SN74CBTLV3251: signal pass the switch ic will be distortion

CALVIN HSU

Other Parts Discussed in Thread: SN74CBTLV3251, TMUX1308

零件編號： SN74CBTLV3251

Hello I want to ask some question about Analog switches & muxes-SN74CBTLV3251
In the datasheet.We can see the internal connection.

My test conditions as follows:
I provide the product VCC=3.3V and S0S1S2 also provide 3.3. B1~B8 set as input.
OE set0 let switch work.

I use function gen to feed the square wave signal 1.2V @10MHZ from b8，meaure A.
The waveform will not be distorted at the beginning.
But as I increase the frequency of signal (11MHZ、12MHZ 13MHZ)
I found A the waveform measured at point A has been distorted into a sinusoidal wave

How to avoid square wave distortion?
In my case I need to measure frequency up to 60MHZ，so I dont want the signal pass the switch ic will be distortion.
I see the bandwidth is 200MHZ ,so I confuse why distortion.
And how to avoid？

If you have a good method please tell me

Thanks

Note：
I have tried different probes (passive, active) to measure A, and the device bandwidth up to 200MHZ, But the signal will also be distorted

10 months ago

0 Rami Mooti1 10 months ago

TI__Mastermind 25993 points

Hey Calvin,

Typically I recommend selecting a mux that has about 5-7x the bandwidth of your square wave you may be working with so you capture some of those early harmonics components but it does seem here that the device should be able to support the frequency. There could be added loses from your setup. Do you have long traces or I've even had faulty probes being my limiting factor when I'm in lab myself doing some testing.

You could try a higher bandwidth device, like the TMUX1308 but I think it may be worthwhile to see if we can get the 3251 to pass these signal since I would expect it to be able to support your use case.