Signal conditioning
HOW TO ACHIEVE ULTRAHIGH ACCURACY WHEN DESIGNING A 21-BIT PRECISION VOLTAGE SOURCE
By Justo Lapiedra, applications engineer, Analog Devices T 70
This article presents a circuit for achieving an ultrahigh accuracy voltage source. The circuit is obtained by combining two 20-bit DACs in parallel to obtain a 21-bit DAC with ±1 LSB accuracy or 0.5 ppm. The overall solution also requires precise operational amplifiers and voltage references that match the performance of the DAC. This article shows a complete problem-solving path when selecting components to achieve this accuracy. Thermal and electromagnetic interference are also considered since they can cause accuracy problems when dealing with a 21-bit DAC.
he state of the art in digital-to- analogue converters (DACs) available today has a 20-bit resolution as its maximum. This is a limiting factor for some applications requiring a higher level of accuracy such as medical imaging or mass spectrometry. This limitation can
be overcome by combining high performance components in a controlled environment. In other words, the accuracy of the overall solution will be determined by the signal chain of all the components in the circuit and their placement. The electronic circuit shown in this article shows how combining high performance components can preserve the individual accuracy toward achieving a high accuracy voltage source. This circuit uses the AD5791 together with the LTZ1000 and the AD8675/AD8676 to achieve a 1 LSB INL at 21 bits. Applications that can benefit from this level of accuracy include medical equipment capable of producing clear images of small anatomical structures. Also, this circuit can produce more accurate test and measurement equipment that can lead toward more accurate manufacturing products. The range of applications where this ultrahigh voltage source can be applied is extensive, and it can serve as a stepping stone toward developing new products that are currently limited by the accuracy of existing semiconductor products. Applications requiring 1 LSB at 21 bits, or 0.5 ppm INL, accuracy include:
SCIENTIFIC, MEDICAL, AND AEROSPACE INSTRUMENTATION
Medical imaging systems Laser beam positioners Vibration systems
Figure 1. The output connection of two ADC5791 DACs.
March 2025 Instrumentation Monthly
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