Simplifying Circuit Calibration With Electrically-Adjustable Resistors

In the field of analog electronics, the pain of achieving precision is the need for calibration. In general, electronic circuits, systems and solutions, both integrated and discrete, are prone to variations in parameter values of their components. These may be variations in the as-manufactured component values, or may be variations over time or temperature. In any case, these variations may degrade circuit performance, and/or reduce fabrication yield. As a result, analog electronics relies on a variety of circuit design, calibration and adjustment techniques, to overcome these variations, and achieve the required performance and precision. Typically, circuit calibration is done by adjusting ("trimming") a resistance element, and the industry relies heavily on a variety of such resistance trimming techniques. Manual trimpots, laser trimming, digital potentiometers, fusible arrays, and other programmable active devices, are each used in certain circumstances.

However, each of these techniques has one or more limitations. For example, they may have limited frequency range, may have limited precision, may not behave like a resistor unless separate power and ground are present, may be adjustable only once or only in one direction, or may be adjusted only during manufacturing before packaging using expensive equipment. Designers of analog and mixed-signal circuits, with even modest requirements for precision, must always consider how the circuit will be adjusted, and which limitation will be the least painful.

Microbridge's Rejustor(TM) (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.

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