I have developed a simple op-amp circuit that makes it easy to measure weighted noise levels or signal-to-noise ratios with my 12-bit and 16-bit PicoScopes. There are PC sound card measurement systems which make it possible to measure weighted noise directly, of course. But the circuit described here is quite versatile and should work with a variety of PC-based oscilloscopes, and I’ve found it also works well with a conventional analog scope.
The circuit consists of a 100X amplifier, A-weighting and C-weighting filters, and a special “hum” filter that I have found useful. It also has a 400-V DC-blocking capacitor and diode clamps at the input, which allow the circuit to be used to probe various locations in a circuit-under-test for noise, without risk to either the circuit or your scope. It has become one of my more frequently used pieces of homemade test equipment. I developed a PC board to make it easy to duplicate, and I thought some fellow DIYers might also find it useful. A white paper describing the circuit and an Eagle board file (*.brd) are available as free downloads from my website: (Downloads – Tavish Design).
I hope a few other DIYers build the circuit and find it useful. Let me know if there are any problems with the link or files.
Scott
The circuit consists of a 100X amplifier, A-weighting and C-weighting filters, and a special “hum” filter that I have found useful. It also has a 400-V DC-blocking capacitor and diode clamps at the input, which allow the circuit to be used to probe various locations in a circuit-under-test for noise, without risk to either the circuit or your scope. It has become one of my more frequently used pieces of homemade test equipment. I developed a PC board to make it easy to duplicate, and I thought some fellow DIYers might also find it useful. A white paper describing the circuit and an Eagle board file (*.brd) are available as free downloads from my website: (Downloads – Tavish Design).
I hope a few other DIYers build the circuit and find it useful. Let me know if there are any problems with the link or files.
Scott