USB isolator breaks galvanic connection between USB host and peripheral. Among other things, this means whatever power and ground noise that exists on one side won?t affect the other. In many cases, the source of noise is PC power supply, however I heard about noisy peripherals too. One of my customers has stage lights controller connected to his laptop adding interference to music playing from laptop?s audio port ? the issue was remedied with USB isolator.
In many cases, isolating peripheral from PC ground reduces noise to undetectable levels. However, for very sensitive equipment, such as USB oscilloscopes, extra steps must me taken to ensure signal integrity. Photo on the left shows 1KHz analog calibrator waveforms displayed on Bitscope 310 USB DSO. Signal amplitude from top to bottom changes from 4V to 400mV to 40mV to 4mV p-p. Left column shows waveform with USB port of the instrument isolated, right column waveforms were obtained with instrument directly connected to the same USB port of the same PC. The results can be easily interpreted ? while 4V signal looks pretty much the same on both pictures, smaller signals show more and more noise and 4mV signal on directly connected Bitscope is hard to interpret, let alone measure.
Photo on the right shows the arrangement. In order to reduce interference to the minimum, isolator is powered from oscilloscope?s 5V regulated power supply. Also, the peripheral cable is kept as short as possible. I recommend using similar arrangement for high-end audio applications ? to obtain best results, don?t use isolator?s own power supply, use power supply of the peripheral, a battery or super clean power source made for audio.
Comment