Dynamic demonstration of diffractive optic analog-to-digital converter scheme.

The design, fabrication, and testing of an acousto-optic-based binary data recorder are described. The data to be recorded are applied to an acousto-optic (AO) Bragg cell illuminated by a pulsed laser diode, and the bit sequence present in the cell is imaged onto a linear detector array. Emphasis was placed on incorporating the optical system and the linear detector array with its control board into a rugged module of modest size capable of recording non-return-to-zero data at rates of 200 Mbits/s or greater. The design specifications of the AO cell and the pulsed laser were based on earlier analysis and proof-of-principle experiments. An in-house-built TI3AsS4 AO cell with a bandwidth of 260 MHz centered at 400 MHz gave 11% diffraction efficiency at the 810 nm wavelength used in the system. When used with a laser pulse of 4 ns full-width at half-maximum, this system had a maximum operating rate of 240 Mbits/s. The same optical system used with an AO cell with 500 MHz bandwidth and a 1.7 ns laser pulse had a maximum rate of 500 Mbits/s. The quality of the optical imaging did not appear to limit the performance, suggesting the possibility of either further increasing the data rate or reducing the size. Possible modifications to explore these options are discussed.

Acousto-optic (AO) cells have been used to implement Fourier plane filtering in coherent optical processing systems. AO cells have large time-bandwidth products (>1000) and high frame rates (>10 kHz). The optical input to the AO cell at the Fourier plane consists of several plane waves travelling at different angles. The Bragg matching condition limits the input field of view of the AO cell in the Fourier plane. However, the finite acoustic wave vector spread, optical birefringence, and acoustic beam steering have been used to overcome this limitation. In this paper the relation between the SBW product of an image that can be processed by the AO cell and its time-bandwidth product is derived and experimentally verified. The AO cell in the Fourier plane is suitable for image morphology, and it is shown that the time-bandwidth product requirement for this application is independent of the size of the structuring element, enabling a comparatively large space-bandwidth input to be processed.

Accurate, low-noise, wideband phased array radar antennas depend on the use of true time delays between microwave elements. A photonic means of generating the required element-to-element phase shifts was developed by Toughlian and Zmuda for systems operating in the VHF frequency range, and extended by Monsay and Caccuitto for operation in the radar C band. The photonic beamformer is based on a heterodyne optical system, in which the reference beam acts as a probe of the acoustic wave in the acousto-optic (AO) cell. It is apparent that the benefits of this photonic system rely greatly on the ability of the probe beam to pick out just the right phase shift/time delay from the acoustic waveform in the AO cell. A basic limitation to system performance could come from intrinsic diffraction effects due to the finite beamwidth of the probe in the AO cell. In addition, the finite size of the photodetector in the system will have an effect on the final SNR. These effects have been studied in detail and their implications for design and performance of the photonic beamformer are discussed. © 1997 Society of Photo-Optical Instrumen- tation Engineers. (S0091-3286(97)01312-3)

A photonic means of generating the element-to-element phase shifts required for the operation of a true time delay radar beamformer was developed previously by Toughlian and Zmuda for systems operating in the VHF frequency range, and extended by Monsay for operation in the radar C band. The photonic beamformer is based on an acousto-optic (AO), heterodyne optical system in which the reference beam acts as a probe of the acoustic wave in the AO cell. The time delay of the acoustic waveform readout by the optical probe from various locations along the length of the AO cell can then be imposed directly on the microwave elements of the radar beamformer, providing the correct phase for each element at whatever frequency drives the AO cell. Fundamental systems-oriented calculations are reported. Results for both optical specifications and radar performance specifications are obtained based on a mathematical model of the photonic delay line previously developed by the author. These results address the use of the photonic delay line in a standard radar beamformer.

A previously described holographic interconnection system uses an array of self-coherent but mutually incoherent sources to generate a set of overlapping holograms in a photorefractive crystal.1,2 In the current work, we assess the performance of this interconnection system experimentally. A linear array of self-coherent but mutually incoherent sources at visible wavelengths is generated by using an acousto-optic (AO) cell (TeO2) and custom analog electronics. Mutual incoherence is obtained by super-imposing a set of diffraction gratings (one for each source) at different frequencies in the AO cell, so that each diffraction grating yields a frequency shift in the corresponding diffracted beam. We present experimental results in Fe:LiNbO3 at 514.5 nm on the fidelity of the photorefractive interconnection in terms of diffraction efficiency, cross talk, and accuracy, as a function of both the number of multiplexed volume holograms and the degree of spatial overlap of the holograms. Some of these experimental results are compared with results obtained from simulation. The measured fidelity of this incoherent/coherent inter connection system is also compared to that of a fully coherent interconnection system.

We review the role of acousto-optic (AO) modulators in programmable real-time image processing. Using one AO cell, 1D high pass filtering and edge enhancement has recently been demonstrated. Two AO cells in tandem can be used to remove asymmetries for using one AO cell. We also show notch filtering characteristics of an AO cell by developing a technique to determine the spatial transfer functions numerically for various cases of beam incidence on an AO modulator. Normal incidence and incidence at twice the Bragg angle are investigated as examples.

Moire contours are seen on a curved surface viewed through a grating when the surface is illuminated with a matched grating. We have been able to replace both the projection and viewing physical gratings with gratings of variable spacing generated in acousto-optic (AO) cells and have been able to observe and record moire contours. The gratings are generated by amplitude modulating 70 MHz AO cells with a 1 to 10 MHz square wave. The gratings become visible on the curved object when the illuminating laser beam is strobed with 50 ns pulses by means of an AO modulator. We give data showing the variation in grating spacing with AO modulation frequency. Figures show the variation of the moire contour spacing with the AO modulation frequency and with target contour. The results for an angled flat plate target are compared with those in the literature.

Digital to Analog Converter (DAC) is the essential block to convert an input digital signal into analog signal. The switching technique is the important parameter that will affect the performance of DAC where to ensure the analog output signal can be obtained without any missing code. The capacitor DAC is most famous architecture used to design the DAC and it produce high power efficiency. But, the number of unit capacitors in DAC increase exponentially due to the increasing of resolution and a DAC block occupies a largest area among many internal blocks in Successive Approximation Register (SAR) Analog to Digital Converter (ADC). The DAC was designed for 14-bit SAr ADC using a hybrid Rc DAC architecture. The design of DAC has been carried out by using 0.18μm CMOS Silterra process Technology. The simulation results are done with 3.3V voltage supply and obtained DNL within -0.39 LSB to 0.238 LSB. It occupies an area of 0.614μm2.

Data acquisition and Signal Processing is an important part of frequency modulated continuous wave (FMCW) radar system. In recent year P2ET-LIPI was developing FMCW navigation radar system in portable size. The main component of data acquisition for navigation radar is highspeed Analog to Digital Conversion (ADC) USB-2020 board and signal processing algorithm has been developed using Visual C# 2015 Community Edition. USB-2020 board has two channel ADC on board with 12 bits resolution and operated in a burst-io mode to get maximum sampling rate at 20 MS/s. A timing generator for synchronization between ADC and linear frequency modulation (LFM) chirp generator is developed using Complex Programmable Logic Device (CPLD) Max II series based on VHSIC hardware description language (VHDL). Signal processing unit consists of windowing function to reduce side- lobe suppression, Fast Fourier Transform (FFT) function to get range information and adaptive threshold using three algorithms of Constant False Alarm Rate (CFAR): Cell Averaging (CA), Order Statistic (OS) and Variable Index (VI) CFAR. The experiment shows that the data acquisition module can capture In-phase and Quadrature (I/Q) beat signal and signal processing algorithm can detect object/target from the noise.

The readout of silicon strip sensors in the upgraded Tracker System of Large Hadron Collider beauty (LHCb) experiment will require a novel complex Application Specific Integrated Circuit (ASIC). The ASIC will extract and digitise analogue signal from the sensor and subsequently will perform digital processing and serial data transmission.One of the key processing blocks, placed in each channel, will be an Analogue to Digital Converter (ADC). A prototype of fast, low-power 6-bit Successive Approximation Register (SAR) ADC was designed, fabricated and tested. The measurements of ADC prototypes confirmed simulation results showing excellent overall performance. In particular, very good resolution with Effective Number Of Bits (ENOB) 5.85 was obtained together with very low power consumption of 0.35 mW at 40 MS/s sampling rate. The results of the performed static and dynamic measurements confirm excellent ADC operation for higher sampling rates up to 80 MS/s.

In this work, we present the computation of minimum noise required at the input of Analog to Digital Converter (ADC) in radar receiver to maintain the required statistics of noise in radar system. The work puts forward the analysis which computes the minimum noise required at the input of the ADC in radar receiver so that the noise introduced by the ADC is comparably negligible so as to maintain the required noise statistics in the receiver. This further ensures that the associated loss is minimal. The work quantitatively presents the gain reduction that can be achieved in the frontend of the receiver as we go for ADCs with higher number of bits. The paper presents detailed analysis of multiple test cases considering ADCs of different bits, the associated loss in Signal to Noise Ratio (SNR) computation and receiver gain variation as compared to a reference ADC.

The structure of the acoustic field defines the key parameters of acousto-optical (AO) devices. To confirm their compliance with the expected values in the presence of multiple real factors, AO crystalline cells require accurate experimental investigation of the acoustic field after being totally assembled. For this purpose, we propose to detect and quantify all the acoustic waves propagating in AO cells using an impulse acoustic microscopy technique. To validate this approach, we have analyzed both theoretically and experimentally the modes, amplitudes, propagation trajectories, and other features of the ultrasonic waves generated inside an AO modulator made of fused quartz. Good correspondence between theoretical and experimental data confirms the effectiveness of the proposed technique.

Data converters bridge the gap between the physical world of analog signals and the abstract world of mathematics and representational data. Digital-toanalog converters (DACs) convert a sequence of digital numbers into an analog signal, and analog-to-digital converters (ADCs) convert an analog signal into a sequence of digital numbers. In this book, the analog signals we will be discussing most will be derived from imagery collected through detecting elements. Data converters have been around longer than you might expect. Walt Kester of Analog Devices published the Analog-Digital Conversion Handbook online in 2004 and included a wonderfully extensive history of data conversion that extended back to the 18th century. Kester outlines an extremely early DAC developed in the early 18th century in the Ottoman Empire. This early data converter was an 8-bit binary-weighted hydraulic DAC used to control water distribution. Nozzle size was weighted for water flow in a binary fashion, allowing controllers to change the flow with 28 or 256 individual settings using only eight nozzles. In this case, the input is coming directly from human operators, and the output is water current, making this also the first documented current DAC with flowing water molecules instead of electrons. Analog-to-digital converters were developed much later. In a 1921 patent, Rainey disclosed what might be the first electro-mechanical ADC for his facsimile system. This converter utilized a light beam, photocells, a galvanometer, and 32 relays to reproduce data printed on a transparency into an "m-hot out of 32" digital word. This is a 5-bit thermometric output similar to a typical 5-bit flash ADC, which will be discussed in Chapter 4. It might be fascinating to image sensor professionals that this ADC utilized photonic components almost 100 years ago. In 1937, Reeves, at the International Telephone and Telegraph Corporation in Paris, is credited with the first all-electronic DAC and ADC design with his pulse code modulation patents. Electronic converters quickly became necessary components in every electronic component interfacing to real-world signals. Jumping forward a little more than 50 years to the late 1980s brings us to the beginning of the era of the low-cost, high-volume image sensor. Eric Fossum, the father of the modern CMOS active pixel sensor, published a very early report of image processing that included ADCs integrated on a focal plane array.2 In Smart CMOS Image Sensors and Applications, Jun Ohta suggests that it is possible that Eklund, Svensson, and Astrom published the first column-level ADC on an image-sensing chip in 1995. So began the revolution in digital imaging systems-on-chip, which has led to the prevalence of high-quality, low-cost image sensors in modern electronics.

With the change in advanced technology and the need for electronic equipments, the development of electronic instruments stimulate more efforts for more innovative ideas and better performance of design. In real world physical values, such as pressure, humidity, temperature and voice can be measured as analog (continuous) signals. However, to process these analog signals by electronic digital equipments, we need to convert these analog signals into digital or discreet signals or binary. In this paper, there are many types of Analog-to-Digital Converters (ADCs) which can be classified according to the applications and concept on which they were designed. ADCs including, Direct conversion ADC (Flash), successive approximation ADC, integrating ADC, Pipeline ADC. In some cases, many comparators are used to reduce the complexity, power and improve the linearity which are also explained in this paper.

Dithering improves the linearity of A/D converters (ADCs). Wagdy and Goff (1994) have developed a criterion for assessing the deviation of ADC transfer characteristics from the unity-gain line. This criterion is based on a closed-form formula for the deviation factor D derived from the characteristic function of the ADC quantization error function. This approach was extended further by Wagdy (1996) to include nonideal ADCs. The results in that work pertain to additive dither, but a closed-form formula for subtractive dither may be very difficult to derive. In this paper, the ADC is modeled and dither is simulated using a software random number generator. First, additive dithering with continuous (analog) uniform (rectangular) probability density function (RPDF) is considered. The cases of an ADC with no errors, single-bit error, or multi-bit errors are investigated. Results are in excellent agreement with the previous ones, which validates the formulae therein. Second, the author presents new results using discrete (digital) rectangular dither (DRPDF). This dither type is generated via a D/A converter (DAC) whose number of bits, k, is greater by del than the ADC number of bits, m. For various values of del, subtractively-dithered ADCs outperform additively-dithered ones as far as D is concerned. Also, the effect of increasing del on D for an ADC is investigated for the subtractive dither case, thus providing some quantitative results which are useful for the designer.