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18-Bit, Linear, Low Noise, Precision Bipolar В±10 V DC Voltage Source (cn0177)
The circuit shown in Figure 1 provides a programmable 18-bit voltage with an output range −10 V to +10 V, ±0.5 LSB integral nonlinearity, ±0.5 LSB differential nonlinearity, and low noise.
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 circuit offers high precision, as well as low noise—this is ensured by the combination of the AD5781, ADR445 and AD8676 precision components.
The reference buffer is critical to the design because the input impedance at the DAC reference input is heavily code dependent and will lead to linearity errors if the DAC reference is not adequately buffered. With a high open-loop gain of 120 dB, the AD8676 has been proven and tested to meet the settling time, offset voltage, and low impedance drive capability required by this circuit application. The AD5781 is characterized and factory calibrated using the AD8676 dual op amp to buffer its voltage reference inputs, further enhancing confidence in partnering the components.
This combination of parts provides industry-leading 18-bit integral nonlinearity (INL) of ±0.5 LSB and differential nonlinearity (DNL) of ±0.5 LSB, with guaranteed monotonicity, as well as low power, small PCB area, and cost effectiveness.
Схемы и диаграммы
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