The AD8400/AD8402/AD8403 provide a single-， dual-， or quad-channel， 256-position， digitally controlled variable resistor （VR） device.1 These devices perform the same electronic adjustment function as a mechanical potentiometer or variable resistor. The AD8400 contains a single variable resistor in the compact SOIC-8 package. The AD8402 contains two independent variable resistors in space-saving SOIC-14 surface-mount packages. The AD8403 contains four independent variable resistors in 24-lead PDIP， SOIC， and TSSOP packages. Each part contains a fixed resistor with a wiper contact that taps the fixed resistor value at a point determined by the digital code loaded into the controlling serial input register. The resistance between the wiper and either endpoint of the fixed resistor varies linearly with respect to the digital code transferred into the VR latch. Each variable resistor offers a completely programmable value of resistance between the A terminal and the wiper or the B terminal and the wiper. The fixed A-to-B terminal resistance of 1 kΩ， 10 kΩ， 50 kΩ， or 100 kΩ has a ±1% channel-to-channel matching tolerance with a nominal temperature coefficient of 500 ppm/°C. A unique switching circuit minimizes the high glitch inherent in traditional switched resistor designs， avoiding any make-before-break or break-before-make operation.