Resistor divider circuits are used in many applications including setting the gain in amplifier circuits, sensors for commercial, mediacal and military markets and pulse squaring elements. This article focusses on amplifier circuits where precision matching of the resistor is required to avoid amplifier output errors and discusses the merits of using resistor network circuits in precision resistor divider circuits.

A resistor divider circuit (R1 and R2) is used in many amplifier circuits to set the reference voltage. As the amplifier gain is directly proportional to the reference voltage any errors in the reference cause errors in the gain. A mismatch in the performance of the resistors in the divider circuit must therefore be avoided.

Two key issues in resistor performance which can cause a mismatch are the resistor tolerance and heating effects. The tolerance and TCR of each resistor must be closely matched and heating effects on one resistor in relation to the other should be avoided. A difference in resistor tolerance effectively means an unplanned difference in resistor values and an amplifier gain error.

Matching of discrete resistors is expensive, time-consuming and totally impracticable for mass production as it involves selecting individual resistors. In most application some alternative method is required.One way to achieve accurate matching of resistance, TCR and to avoid rogue heating effects is to use a resistor network in which all the resistors are made using the same process. Thick film technology is a technology used in many resistor network designs. Resistors with similar aspect ratios may be constructed using common inks, track lengths and ink thicknesses to produce matched resistor elements.

The common substrate material, the close proximity of the resistors and the common manufacturing process means that resistors have similar tolerances and TCR performance and are not prone to heating effects on one resistor in relation to the other. The resistors may be trimmed if necessary for optimal resistance matching.

A further advantage of a thick film resistor network is space saving on board as the network minimises the area between resistor devices. Further space savings are achieved if the network is constructed as a single in line device. This construction is also easier to cool than conventionally mounted devices.

Resistor networks therefore offers a number of advantages over discrete, conventionally mounted, devices in precision amplifier applications. Various substrate materials are available but for many applications thick film technology is preferred due to the high packaging density, its mechanical properties and excellent thermal performance. Thick film technology also facilitates resistor trimming for optimal resistance matching.