52 Analog Operation in the Voltage Switching Mode

Some useful application circuits result if the R-2R ladder is

operated in the voltage switching mode There are two very

important things to remember when using the DAC in the

positive since there are parasitic diodes to ground on the

negative To maintain a degradation of linearity less than

g

Figures 6 and 7 show these errors for the

voltage switching mode This operation appears unusual

shown in

Figure 8

gain stage as shown in

Figure 9

Notice that this is unipolar operation since all voltages are

positive A bipolar output voltage can be obtained by using a

single op amp as shown in

Figure 10 For a digital input

zero volts The external op amp now has a single input of

a

input of all zeros As the digital code increases the output

Notice that the gain of the op amp to voltages which are

voltage of the op amp depends on both of these inputs and

is given by

FIGURE 6

FIGURE 7

DIGITAL INPUT CODE

FIGURE 8 Voltage Mode Switching

TLH5688 – 12

FIGURE 9 Amplifying the Voltage Mode Output (Single Supply Operation)

10