Analog Angle Article

Configurable analog front ends bridge NDIR gas, pH-sensing transducers and MCUs

Though not as glamorous or attention-getting as the various sensors now packed into consumer products such as smart phones or tablets, the instrumentation world is where you'll find amazing diversity in real-world phenomena to be sensed—and the specialized transducers which make that possible.

And that's the problem : many of the parameters to be senses are simple to describe, but hard to actually catch: think temperature, for example, which is so “basic” yet requires so many very different types of sensors which, in turn, are available in thousands of specific sensor styles, designs, and constructs. 

The LMP91050 for nondispersive infrared gas sensing

and the LMP91200 for pH sensing, both from Texas Instruments,

provide highly integrated analog front-end interfaces

between these specialized sensors and a system processor.

Two analog front end (AFE) ICs from Texas Instruments strive to greatly simplify the path between a sensor and associated processor:

The LMP91050 AFE for nondispersive infrared (NDIR) gas sensing supports multiple thermopile sensors for NDIR sensing, indoor CO2 monitoring, demand control ventilation, HVAC, alcohol breath analysis, greenhouse gas monitoring and Freon detection. It integrates a programmable gain amplifier (PGA), “dark phase” offset-cancellation circuitry, adjustable common-mode generator, and SPI interface to simplify system design. The internal programmable gain amplifier (PGA) has low-gain and high-gain ranges, so the device can be used with thermopiles having different sensitivities.

Critical “close-in” specifications include gain drift of just 100 ppm/° C (maximum), output offset drift of 1.2 mV/° C, phase-delay variation of 500 ns, low noise of 0.1 µV rms (0.1 to 10 Hz), and operation between -40° C to 105° C.

The LMP91050 gas-sensing AFE is available in a 10-lead, 3 mm × 4.9 mm MSOP package, priced at $1.32 in 1,000-unit quantities, and is available in volume today.

The LMP91200 AFE for pH-sensing supports two-electrode pH sensors, often used in analyzer platforms for emissions monitoring, steam and water quality monitoring, chemical/petrochemical plants, and food processing. It integrates a PGA, ultra-low input-bias pH buffer, signal guarding, temperature and measurement calibration, and common-mode generation and diagnostics circuitry.

The IC operates from 1.8 V to 5.5 V and -40° C to 125° C, with a guaranteed low pH-buffer input-bias current across the operating range. It is housed in a 16-lead 5 mm × 6.4 mm TSSOP package, priced at $3.90 in 1,000-unit quantities, with immediate volume availability.

Support and additional information : Both the LMP91050 and LMP91200 AFEs work with TI’s WEBENCH® Sensor AFE Designer software and bench-top development system. These tools allow engineers to select a sensor, design and configure the solution, and download configuration data to the sensor AFE for immediate prototyping.

For more information and to order samples, visit

0 comments on “Configurable analog front ends bridge NDIR gas, pH-sensing transducers and MCUs

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.