How to design a 10uA constant current

[ejcmos]

I am designing a 10uA contant current as reference current.
I have designed a bandgap reference voltage of 1.2V. In order to generate 10uA constant current, I use a feedback OP drive PMOS to pass 1.2V voltage to 120k resistor. The resistor 120k is too large to be implemented in CMOS process. Can I have other solutions?
Thank you.

 

[godfreyl]

How about a Widlar current source?

 

[nitishn5]

Which process are you using?

120k is not that large. Use resistors with minimum widths and you can get a resistor with the least area.

 

[crutschow]

Note that the absolute resistance value of diffusion resistors has a wide tolerance so there will be a corresponding tolerance in your current value. Is that acceptable?

 

[nitishn5]

The current you would get would be a Vbg/R current. It would vary with the resistor variations.
But if you want to reproduce the voltage, you can put that current into another resistor and get the exact bandgap voltage.