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Sensor interface AFE simplifies sensor conditioning

Posted: 07 Sep 2015 ?? ?Print Version ?Bookmark and Share

Keywords:Sensors? analogue-to-digital converter? ADC? DAC? Sensor conditioning?

Sensors are employed in a variety of consumer and industrial markets from cell phones and tablets to precision detection, distance measurement, identification/image processing and process instrumentation applications. Many of these systems incorporate multiple analogue sensors to make devices more intelligent, efficient and productive. These sensors can be used to detect pressure, temperature, force, position, temperature, light, flow, sound, speed, heat, etc. The amount of sensors in just the major appliances in your home may surprise you.

Today's washing machines, for example, have sensors that detect motor current, drum speed, water level, water flow, water temperature, out of balance, door open/closed and some even employ touch sensor buttons for cycle control. High efficiency top load washers determine the water level for each load based on the weight of clothing in each load. Sensors and sensor interface technology enable the long list of efficiency and safety features in today's home appliances.

Analogue sensors produce an electrical signal that is usually very small, surrounded by noise. In many cases, no two sensors are alike, each sensor carries its own unique noise signature and introduces its own offset into the signal path. Calibrating the system, differentiating signal from noise and amplifying it are crucial to end system performance. Between the analogue sensor and digital signal processing lies an important electronic interface that conditions the electrical signal to ensure it lies within the range of the downstream ADC (analogue-to-digital converter).

Today's industrial systems utilise multiple sensors and sensor types, creating even larger demands on the sensor conditioning element. Systems with multiple sensors require various levels of calibration and amplification to adequately process the sensor signals and transfer them to the downstream ADC. The expanding use of sensors in our electronic devices and equipment has increased the need for more versatile, lower cost sensor interface solutions.

Sensor conditioning functions can be obtained with discrete solutions that use multiple components. In many cases, discrete sensor interface solutions give up variable gain or adjustable offset for each sensor input. Discrete solutions often draw higher power, require larger real estate and have longer design times than an integrated solution. Integrated sensor interface analogue front ends (AFEs) are available from many suppliers. Most include a processor that may be duplicated in the customer's end system and may include high level math and memory protection that is not required in most applications, adding cost.

The XR10910 sensor interface AFE from Exar offers a lower cost integrated solution that integrates high channel count and functionality in a tiny footprint that is lower power than competing devices. The XR10910's feature set is touted to provide more design flexibility than discrete or competing AFE solutions.

16:1 sensor interface AFE
The XR10910 sensor interface includes a 16:1 differential multiplexor, a programmable gain instrumentation amplifier, a 10bit offset correction DAC (digital-to-analogue converter) and an LDO (low dropout regulator). The functions and features of the XR10910 are controlled by an I2C interface and has the performance and feature set to complement today's microcontrollers (MCUs) or field-programmable gate arrays (FPGAs) with embedded ADCs. Figure 1 illustrates the block diagram of the XR10910.

Figure 1: Sensor interface block diagram.

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