Hans-Joachim Jentschel

RF-BIST: Loopback Spectral Signature Analysis

Built-in self-test (BIST) becomes important also for more complex structures like complete front-ends. In order to bring down the costs for the test overhead, spectral signature analysis at system level seems to be a promising concept. Investigations that have been carried out are targeted on the most challenging problems: generation of the test signature, evaluation of the signature response, implementation of the concept and verification by simulation. From investigations, it can be concluded that the concept is suitable, especially in the case of transceiver-type DUT.

An integrated wideband-IF-receiver architecture for mobile terminals

A wideband-IF receiver architecture is described for use in mobile terminals capable of receiving multiple standards like GSM, UMTS, DECT, etc. The architecture uses a single down-conversion and digitizes the wanted signal at high intermediate frequencies. The wideband nature of the architecture ensures a great adaptability to various mobile standards. It denotes a step into the direction of a fully reconfigurable software radio due to the shift of the ADC to higher frequencies. The paper is focused on the realization of the analog part of the receiver.

An effort reduced six-port direct conversion receiver and its calibration

Well-known receiver architectures, such as wideband-IF-receivers or zero-IF-receivers, usually require highly accurate component matching. For the realization of a software defined radio (SDR) device, the requirement of adjustability supervenes. Contemporarily, much effort is being made to develop tunable circuits and also to find new algorithms for digital elimination of analog signal distortions, etc. In order to reduce the effort for the analog receiver front-end and to bridge the gap between system architectures and circuit technologies, the alternative six-port receiver was investigated. Based on the six-port structure, we present a five-port receiver front-end architecture with signal path mismatch cancellation. To be able to regenerate the IQ-components, a calibration technique is presented based on the proposed architecture. Therefore, known algorithms can be utilized after the calibration. The main focus is the technical feasibility of the front-end in SDR mobile terminals.

Qualification of traffic data by Bayesian network data fusion

In this paper a method is introduced based on the concept of Bayesian networks (BNs), which is applied to model sensor fusion. Sensors can be characterised as real dynamical systems with specific physical functional principles, allowing to determine the value of a physical state of interest within certain ranges of tolerance. The measurements of the sensors are affected by external, e.g. environmental conditions, and internal conditions, e.g. the physical life of the sensor and its components. These effects can cause selection bias, which yields corrupted data. For this reason, the underlying process, the measurements, the external and internal conditions are considered in the BN model for data fusion. The effectiveness of the approach is underlined on the basis of vehicle classification in traffic surveillance. The results of our simulations show, that the accuracy of the estimates of the vehicle classes is increased by more than 60%.

A virtual clock enhancement method for DDS using an analog delay line

In this paper, we describe an analog delay line (DL) used for virtual clock enhancement in a direct digital synthesis (DDS). The novelty of the proposed method is the immediate application of the output signal of the phase accumulator for the generation of the desired frequency. To obtain the necessary spectral purity of the generated frequency, additional digital signal processing (DSP) based on a delay-locked loop (DLL) and noise shaping is applied. The consequences of nonlinear effects within the DL for the spectral performance of the DDS are explained.

Nonlinearity analysis of power detectors in direct conversion receivers utilizing six-port technology

Within the six-port or five-port receiver, additive mixing followed by squaring of the respective signal is realized. For the squaring, power detectors are utilized. In this article, we investigate the influence of higher order nonlinearities of the power detectors. The focus is on the distortion of the baseband signal by nonlinear fractions which originate from the RF-signal. Among other things, it will be deviated that even the most simple power detector realizations can guarantee a sufficient transmission quality.

Adaptive learning of Bayesian Networks for the qualification of traffic data by Contaminated Dirichlet Density Functions

The concept of Bayesian networks (BNs) is an established method to model data fusion in sensor networks of several equal or different sensors. Although the method is powerful, there is a particular need for accurate sensors, the consideration of the affecting external, e.g. environmental conditions, and internal influences, e.g. the physical life of the sensor, in the sensor model and an accurate a-priori knowledge about the underlying process. In this paper an adaptive algorithm for learning BNs is introduced, which is applied to update the time-variant a-priori probabilities in sensor networks. This algorithm makes use of contaminated Dirichlet density functions (CDDFs). The effectiveness of adaptive learning is demonstrated for vehicle classification in traffic surveillance.

Semi-Blind Cancellation of IQ-Imbalances

The technical realization of modern wireless receivers yields significant interfering IQ-imbalances, which have to be compensated digitally. To cancel these IQ-imbalances, we propose an algorithm using iterative blind source separation (IBSS) as well as information about the modulation scheme used (hence the term semi-blind). The novelty of our approach lies in the fact that we match the nonlinearity involved in the IBSS algorithm to the probability density function of the source signals. Moreover, we use approximations of the ideal non-linearity to achieve low computational complexity. For severe IQ-mismatch, the algorithm leads to 0.2 dB insertion loss in an AWGN channel and with 16-QAM modulation.

An approach to model-based testing of mixed-signal SiPs

Linear and non-linear Model-based Testing (MbT) has been developed in the past for mixed-signal devices. For Digital- to-Analog Converters (DACs) with a static nonlinear transfer characteristic, linear MbT has even been adopted in production test. The core principle of MbT is to parameterize a model of the on-chip error sources based on the measurements that are performed on the Device Under Test (DUT). The model parameters are then used in order to determine whether the DUT passes or fails the test. Using a linear model reduces the computational effort in applying MbT to multiplying matrices during production test. For non-linear models, the computational effort is larger. In this paper, we report a generalization of MbT applied to combinations of static nonlinearities and dynamic linear systems. The specific example of a DAC followed by a low-pass filter is found, for example, at the boundary between the digital baseband and the RF front-end of a typical transceiver. One technology of integrating the digital baseband and the RF front-end is System-in-Package (SiP). Limited access to internal signals, such as the DAC output in our example, poses particular problems for parameterizing a linear error source model. With our generalization, we provide a reference MbT which allows us to evaluate and compare various linear and non-linear MbT approaches with respect to a specific test application.

Six-Port Architecture based Receiver for MB-OFDM UWB Systems

In this paper, we present the investigation of a six-port architecture based receiver for multi-band OFDM ultra- wide band (UWB) systems. An UWB system simulator is implemented in MATLAB for specification compliant signal processing according to and is represented by transmitter and receiver models. A six-port based receiver is presented which is used in the RF front-end of an UWB system. Its model includes six-port specific errors addressed in following case studies. Additionally, a performance influencing receiver environment is taken into account when we investigate the suitability of six-port architecture for UWB. We conclude this work by system performance evaluation under the considered application scenario.