6 Summary

This document has shown how proper DC coupling frontends between FDAs and ADCs can be developed quickly and easily, as long as the noted pitfalls above are avoided. First, understand that an amplifier is required in order to DC couple. Baluns and transformers cannot be used in this type of application scenarios. Also keep in mind that an amplifier adds noise to the overall receiver signal chain, and therefore an AAF must be employed between the two devices to minimize the noise in the output spectrum. Check to make sure the amplifier of choice and ADC are DC compatible, and the common mode voltages are in the normal range of operation of both devices. This is paramount to make a DC coupled design successful. Using handy FDA DIFF Calculator spreadsheets and other tools available on the internet is a good place to start to make sure each device is within the compliance range of other devices. Lastly, use the 5-step process as a guide in which to develop a DC coupled frontend design, otherwise, the next receiver signal chain can clip early or not reach the ADC’s full-scale range at all, wreaking dynamic range havoc.