how to design a accurate constant current source?

[liusupeng]

how to design a constant current source which is invariant to temperature and process variantions?

 

[erikl]

There are methods to stabilise CC against temperature (and voltage) variations. Against process variations you need an external CC or CV comparison source.

 

[horzcat]

There are many ways. There are plenty of common circuits available. You can use a current mirror circuit.

 

[tzg6sa]

Design a voltage source, like a bandgap and derive the current from its output.

 

[dick_freebird]

If you want process-invariant, you either need an
invariant process (good luck) or a trimming scheme.
And since "natural" tempco also carries some process
sensitivity, double down on that.

 

[alikaramih]

See chapters 5 and 11 of Razavi's Design of Analog CMOS ICs

 

[frankliner]

Use a bandgap reference as a process independent voltage source. Then use a voltage to current converter. Use an external resistor, or use trimming with an internal resistor. When using internal resistor + trimming the addition of a NTAT current sink in parallel to the resistor may be necessary to get temperature independence.

 

[snafflekid]

you can combine n and p type resistors in series, which have different tempcos, to create a resistor that cancels the tempco of delta-Vbe. Make the resistors physically large to minimize the impact of process variation. delta-Vbe is not very process sensitive

 

[leo_o2]

Bandgap voltage/external resistor is a good choice.