This is a current mirror, a device that uses the current in one half of the circuit to control the current in the other half. The current is the same in both halves. The switch on the left changes the current in the left half, which is mirrored in the right half. The switch on the right causes the resistor to be shunted, but the current mirror ensures that the current does not change. If the left MOSFET is in saturation, its current is determined solely by the gate-source voltage. The left MOSFET has its gate and drain tied together, so the drain voltage sets the current. The right MOSFET has the same gate-source voltage, so the current must be the same as long as it is in saturation.
This page is a utility for simulating токове зеркало online with specified initial values.









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