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OPA2683 as a MUX

Moshe Avigdor89344
Prodigy 120 points
Other Parts Discussed in Thread: OPA2683, OPA683, OPA4872

Hello,

Please advice about using the 2 * OPA2683 as a switch (gain1 and gain 10 with the same source)

1. Do we have to add resistors 78ohm at the opamp output (Please look at fig 12 page 17 in data sheet)  we think to use 10 ohm.

 Vcc=+-5v

Gain is +1 and +10

Signal input AC couple.

Best regards

Moshe

 

 

  • 0
    TI__Expert 4950 points

    Moshe,

    6813.OPA683 MUX.TSC

    See attached schematic.  I worked 2 different options.

     With the OPA2683 as a MUX, you will need to adjust the output series resistor so that at any given time Rs || (Rs + Rf + Rg) = Rload.  To compensate for the gain loss in the passive network the gain will have to be increased.

    An alternative approach is to use a single OPA683, followed by a MUX such as the OPA4872.  The MUX will do the switching and will bypass the gain and output impedance adjustment.

     This second approach is better if you are trying to transmit any kind of power into the load.  10ohm may load the driving side too much and may be on the low side if both amplifier were turned on simultaneously.  Also, you would not be driving a matched load and would lose the benefit of the transmission line.

     Note that I adjusted the feedback resistor of the OPA683 to match the datasheet recommendations.

     

  • 0 in reply to Xavier Ramus
    Prodigy 120 points

    Thanks Xavier,

    Did send you the simulation.

    BR

    Moshe