Two 8-bit dacs make a 12-bit dac

Description: Two MC1408 8-bit D/A converters, designated A and B in the circuit diagram, are utilized. The four least significant bits of A are grounded. The four most significant bits of a 12-bit data input are connected to the remaining four input pins of A. The eight least significant bits of the 12-bit data are connected to the eight input pins of B. The four most significant bits of the 12-bit data carry a weight of 16 compared to the remaining eight bits. Therefore, the output from B is scaled down by a factor of 16 and combined with the output from A using a summing operational amplifier configuration, labeled D. A voltage regulator chip, LM7236, is employed to deliver a precise reference voltage of 2 V for the MC1408.

The full-scale voltage of the converter is calculated as V_full-scale = 9.9609 + 1(9.375), resulting in a maximum output of 9.9976 V. The converter exhibits a step size of 2.4 mV, indicating the smallest change in output voltage corresponding to a one-bit change in the digital input.

In this circuit, the two MC1408 D/A converters work in tandem to achieve a higher resolution output. By grounding the least significant bits of converter A, the design focuses on utilizing the more significant bits of the data input for critical output precision. The operational amplifier configuration plays a crucial role in summing the outputs from both converters, with the output from converter B being attenuated by a factor of 16. This attenuation is essential for ensuring that the contributions from both converters are balanced, thereby providing a smooth and accurate analog output.

The LM7236 voltage regulator is integral to the circuit, as it establishes a stable reference voltage of 2 V, which is vital for the accurate operation of the D/A converters. The reference voltage ensures that the converters operate within their specified range, allowing for precise digital-to-analog conversion. The calculated full-scale voltage and step size of the converter further emphasize the design's capability to produce a finely tuned output, suitable for applications requiring high precision and stability in analog signal generation.Two MC1408—8-bit D/A converters, A and in the circuit diagram, are used. The four least-significant bits of A are tied to zero. The four most significant bits of the 12-bit data are connected to the remaining four input pins. The eight least significant bits of the 12-bit data are connected to the eight input pins of B. The four most significant bits of the 12-bit data together have a weight of 16 relative to the remaining eight bits. Hence, the output from is reduced by a factor of 16 and summed with the output from A using the summing op-amp configuration D.

Voltage regulator chip, LM7236, is used to provide an accurate reference voltage, 2 V, for the MC1408. The full-scale voltage of the converter is Vie 9.9609 + 1 (9.375) or 9.9976 V. The step size of the converter is 2.4 mV.