Tag: Noise inspector

Measuring choke inductance

Recently, I built the “Noise Inspector” with the objective to help me measuring inductance and transformers. After working with it for a little while I realised that the proposed testing circuit wasn’t correct. The bias current of the inductor under test won’t allow the use of the noise inspector unless the loop back to the variable HT supply is done before the sensing resistor:
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Yet, there is a limitation with the above circuit. Unless we add an amplifier between the generator and the test circuit, the DUT will only see a couple of volts (rms) and measured inductance will be lower than the expected. Continue reading “Measuring choke inductance”

The Noise Inspector

Detecting those little creatures from the bottom

When recently measured the performance of my CCS designs, I found that I wasn’t able to measure below -114dBV (2uV) and therefore limited my ability to measure CCS impedance. I was also keen to measure inductors, transformers and other reactive components to derive 2 or 3 component models for more accurate simulations during the design process. A preamplifier was in order, so I looked at options with some of the ICs I had at hand. A very nice suggestion from Burr Brown/Texas Instruments is shown below. The INA106 is a precision 10x differential amplifier. Not a cheap device, but quality does comes with it unfortunately. When coupled with a pair of OPA37, a very accurate differential preamplifier can be built with extremely low noise and distortion:20140118-184418.jpg

Continue reading “The Noise Inspector”