Handheld Oscilloscope Measures Power Supply Ripple

This picture shows the transient voltage response to a step function as the stimulus to the device. Oscium’s handheld oscilloscope and iOS-based software simplifies the process for measuring this and other parameters of interest.

There are several parameters worth mentioning that are used to characterize the transient behavior of a power supply’s output or other type of waveform. Transients in power, current, and voltage are temporary conditions and not part of the characteristics associated with steady state behavior. These are some of the frequently referenced transients used to describe the short term behavior of the signal or waveform of interest.

  • Current: In-rush current is an example of a transient current measurement. As the capacitors in a circuit charge (following an RC time constant behavior) the current draw is at its highest at the start and then decreases until it reaches the nominal value for steady state operation.
  • Voltage: Voltage transients are used in making timing and switching measurements, and to quantify signal integrity for analog, power, logic and data/clock waveforms. The iMSO app that runs on iOS devices lets users put cursors at different points on the screen to measure the transients of the captured waveform.
  • Ripple: Amplitude and Frequency: Ripple is a voltage transient that can negatively impact the performance of some devices and its effects sometimes appear in the most unlikely places. For example, consider an amplifier that is powered from a +5 V supply with 50 mVpk-pk of ripple 10 kHz. The amplitude ripple, if it’s sufficiently large, will obviously affect the bias voltage of the amplifier, but it would be a straight forward problem to diagnose. However, effects of the ripple’s frequency component might be more subtle and difficult to identify. The amplifier might have stability problems stemming from the 10 kHz signal superimposed on its voltage supply.

Power Supply Rejection Ratio Impacts Circuit’s Performance

The attached Application Note from Texas Instruments discusses how too little power supply noise rejection will degrade the performance of critical components in the powered circuit. Some of the electrical components most sensitive to power supply noise (ripple: amplitude and frequency) are analog-to-digital converters and digital-to-analog converters, amplifiers, voltage references, voltage controlled oscillators, and many digital components used for embedded programming. This App Note briefly summarizes some frequently affected circuits and provides readers with helpful mitigation techniques.

PDF icon Power Supply Noise Performance - TI Article.pdf