Rob Reeder
Analog Devices

With the push into higher-frequency IF sampling, the analog inputs and overall front-end design of the A/D converter have become crucial elements of receiver design. Many applications are migrating to super-Nyquist sampling in order to eliminate a mix-down stage in the system design. Amplifiers pose a problem at these high frequencies, because high performance isn't as easy to achieve as in the Nyquist applications for which they are typically used. In addition, the amplifier's inherent noise will degrade the ADC's signal-to-noise ratio (SNR), no matter what input frequency is used. A transformer provides the designer with a relatively easy solution that resolves the noise issue, while providing a good coupling mechanism for high-frequency inputs.