how can design the ptat ?

[qqmz]

hello:

how can decide the parameters of the mos-transistor? the circuit schematic is in the razavi's book "the design of analog integrate circuit" page 325, 11.31(b) .


i want to get a 50uA , i got the value , but the value change a lot when i choose the different power such as when i change the power from 3v to 2.7v ,the value change from 50u to 35u ,why ?



thank you !!!

 

[Humungus]

Whitout seeing the schematic I guess either some of your transistors are operating in the linear region or their channel length is much too short.

 

[qqmz]

now ,i got a value 50 which do not change too much with the power, but it change a lot with the temperture, such as it change from 40 to 70u when the temperture change from -25 to 125,


why ?

 

[jodenma]

maybe yous circuit model changed with temperature,
if you want get good current ,maybe VBG add BIAS is best

 

[qqmz]

maybe i need to choose one vbg add bias circuit to get a good current source ,

the ptat changed too much with the temperture !!!1

 

[sunking]

use current bias the circuit

 

[nuiscet]

maybe amp is operating in the linear region.