Using ADG707 diffpair channels for single ended signals

Hi

I'm gonna use all of ADG707 multiplexers' channels for single-ended signals, can I do that? I mean I want to use ADG707 as a dual single-ended 8:1 multiplexer.

If it is not permitted please say how we can use this part as single ended part? what do you think if I use 8 A channels (S1A to S8A) for 8 single-ended analog signals and terminating 8 B channels (S1B to S8B) with for example 50 ohm to ground.

Thanks,

  • 0
    •  Analog Employees 
    on Apr 20, 2021 9:56 AM

    Hi Dave,

    The ADG707 is a Differential 8 to 1 Multiplexer.

    If you terminate the 8B channels(S1B to S8B), then the ADG707 will be configured as a differential 4-to-1 multiplexer. Therefore you will have 8 input channels to one output, but if you look at the truth table below: (ADG707 pg 6).

     

    When ON switch pair 1 is enabled S1A & S2A channels are turned ON.

    The same for switch pair 2, S3A & S4A etc. 

    Therefore it is not possible to enable a single channel, instead a dual channel will be enabled.

    If you want to use an ADG7xx series precision single 8 to 1 multiplexer , I would recommend using the ADG708.

    Please let me know if you need any more information.

    Regards,

    Kevin

  • Thank you for your attention but I don't think so, I think probably your answer is not correct, here is block diagram of ADG707!

    page 1, ADG707 datasheet

    it means relate to its true table when S1A is enable, S1B is enable too, indeed from these picture I think when ON switch pair 1 is enabled S1A & S1B channels are turned ON to have a diff pair signals on output as DA and DB each time! so if I feed S1A to S8A channels with some single-ended signals and terminated 8B channels(S1B to S8B), indeed for example when ON switch pair 1 is enabled, S1A(single-ended signal) and S1B(ground so nothing) channels are turned on

    yeah I know some good parts of these series but I've bought ADG707 and I would prefer to use this part for single-ended purpose, I would really appreciated if you inform me that exactly it is possible or not and if it is not possible let me know why and what problem will occur

    another scenario is that I feed S1A to S8B(all 16 channels) totally with single-ended signals (no ground and not diff pairs), what will happen, why it is not correct? I guess ADG707 is just a channel selector switch so it will pass all my single-ended signals as can pass diff pair signals, isn't that so?

  • +1
    •  Analog Employees 
    on Apr 20, 2021 1:51 PM in reply to Nalj

    Hi David,

    Apologies I misread the questions you proposed, so there was a little bit of confusion.

    You are correct, the switch pair enabled is S1A & S1B, S2A & S2B etc.

    If you want to use the ADG707 as a 8 to 1 single multiplexer, then connecting S1B - S8B to GND and using S1A - S8A as single ended channels is the correct thing to do.

    The truth table below will behave in the same fashion, but you will not be utilizing S1B-S8B.

    So when EN is high and A0, A1 and A2 are low S1A & S1B will be ON, but only S1A will conduct the input signal on your application.

      

    The other scenario you refer to, if you feed each input (S1A - S8B) with input signals.

    Half (S1A-S8A) will be outputted from DA and the other half (S1B - S8B) will be outputted from DB.

    Therefore only (S1A-S8A) are singled ended to the same drain and (S1B - S8B) are single ended to the other drain. 

    It acts as a differential pair for the inputs A & B source inputs to the ADG707 switch.

    So if you input signals to all source inputs of the switch it will behave as stated in the datasheet.

    If you connect (S1B - S8B) inputs to GND and use only (S1A - S8A) inputs, you will no longer use the device under normal conditions and no longer use ADG707 as a differential pair.

    I hope this answers your questions, let me know if you need any more information.

    Kevin