I have a Tektronix P6245 active probe (allows only DC input) and wish to use it to see noise on various power supply rails. I've done this already on a +3.3V rail, and can get sufficient DC offset on the scope (Tek TDS744a) to see millivolts.
However, it gets tricky with higher voltages (within the probe limits). For example, a +12V DC rail is tough. Bringing the vertical resolution to a level that will provide meaningful data is simply not possible.
I'm considering a dc blocking capacitor between the probe and the rail under test. Is this a reasonable option? Any suggestions for best way to do this?
Answer
Yes, go ahead and use a DC blocking cap. Active probes do have high input impedance, so peculiarities of capacitor actual R-L-C do not matter much. If you need more accuracy along the spectrum, you can always calibrate your tip.
I usually use the standard Tektronix tip (plug), shave the sharp edge flat (with Dremel), and solder a 0603 ceramic capacitor as a new tip. A 0.1uF 25V MLCC cap should give you a bandwidth from about 1.6Hz and up.
CAUTION: However, be aware that the single-ended probe must have good grounding, so be careful not to pick up noise on the ground lead over the air, or from improper grounding point. Instead of long lead, use a pogo-pin (spring-loaded) plug into ground receptacle of the P6245 probe, and have an open ground surface near your point of measurement. You will need to properly align both tips to make good connection.
No comments:
Post a Comment