TABLE OF CONTENTS Potentiometers are one of the last bastions of electro-mechanical components in the face of the avalanche of digital silicon. They are bulky, unpredictable and unreliable, and can be a problem in fast circuitry; parasitic effects abound, and you can really only use them where the signal frequency times the circuit resistance is less than 10 6 Hz-. They add time and money at the test and calibration stage of the production cycle. Many of their functions can be taken over by microprocessor-controlled digital equivalents. For instance, a classical use for the standard trimpot is to null out that bugbear of analogue amplifiers, the offset voltage. In the days when op-amps had offsets measured in tens of millivolts, this was a very necessary function. But op-amps are now available at reasonable prices with offsets below half a millivolt, and if this is not enough it is often feasible to use a chopper stabilised device whose effective offset is limited only by thermal effects to a few microvolts. Alternatively, the intelligence of a microprocessor can be used to dynamically calibrate out the offset of a cheap op-amp by frequently auto zeroing the entire A-D subsystem. Equally, the gain of a network can be trimmed using a resistive D-A converter rather than a trimpot.
Nevertheless, there will remain applications where a pot is overall the best solution to a given circuit problem: digital implementations have been eschewed for other reasons, or the inherent linearity and lack of...
