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Pulse Generator Source Impedance

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Member level 3
May 11, 2009
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I plan to use an Agilent 81111A Pulse Generator (with complementary outputs) to provide the control to my drive circuit for my SPDT switch. The SPDT switch can be found here:

Pulse Generator here: **broken link removed**

Does my source impedance have to be 50Ohm for my drive circuit to control the switch? The setting on the source impedance can be 50Ohm or 1kOhm. I know it's an RF switch and the RF ins and outs are 50Ohm. Not sure about the control.


The unit has a display that shows output voltage. That display is ONLY accurate if you put either a 50 ohm or 1K ohm load on it, and select the appropriate command. If you do not have that correct load impedance...the actual voltage delivered to the load will have an error on it. That is not really a just have to set the unit to a different output voltage. The key here is to not have a voltage on the control pin higher than the switch can handle, or you might blow it up. Like if you told the unit to expect a 50 ohm load, but had a high impedance load instead.

If you plan on high speed switching, I would put a 50 ohm resistor to ground right at the switch, connect the switch to the pulser with a coax cable, and select 50 ohm load impedance. You will have accurate voltages, and less of a pulse reflection.

Attached is a jpg of my control circuit that goes to the switch. It will do 0 & -5V output differential from2.5 ns rise and fall 0-5V or 0-2.5V from pulse generator.

What do you think? 50Ohm setting or 1kOhm setting?

Thanks for the reply.


  • high speed level xlator.JPG
    high speed level xlator.JPG
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