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Challenges in cloning ADC that hit end-of-life

Posted: 18 Jan 2013 ?? ?Print Version ?Bookmark and Share

Keywords:analogue-to-digital converter? Signal-to-Noise? Voltage Standing Wave Ratio?

Most importantly, the input impedance characteristics of the A/D had to be tweaked such that the Voltage Standing Wave Ratio (VSWR), a critical parameter in a communication system, matched the performance of the original design over a defined frequency range. VSWR gives an indication of the amount of signal reflection back to the input signal from the A/D converter or, in another words, it is the amount of return loss. As shown in figure 3, the VSWR ratio has to be actively trimmed and tweaked on every unit in order to meet the requirement.

The layout of the A/D required delicate routing of signals, ground traces, and distribution of the power supplies in order to mimic the performance of the old A/D. Extra substrate layers and conductor runs were used in the design to accommodate the pin-out assignment and to avoid any signal coupling that could deteriorate the accuracy of the converter. The power supply and ground planes along with bypass capacitor layout were critical in order to avoid any kickback and contamination of sensitive signal paths as well as analogue sections of the converter.

Figure 3: VSWR unit trim to achieve specification.

In its completion, the design was a form-and-fit solution that allowed our customer to drop the new component into the existing socket without change to the PCB or the system. This end user was able to keep the same documentation, test systems, and procedures C and simply add Datel as the qualified supplier of the A/D converter.

The new design showed an improvement in the overall accuracy of the radar system C a by-product of the cooperation between both of the companies' engineering teams. While an equivalent part was the only requirement, the Datel A/D product was a functional upgrade to the system. The two-tone modulation FFT test for a typical unit is shown in figure 4, where all the spurs created are less than -90dBFS. This experiment gave our customer a strong confidence in our engineering and process capabilities. Two years later, the same customer approached Datel to provide a pin-to-pin upgrade of the product at twice the sampling rate and with an improved Signal-to-Noise Ratio.

Figure 4: Two-tone intermodulation test.

Military applications tend to run for long periods of time, and therefore, a long-term supplier is required for this market. At Datel we have been a supplier for over 35 years to many military and medical programs, and understand the importance of keeping products alive and viable for a long period.

About the author
Tony Khazen is currently the Director of the DATEL, a Business Unit of Murata Power Solutions. Khazen has been employed by the company for 23 years. Khazen started as a Design Engineer at DATEL in 1988 and in 1992 he was appointed as the Data Acquisition Engineering Manager.

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