Oscilloscopes often are used to measure power supply, linear regulator, and reference noise. Since an oscilloscope has a sensitivity in the range of 2 mV per division, a substantial voltage gain must be added to see the ripple and noise, which is often in microvolts. This gain is usually accomplished using a “low-noise” operational amplifier or several cascaded low-noise op amps. An active filter follows the op amps, providing high pass and low pass elements, to meet the desired measurement bandwidth with the entire circuit constructed in a Faraday shield. (A paint can serves this purpose.) Several IC manufacturers have application notes describing the measurement.
top of page
bottom of page