ontheverge wrote on Sep 28th, 2010, 2:31pm:Hi,
Placing MOSFETs in their own well is effective in eliminating body effect. my quesiton is, is this method widely used in practical? or it's just for simplifying the design?
thanks,
Stephen
Depending on your process technology, this option may actually be very attractive in some cases, and sometimes even necessary. There are many reasons for tying bulk-source, some of which are:
1. Reduced body effect
2. As a result of 1, you may have better headroom and mismatch
3. Avoiding overvoltage condition in charge-pumps (voltage boosters).
4. Higher output impedance in cascoded mirrors or gain-boosted amps.
The most common situation where this is needed and usually supported by the foundry is for high-voltage design. Eliminating body effect may be desirable for a designer but body effect by itself is seldom a killer. Overvoltage on the other hand is a killer.
Vivek