Dear Ianp:
Thank you at first!
I'm still have some query about this circuit.
The resistants-RE will change a lot when temp rise,so IC=VIN/RE will change too,how can i keep IC constant?
Dear Copoler,
Is it possible you could replace that Re by switch cap n/w. Capaciors are prone less to corner and parameter variation.
Else you need to use some other configuration, or take Re offchip and use a precesion resistor