When selecting RMS-to-DC converters for applications, key specifications and their test conditions must be considered. Wide dynamic range, quick settling time, and tight accuracy ratings are all key parameters to look for in converters. When looking at power ratings, however, there is a trade off that needs to be considered; low power parts are good for portable applications and longer battery life, but higher power parts can achieve higher bandwidth and accuracy ratings in systems not as concerned about energy usage. Besides these key specifications, auxiliary options can offer advantages to the designer. For example, the AD637 has a log output (dB) feature which will ease the design of audio meters. Some RMS-to-DC converters, such as the AD737, have a high input impedance option, enabling error free interface to non-zero source impedances.