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TMUX1574: Could it support analog output?

Part Number: TMUX1574

Hi team,

Customer hopes to use it output analog sine wave.

Input would be 1Vpp(S1) and 3Vpp(S2) 100kHz sine wave.

They need the output be totally the same as S1 or S2.

Could TMUX1574 support this function?

If not, which part do you recommend?

Thank you.

Best Regards,

Cindy

  • This is supported, if the voltages are not below GND (see VS and VD in the recommended operating conditions.)

  • Hi Cindy,

    This part cannot support negative voltages - if the sine waves are biased where the lowest voltage = 0V then there shouldn't be any issue passing the signal. 

    Also one note of importance - every mux / switch will attenuate  and/or distort the signal being passed through it. To the degree that this occurs depends on the load impedance compared to the on resistance of the mux. The parasitic capacitance of the mux + the load capacitance of the system can cause distortion of higher frequency signals and higher frequency content harmonics. At 100KHz the parasitic capacitances should be negligible  and not have a great impact of system performance; but the on resistance can have an impact. So knowing the load impedance would be very helpful.

    If the application will not allow for a DC bias to keep the sine waves >= 0V for all operation then I'd like to ask a couple more questions to make sure I suggest the best possible solution:

    1. What power rails are available to use by the device? 

    2. What is the load resistance and load capacitance - At 100KHz you will most likely be able to treat the parasitic capacitance as open circuits. This leads to the signal attenuation being:    Voltage Across Switch = R_On/(R_On + R_Load)  -> lead to the proportion of the signal that is lost over the switch. If R_Load >> R_On then the attenuation ~ 0% - but I want to confirm the loading conditions if possible.

    3. Is the application using all 4 channels of the device? As this switch contains 4,  2:1 switches.

    Please let me know if a DC voltage already exists - of if it doesn't if you could give me a bit more details on the application with the questions I listed above to make sure that I can suggest the best possible solution.

    Best,

    Parker Dodson

  • Hi Parker,

    Thanks for your reply in detail.

    To answer your question:

    The input analog signals are all above 0V and device receiving terminal voltage is +3V3 range.
    The impedance of the receiving end is RL=204Ohm, CL=4pF.
    All 4 channel will be used.

    Do you think if they will have signal distortion problem with RL=204ohm?

    Thank you.

    Best Regards,

    Cindy

  • Hi Cindy,

    There will be some signal attenuation but not much:

    At 3.3V supplies you can use the typical response curves shown above (found in the datasheet):

    for a 1Vp-p signal (0V to 1V) @ 100KHz:

    At Room Temp: On Resistance increases with input voltage from ~1.1Ohms to ~1.2 Ohms over the input voltage range. With the 204 ohm load the sine wave received will have lost between 0.54% and 0.58% of the input signal. There is some very slight distortion that can occur due the on resistance being non-linear. However As you can see the difference of attenuation between min and max is only at 0.04% so it is very low.

    At Max Temp:  On Resistance increases with input voltage from ~1.6Ohms to ~1.7 Ohms over the input voltage range based on the above graph. With the 204 Ohm load the sine wave received will have lost between 0.78% and 0.83%. Once again from the graphs this will cause very little change to the sine wave going through the device.

    For a 3Vp-p signal (0V to 3V) @ 100KHz:

    At Room Temp: On Resistance increases with input voltage from ~1.1Ohms to ~1.4 Ohms over the input voltage range. With the 204 ohm load the sine wave received will have lost between 0.54% and 0.68% of the input signal.  The difference in attenuation over the range is 0.14% so it is still very low, and very small changes in the attenuation lead to lower distortion  

    At Max Temp:  On Resistance increases with input voltage from ~1.6Ohms to ~2 Ohms over the input voltage range based on the above graph. With the 204 Ohm load the sine wave received will have lost between 0.78% and 0.97%. Once again from the graphs this will cause very little change to the sine wave going through the device as the range of differences in attenuation is only 0.19%.

    However are some rare edge cases that we do spec for, and while the vast majority of operating scenarios are going to relate to the cases I described above we do have some absolute worst case corners

    Worst Case Attenuation - RON = 4.5 Ohms -> Attenuation = 4.5/208.5 = 2.16% signal loss with 204 Ohm Load

    Worst Case RON Flatness = 1.8 Ohms -> Difference in Attenuation -> 0.87% difference at worst case Flatness (Still < 1%, good for low distortion)

    So in short,  in most use cases you are looking at a attenuation of < 1% and it will introduce very little distortion as typically the difference in attenuation seen by the signal is going to be <0.2% in most cases. If the unlikely event occurs and worst case device performance is seen the attenuation should still be low and the difference in attenuation is going to be < 1% which mean it won't add too much distortion to the system.

    This switch has a lower R_on and low Capacitance which makes it a good fit for low distortion/ low attenuation designs.

    If you have any other questions please let me know!

    Best,

    Parker Dodson