Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Analysis of complex waves
Reexamination Certificate
2001-11-30
2003-10-28
Hirshfeld, Andrew H. (Department: 2854)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Analysis of complex waves
C324S076220, C324S658000, C324S606000, C324S765010, C330S002000, C330S251000, C330S277000
Reexamination Certificate
active
06639393
ABSTRACT:
BACKGROUND
The present invention relates to analyzing the behavior of a high frequency device, in particular, a device for use in high power high frequency amplifier, such as an amplifier for use in a mobile telephone network base-station. The invention also relates to a method of improving the performance of circuits including such a device.
It is desirous to improve the efficiency and power capabilities of amplifiers for use in mobile communication base stations and therefore also to provide a design tool for designing such amplifiers. One possible method of improving the design of such amplifiers includes conducting a theoretical analysis of terminal voltage and current waveforms with the aim of analyzing and improving the modes of operation of the amplifier required for high efficiency, linearity and power. The behavior of such amplifiers, being non-linear over much of their operating range, is rather complicated and difficult to define accurately. Such theoretical analysis is therefore generally inadequate when seeking to characterize the behavior of an amplifier with sufficient accuracy to enable its performance to be improved.
Experimental measurement and analysis of waveforms (including RF load lines, for example) would not of course suffer from the disadvantages associated with theoretical analysis. However, measurement systems of the prior art are generally unable to measure the behavior of such amplifiers over a sufficiently wide power band at sufficiently high frequencies. Measurement systems having such power and frequency ratings tend to be prohibitively expensive, inefficient and/or do not provide sufficient data to facilitate the improvement of the design of circuits incorporating the device under test. In particular, one measurement method of the prior art that is able to characterize the behavior of such amplifiers, the method including using a measurement system based on a vector network analyzer (VNA), is able only to provide limited data concerning the linear behavior of the amplifier. That prior art method is not able to provide any data concerning absolute values relating to the power and relative phase of waveforms outputted by the amplifier in response to input waveforms of known frequencies nor is it a straightforward matter to obtain useful information concerning the non-linear behavior of the device.
SUMMARY
The present invention thus seeks to provide an improved method of measuring the response of an electronic device to a high frequency input signal, an analyzer suitable for use in such a method, and an improved method of designing and manufacturing a high frequency device.
According to a first aspect of the invention there is provided a method of measuring the response of an electronic device to a high frequency input signal, the method comprising the steps of
a) providing an electronic device having a port able to receive and/or send high frequency signals,
b) providing a measurement system including a measurement unit for measuring high frequency signals and including a signal path connecting the measurement unit to the port of the device,
c) applying a signal to the device and measuring with the measurement unit via the signal path two independent waveforms at the port of the device, and
d) processing signals representative of the waves as measured by the measurement system, with the use of calibration data, to compensate for the influence of the measurement system on the waves between the port of the device and the measurement unit and to produce output signals from which the absolute values of the magnitude and phase of waves at the port of the device may be directly ascertained, wherein
the calibration data includes data ascertained by making measurements with a real network, the real network being connected to a portion of the signal path that in use connects to the port of the device, the influence of the real network on the measurements made with the real network being known, for example, by measuring the behavior of the real network under a plurality of conditions resulting from the application of a plurality of standards to the real network.
Thus the invention provides a method by which it is possible to ascertain the behavior of a device by obtaining data concerning the absolute values of waveforms, for example current and voltage waveforms, exhibited at the or each port of the device in response to a known input waveform. Obtaining such data will enable the design of circuits including such devices to be improved in a more efficient manner or in a more cost-effective manner than hitherto possible.
The advantages of the invention are facilitated by the calibration procedures used and in particular the use of the calibration data. (It will of course be understood that the process of calibration may in the present context simply mean improving the accuracy of the results of the measurements and/or improving the amount of information available regarding the behavior of the device.) System calibration procedures for 2-port measurement systems have been developed since the beginning of automated network analysis in the late 60's and many known calibration procedures, which allow different levels of accuracy depending on the desired application, are now available. Such calibration procedures are performed with the aim of improving accuracy and creating a well-defined measurement reference plane and are therefore very similar in function to the steps of ascertaining and using the first and second calibration data in respect of the present invention. However, most established prior art calibration procedures suffer from the disadvantage that they operate on s-parameters, which are defined as traveling wave ratios. As a consequence, only relative measurements are calibrated and absolute power and phase information of incoming and outgoing waves remain undetermined. This is a disadvantage that the present invention is able to avoid or mitigate. Thus, the accurate measurements of magnitude and phase of the traveling waves at the measurement reference plane at the port of the device under test is facilitated by the invention. The absolute voltage and current waveforms at terminals of the device may also be ascertained.
A recently proposed measurement system which also seeks to address the disadvantages associated with the prior art is built around two synchronized microwave transition analyzers (MTAs)(providing four input channels for measuring the incident and reflected waveforms at each of the two ports of the device under test), with calibration based on the availability of a multi-tone reference generator, which has an accurately known output impedance, and in respect of which the absolute amplitudes and relative phases of all frequency components are stable and accurately specified. The reference generator is itself calibrated by a broadband accurate signal analyzer, using a ‘nose-to-nose’ procedure (where the reference generator is linked directly to the signal analyzer). Obtaining data regarding the behavior of a device with a system that is calibrated by using a multi-tone reference generator and a broadband accurate signal generator is however very expensive. The method of the present invention does not however require the provision of such components.
It will be understood that the term “real network” as used herein covers within its scope any physical means, device or circuit that is able to carry signals from a first point to a second point. Of course, any such real network will have a influence on the signals so carried, which may be significant at high frequencies.
The calibration data is advantageously ascertained before the other steps of the method are performed. The steps of the method that require calibration data to be used may simply access the relevant calibration data from a data store, in which previously ascertained calibration data has been stored. Alternatively, the method may include steps in which the measurement system is used to ascertain the calibration data by performing one or more calibration steps. (Such
Benedikt Johannes
Tasker Paul Juan
Hamdan Wasseem H.
Hirshfeld Andrew H.
University College Cardiff Consultants Ltd.
Wolf Greenfield and Sacks, P.C.
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