FAQ: How is voltage noise of an LDO measured?

Document created by KenM on Apr 20, 2011Last modified by AndyR on Jan 31, 2012
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How is voltage noise of a LDO measured?




LDO noise is measured two ways 1) Total RMS noise over a specified bandwidth, and 2) Noise spectral density at several frequencies over a specified range.  To measure the RMS noise, the noise of the LDO is amplified with a low noise preamp before being measured with a true RMS voltmeter.  The preamp bandwidth is 10Hz to100kHz, and is set by fourth order filters.  The preamp gain is 60dB with a noise floor of less than 1uVrms referred to the input. The noise spectral density measurements are made with a lock-in amplifier with a 1Hz bandwidth.  This is essentially a narrowband receiver that can be tuned over a wide range of frequencies.  The noise spectral density per root Hertz is measured with a voltmeter and a plot of the Noise Spectral Density vs Frequency is generated.