The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> Analog Design >> Good layout of bootstrapped switch?
https://designers-guide.org/forum/YaBB.pl?num=1436366105

Message started by spectrallypure on Jul 8^th, 2015, 7:35am

Title: Good layout of bootstrapped switch?
Post by spectrallypure on Jul 8^th, 2015, 7:35am

Hi! I have designed a classic bootstrapped switch for use in a 1GSa/s ADC, and now I need to layout it. According to my simulations, the effect of the parasitics is CRITICAL for the performance of the switch, so the layout must be done with lots of care.

Since I haven't laid out a bootstrapped switch before, I have no idea what could be a good starting point. Could someone please share any bootstrapped switch layouts, or point me to any references where I can see any examples of how to layout this cell?

Thanks in advance for any help!

Cheers,

Jorge.

P.S. I'm talking about the classic Abo-type boostrapped switch; c.f. attached schematic.

Title: Re: Good layout of bootstrapped switch?
Post by rfmagic on Jul 23^rd, 2015, 12:00pm

Hi,

The main challenge in bootstrap switches layout is to keep the signal path as short as possible in order to avoid too much parasitic effects.
As the bootstrapping circuitry increases the layout size considerably, what you really care about is that the signal path from source to drain in the switch will be very short without too many interactions with the bootstrapping.
The circuit you are presenting is very nice conceptually but you should consider improving it by sharing as much elements as possible i.e. sharing capacitors between other similar cells with the same phases etc..