I have tried to use the QS4A205 (a CMOS ANALOG FOUR-CHANNEL SPDT MUX) where 2 buffered DAC outputs are connected to the SPDT inputs and the output of the MUX is connected to a low current draw node (max 10mA). Unfortunately, I cannot seem to get this working and I believe that I am missing something in my schematics.

This image shows a description of what I have tried but did not get it to work. Can anyone please be kind as to suggestions on getting this to work? Also, do I need to have the transmission lines in and out of the MUX matched to a 50 ohm impedance?

I appreciate any help with this, thank you.

Here's a link to the datasheet QS4A205 Datasheet


EDIT: here is the initial schematic design, the less detailed schematic above was done on breadboard not as a pcb. Initial PCB schematic

  • \$\begingroup\$ Well, there's a lot missing from your schematic including the power pins and control pins. And even the pin names of the pins that are shown are missing (or at least, do not match those in the datasheet). \$\endgroup\$
    – DKNguyen
    Commented May 27, 2022 at 1:55
  • \$\begingroup\$ @DKNguyen my apologies, i've attached the full schematic. thanks. \$\endgroup\$
    – user49706
    Commented May 27, 2022 at 2:47
  • \$\begingroup\$ The datasheet says (top of page 3) that the analogue signal voltage range is from -0.5V to +4V, when used with a 5V supply. Are you complying with this condition? \$\endgroup\$ Commented May 27, 2022 at 8:38
  • \$\begingroup\$ @SimonFitch yes, i am. my application involves 0V - 3.3V. do you think it would be necessary to include series and parallel resistors to the input and output of the mux? \$\endgroup\$
    – user49706
    Commented May 27, 2022 at 13:55
  • \$\begingroup\$ @user49706 No, not necessarily, unless they are to scale the input voltage to be within those voltage constraints, or there's something else you're not saying. For instance, unless you tell people the source and purpose of your signals, and what frequencies you expect them to be, it's not possible to say whether you need to consider transmission lines or 50Ω termination. These considerations are almost certainly not the cause of your problems though. As to why it's not working with any signal, it's not clear to me. \$\endgroup\$ Commented May 27, 2022 at 14:26


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