Digital Attenuator

05 DO D1 0 D2 0 D3 0 D4 0 D5 0 D6 0 D7 0 Digitally controlled attenuators almost invariably use some kind of tapped re- sistor network to simulate a poten- tiometer. This solution is fine as long as the number of steps required is small. When finer control is required, how- ever, the normal tapped resistor net- work is hardly ever used because of the large number of components that would be required. The circuit shown here of- fers relatively high resolution (attenu- ation range: 48 dB) whilst requiring few components only. The technique used is similar to that of multiplying DACs (digital-to-analogue converters). In a conventional R-2R lad- der DAC, the output voltage is given by (Uref/384)N„ where N is the binary number applied to the inputs. The direct dependance of the output volt- age on Uref makes it easy to obtain a variable attenuator by substituting the input for Uref. The output will then be (U,./384)N. The R-2R ladder network used here is composed of resistors RI to R...