Syukri said:It's always imposibble even in higher bit.
but your speed will suffer...
resistor string is very output is very stable but at low speed.
The common string DAC is one of the oldest and simplest DAC circuit concepts. Resistor-string DAC implementations are inherently monotonic by design and are characterized by simplicity, small size (per resistor), and low power consumption.
But a major drawback is that 2N resistors are required to implement it directly—e.g., 16,384 for 14 bits. In order to reduce the number of resistors and die size, the AD5532 incorporates two 128-resistor strings (7 bits)—a main string DAC for the 7 more signifi cant bits, and a 7-bit sub string DAC. The basic architecture is shown in Figure 3 (US patent 5,969,657). The sub string DAC straddles up and down the main string, always in parallel with one of the main string resistors.