Signal conditioning


Figure 5. A 21-bit DNL plot.


the LSB size of the AD5791. For example, for a 22-bit DAC, the output of four DACs shall be connected in parallel. From a performance perspective, the main concern is the noise, especially considering that for a 20 V voltage span, the LSB size is 4.77 µV. No measurements have been conducted at this level in this article. To evaluate this circuit, a dedicated board with four DACs mounted would be necessary.


RESULTS


Figure 4 shows the INL performance of the two AD5791 DACs connected to achieve 21-bit


INL accuracy. These results show an INL below ±1 LSB, which was the goal of this exercise. These results were obtained under controlled temperature conditions, with the entire setup enclosed in an EMF blocking enclosure. Figure 5 displays the DNL for the 21-bit configuration, demonstrating its mono- tonicity. The DNL results exhibit a discrete number of valid DNL codes. This is attributed to the limitations of the DVM used, considering that the LSB size of the 21-bit configuration is only 9.53 µV. These results were obtained using the 3458A DVM, an 8.5-digit voltmeter, and a standard


TABLE 1. OBTAINING A 21-BIT CODE EXAMPLE 21-Bit Code Even, for example: 0x10 Odd, for example: 0x11 Instrumentation Monthly March 2025 DAC A: 20-Bit Code 0x8 0x8 DAC B: 20-Bit Code 0x8 0x9


laboratory power supply. The voltage measurements were taken with a time window of 20 ms, corresponding to the 50 Hz frequency of the mains in Europe, where the measurements were carried out.


CONCLUSION


Combining two AD5791 20-bit DACs makes it possible to achieve a 21-bit DAC performance with 1 LSB INL. However, it is crucial to pay attention to the entire signal chain to minimise accuracy errors. Additionally, external factors such as temperature and electromagnetic interference can impact the output of the system. For further work, it is recommended to build this circuit on a PCB to enhance signal integrity and minimise external noise coupling. In addition to INL and DNL measurements, it is recommended to measure other parameters, such as noise figures to further extend the characterisation of the system. To facilitate this, the use of a new dedicated PCB is recommended.


Analog Devices www.analog.com


73


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84