Jacques Oksman

Wideband, Bandpass, and Versatile Hybrid Filter Bank A/D Conversion for Software Radio

This paper deals with analog-to-digital (A/D) conversion for future software/cognitive radio systems. For these applications, A/D converters should convert wideband signals and offer high resolutions. In order to achieve this and to overcome technological limitations, the A/D conversion systems should be versatile, i.e., it should be possible to adapt the conversion characteristics (resolution and bandwidth) by software. This work studies and adapts hybrid filter banks (HFBs) in this context. First, HFBs, which can provide a large conversion bandwidth, are extended to bandpass sampling, thus minimizing the sampling frequency. Then, we provide efficient ways of improving the HFB resolution in a smaller frequency band, only by reprogramming the digital part. Moreover, this paper takes into account the main drawback of HFBs which is their very high sensitivity to analog imperfections. Simulation results are presented to demonstrate the performance of HFBs.

Influences of oversampling and analog imperfections on Hybrid Filter Bank A/D converters

Hybrid filter banks (HFB) are considered as good candidate for implementing wide-band, high-frequency A/D parallel converters. The performance of HFB (original and two- stage) structures is analyzed for different values of oversampling ratios leading to the choice of the optimal value. The electronic elements of the analysis filter bank of HFB structure are considered with real constraints (realization errors and drifts). Real analysis filters of HFB are considered with the analog elements for which the real values are randomly Gaussian-distributed. Sensitivity to the deviations from real values is simulated and the performance of two HFB (original and two-stage) structures are compared. The possible methods for decreasing the sensitivity to realization errors such as Total Least Squares (TLS) optimization are discussed. Original structure is found to be a better candidate rather than the two-stage one in practical cases. However, it is shown that a blind estimation method would be necessary to compensate the realization errors for practically implementing the HFB-based A/D converters.

A Manchester code generator running at 1 GHz

A new Manchester code generator designed at transistor level is presented in this paper. This generator uses 32 transistors and has the same complexity as a standard D flip-flop. It is intended to be used in a complex optical communication system. The main benefit of this design is to use a clock signal running at the same frequency as the data. Output changes on the rising edge and falling edge of the clock. Simulations results show a correct behavior up to 1 Gbit/s data rate with a 0.35 /spl mu/ CMOS technology within a commercial temperature range.

Design and construction of the high-speed optoelectronic memory system demonstrator

The high-speed optoelectronic memory system project is concerned with the reduction of latency within multiprocessor computer systems (a key problem) by the use of optoelectronics and associated packaging technologies. System demonstrators have been constructed to enable the evaluation of the technologies in terms of manufacturability. The system combines fiber, free space, and planar integrated optical waveguide technologies to augment the electronic memory and the processor components. Modeling and simulation techniques were developed toward the analysis and design of board-integrated waveguide transmission characteristics and optical interfacing. We describe the fabrication, assembly, and simulation of the major components within the system.

Operation of an optoelectronic crossbar switch containing a terabit-per-second free-space optical interconnect

The experimental operation of a terabit-per-second scale optoelectronic connection to a silicon very-large-scale-integrated circuit is described. A demonstrator system, in the form of an optoelectronic crossbar switch, has been constructed as a technology test bed. The assembly and testing of the components making up the system, including a flip-chipped InGaAs-GaAs optical interface chip, are reported. Using optical inputs to the electronic switching chip, single-channel routing of data through the system at the design rate of 250 Mb/s (without internal fan-out) was achieved. With 4000 optical inputs, this corresponds to a potential aggregate data input of a terabit per second into the single 14.6 /spl times/ 15.6 mm CMOS chip. In addition 50-Mb/s data rates were switched utilizing the full internal optical fan-out included in the system to complete the required connectivity. This simultaneous input of data across the chip corresponds to an aggregate data input of 0.2 Tb/s. The experimental system also utilized optical distribution of clock signals across the CMOS chip.

Sensitivity of Time-Division Multiplexing Parallel A/D Converters to Analog Imperfection

In this paper, the Time-Division Multiplexing (TDM) architecture for the Hybrid Filter Bank (HFB) A/D Converters (ADCs) is studied in the time domain. Giving a brief survey on the TDM structure, the classical and TDM HFB-based ADCs are compared in terms of the output resolution for some input signals. To study the sensitivity to the realization errors, both structures are simulated assuming the same realization errors in the analysis filter banks. The TDM HFB-based ADC exhibits a better performance either in the presence or in the absence of realization errors than the classical one. Besides, the input-output relationship is demonstrated to be Linear Time-Invariant (LTI) for the TDM HFB, but it is non-LTI in the the classical HFB case. Thus, it is possible only in the TDM case that a blind deconvolution method is employed for adaptively compensating the realization errors.

On hybrid filter bank A/D converters with arbitrary over-sampling rate

Hybrid filter banks (HFB) analog/digital (A/D) systems permit wide-band, high frequency conversion. This paper presents a method for designing output digital filters of the HFB, when analog input filters are easy-to-implement (typically second order) and consequently can work at high rate. The constraint of quantization noise amplification due to the digital output filters is taken into account by using the Lagrange multiplier method. In order to improve quality of the output signal in spite of this constraint, degrees of freedom are added by using a K-channels HFB associated with an oversampling factor M less than K and by imposing a condition stronger than that of Nyquist on the input signal.

Optimization of the noise transfer function of Extended-Frequency-Band-Decomposition sigma-delta A/D converters

Frequency-band-decomposition (FBD) is a good candidate to increase the bandwidths of ADC converters based on sigma-delta modulators. Each modulator processes a part of the input signal band and is followed by a digital filter. In the case of large mismatches in the analog modulators, a new solution, called extended frequency-band-decomposition (EFBD) can be used. This solution allows for, for example, a four percent error in the central frequencies without significant degradation in the performance when the digital processing part is appeared to the analog modulators. A calibration of the digital part is thus required to reach these theoretical performance. This paper will focus on a self-calibration algorithm for an EFBD. The algorithm helps minimize the quantization noise of the EFBD.

A Wide-Band A/D Converter for the Software-Defined Radio System

The HFB structure is a suitable candidate to realize a wide-band A/D convertor for the software-defined radio (SDR) systems. Two MIMO time-division multiplexing (TDM) and subband HFB architectures are compared with the classical one in this paper. Simulating in the timedomain, the MIMO HFBs exhibit a better performance than the classical one in terms of output resolution as well as the sensitivity to the realization errors of analysis filter bank. In opposite to the classical HFB case, the MIMO HFBs provide an LTI input-output relation. It is shown that the blind estimation and noise cancelation techniques may be used in the MIMO case for correcting the realization errors. The MIMO and classical HFBs are compared in terms of computational complexity as well.

Online Estimation of Time-Varying Volatility Using a Continuous-Discrete LMS Algorithm

The following paper addresses a problem of inference in financial engineering, namely, online time-varying volatility estimation. The proposed method is based on an adaptive predictor for the stock price, built from an implicit integration formula. An estimate for the current volatility value which minimizes the mean square prediction error is calculated recursively using an LMS algorithm. The method is then validated on several synthetic examples as well as on real data. Throughout the illustration, the proposed method is compared with both UKF and offline volatility estimation.