Users of Vector Network Analyzers (VNAs) often need to estimate and strive to optimize their instrument’s measurement speed. Many RF Engineers are interested in the tradeoffs between speed, accuracy and resolution in VNA measurements, especially those striving to achieve optimal automation of the instrument integrated in a larger measurement system or production environment. This application note details the determining factors for measurement cycle time in Copper Mountain Technologies VNAs. Generally speaking, the measurement cycle for any VNA consists of three major components: the per-point tuning and settling time of the generator, the per point measurement time, and a per-sweep time needed to process and transfer results, switch the generator between output ports, and return the generator to the start frequency. An additional, user-programmable delay between points is available in CMT instruments, which may be useful for integration with external equipment or DUTs with settling times of their own. As will be seen, some of the delay components are effectively fixed, while others depend upon the measurement parameters and thus may be optimized by the user.

Power integrity measurements are essential in all modern electronics, including RF and Microwave circuits. Poor power integrity results in spurs and degraded phase noise. As is the case with RF and high speed signals the goal is a flat, frequency independent impedance. Unlike RF and high speed signals, the magnitude of the impedance is not defined, and must be determined based on the circuit noise tolerance. The power distribution network (PDN) measurement includes the voltage regulator, printed circuit board planes and decoupling capacitors. Measuring capacitors, ferrite beads and the PDN impedance can be a challenge, including very low impedance magnitudes large dynamic range and a wide frequency range. For example, the impedance of a 10 nF capacitor at 20 kHz is approximately 800 Ω while at its series resonant frequency it is on the order of 10 mΩ. Similarly, a ferrite bead might be 10 mΩ at 20 kHz and more than 500 Ω at resonance occurring as high as 100 MHz or more.

High input power requirements of some Devices Under Test (DUTs) introduce challenges to the measurement therefore. Various measurement techniques such as load-pull analysis and noise figure measurement may also require a higher input power to the DUT than the maximum output power of the VNA.