A Practical Guide to Isolation Amplifier Selection

Whether distributing a house standard, adding a distribution module in a larger circuit design, or just working with a measurement system on the bench, one must be aware of how a number of distribution amplifier parameters can make or break an entire system's performance. This paper looks at a high performance quartz oscillator, a hydrogen maser, and a rubidium fountain's performance both in the short-term and long-term to develop a model of the signals that one may want to measure or distribute. Two different classes of distribution amplifiers are then reviewed to see how they compare to the sources presented earlier. The front-to-back isolation and phase noise of a distribution amplifier are not the only important parameters that need to be considered. Other important terms such as the return loss, stability over temperature, port-to-port isolation, differential delay over temperature, construction techniques, and design practices must be taken into account. Most of these parameters can be rigorously related in an equation to deliver an expected level of performance from the system. Typical manufacturing and design practices that are necessary to ensure a reliable device are presented. The goal of the paper being to better equip the reader with the skills to evaluate distribution amplifiers to find the one that best fits the needs and expectations in both reliability and overall system performance.