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Design >> Analog Design >> Measuring Noise in Bandgap References
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Message started by vishalg007 on Aug 18^th, 2006, 11:14am

Title: Measuring Noise in Bandgap References
Post by vishalg007 on Aug 18^th, 2006, 11:14am

In a number of datasheets for voltage references, noise is quoted for 0.1Hz < f < 10Hz and 10Hz < f < 1KHz. How are these measurements made (especially those in the low frequency ranges)? Can a spectrum analyzer be used (the one I have is a 20Hz - 8GHz R&H Analyzer)?

Title: Re: Measuring Noise in Bandgap References
Post by loose-electron on Aug 18^th, 2006, 1:42pm

In addition to the spectrum analyszer, you generally need a couple of other things.

1. A low noise amplifier suitable for amplifying the DC voltage noise up to something measurable. (Frequently this is AC coupled)

2. A methodolgy where you can do the measurements and math to remove the additive noise of the LNA, spectrum analyzer and associated circuits. Also, if you need to revert to AC coupling, you need to be able to measure the spectral profile of the coupling and remove the high pass filter characteristics of that.

A good sanity check when you have all of this set up is to measure the noise of a resistor. You know what the theoretical of that should be, and it serves as a good test case to validate both the additive noise and spectral weighting of your test setup.

There are low frequency spectrum analyzers out there that go down to fractions of a hertz, they get used in control system work and other "near DC" applications.

Jerry