The AD713 is an excellent output amplifier for CMOS DACs.
It can be used to perform both 2 and 4 quadrant operation. The
output impedance of a DAC using an inverted R-2R ladder
approaches R for codes containing many “1”s, 3R for codes containing
a single “1” and infinity for codes containing all zeros.
For example, the output resistance of the AD7545 will modulate
between 11 kΩ and 33 kΩ. Therefore, with the DAC’s
internal feedback resistance of 11 kΩ, the noise gain will vary
from 2 to 4/3. This changing noise gain modulates the effect of
the input offset voltage of the amplifier, resulting in nonlinear
DAC amplifier performance. The AD713, with its guaranteed
1.5 mV input offset voltage, minimizes this effect achieving
12-bit performance.
Figures 16 and 17 show