Efficient BJT Constant Current Source for Precise Current Regulation

[likephysics]

I need a constant current source ckt which can source current in the range of 0.1 to 1mA, with +/-1% tolerance, with Vcc 3.3v
Any ideas?
I found this - http://www.ecircuitcenter.com/Circuits_Audio_Amp/BJT Current_Source/BJT_Current_Source.htm
But no info on tolerance.
What happens to Io with change in beta?

 

[technician]

A good starting point would be a single transistor with you load in the collector circuit.
The current would be set with the bias voltage at the base (eg 1.7V) and the value of the emitter resistance (eg 1k).
This would give an emitter and collector current of more or less I = 1V/1k...1mA

 

[jim hardy]

put your load in feedback of an inverting opamp and present it with desired current
you'll need a rail-to-rail amplifier
unless you can supply it from a higher Vcc source...

here's an old link where we helped a guy with a bigger current source. the concepts should apply.
http://www.discovercircuits.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=13046&page=1

 

[likephysics]

I should have mentioned before. My load is connected to ground.
I am trying to make a low voltage(0.2v or 0.3v), voltage reference using constant current source.
I could use a standard voltage ref and divide it using resistors. But I thought using current source would be cool.
There are a few voltage ref chips available with low voltage. But I am more interested in the current source.