Image sensing in astigmatism applications requires ultra-low noise and high bit rate linear array image sensors for high sensitivity and high speed measurements. In order to reduce the dark noise of the detector and further improve the measurement sensitivity, a thermoelectric cooler (TEC) is required. To meet these requirements, high performance electronics are also needed to interface with the sensors. Sampling data from a sensor requires an amplifier with low noise and fast settling time and a low noise precision analog-to-digital converter (ADC). TEC requires precision current control and voltage limiting for precise temperature control. Power management electronics must be able to provide the high power required by the TEC and the low noise required by the sampling circuitry. Finally, a good PCB layout is critical to avoid the magnetic or conductive coupling interference of the switching signals of high power supplies to precision sampling electronics.

Designing a system with discrete electronics to interface with these complex, high-performance sensors has been a challenge in the past, requiring careful trade-offs in size, complexity, and performance. Hamamatsu Photonics, Inc. and Analog Devices consider this an opportunity to combine their expertise to create reference designs for the Hamamatsu G920x InGaAs linear image sensor family, with Hamamatsu providing sensors and system components, and Analog Devices designing analog front end (AFE) boards. This reference design allows for modular evaluation by connecting to the FPGA carrier card via the FMC connector. ADI's ¦ÌModule® regulators are used to provide a compact, optimized layout for the most challenging layouts in the design. For example, the LTM8053¦ÌModule buck regulator integrates magnetic components into the internal layout, greatly reducing electromagnetic noise. By providing a compact, optimized layout and reducing the number of components, these highly integrated products enable smaller solutions without compromising performance.

Figure 1. Image sensor reference design simplified block diagram

There are three key high-integration products that help achieve this compact, high-performance AFE design:

The ADAQ7980 is a single-chip, high performance, 16-bit, 1 MSPS SAR ADC data acquisition system module. The ADAQ7980 features a high precision SAR ADC with integrated ADC driver, reference buffer, LDO regulator, precision passive components and decoupling components.

The ADN8835 is a precision TEC controller that integrates a 3 A power FET tube. The ADN8835 accurately controls the temperature of the sensor without the need for an external discrete power FET tube.

The LTM8053 is an ultra low noise 3.5 A Silent Switcher® ¦ÌModule step-down switching regulator. The LTM8053 integrates the switching controller, power switch, inductor and all supporting components into one compact package for optimum noise performance.

These products demonstrate key features of ADI's highly integrated products, including reduced BOM complexity and reduced board space, optimized performance by eliminating board-level parasitics in critical circuits, and by providing more signal chains. Performance specifications for devices to reduce system errors and uncertainties. The complete AFE solution also includes other high-performance devices from Analog Devices, such as the ADR4550 precision reference and the ADA4807 high-speed precision amplifier. The AFE can also synchronize the clocks of the LTM8053 and ADN8835 with the sample clocks supplied to the sensor and the ADAQ7980.

Figure 2. Top view of the InGaAs array sensor interface board developed by Analog Devices

In summary, Analog Devices partnered with Hamamatsu Photonics, Inc. to develop a high-performance reference design for the Hamamatsu G920x linear array NIR/SWIR InGaAs image sensor family. These linear array InGaAs image sensors feature high sampling speeds and integrate TEC to dissipate the optical detectors for ultra-low noise operation. This makes it an excellent choice for high performance NIR/SWIR spectroscopy applications such as natural gas and mineral identification. ADI's AFE boards are designed to interface with these sensors, and ADI's highly integrated products enable high performance and compact size.

About the Author

Scott Hunt is a systems applications engineer in the Instrumentation Marketing Division of Analog Devices (Wilmington, MA) specializing in scientific instrumentation. In 2011, Scott joined Analog Devices as a product application engineer and was responsible for high-performance integrated precision amplifiers such as instrumentation amplifiers. He then moved to the Instrumentation Marketing Division in 2016. He holds a bachelor's degree in electrical and computer systems engineering from Rensselaer Polytechnic Institute. Scott received the ADI's 2015 Outstanding Technical Writing Award and the 2015 Outstanding Program Support Award.