Programmable current laser drive circuit
For high speed settling, I'd dump M1 altogether if possible and use a high current opamp to feed the laser directly, that way you avoid the problems that come from driving the capacitive gate (using a fast BJT instead would also probably work as fixed base current means fixed collector current. M2 would interfere with the current measurement a little as it has some resistance. Using a pull down on the dac instead (or a DAC with an output disable function) means you can use really small high speed transistors. While using the opamp to drive the laser directly ensures a real fast stable response as there is the bare minimum of unwanted parasitics. (make R2 a kOhm or more and make M1 a really low output capacitance part otherwise you'll get a low pass filter)







simulate this circuit &ndash; Schematic created using CircuitLab

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