Why increase the lengths of the devices improve PSRR ?

Status
Not open for further replies.
R

rom0011

Newbie level 5
Joined
Dec 31, 2009
Messages
10
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,357
hi all:

Increase the lengths of the devices and scale the widths accordingly
improve the PSRR.

Is this because the MOS gate decouple from vdd noise through larger Cgs
capacitor?
 

if you are talking about PSRR in Band gap reference, LDO. then please refer some really good IEEE paper publish by Georgia Tech guys like Vishal Gupta, Dr.Rincon Mora. this will definitely give you some real insight.
 

Short channel FETs have significant Id/Vds slope (lambda
in old school models, a lower than desired output impedance).
The field "push-back" of the drain-body junction shortens
the channel by a voltage-proportional distance. On a longer
FET, this increment matters less.

Power supply voltage imposes a variable on some devices'
applied voltage & current, which must be nulled by an input
difference (closed loop) or results in an output drift (open
loop).
 

By increasing the L and maintaining the same w/l , the Ro will increase and hence loop gain will increase and so the PSRR will improve.(the PSRR is typically the inverse transfer function of the loop gain).
 

increasing L of devices increase R0 ( output impedance) of mosfets ..

cascode shielding principle applies here
output node gets shielded from supply noise due to cascode action
 

Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…