Analog Automated Temperature Compensation Chip - Microbridge MBT-303-A Rejustor

Microbridge Technologies recently introduced new passive (analog) electronic Temperature Compensation (eTC) divider which called MBT-303-A rejustor (re-adjustable resistor). The new product enable automated compensation for temperature drift using only analog components. MBT-303-A rejustor is ideal for managing temperature in optical systems, precise analog circuits, sensors, and power supply compensation and calibration across a wide range of aerospace, military, automotive, medical, industrial, and consumer applications.

The MBT-303-A is a high accuracy dual 30K ohm divider (two resistors in series) where each resistor can be set to any value between 21K and 30K ohms 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.

Bob Frostholm, Marketing and Strategic Alliances at Microbridge, stated:

This is perhaps the most important improvement to the resistor in more than a century…

…Automated calibration and temperature compensation in the analog domain has not been possible until now. Analog 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 analog environment, yielding more accurate sensors, power-management devices, opto-electronics, and analog amplifiers.

Microbridge claimed, the eTC-based MBT-303-A, configured using Microbridge's Rejust-it software, is the first passive device to solve analog problems in the analog domain.  

About Microbridge’s Rejustor(TM)
Microbridge’s Rejustor (electronically readjustable resistor) is a passive, VLSI- and MEMS-compatible adjustable micro-resistor. It is non-volatile (i.e. doesn’t need any power to hold its adjustment), and it is re-adjustable many times, bi-directionally, to very high precision (e.g. 0.1% to 0.002%, depending on a variety of factors), using only electrical signals. Rejustors can also be Temperature Coefficient matched with other Rejustors, or can be used in-circuit to compensate for offsets and Temperature Coefficient variations in other analog circuit elements, again using only electrical signals. All adjustments can be carried out at low voltage and low current before and/or after packaging.

Microbridge’s Rejustor Technology
The Rejustor technique is based on the inherent instability of certain materials at high temperatures. In standard CMOS IC technologies, polycrystalline CVD-deposited silicon is one example of such a high temperature-mutable material. Instability at any temperature is typically seen as a disadvantage, but in this case it is used advantageously to allow high-precision trimming…
…For several decades, researchers and patent authors have reported that polysilicon (embedded in typical integrated circuits or in suspended microstructures), became thermally unstable at high temperatures. The prior art has shown that the resistance of polysilicon can be adjusted by passing current through it, or, in general, by heating it to high temperatures. It was also demonstrated that one could decrease resistance quickly, by using high-temperature pulses, and increase resistance more slowly by heating at temperatures lower than those required for resistance decrease…
…While many researchers have noticed high temperature instability, most of the prior art on intentional thermal adjustment of resistors has addressed simple integrated resistors which were not thermally-isolated on microstructures.

About eTC
Electronic Temperature Compensation (eTC) is the underlying technology behind the high accuracy of rejustors. eTC thermally isolates resistive films typically found in integrated circuits and, through the use of a highly localized and electrically-controlled heat source, adjusts the annealing of polysilicon crystal structures to deterministically control resistance. eTC can be utilized as a passive component such as a rejustor or implemented directly on an IC.

eTC-based MBT-303-A rejustor enables automated adjustment of both resistance and the Temperature Coefficient of Resistance (TCR). Control of TCR that is independent of ohmic value enables the MBT-303-A to provide one to two orders of magnitude performance improvement for analog designs. This independency also maintain consistency of resistance over an extended temperature range for circuits that require set-on-test calibration and compensation.

Variations in temperature can wreak havoc in even the most carefully designed analog systems since even small changes in temperature can alter performance and precision. Temperature compensation improves the precision of analog circuits in applications across the board, including increasing accuracy in catheters, adjusting power supplies, tuning LCD panel displays,  replacing digital potentiometers, calibrating sensors, etc.

Traditionally, engineers have had to compensate for changes in temperature using complex digital circuitry compromised of a microprocessor and D/A converters 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’s 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 analog circuits to the level of higher precision circuits.

MBT-303-A passive rejustor is available in a 16-lead QFN package or 8-pin SOIC package. It is  currently sampling. Price: US$1.67 each (1K unit qty).

More info: Microbridge’s MBT-303-A Rejustor: Analog Automated Electronic Temperature Compensation Chip