Self-calibration Technique Research Articles

In-vivo cell and tissue monitoring with active implants.

Active implant systems are becoming increasingly important in modern medicine. We describe the development of an implantable system for the monitoring of dissolved oxygen. Tissue oxygen saturation plays a leading role in many pathophysiological processes in the human body such as the growth of malignant tumors or the viability of transplanted organs. The implant allows monitoring the tissue oxygenation in vivo with a wireless interface to an external device. An improved self-calibration technique is described to minimize sensor drift with electrochemical sensors in vivo for a better long term stability of the implant system. The sensor was coated with a hydrogel membrane to avoid convection artifacts during calibration procedure.

Field of view for near-field aperture synthesis imaging.

Aperture synthesis techniques are increasingly being employed to provide high angular resolution images in situations where the object of interest is in the near field of the interferometric array. Previous work has showed that an aperture synthesis array can be refocused on an object in the near field of an array, provided that the object is smaller than the effective Fresnel zone size corresponding to the array-object range. We show here that, under paraxial conditions, standard interferometric techniques can be used to image objects that are substantially larger than this limit. We also note that interferometric self-calibration and phase-closure image-reconstruction techniques can be used to achieve near-field refocusing without requiring accurate object range information. We use our results to show that the field of view for high-resolution aperture synthesis imaging of geosynchronous satellites from the ground can be considerably larger than the largest satellites in Earth orbit.

Self-calibration of vision parameters via genetic algorithms with simulated binary crossover and laser line projection

A self-calibration technique based on genetic algorithms (GAs) with simulated binary crossover (SBX) and laser line imaging is presented. In this technique, the GA determines the vision parameters based on perspective projection geometry. The GA is constructed by means of an objective function, which is deduced from the equations of the laser line projection. To minimize the objective function, the GA performs a recombination of chromosomes through the SBX. This procedure provides the vision parameters, which are represented as chromosomes. The approach of the proposed GA is to achieve calibration and recalibration without external references and physical measurements. Thus, limitations caused by the missing of references are overcome to make self-calibration and three-dimensional (3-D) vision. Therefore, the proposed technique improves the self-calibration obtained by GAs with references. Additionally, 3-D vision is carried out via laser line position and vision parameters. The contribution of the proposed method is elucidated based on the accuracy of the self-calibration, which is performed with GAs.

Built-in Self-Calibration and Digital-Trim Technique for 14-Bit SAR ADCs Achieving ±1 LSB INL

Several state-of-the-art monitoring and control systems, such as dc motor controllers, power line monitoring and protection systems, instrumentation systems, and battery monitors, require direct digitization of high-voltage (HV) input signals. Analog-to-digital converters (ADCs) that can digitize HV signals require high linearity and low-voltage coefficient capacitors. A built-in self-calibration and digital-trim algorithm correcting static mismatches in capacitive digital-to-analog converter (DAC) used in successive approximation register analog-to-digital converters (SAR ADCs) is proposed. The algorithm uses a dynamic error correction (DEC) capacitor to cancel the static errors occurring in each capacitor of the array as the first step upon power-up and eliminates the need for an extra calibration DAC. Self-trimming is performed digitally during normal ADC operation. The algorithm is implemented on a 14-bit HV input range SAR ADC with integrated DEC capacitors. The IC is fabricated in 0.6- $\mu $ m HV-compliant CMOS process, accepting up to $24V_{\rm pp}$ differential input signal. The proposed approach achieves 73.32-dB signal-to-noise and distortion ratio, which is an improvement of 12.03 dB after self-calibration at 400-kS/s sampling rate, consuming 90 mW from a ±15 V supply. The calibration circuitry occupies 28% of the capacitor DAC and consumes $^{2}$ .

Where is the fuzz? Undetected Lymanαnebulae around quasars atz~ 2.3

We observed a small sample of 5 radio-quiet QSOs with integral field spectroscopy to search for possible extended emission in the Ly$\alpha$ line. We subtracted the QSO point sources using a simple PSF self-calibration technique that takes advantage of the simultaneous availability of spatial and spectral information. In 4 of the 5 objects we find no significant traces of extended Ly$\alpha$ emission beyond the contribution of the QSO nuclei itself, while in UM 247 there is evidence for a weak and spatially quite compact excess in the Ly$\alpha$ line at several kpc outside the nucleus. For all objects in our sample we estimated detection limits for extended, smoothly distributed Ly$\alpha$ emission by adding fake nebulosities into the datacubes and trying to recover them after PSF subtraction. Our observations are consistent with other studies showing that giant Ly$\alpha$ nebulae such as those found recently around some quasars are very rare. Ly$\alpha$ fuzz around typical radio-quiet QSOs is fainter, less extended and is therefore much harder to detect. The faintness of these structures is consistent with the idea that radio-quiet QSOs typically reside in dark matter haloes of modest masses.

On the analysis of inhomogeneous magnetic field spectrometer for laser-driven ion acceleration.

We present a detailed study of the use of a non-parallel, inhomogeneous magnetic field spectrometer for the investigation of laser-accelerated ion beams. Employing a wedged yoke design, we demonstrate the feasibility of an in-situ self-calibration technique of the non-uniform magnetic field and show that high-precision measurements of ion energies are possible in a wide-angle configuration. We also discuss the implications of a stacked detector system for unambiguous identification of different ion species present in the ion beam and explore the feasibility of detection of high energy particles beyond 100 MeV/amu in radiation harsh environments.

基于正交消隐点无穷单应的摄像机内参数自标定方法

基于正交消隐点无穷单应的摄像机内参数自标定方法

A 0.1–5.0 GHz Reconfigurable Transmitter With Dual-Mode Power Amplifier and Digitally-Assisted Self-Calibration for Private Network Communications

A 0.1-5.0 GHz 65 nm CMOS reconfigurable transmitter for private network wireless communications is presented. The transmitter integrates a 0.1-1.5 GHz high-efficiency dual-mode power amplifier to support low-cost narrowband applications and a 0.45-5.0 GHz efficiency-optimized pre-power amplifier to support high-performance wideband applications. A wideband PLL frequency synthesizer, DACs with reconfigurable sampling rate and the reconfigurable digital baseband processing with standard JESD207 interface are all included to implement the highly-integrated transmitter. Specifically, with the proposed digitally-assisted self-calibration technique for LO leakage and image rejection, the transmitter achieves 52 dBc LO leakage and >53 dBc image rejection ratio (IRR), showing 20 dB and 30 dB improvement compared with the un-calibrated cases, respectively. The system verifications have demonstrated an EVM of 1.7% for 905 MHz EDGE with 19.5 dBm output power, and an EVM of 3.2% for LTE Band42 with 5.5 dBm output power. This proposed transmitter has achieved the comparable or even better performance in linearity, noise floor and power consumption compared with the state-of-the-art reconfigurable transmitters.

Digital foreground calibration of capacitor mismatch for SAR ADCs

A foreground digital self-calibration technique that improves capacitor matching of a digital-to-analogue converter (DAC) employed in successive approximation register (SAR) analogue-to-digital converters (ADCs) is presented. By exploiting an antisymmetric behaviour of capacitor mismatch errors in SAR ADCs and the proposed DAC switching scheme, the calibration technique significantly reduces capacitor mismatch errors without resorting to extensive computation or dedicated circuits.

Self-calibrating lensless inline-holographic microscopy by a sample holder with reference structures.

A self-calibration technique for lensless compact chip-microscopes based on inline holography with pinhole illumination is presented. The pinhole illumination wave acts as reference and is needed for the reconstruction process. This reference wave is assumed to be spherical, so that its phase is already determined by the position of the pinhole in relation to the image sensor. It is shown that the reconstructed spatial resolution is strongly dependent on the estimation for the pinhole to sensor distance. A precision in the range of tens of microns was reached for microscopic imaging with a spatial resolution in the range of one micron. Therefore additional reference crosses are prepared lithographically on the sample holder. The hologram, which contains the optical information about the sample as well as the reference crosses, is used for calibration and image reconstruction at the same time. The presented technique was tested to allow the reconstruction of a spatial resolution corresponding to the limit of detection apertures of about 0.66. The technique was applied to holograms of test beads and blood smear samples.

Quality Assessment of Self-Calibration with Distortion Estimation for Grid Point Images

Abstract. Recently, a camera self-calibration algorithm was reported which solves for pose, focal length and radial distortion using a minimal set of four 2D-to-3D point correspondences. In this paper, we present an empirical analysis of the algorithm’s accuracy using highfidelity point correspondences. In particular, we use images of circular markers arranged in a regular planar grid, obtain the centroids of the marker images, and pass those as input point correspondences to the algorithm. We compare the resulting reprojection errors against those obtained from a benchmark calibration based on the same data. Our experiments show that for low-noise point images the self-calibration technique performs at least as good as the benchmark with a simplified distortion model.

A self-calibration technique for wide tuning range PLLs

This paper presents a new calibration technique applicable for wide tuning range phase locked loops (PLLs) using very low gain voltage controlled oscillators (VCO). This technique uses the PLL main loop for the coarse and fine tuning of the VCO. Instead of using two loops which has been reported in previous works, in this work the VCO tuning voltage is used to calibrate the VCO switch capacitor array. Since the proposed calibration circuit operates in a closed loop form, it can be used for channel selection as well as adjusting for process, voltage and temperature variations. In addition, the calibration circuit has been used to set the VCO tail current in order to optimize VCO phase noise. A prototype frequency synthesizer has been designed in 0.18-μm CMOS process to work for a frequency range from 2.4 to 2.72 GHz. Simulation results show that using the proposed technique, a spur level of ?60 dB at 5 MHz offset from carrier was achieved while having negligible power overhead.

An IQ mismatch calibration and compensation technique for wideband wireless transceivers

An IQ mismatch calibration and compensation technique based on the digital baseband for wideband wireless communication transmitters is proposed. The digital baseband transmits the signal used for IQ mismatch calibration. The signal passes through the RF transmitter path, the calibration loop (which is composed of a square power detector and a band-pass filter in the RF transceiver) and the variable gain amplifier of the receiver. The digital baseband samples the signal for IQ mismatch estimation and compensates for it. Compared with the self-calibration technique in the RF chip, the proposed technique saves area and power consumption for the wireless local area network solution. This technique has been successfully used for the 802.11n system and satisfies the requirement of the standard by achieving over 50 dB image suppression.

Study of the influence of fringe edge on MEMS capacitive accelerometers self-calibration

This paper is the follow-up of the research we conduct to improve the self-calibration precision of high-precision MEMS capacitive accelerometers. In the previous published study, we have analyzed the influence of DRIE fabrication error on the dynamic self-calibration. In this paper, the influence of fringe effect on the self-calibration is discussed in order to improve the self-calibration precision further more, and the results has proved the feasibility of this self-calibration technique. Aimed at the capacitive accelerometer in this paper, the self-calibration error is only 0.18 % in closed-loop circuit, which is approach to the absolute calibration error of laser interferometer (0.5---1 %), which can satisfy the demand of high-precision sensors. In open-loop circuit, the fringe effect influences the self-calibration obviously and the error reaches 24.2 %, but it can be reduced to 1.49 % by correcting the actuation voltage. The method proposed in this paper may be used to develop full-automatic self-calibration system integrated on circuit board in the future.

The detrimental effect of increasing the number of cameras on self-calibration for tomographic PIV

It is commonly assumed that adding cameras is beneficial for the accuracy of multiple-camera systems. This tautological assertion is most certainly true for tomographic particle image velocimetry and 3D particle-tracking velocimetry systems, where the search area on each image for the particle corresponding to a 3D trial position is small (typically less than the particle image diameter). On the other hand, when it comes to larger search areas (due to, for example, calibration uncertainties), quite surprisingly, increasing the number of cameras might have a detrimental effect. Under some conditions, this is the case for the volumetric self-calibration technique (Wieneke 2008 Exp. Fluids 45 549–56), in which the residual calibration error and misalignments of the cameras are corrected by statistically searching matching particles over a search area larger than the expected maximum calibration error. In this work, the loss of signal in the self-calibration for systems with three or more cameras is discussed. Two readily implementable solutions are provided to reduce this source of error. The algorithms are tested on synthetic and real images.

A two-step A/D conversion and column self-calibration technique for low noise CMOS image sensors.

In this paper, a 120 frames per second (fps) low noise CMOS Image Sensor (CIS) based on a Two-Step Single Slope ADC (TS SS ADC) and column self-calibration technique is proposed. The TS SS ADC is suitable for high speed video systems because its conversion speed is much faster (by more than 10 times) than that of the Single Slope ADC (SS ADC). However, there exist some mismatching errors between the coarse block and the fine block due to the 2-step operation of the TS SS ADC. In general, this makes it difficult to implement the TS SS ADC beyond a 10-bit resolution. In order to improve such errors, a new 4-input comparator is discussed and a high resolution TS SS ADC is proposed. Further, a feedback circuit that enables column self-calibration to reduce the Fixed Pattern Noise (FPN) is also described. The proposed chip has been fabricated with 0.13 μm Samsung CIS technology and the chip satisfies the VGA resolution. The pixel is based on the 4-TR Active Pixel Sensor (APS). The high frame rate of 120 fps is achieved at the VGA resolution. The measured FPN is 0.38 LSB, and measured dynamic range is about 64.6 dB.

Autonomous Star Camera Calibration and Spacecraft Attitude Determination

This paper presents two methods of star camera calibration to determine camera calibrating parameters (like principal point, focal length etc) along with lens distortions (radial and decentering). First method works autonomously utilizing star coordinates in three consecutive image frames thus independent of star identification or biased attitude information. The parameters obtained in autonomous self-calibration technique helps to identify the imaged stars with the cataloged stars. Least Square based second method utilizes inertial star coordinates to determine satellite attitude and star camera parameters with lens radial distortion, both independent of each other. Camera parameters determined by the second method are more accurate than the first method of camera self calibration. Moreover, unlike most of the attitude determination algorithms where attitude of the satellite depend on the camera calibrating parameters, the second method has the advantage of computing spacecraft attitude independent of camera calibrating parameters except lens distortions (radial). Finally Kalman filter based sequential estimation scheme is employed to filter out the noise of the LS based estimation.

A carrier leakage calibration and compensation technique for wideband wireless transceiver

A carrier leakage calibration and compensation technique based on digital baseband for a wideband wireless communication transceiver is proposed. The digital baseband transmits a calibration signal, samples the signal which passes through the transmitter path and the calibration loop in the RF chip, measures the carrier leakage by analyzing the sampled data and compensates it. Compared with a self-calibration technique in the RF chip, the proposed technique saves area and power consumption for the wireless local area network (WLAN) solution. This technique has been successfully used for 802.1 1n system and satisfies the requirement of the standard by achieving over 50 dB carrier leakage suppression.

Blind Self-Calibration Technique for I/Q Imbalances and DC-Offsets

The gain/phase imbalances and DC-offsets in the in-phase and quadrature branches in direct conversion transmitters (DCTs) are main sources of errors, especially at microwave frequencies and above. These impairments distort the spectrum of the transmitted signal and degrade the communications performance. In this paper, a blind technique based on higher order statistics is proposed to estimate the calibration parameters in order to compensate for these impairments. By minimizing a cost function composed of second and fourth moments of the modulator output signal, the DC-offsets, gain imbalance, and phase imbalance can be successively calibrated. The convergence of the proposed technique is also analyzed. This technique is blind in the sense that it does not require any prior knowledge about the DCT input signal, and is applicable to many communications systems including QAM, OFDM, and SC-FDMA. Computer simulations and experiments at 20 GHz demonstrate that the proposed technique can significantly improve the DCT performance in terms of local oscillator leakage and image suppressions.

Heater Self-Calibration Technique for Shape Prediction of Fiber Tapers

In the production of tapered optical fibers, it is important to control the fiber shape according to application-dependent requirements and to ensure adiabatic tapers. Especially in the transition regions, the fiber shape depends on the heater properties. The axial viscosity profile of the fiber within the heater can, however, be hard to access and is therefore often approximated by assuming a uniform temperature distribution. We present a method for easy experimental calibration of the viscosity profile within the heater. This allows the determination of the resultant fiber shape for arbitrary pulling procedures, using only an additional camera and the fiber drawing setup itself. We find very good agreement between the modeled and measured fiber shape.