8.1.2 Bipolar Operation Using the DAC7811

The DAC7811, as a 2-quadrant multiplying DAC, can be used to generate a unipolar output. The polarity of the full-scale output IOUT is the inverse of the input reference voltage at VREF.

Some applications require full 4-quadrant multiplying capabilities or bipolar output swing. As shown in Figure 29, external op amp U3 is added as a summing amp and has a gain of 2X that widens the output span to 5 V. A 4-quadrant multiplying circuit is implemented by using a 2.5-V offset of the reference voltage to bias U3. According to the circuit transfer equation given in Equation 2, input data (D) from code 0 to full-scale produces output voltages of VOUT = –2.5 V to VOUT = +2.5 V

Equation 2.

External resistance mismatching is the significant error in Figure 29.

Figure 29. Bipolar Output Circuit