Pulse Generator Source Impedance

Discussion in 'General Electronics Chat' started by Management, May 1, 2011.

  1. Management

    Thread Starter Active Member

    Sep 18, 2007
    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: http://www.metrictest.com/catalog/pdfs/product_pdfs/hp_81100.pdf

    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.

  2. ifixit

    Distinguished Member

    Nov 20, 2008
    Hi Management,

    Yes. Set for 50Ω to ensure you can drive the transmission line properly. Also, terminate the control input with a 50Ω resistor close to the control input (Vc).

    The spec says the TSG2603 control input uses 2.25mA max at -7V so that implies about 3KΩ input impedance. This allows the user to terminate with whatever impedance they like, 50, 75, 100, or whatever. If you are switching at very low frequencies then you don't need to worry about terminating at all.

    What is your switching frequency going to be?

    The RF path through the switch does not have a specific impedance specified in order to be usable for various impedance. e.g. 50Ω or 75Ω. Use 50Ω if possible, as triquint provides S-parm data for that impedance. It would be a good idea to mount the switch in the signal path such that reflections from opened transmission lines don't cause a problem in other parts of the circuit.