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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.
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