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What is Current Mirror
• A Current Mirror in a circuit is used to copy a current through one active device by controlling the current in another active device of a circuit, keeping the output current constant regardless of loading.
Why Current Mirror:
○ Current Mirror is used as a Load.
○ In ICs if we use Resistors as Load they will consume more space.
○ So, to overcome this "current mirrors" are used in place of resistors.
Current Mirror:
○ For NMOS always "Source" should be connected to the ground.
○ For Current Mirror VGS1=VGS2 and both the transistors Q1 and Q2 must be operated in Active Region.
○ Since "Drain" is connected to "Gate" it is like a Diode with "Base" and "Collector" shorted.
○ So only current flow in only one direction
○ Both the Transistors Q1 and Q2 must be of same size.
A current mirror is a type of circuit that is used to replicate a current flowing through one device to another device. The purpose of a current mirror is to provide a fixed, proportional, or adjustable current that is independent of the voltage supply and load conditions.
In a typical current mirror circuit, the input current is applied to the gate or base of the input device, which could be a bipolar junction transistor (BJT) or a metal-oxide-semiconductor field-effect transistor (MOSFET). The output current is taken from the collector or drain of the output device, which is typically the same type of device as the input.
The operation of a current mirror is based on the principle that the current flowing through a device is proportional to its voltage drop. By controlling the voltage drop across the input device, the current flowing through it can be replicated at the output device.
Current mirrors are widely used in a variety of applications, including current sources, voltage references, current amplifiers, and active loads. They are widely used in integrated circuits, particularly in power management, where they are used to control the current supplied to a load, or to provide a constant current for charging or discharging a capacitor.
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