Problem:

my photo diode recieves pulses of width 10ns-150ns and repeating at rate of 1Hz-50KHz

the current from photo diode depending on incident light can go from 10nA-100mA, so i have two photo diodes to cover the dynamic range, what i want to do is limit the current from a photo diode to 5mA lets say in one channel

My application needs me to do current limiting, so for this i found a hope with this patent

which has the basic circuit as below

typically i want to replace the I1 with my photo diode and in the question here even i tried to realize the circuit with suggestions in answers and even got few decent results

but the problem is i am not able to make out this circuit in my mind in terms of current, when i observed in simulation the diode connected FET 52 does the job of discharging the excess current and current sources 30 and 40 are the saturation currents

fully realized circuit:

Problem:

my photo diode recieves pulses of width 10ns-150ns and repeating at rate of 1Hz-50KHz

the current from photo diode depending on incident light can go from 10nA-100mA, so i have two photo diodes to cover the dynamic range, what i want to do is limit the current from a photo diode to 5mA lets say in one channel

My application needs me to do current limiting, so for this i found a hope with this patent

which has the basic circuit as below

typically i want to replace the I1 with my photo diode and in the question here even i tried to realize the circuit with suggestions in answers and even got few decent results

but the problem is i am not able to make out this circuit in my mind in terms of current, when i observed in simulation the diode connected FET 52 does the job of discharging the excess current and current sources 30 and 40 are the saturation currents

fully realized circuit: