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Design >> Mixed-Signal Design >> Analog MUX for high-speed ADC
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Message started by ywguo on Aug 28^th, 2006, 1:40am

Title: Analog MUX for high-speed ADC
Post by ywguo on Aug 28^th, 2006, 1:40am

Hi Guys,

I am designing a high-speed ADC, which requires an analog MUX put at the front-end. For eg., a 2:1 MUX preceding the ADC.

Many SAR ADCs have analog MUX at the front-end, like 5:1 MUX or 8:1 MUX. They are usually complemetary MOS switch, because SAR ADCs have low conversion rate.

However, I need an analog MUX for a pipleined ADC with >100MS/s sampling rate, which . Should I use a bootstrapped switch? Or simply use a very large complementary MOS switch?

Any comments are very appreciated.

Thanks

Yawei

Title: Re: Analog MUX for high-speed ADC
Post by vivkr on Aug 28^th, 2006, 6:57am

Hi Yawei,

Does your ADC have a sampling switch (no buffer) upfront? If so, then you can simply create
the MUX functionality by placing multiple switches in parallel, all tied to different input channels,
and use some digital logic to allow only 1 channel to be sampled at a time. This is easily done.

I would use a bootstrapped switch as the performance is much superior although reliability is atleast of some concern even with the best designs if you are working in short-channel regime. CMOS transmission gates will get really big and will not be linear enough.

By the way, be careful that the logic implementing your MUX function does not ruin the analog performance of your switch. What are you using the MUX for?

Regards
Vivek

Title: Re: Analog MUX for high-speed ADC
Post by ywguo on Aug 28^th, 2006, 9:52pm

Hi Vivek,

I am designing a display interface composed of 2:1 MUX, clamp, PGA and 10-bit ADC. It is used to sample video signals like YPbPr, RGB, etc. I think the linearity must be important. The sampling rate must be more than 100MS/s.

Thanks
Yawei