Isolation, of course, is just that same measurement in reverse. PSRR may be evaluated by injecting a signal from port 1 of a VNA into the regulator and observing the frequency response on the output as measured by port 2. Significant peaks or valleys in the output impedance are opportunities for noise development, and large peaks may indicate latent instability. The ideal output impedance of a power supply such as a switching regulator or a low drop out (LDO) regulator is “flat” from very low frequencies to the highest frequency which is present in the circuit.įor digital circuits, this highest frequency is approximately 0.35 divided by the typical rise-time of the digital signals. Each of these measurements are important to verify and optimize a design for best stability and noise performance. Possible power supply measurements include output impedance, output stability, power supply rejection ratio (PSRR), and reverse isolation.

It might be surprising to learn that this versatile tool may also be used to measure and optimize the power supply systems which drive digital, analog, or RF circuits. A vector network analyzer (VNA) is an essential measurement tool for RF design and is often used to characterize the performance properties of filters, amplifiers, antennas, and the like.

Vna network analyzer