Active Probe Reaches 3 GHz
When you think of a scope probe, you usually think of what is basically a wire with a spring hook and an attenuator. Those are passive probes. [Kerry Wong] shows off a pre-release active probe that sidesteps some problems with those ordinary passive probes.
The trick is that passive probes have input capacitance that interferes with very high-frequency signals. They also tend to have less noise. Although the probe isn’t on the market yet, it is set to debut at a price lower than competitive probes. Still, be warned. The reason you don’t see them more often is that $1,000 is relatively inexpensive for an active probe.
Because the probe is pretty hefty, it comes with a tripod that can hold it while you use it. [Kerry] connects some probe adapters to a PCB with two square wave oscillators. Square waves are a good test waveform because they have odd-numbered harmonics that rise well above the target frequency.
The probe adapters are a little longer than you might like, which causes some ringing on the input signal. However, if you compare the results to a standard passive probe, you’ll quickly see the value of the active probe setup.
You can save some money if you roll your own, of course. Most of the ones we’ve seen don’t quite make 3 GHz, though.
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