from an Open Standard 3 and a Short Standard 5. The device V.3 in Fig. 3, on the other hand, includes a Short Open Standard, which is modularly constructed from a Short Standard 5 and an Open Standard 3.

[0027] It is particularly important to note that none of the devices V.1 to V.3 include a Thru standard.

[0028] In a method according to the invention for calibrating the measurement fixture 4, the measurement fixture 4 is first measured in device V.1. Subsequently, the measurement fixture 4 is measured in device V.2. After that, the measurement fixture 4 is measured in device V.3. Subsequently, the required calibration equations are calculated based on the results of the three measurements. A method based on the 16-term error model is used for this purpose. The 16-term error model captures all relevant high-frequency properties of a two-port device. However, it can also be extended to multi-port applications. The calculation method used here, which is based on the 16-term error model, can also be extended to multi-port applications.

[0029] In the method according to the invention, four simplifications are made to the 16-term error model. These simplifications are reciprocity, nearly equal reflection factors at the inputs, nearly equal reflection factors at the outputs, and nearly equal transmission paths.

[0030] If the 16-term error model is considered mathematically, equation (1) can be formulated as follows: Etotal=(E1E2E3E4)

[0031] The submatrices consist of the S-parameters (scatter parameters) of the error gate. These can be represented in detail using equations (2) to (5): E1=(e00e03e30e33)E2=(e01e02e31e32)E3=(e10e13e20e23)E4=(e11e12e21e22)

[0032] The 16 parameters thus combined are reduced to six different parameters. These can be summarized in the following submatrices: E1MOS16=(e00e03e03e00)E2MOS16=(e01e02e02e01)E3MOS16=E2MOS16E4MOS16=(e11e12e12e11)

[0033] In the Fig. In the signal flow graphs shown in Figure 4, the incoming waves with a i and the outgoing waves with b i Sufficiently similar reflection factors must be present at the inputs of the measurement fixture. In addition, both reflection factors must be sufficiently similar in the plane of the DUT (e 11 ≅ e 22 ). In addition, the transmission properties of the two connections must be sufficiently similar and reciprocity must be ensured (e 10 ≅ e 01 , ≅ e 23 ≅ e 32 In summary, all quantities that are shown in the signal flow graph in Fig.4 are represented with the same line type, have sufficiently similar or essentially identical properties. If these requirements are met, a reduction of the parameters to be determined from 16 to 6 in the S-parameter representation is possible. In the linear-in-T form, there are 8 different terms, 7 of which are linearly independent. This introduces a reduction in the number of parameters to be determined.

[0034] The linear-in-T form is determined by the relationship between the incoming and outgoing complex wave quantities a i or b i The calibration problem can be described with this approach according to equation (11), in which the parameters (vector t) to be determined are only linearly included in the problem. This fact also gives rise to the name. The matrix A is composed of the measured values ​​and the knowledge of the standards used. (b0b3a0a3)=(T1T2T3T4)⋅(a1a2b1b2) A⋅t=0

[0035] Converting the matrices to the linear-in-T form, which is advantageous for calibration, results in seven different parameters. The conversion equations (12) to (15) are used: T1=E2−E1E1−1E4T2=E1E3−1T3=−E3−1E4T4=E3−1

[0036] With these newly generated matrices, the system of equations that must be solved to determine the parameters of the measuring fixture 4 can be set up.

[0037] A set of equations necessary for the solution can now be generated using the results of the three measurements of the measuring fixture 4. The resulting system of equations, for the case of a measuring fixture with two connections, is shown in equation (16): (M010−M⋅SmMO11−M⋅SmMO12−SmMO11−SmMO120O01−O⋅SmMO12−O⋅SmMO11−SmMO12−SmMO110M01−M⋅SmMO21−M⋅SmMO22−SmMO21−SmMO22O010 −O⋅SmMO22−O⋅SmMO21−SmMO22−SmMO21O010−O⋅SmOS11−O⋅SmOS12−SmOS11−SmOS120S01−S⋅SmOS12−S⋅SmOS11−SmOS12−SmOS110O01−O⋅SmO S21−O⋅SmOS22−SmOS21−SmOS22S010−S⋅SmOS22−S⋅SmOS21−SmOS22−SmOS21S010−S⋅SmSM11−S⋅SmSM12−SmSM11−SmSM120M01−M⋅SmSM12−M⋅ SmSM11−SmSM12−SmSM110S01−S⋅SmSM21−S⋅SmSM22−SmSM21−SmSM22M010−M⋅SmSM22−M⋅SmSM21−SmSM22−SmSM21)⋅(t1t2t3t4t5t6t7t8)=0

[0038] The expressions with SmXY describe ij the measured S-parameters, and the variables M, S and O are the calibration standards assumed to be known.

[0039] The result of the system of equations (16) determines all parameters depending on a freely chosen error gate parameter, for example, t7. In order to be able to correctly determine all error gate parameters in terms of magnitude and phase, a determining equation for t7 can be derived from the relationship (17). This takes advantage of the fact that the parameter was initially arbitrarily chosen to be 1. t7=e01e012−e022=!1

[0040] Using the relationships that arise during the transformation, the parameter t7 can be determined up to the sign according to equation (18): t712=E3eval(1,1)⋅E2eval(1,1)−(E2eval(1,2)E2eval(2,2))2⋅E3eval(1,1)⋅E2eval(1,1)±E3eval(1,1)⋅E2eval(1,1)

[0041] The correct sign can then be determined, for example, by knowing the mechanical length of the supply lines.

[0042] The invention is not limited to the embodiment described here, but rather the scope of protection is determined by the patent claims. List of reference symbols 1.1, 1.2 connection port 2 Match Standard 3 Open Standard 4 measuring holder 5 Short Standard V.1,V.2,V.3 device

Claims

[1] Method for calibrating and / or characterizing a multi-port, in particular a measuring fixture (4), characterized by that no through connection and / or no thru standard is used, wherein a match-open standard and / or an open-short standard and / or a short-open standard is used and wherein a sign of a calibration parameter is determined via knowledge of a mechanical length of a feed line. [2] Computer program for carrying out the method according to claim 1. [3] Computer program product, characterized by that it comprises and / or implements a computer program according to claim 2. [4] Data carrier, characterized by that a computer program and / or computer program product according to one of claims 2 or 3 is stored thereon. [5] Hardware component, characterized by an electronic circuit suitable for carrying out the method according to claim 1. [6] Device (V.1, V.2, V.3) for calibrating and / or characterising a multi-port, in particular a measuring holder (4), with a network analyser, at least one supply line and at least one connection port (1.1, 1.2), characterized by that the device (V.1, V.2, V.3) does not comprise a thru standard and / or a through connection, wherein the device (V.1, V.2, V.3) has a match-open standard, an open-short standard and a short-open standard and wherein the multi-port is a two-port, wherein the two-port is a measuring fixture (4) and / or a measuring base, wherein the measuring fixture (4) has a fixed length.

Images