Measuring High Impedance Sources Using Audio Analyzers
应用文章
This note details the input impedance of the U8903B Audio Analyzer, and shows that this needs to be understood and carefully considered when measuring high impedance sources. A method of using an impedance matching attenuator to overcome high impedance measurement problems is described and a simple accessory is demonstrated which uses the U8903-109 BNC accessory kit. Methods for aligning such a matching attenuator and compensating for its loss are shown alongside the ease with which frequency response measurements can be made on the U8903B.
Input Impedance
Audio Analyzers such as U8903B invariably have an unbalanced input resistance of 100 kΩ. This is relatively high by most standards but compared to an Oscilloscope or DMM is it actually quite low. Users therefore need to be aware of potential divider effects when measuring sources with output impedance of more than some 10’s of ohms.