Resistors compensate for temperature drift

Having two rejustor elements in the same package makes it easier to implement divider networks where resistors must be equally matched.

Microbridge Technologies has released the MBT-303-A rejustor (re-adjustable resistor), the world's first passive electronic temperature compensation (eTC) divider, ideal for managing temperature in precise analogue circuits, optical systems, sensors, and power supply compensation and calibration across a wide range of military, aerospace, automotive, industrial, medical, and consumer applications.

The first in a family of resistor dividers and networks employing eTC technology, the MBT-303-A is a high accuracy dual 30kohm divider (two resistors in series) where each resistor can be set to any value between 21 and 30kohm with an accuracy of 0.01%.

Having two rejustor elements in the same package makes it easier to implement divider networks where resistors must be equally matched.

The MBT-303-A rejustor enables automated, independent adjustment of both resistance and the temperature coefficient of resistance (TCR), which determines how resistance changes as the temperature changes.

Control of TCR that is independent of ohmic value enables the MBT-303-A to not only provide one to two orders of magnitude performance improvement for analogue designs but also maintain consistency of resistance over an extended temperature range for circuits that require set-on-test calibration and compensation.

Until now it has not been possible to automate the adjustment process to compensate for temperature-induced drift using only analogue components.

The eTC-based MBT-303-A, configured using Microbridge's Rejust-it software, is the first passive device to solve analogue problems in the analogue domain using devices that are suitable for small-volume niche markets to mass produced commercial products.

"This is perhaps the most important improvement to the resistor in more than a century", said Bob Frostholm, Vice President, Marketing and Strategic Alliances at Microbridge.

"Automated calibration and temperature compensation in the analogue domain has not been possible until now".

"Analogue engineers have been forced to use inadequate solutions in the past because this technology wasn't available".

"Rejustors based on eTC technology provide better response to the analogue environment, yielding more accurate sensors, power-management devices, opto-electronics, and analogue amplifiers".

Variations in temperature can wreak havoc in even the most carefully designed analogue systems since even small changes in temperature can alter performance and precision.

Additionally, manufacturing variances in circuits require that compensation be adjusted for each individual circuit.

Temperature compensation improves the precision of analogue circuits in applications across the board, including increasing accuracy in catheters, tuning LCD panel displays, adjusting power supplies, calibrating sensors of all kinds, replacing digital potentiometers, and superseding less efficient compensation techniques such as fuses or laser trimming.

Rejustors shift compensation in temperature-sensitive applications from an active process to a passive one.

Traditionally, engineers have had to compensate for changes in temperature using complex digital circuitry compromised of a microprocessor and D/A convertors switching out fixed resistances.

This approach is limited in accuracy (about .1% for a compensation circuit employing 10 switches) and consumes a notable amount of power.

The additional circuitry involved also adds further uncertainties that reduce accuracy.

Rejustors eliminate many of the detrimental side-effects associated with digital compensation to achieve accurate and cost-effective temperature compensation.

In-circuit adjustability of both ohmic resistance and TCR, as well as support for positive and negative temperature coefficients, enables developers to apply compensation after devices such as sensors are fully manufactured and hermetically sealed.

Rejustors also eliminate the need for thin and thick film laser trimming currently used in IC manufacturing.

The MBT-303-A requires no power source during operation, does not suffer from wiper resistance, and no external temperature sensor is required since the rejustor is its own temperature sensor as well as adjustment controller.

Rejustors are capable of replacing complex digital potentiometers and can be used to raise the performance of lower cost analogue circuits to the level of higher precision circuits".

""Rejustors are ideal for precision analogue systems and will transform how the electronics industry compensates devices sensitive to temperature variations", said Richard Wawrzyniak, Sr.

market analyst, ASIC and SoC.

"Rejustors achieve true cost savings by reducing system complexity while increasing accuracy across the entire spectrum of electronic applications".

Available in a 16-lead QFN package or 8-pin SOIC package, the new MBT-303-A passive rejustor is currently sampling and costs US $1.67 each in quantities of 1000.

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