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I need to route one of several analog signals to a single ADC input, using digital control signals. I have done this in the past using the 4051 multiplexer IC (or the more modern 74HC4051), but this time the signals are high frequency (about 100MHz) and should not be distorted or attenuated by the multiplexer. However, I have no idea on the bandwidth of a regular 4051 or 74HC4051, the datasheets I have found don't have this information.

What kind of parameter should I look for on the datasheet to understand the analog bandwidth of such a multiplexer?

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    \$\begingroup\$ The datasheet has a frequency response on page 23. \$\endgroup\$ – Eugene Sh. Aug 26 '16 at 16:50
  • \$\begingroup\$ Oh my, thanks a lot, and sorry for overlooking that page... \$\endgroup\$ – Marcovecchio Aug 26 '16 at 16:51
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    \$\begingroup\$ @EugeneSh., i am suspect of the labeling. is this part good to \$10^5\$ kHz or to \$10^5\$ Hz? if the former, i guess the part is good enough for the OP. \$\endgroup\$ – robert bristow-johnson Aug 27 '16 at 6:14
  • \$\begingroup\$ @robertbristow-johnson, it's really khz, the TI datasheet shows a similar chart confirming the information. Indeed, this part is enough for my needs, thanks! \$\endgroup\$ – Marcovecchio Aug 29 '16 at 14:04
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If you can live with an off state isolation of approximately 27 dB at 100 MHz then you are OK: -

enter image description here

Bear in mind that RL (in the circuit above) "helps" the figure be as high as 27 dB so if your ADC input is high impedance then it's going to be a lot worse than 27 dB. Ditto CL.

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  • \$\begingroup\$ Is the on-resistance of the multiplexer gonna play any role in the input? \$\endgroup\$ – ammar.cma Aug 26 '16 at 21:53
  • \$\begingroup\$ @ammar.cma I don't understand your question - be specific. \$\endgroup\$ – Andy aka Aug 27 '16 at 9:36
  • \$\begingroup\$ The one resistance of the multiplexer such as CD4051. When you select a input let's say i(0) that is multiplexed to output. There is something called on resistance. page 7 on datasheet. My question : Will it affect the output in any manner? @Andy aka \$\endgroup\$ – ammar.cma Aug 27 '16 at 9:53
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    \$\begingroup\$ On-resistance is the switch's resistance when activated and sure, you can't put amps through it like a relay so, any load on the output has to respect the presense of this on-resistance. Some devices have sub-1ohm on resistance of course. \$\endgroup\$ – Andy aka Aug 27 '16 at 10:42
  • \$\begingroup\$ @Andyaka, thanks for mentioning the isolation, this is an important parameter, and I guess 27dB is good enough, but I'll do some testing to confirm. \$\endgroup\$ – Marcovecchio Aug 29 '16 at 14:06

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