Blind Calibration Research Articles

A 12-Bit 200-MHz CMOS ADC

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A pipelined ADC incorporates a blind LMS calibration algorithm to correct for capacitor mismatches, residue gain error, and op amp nonlinearity. The calibration applies 128 levels and their perturbed values, computing 128 local errors across the input range and driving the mean square of these errors to zero. Fabricated in 90-nm digital CMOS technology, the ADC achieves a DNL of 0.78 LSB, an INL of 1.7 LSB, and an SNDR of 62 dB at an analog input frequency of 91 MHz while consuming 348 mW from a 1.2 V supply. </para>

Blind Calibration of Timing Skew in Time-Interleaved Analog-to-Digital Converters

The performance of time-interleaved analog-to-digital converters is often significantly degraded by timing mismatch errors. We develop methods for performing blind calibration of such converters, i.e., for estimating the unknown time-skew parameters and for performing signal reconstruction from these estimates. The methods are low in complexity and allow for accurate calibration in systems with large numbers of converters, provided that the skews are sufficiently small in magnitude. We also present modifications to calibrate gain mismatch as well as adaptive sequential methods of implementation. Performance and complexity analysis is provided to support the viability of the methods.

DOA estimation with uniform linear arrays in the presence of mutual coupling via blind calibration

Direction-of-arrival (DOA) estimation in the presence of mutual coupling is a widely studied problem in the field of array signal processing. Most of the previous methods tried to estimate the DOAs by compensating the effect of mutual coupling with measured antenna impedances, which is not an effective way because the impedances are often time-variant. A blind calibrating method is proposed in this paper to deal with the problem of DOA estimation with uniform linear arrays in the presence of mutual coupling. This method exploits the complex symmetric Toeplitz form of the mutual coupling matrix (MCM) of unitary linear arrays (ULA), and transforms conventional direction finding methods from testing the orthogonality between the signal and noise subspaces to checking the rank deficiency of a projected matrix, eliminating most of the influence brought in by the effect of mutual coupling. Simulation results are presented to show the satisfying performance of the new method.

3-D Aspect in the Five-Port Technique for Zero-IF Receivers and a New Blind Calibration Method

The five- or six-port circuit uses one or two additional outputs in comparison with classical homodyne demodulators. This paper demonstrates that the five- or six-port technique can take advantage of this particularity. The geometrical approach allows us to represent the 3-D aspect of the five-port technique. This study in space demonstrates the natural rejection of the even-order signal at the output of the direct receiver five-port circuit. Another benefit of this geometrical approach is a new blind calibration method. Many calibration methods have been proposed for the five-port circuit used as a homodyne receiver. Most of these methods were hard to be embedded and updated. This paper presents a new blind calibration method without any constraint on the system or the signal and with less algorithm computation cost.

Blind Calibration of Timing Offsets for Four-Channel Time-Interleaved ADCs

In this paper, we describe a blind calibration method for timing mismatches in a four-channel time-interleaved analog-to-digital converter (ADC). The proposed method requires that the input signal should be slightly oversampled. This ensures that there exists a frequency band around the zero frequency where the Fourier transforms of the four ADC subchannels contain only three alias components, instead of four. Then the matrix power spectral density (PSD) of the ADC subchannels is rank deficient over this frequency band. Accordingly, when the timing offsets are known, we can construct a filter bank that nulls the vector signal at the ADC outputs. We employ a parametrization of this filter bank to develop an adaptive null steering algorithm for estimating the ADC timing offsets. The null steering filter bank employs seven fixed finite-impulse response filters and three unknown timing offset parameters which are estimated by using an adaptive stochastic gradient technique. A convergence analysis is presented for the blind calibration method. Numerical simulations for a bandlimited white noise input and for inputs containing several sinusoidal components demonstrate the effectiveness of the proposed technique

Adaptive blind calibration of timing offset and gain mismatch for two-channel time-interleaved ADCs

In this paper, we describe a blind calibration method for gain and timing mismatches in a two-channel time-interleaved low-pass analog-to-digital converters (ADC). The method requires that the input signal should be slightly oversampled. This ensures that there exists a frequency band around the zero frequency where the Fourier transforms of the ADC subchannels are alias free. Low-pass filtering the ADC subchannels to this alias-free band reduces the blind calibration problem to a conventional gain and time delay estimation problem for an unknown signal in noise. An adaptive filtering structure with three fixed FIR filters and two adaptive gain and delay parameters is employed to achieve the calibration. A convergence analysis is presented for the blind calibration technique. Numerical simulations for a bandlimited white noise input and for inputs containing several sinusoidal components demonstrate the effectiveness of the proposed method

Reply to the Comments on "Blind Calibration and DOA Estimation With Uniform Circular Arrays in the Presence of Mutual Coupling"

This paper presents the reply to the comments made by Gao et al. on blind calibration and DOA estimation with uniform circular arrays in the presence of mutual coupling

Blind Calibration and DOA Estimation With Uniform Circular Arrays in the Presence of Mutual Coupling

In smart antenna systems, mutual coupling between elements can significantly degrade the performance of array processing algorithms. Based on the special structure of coupling matrix, this letter presents a subspace-based blind calibration method for uniform circular arrays. The method uses the incident signals to carry out both direction of arrival (DOA) estimation and array calibration simultaneously. In addition, the parameter identifiability condition is also provided. Finally, representative computer simulation results are given to demonstrate the effectiveness and behavior of the proposed method

Comments on "Blind Calibration and DOA Estimation With Uniform Circular Arrays in the Presence of Mutual Coupling"

A modification of the proposed algorithm is suggested for better numerical stability and less computation load. The overlooked parameter identifiability problem of the proposed algorithm is discussed in detail. Besides, solution to the ambiguous DOA estimates is also proposed.

Synthetic aperture radar–moving target indicator processing of multi-channel airborne radar measurement data

Coherent signal processing methods for combining the data that are collected via a multi-channel airborne radar system for moving target detection and image formation, are examined. Methods that convert multi-channel radar data into dual along-track monopulse synthetic aperture radar (SAR) signals of the radiated scene, are studied. A two-dimensional adaptive filtering method that projects the data in one synthesised SAR channel into the signal subspace of the other, is used for blind calibration of the monopulse SAR signals and generation of the moving target indication statistic. The merits of these algorithms are studied using the data from the multi-channel airborne radar measurement system that has been developed by the Air Force Research Laboratory at Rome, New York.

A wideband cascaded sigma-delta modulator with improved nonlinearity effects

This work presents a wideband cascaded sigma-delta modulator (CLFSDM) that reduces the nonlinearity effects of components. This architecture offers a new noise-shaping function to achieve high resolution in wideband applications and reduce digital-analogue converter (DAC) mismatch from the multi-bit feedback. Moreover, the error cancellation schemes can be added in the digital circuit part to cancel the coarse quantization errors and thus effectively reduce the non-ideal effects such as DAC mismatch. The mismatches between the two stages, such as in the gain error and pole error, may seriously degrade performance. The blind on-line calibration technique is used to eliminate these imperfect analogue circuit errors in the digital circuit. Accordingly, this architecture can reduce the over sampling ratio (OSR), and the in-band noise can be significantly suppressed to achieve a high resolution in Matlab and Switcap2 simulations. Simulation results indicate this sigma-delta modulator is very efficient in wide bandwidth applications.

Moving target detection and imaging using an X band along-track monopulse SAR

Moving target detection and imaging results for an X band spotlight synthetic aperture radar (SAR) system that utilizes an along-track monopulse configuration for its data collection is presented. The theoretical foundation of the processing that is used on these data is based on our earlier work in which a two-dimensional signal subspace processing (adaptive filtering) method was used to calibrate the monostatic and bistatic radars of the monopulse SAR system. The blind calibration of the two channels enables the user to null the stationary scene, and detect the moving targets. Next, a measure that we call SAR ambiguity function is used to estimate the relative speed of a detected moving target. The resultant estimate is then used to image the moving target.

Adaptive digital correction of analog errors in MASH ADCs. I. Off-line and blind on-line calibration

Cascaded delta-sigma (MASH) modulators for higher order oversampled analog-to-digital conversion rely on precise matching of contributions from different quantizers to cancel lower order quantization noise from intermediate delta-sigma stages. This first part of the paper studies the effect of analog imperfections in the implementation, such as finite gain of the amplifiers and capacitor ratio mismatch, and presents algorithms and architectures for digital correction of such analog imperfections, as well as gain and spectral distortion in the signal transfer function. Digital correction is implemented by linear finite-impulse response (FIR) filters, of which the coefficients are determined through adaptive off line or on-line calibration. Of particular interest is an on-line "blind" calibration technique, that uses no reference and operates directly on the digital output during conversion, with the only requirement on the unknown input signal that its spectrum be bandlimited. Behavioral simulations on dual-quantization oversampled converters demonstrate near-perfect adaptive correction and significant improvements in signal-to-quantization-noise performance over the uncalibrated case, using as few as 5 FIR coefficients. An alternative on line adaptation technique using test signal injection and experimental results from silicon are presented in the second part, in a companion paper.

Atomic Force Microscopy Calibration Methods for Lateral Force, Elasticity, and Viscosity

Due to huge uncertainties in the geometric dimensions of atomic force microscopy (AFM) probes, samples' rheological properties and lateral forces are difficult to measure and compare quantitatively. Hence, mathematical calibration methods fail to calibrate AFM probes accurately. To solve this problem, we will introduce in this paper “blind calibration methods” to determine quantitatively lateral forces, elastic constants and viscosity. For lateral force, a geometry factor is used to calibrate any cantilever using this “blind method”. The essential part of this method is a calibration standard sample that is commercially available. We have chosen silicon for our calibration standard sample and will discuss a cleaning procedure for reproducible lateral force measurements. We will provide an absolute friction value, which will serve as one of three parameters necessary to obtain the geometry factor. The other two components being the normal spring constant and the relative friction signal measured with the cantilever of interest. Further, we will discuss force modulation measurements and the problems that occur around resonances. We will provide a procedure to determine elastic constants also based on the silicon calibration standard. Finally, the “blind calibration method” will also be used to achieve kinematic viscosity values.

Automated Determination of Fat in Milk: Preliminary and Collaborative Studies

Abstract The principles and operation of an Auto-Analyzer system are described and the system was compared to the Babcock method. Initial calibration studies verified the manufacturer’s claim of linear response between 2 and 6% fat. Homogenization and heat treatment caused slightly higher and lower results by the AutoAnalyzer system and the Milko-tester, respectively, when raw milk was used for calibration. Use of formalin as a preservative resulted in a positive bias of less than 0.04% fat. Mercuric chloride and potassium dichromate caused no effect. Standard deviation of the difference from the Babcock method for the calibration studies was less than 0.05%. The standard deviations ranged from 0.031 to 0.077 for 345 raw milk samples from individual dairy farms. Collaborative studies encompassed 15 samples ranging from 3 to 6% fat, including 3 blind duplicates plus calibration standards. Samples were analyzed in triplicate by 6 laboratories, using 2 methods of AutoAnalyzer calibration. The standard deviation was less for the AutoAnalyzer than for the Babcock method (0.048 and 0.047% fat, respectively). Differences between 3 pairs of blind duplicates were 0.013, 0.021, and 0.012% fat by the Babcock and AutoAnalyzer analyses, respectively.