A current mirror is a fundamental component used in amplifier circuits to accurately replicate or mirror the current flowing through one transistor (or other active device) into another transistor. This circuit configuration is essential for various reasons, primarily to ensure a stable and consistent biasing of transistors and improve the performance of amplifiers. The role of a current mirror in amplifier circuits can be explained as follows:
Biasing: Transistors in amplifier circuits require a stable biasing voltage or current to operate in their active region. By using a current mirror, the bias current can be precisely controlled, leading to better stability and consistent performance of the amplifier.
Amplification: In many amplifier configurations, such as differential amplifiers or cascode amplifiers, the performance relies on matched transistors with identical bias currents. Current mirrors are employed to achieve this matching, ensuring that both sides of the amplifier circuit amplify signals equally, leading to balanced and symmetrical output.
Current Sensing: Current mirrors are also used in various sensing circuits, where the magnitude of a current needs to be accurately determined. The mirrored current can be directed to a sensing circuit, enabling accurate current measurements and feedback control.
Load Sharing: In some amplifier designs, the current mirror is used to distribute current among multiple branches or stages. This load sharing helps in efficient utilization of current sources and improves overall amplifier efficiency.
Reference Generation: Current mirrors can be utilized to generate a stable and precise reference current. This reference current can then be used in other parts of the circuit, such as biasing or calibration circuits.
Frequency Compensation: Current mirrors can be used in compensation techniques to enhance the bandwidth and stability of amplifiers, particularly in high-frequency applications.
It's important to note that current mirrors are implemented using different configurations, such as simple two-transistor mirror, Wilson current mirror, cascode current mirror, and many others, each with its advantages and limitations. The choice of the specific current mirror configuration depends on the amplifier's requirements, performance goals, and the technology used in the integrated circuit design.