Monitor the CMOS level with 50 Ohm oscillograph

Status
Not open for further replies.
C

chang830

Full Member level 5
Joined
Feb 11, 2006
Messages
267
Helped
14
Reputation
28
Reaction score
3
Trophy points
1,298
Activity points
3,424
Hi,
My circuit oupts the TTL/CMOS level, but my oscillograph only have 50 Ohm interface. How can I use this oscillograph to monitor the CMOS output? Adding a series high resistor can work?

Thanks
 

Adding a higher value series resitor will further lower the signal amplitude due to the voltage divider action, and the mismatch may cause ringing on the monitored signal. I think you be better off using a series 50 ohm resistor, just keep in mind that the signal level will be half of the regular TLL/CMOS levels.
 

    C

    chang830

    Points: 2
    Helpful Answer Positive Rating
If carefully constructed, a series resistor into 50 ohms makes an excellent wide-bandwidth low-capacitance probe - much better than typical 10X 10-megohm passive probes. However, the resistance probe will load your circuit somewhat, but that's usually not too important when probing RF and high-speed logic. You must decide if the load will affect your project. Also, it is an attenuator, so you need an oscilloscope with sufficient gain.

I have two multi-GHz Tektronix probes that contain little more than a series resistor. One is a 10X probe using a 450 ohm resistor, the other is a 100X probe using a 4950 ohm resistor.

You can build good resistance probes yourself. Here is one way to do it:
https://www.emcesd.com/1ghzprob.htm
 

    C

    chang830

    Points: 2
    Helpful Answer Positive Rating
Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…