DC Offset Effects Research Articles

OTA based frequency tuning system with reduced effect of DC offsets

An on-line tuning system based on the master–slave technique is proposed in this paper. Each stage of the system is realized by employing only operational transconductance amplifiers (OTAs). The most significant advantage of the introduced topology is the reduction of the influence of the dc offset terms which are critical about the performance of such systems. In addition, an attractive benefit is the suitability for implementing the resulted configurations in both integrated and discrete-component forms using only the same type of active element. The validation of the proposed topology is achieved through simulation and experimental results.

Digital LMS adaptation of analog filters without gradient information

The least mean square (LMS) algorithm has practical problems in the analog domain mainly due to DC offset effects. If digital LMS adaptation is used, a digitizer (analog-to-digital converter or comparator) is required for each gradient signal as well as the filter output. Furthermore, in some cases the state signals are not available anywhere in the analog signal path necessitating additional analog filters. Here, techniques for digitally estimating the gradient signals required for the LMS adaptation of analog filters are described. The techniques are free from DC offset effects and do not require access to the filter's internal state signals. Digitizers are required only on the input and error signal. The convergence rate and misadjustment are identical to traditional LMS adaptation, but an additional matrix multiplication is required for each iteration. Hence, analog circuit complexity is reduced but digital circuit complexity is increased with no change in overall performance making it an attractive option for mixed-signal integrated systems in digital CMOS. Signed and subsampled variations of the adaptive algorithm can provide a further reduction in analog and digital circuit complexity, but with a slower convergence rate. Theoretical analyses, behavioral simulations, and experimental results from an integrated filter are all presented.

Comparison of DC offset effects in four LMS adaptive algorithms

It is well known that DC offsets degrade the performance of analog adaptive filters. In this paper, the effects of DC offsets on four variations of the stochastic gradient algorithm are analyzed. Assuming a Gaussian probability distribution for the input signal and error signal, the output mean squared error (MSE) performance in the presence of DC offsets is evaluated for each of the algorithms. The theoretical work is compared with computer simulations and the results, together with convergence properties of each of the algorithms and their respective hardware requirements, are used in selecting the most appropriate algorithm. Although a Gaussian input distribution is assumed, it may reasonably be inferred that the critical results obtained should also hold for other input distributions. >

Continuous-time LMS adaptive recursive filters

An approach for implementing continuous-time adaptive recursive filters is presented. The resulting filters should be capable of operating on much higher signal frequencies than their digital counterparts since no sampling is required. With respect to implementation problems, the effects of DC offsets are investigated and formulas derived so that these effects can be estimated and reduced. It is shown that the DC offset performance is strongly affected by the choice of structure for the adaptive filter. Experimental results from a discrete prototype are given where accurate adaption is observed and DC offset effects are compared to theoretical predictions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>