18-Bit, Linear, Low Noise, Precision Bipolar В±10 V DC Voltage Source (CN0200)
The circuit shown in Figure 1 is an 18-bit linear, low noise, precision bipolar (±10 V) voltage source with a minimum amount of external components. The AD5780 DAC is an 18-bit, unbuffered voltage output DAC operating from a bipolar supply of up to 33 V. The AD5780 accepts a positive reference input range of 5 V to VDD − 2.5 V, and a negative reference input range of VSS + 2.5 V to 0 V. Both reference inputs are buffered on the chip, and external buffers are not required. The AD5780 offers a relative accuracy specification of ±1 LSB maximum, and operation is guaranteed monotonic, with a ±1 LSB maximum DNL specification.
The AD8675 precision op amp has low offset voltage (75 μV maximum), low noise (2.8 nV/√Hz typical), and is an optimum output buffer for the AD5780. The AD5780 has two internal matched feedforward and feedback resistors, which are connected to the AD8675 op amp and provide the 10 V offset voltage. This allows an output voltage swing of ±10 V with a single external 10 V reference.
The digital input to the circuit is serial and is compatible with standard SPI, QSPI, MICROWIRE®, and DSP interface standards. For high accuracy applications, the compact circuit offers high precision, as well as low noise—this is ensured by the combination of the AD5780, ADR445, and AD8675 precision components.
This combination of parts provides industry-leading 18-bit integral nonlinearity (INL) of ±1 LSB and differential nonlinearity (DNL) of ±0.75 LSB, with guaranteed monotonicity, as well as low power, small PCB area, and cost effectiveness in an LFCSP package.
Figure 1. 18-Bit Accurate, ±10V Voltage Source (Simplified Schematic: All Connections and Decoupling Not Shown)
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