I use an 7 GS/s ADC to acquire data with an frequency of 2 GHz. The input range of the device is between -0.35 and 0.35 volts. My signal is also between this range, but sometimes there is a short burst over 0.35 volts. So I have to protect the input of the ADC for signals with a higher level than 3.5 volts.

I don't think that it is a good idea to build my own small circuit with a diode protection circuit by signals with 2GHz.

How can I limit higher voltage? I tried to search for HF-Limiter, but most of the had an static attenuation.

I was searching on this site: http://www.minicircuits.com/

  • \$\begingroup\$ Diode protection is fine if you have the correct low-capacitance transient suppression diodes. \$\endgroup\$
    – pjc50
    Commented Oct 2, 2014 at 9:25
  • 1
    \$\begingroup\$ Add a link to the ADC. The linear input range MIGHT not be the maximum safe input range. If the latter is greater, you can use that fact to simplify the protection. \$\endgroup\$
    – user16324
    Commented Oct 2, 2014 at 12:36
  • \$\begingroup\$ spdevices.com/… \$\endgroup\$
    – REMberry
    Commented Oct 2, 2014 at 12:48
  • \$\begingroup\$ What are you using to drive the ADC? Depending on the drive strength and output impedance you may have margin for some low-parasitic diodes. Also, do you have noise margin? If you have enough you may be able to get away with a voltage-limiting amplifier \$\endgroup\$
    – Daniel V
    Commented Sep 6, 2016 at 16:35
  • 1
    \$\begingroup\$ I found a HF-Limiter wich has best specifications for my purpose. \$\endgroup\$
    – REMberry
    Commented Sep 7, 2016 at 19:07

1 Answer 1


Consider common mode and differential mode impedances. (Zcm, Zdm)

Consider EM coupling impedances from stray sources, which depends on layout geometry.

Determine the spectrum of the burst with Spectrum Analyzer or DSO with suitable method such as in situ stripline proper impedance matched -10dB directional couplers.

In order to improve CMRR of an unbalanced line, you need a differential input or a BALUN rated over those frequencies. A Balun raises Zcm while maintaining Zdm to improve CMRR of stray noise. This can be a hybrid Txfm or a ferrite bead with both sig+gnd passed thru.with n turns using AWG 30-36 magnet wire similar to a 3dB splitter materials.

See if this helps you prevent the burst and verify it.

I trust you are using semi-rigid copper cable thruout, with high quality connectors.


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