Unlock High-Frequency Oscilloscope Signals with James Wilson’s 2GHz Active Probe

Unlock High-Frequency Oscilloscope Signals with James Wilson’s 2GHz Active Probe

James Wilson’s 2GHz active probe offers a breakthrough in open-source design, achieving a flat frequency response with easily accessible components. This probe is a valuable tool for electrical engineers seeking affordable, high-performance signal acquisition.

Oscilloscopes are essential for circuit debugging and characterization, but the quality of the signal fed into them is crucial. A creative technologist, Wilson has developed an open-source single-ended 2GHz active probe, providing a nearly flat frequency response using DIY-friendly components. This design stands out as a cost-effective alternative to the expensive, proprietary active probes on the market.

Passive probes are suitable for general-purpose use, offering bandwidths of a few hundred megahertz but with significant capacitive loading (10-15 picofarads). Active probes, on the other hand, provide higher bandwidth and lower capacitive loading but are typically costly and vendor-specific. Wilson’s 2GHz active probe design overcomes these limitations. It uses readily available components, such as a 3GHz JFET amplifier from Texas Instruments in a SOIC package, a four-layer PCB from OSH Park (non-impedance controlled), and passive components no smaller than 0402.

2GHz probe response
2GHz probe response

The probe achieves impressive specifications:

  • DC–2GHz analog bandwidth
  • 10:1 attenuation
  • input impedance of 1 MΩ // 1 pF
  • 50 Ω output impedance

The probe comprises three main blocks: an input network, a composite amplifier, and a power supply, each featuring unique design tricks. For instance, the input network includes a frequency compensation capacitor. Although a trimmer capacitor might seem ideal, its parasitics are problematic. Wilson experimented with a plate capacitor, trimming copper to achieve the desired effect, though this method is irreversible.

Wilson has refined the probe through three revisions, with the third achieving a flat response from DC to a -3 dB bandwidth of 2GHz. The probe’s 50-ohm SMA output and barrel jack power supply ensure compatibility with almost any oscilloscope or 50-ohm test tool, adding versatility to its application.

You can access the Altium design files and PCB Gerbers from this GitHub repository. Wilson also included simulation files from an open-source field solver called openEMS, which provided the simulations for the transmission line.

Check out the 2GHz active probe blog post for detailed explanations of the entire circuit.

Please follow and like us:
Pin Share
Notify of

Inline Feedbacks
View all comments
Get new posts by email:
Get new posts by email:

Join 97,426 other subscribers