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TMUX1511: Small analog signals

Part Number: TMUX1511
Other Parts Discussed in Thread: TMUX1112

Is the TMUX1511 a good choice for very small analog signals? In the datasheet of the "predecessor" of the TMUX1511, the SN74CB3Q3125 

it is stated that a charge pump is used. Will this result in some kind of signal of the charge pump switching frequency to end up in the analog input/output signal?

If so, in what dB range could this be expected?

Is there some documentation available that clearly describes the internal behavior of the TMUX1511?

Thank you very much,

Ed

  • Hi Ed,

    We have not seen issue relating to frequency leakage from internal circuity, so it isn't something that we typically test for as our output tests don't show significant measurable error for the charge pump.  Charge pump circuitry in multiplexers biggest design concern is actually the extra power that the charge pump will consume. We do spec signal feed through and interference with off isolation and cross talk specifications -  To see frequency dependent error due to signal leak through see below:

    Off Isolation -> The switch is disabled but there is a signal on the disabled channel. The signal has a -90dB gain at f = 100KHz.

    The channel to channel cross talk can also cause interference -> two enabled channels interfering with each other - at f = 100KHz we are at a -90dB gain as well. 

    These are the two specs that relate to frequency leak through, as these specs can impact performance of the parts performance, and these are the main concerns with frequency dependent errors.

    If you have another question or would like any additional clarification please let me know!

    Best,

    Parker Dodson

  • Thanks  Parker for your reply.

    Regarding the charge pump in the analog switches, does the TMUX1112 have a charge pump?

    Thank you very much in advance.

    Kind Regards,

    Ed

  • Hi Ed,

    No Problem - I am glad to help out!

    But no the TMUX1112 does not use a charge pump and has a transmission gate topology which allows it to pass rail to rail voltages. 

    You can differentiate the type of topology from looking at the On Resistance Graph, as there are typically 2 peaks that mark the higher plateau of on resistance - typically in the middle of the signal range. This is  highlighted below.  

    This graph is the resulting impedance curve when you use a transmission gate topology (PFET and NFET in parallel) - see below for a generic Transmission gate resistance curve for each component:

    For more information on how to tell what kind of architecture a switch employs please see our Precision Lab video on common switch architectures here

    If you have any other question please let me know!

    Best,

    Parker Dodson

  • Thank you very much Parker.

    Kind Regards,

    Ed