DACs are normally switched current devices designed to drive the current-summing junction of an operational amplifier. Figure 8.2 shows a simple 4-bit DAC.

**Figure 8.2:** The current DAC uses the summing input to an
op-amp to yield a voltage output. LSB and MSB refer to the least and
most significant bits of a binary number.

Each current is proportional to the value of a bit position in a binary number.

The design requires a number of different precisely defined resistor values. We can improve the circuit by replacing it with a circuit that requires fewer distinct resistor values.

Tue Jul 13 16:55:15 EDT 1999