The circuit shown in Figure 1 provides a precision, 16-bit, ±2.5 V low-drift bipolar voltage output, operating from a single +10 V to +15 V supply. The unipolar voltage output of the AD5668 8-channel denseDAC is amplified and level shifted by the AD8638 auto-zero op amp. The maximum drift contribution of the AD8638 is only 0.06 ppm/°C. The external reference REF192 ensures a maximum drift of 5 ppm/°C (E-grade) and provides a low-impedance pseudo-ground voltage for the AD8638 level gain and conversion circuitry.

This circuit provides an efficient solution to a problem that often occurs in systems using a single +12 V supply rail. Proper printed circuit board (PCB) layout and grounding techniques ensure that the ADP2300 switching regulator does not degrade the circuit's overall performance.

The AD5668 is a 16-bit, 8-channel, voltage output dense DAC controlled through an SPI interface . It contains an on-chip voltage reference with a maximum drift of 10ppm/°C. On power-up, the on-chip voltage reference is turned off, allowing an external voltage reference to be used. The internal voltage reference is enabled via a software write. The external REF192 is used in the circuit shown in Figure 1 because a low output impedance is required to drive the 2.5 V pseudo-ground reference of the AD8638 op amp.

The output voltage of the AD5668 is 0V to 2.5V at TP1, and this signal drives the non-inverting input of the AD8638 op amp. The signal gain of the operational amplifier is 1+R2/R1, so it is equal to 2 when R1=R2. By driving R1 with a 2.5V reference voltage, a negative offset of 2.5V is injected into the op amp output. Therefore, the bipolar output voltage of TP2 swings from −2.5V to +2.5V.

The circuit is powered by a single power supply with a nominal voltage of 12V that can vary between 10V and 15V. The regulated −5 V supply rail is generated by connecting an ADP2300 switching regulator in an inverting buck-boost configuration. This circuit can be designed using the ADIsimPower program available at www.analog.com/ADIsimPower . The L1 coupled inductor is used to generate the unregulated 5V supply for the circuit in the Zeta configuration. This circuit is capable of producing high efficiency for smaller output currents.

Figures 2 and 3 show the integral nonlinearity (INL) and differential nonlinearity (DNL) measured at TP2 (bipolar output), respectively.

Figures 4 and 5 show INL and DNL, ​​respectively, measured at TP1 (unipolar DAC output).