A linear image sensor capable of high-speed measurement and high sensitivity should be designed like this!

Sampling data from the sensor requires an amplifier with low noise and fast settling time and a low noise precision analog-to-digital converter (ADC). The TEC requires precision current control and voltage limiting to accurately control the temperature. The power management electronics must be able to provide the high power required by the TEC and the low noise required by the sampling circuit. Finally, good PCB layout is critical to avoid magnetic or conductive coupling interference from the switching signals of the high power supply to the precision sampling electronics.

Designing a system to interface with these complex, high-performance sensors using discrete electronics has historically been a challenge, requiring careful tradeoffs between size, complexity, and performance. Hamamatsu Photonics, Inc. and Analog Devices saw this as an opportunity and combined their expertise to create a reference design for the Hamamatsu G920x InGaAs linear image sensor family, with Hamamatsu providing the sensor and system components and Analog Devices designing the analog front end (AFE) board.

This reference design allows modular evaluation by connecting to an FPGA carrier card via an FMC connector. ADI's μModule regulators are used to provide compact, optimized layouts for the most challenging layout parts of the design. For example, the LTM8053 μModule 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 also enable smaller solutions without compromising performance.

Figure 1. Simplified block diagram of the image sensor reference design.

There are three key highly integrated products that enable 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 uses a high-precision SAR ADC and integrates an ADC driver, reference voltage buffer, LDO regulator, precision passive components, and decoupling components.

• The ADN8835 is a precision TEC controller with an integrated 3A power FET. The ADN8835 can accurately control the temperature of the sensor without the need for an external discrete power FET.

• The LTM8053 is an ultralow noise 3.5A Silent Switcher® μModule step-down switching regulator. The LTM8053 integrates the switching controller, power switches, inductor and all supporting components into a compact package for optimal noise performance.

These products demonstrate the key features of ADI's highly integrated products, including reducing BOM complexity and board space, optimizing performance by eliminating board-level parasitics in critical circuits, and reducing system errors and uncertainties by providing devices with performance specifications that integrate more signal chains. The complete AFE solution also includes other high-performance devices from ADI, such as the ADR4550 precision voltage reference and the ADA4807 high-speed precision amplifier. The AFE can also synchronize the clocks of the LTM8053 and ADN8835 with the sampling clocks provided to the sensors and ADAQ7980.

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

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