How does a current mirror replicate the current of a reference source?
1 Answer
A current mirror is a circuit arrangement used in electronics to replicate or copy the current of a reference source and feed it to another circuit or load. The primary objective of a current mirror is to maintain a constant ratio of currents between the reference source and the replicated current. This allows the circuit to provide a stable and accurate current source or sink to the load.
The basic concept of a current mirror involves using the characteristics of matched transistors. A matched transistor pair consists of two transistors with nearly identical electrical properties, such as threshold voltage, mobility, and dimensions. In an ideal scenario, when two transistors are matched perfectly, the ratio of their collector currents will be equal to the ratio of their emitter currents.
Here's how a simple NPN transistor current mirror works:
Reference Current Source: The reference current source is the source of the current you want to replicate. It is usually a constant current source or a transistor biased to operate in the saturation region, ensuring a relatively constant current flows through its collector-emitter path.
Mirror Transistor: The mirror transistor is another NPN transistor, which acts as the output device to replicate the reference current. It is connected in such a way that its collector current is forced to be equal to the reference current.
Biasing: To maintain the proper operating conditions, the base of the mirror transistor is connected to a biasing network. This network ensures that the mirror transistor is biased in the active region, where it can accurately replicate the current.
Matching: The key to a successful current mirror lies in the matching of the transistors. If the transistors are well-matched, their base-emitter voltages will be nearly identical, and the collector current of the mirror transistor will be very close to the reference current.
Load: The load is connected to the collector of the mirror transistor, and it draws the replicated current.
It's important to note that no current mirror is entirely perfect, as there are always some mismatch and manufacturing variations between transistors. However, with careful design and selection of transistors, it's possible to achieve high accuracy and stability in the replicated current.
Current mirrors are widely used in various applications, such as biasing circuits, voltage references, and operational amplifiers, where a stable and precise current source or sink is required. By using the current mirror configuration, the circuit can benefit from the stable and well-defined characteristics of the reference current source without the need for an additional independent current source.
The basic concept of a current mirror involves using the characteristics of matched transistors. A matched transistor pair consists of two transistors with nearly identical electrical properties, such as threshold voltage, mobility, and dimensions. In an ideal scenario, when two transistors are matched perfectly, the ratio of their collector currents will be equal to the ratio of their emitter currents.
Here's how a simple NPN transistor current mirror works:
Reference Current Source: The reference current source is the source of the current you want to replicate. It is usually a constant current source or a transistor biased to operate in the saturation region, ensuring a relatively constant current flows through its collector-emitter path.
Mirror Transistor: The mirror transistor is another NPN transistor, which acts as the output device to replicate the reference current. It is connected in such a way that its collector current is forced to be equal to the reference current.
Biasing: To maintain the proper operating conditions, the base of the mirror transistor is connected to a biasing network. This network ensures that the mirror transistor is biased in the active region, where it can accurately replicate the current.
Matching: The key to a successful current mirror lies in the matching of the transistors. If the transistors are well-matched, their base-emitter voltages will be nearly identical, and the collector current of the mirror transistor will be very close to the reference current.
Load: The load is connected to the collector of the mirror transistor, and it draws the replicated current.
It's important to note that no current mirror is entirely perfect, as there are always some mismatch and manufacturing variations between transistors. However, with careful design and selection of transistors, it's possible to achieve high accuracy and stability in the replicated current.
Current mirrors are widely used in various applications, such as biasing circuits, voltage references, and operational amplifiers, where a stable and precise current source or sink is required. By using the current mirror configuration, the circuit can benefit from the stable and well-defined characteristics of the reference current source without the need for an additional independent current source.