Current mirrors are a fundamental concept in analog electronic circuits that allow a copy of one current to be mirrored or replicated in another branch of the circuit. They are widely used in integrated circuits to provide a stable and accurately controlled current source or sink, which is crucial for various applications. The basic idea behind a current mirror is to use a transistor or a group of transistors to generate a current that is proportional to a reference current.
There are two main types of current mirrors:
NPN Bipolar Transistor Current Mirror: In this type, two or more NPN bipolar transistors are connected in such a way that the base-emitter voltage of one transistor is used to establish a reference current, and this current is mirrored by another transistor. The mirrored current is typically a scaled version of the reference current, determined by the transistor sizes and configuration.
NMOS or PMOS Transistor Current Mirror: This type of current mirror uses two or more NMOS or PMOS transistors to achieve the same purpose. The principle is similar, with one transistor acting as the reference to generate a current, and the other transistor mirroring this current.
Applications of Current Mirrors in Electronic Circuits:
Biasing Circuits: Current mirrors are commonly used in biasing circuits to generate stable and accurately defined currents that set the operating point of other active devices, such as amplifiers and differential pairs. This ensures consistent and predictable performance of the circuit.
Current Sources and Current Sinks: Current mirrors are used to create precise current sources or sinks, which are essential in various applications like analog-to-digital converters (ADCs), digital-to-analog converters (DACs), and voltage regulators.
Operational Amplifiers: Current mirrors are often used in the input stage of operational amplifiers to maintain symmetry and balance between the input differential pair.
Temperature Compensation: Current mirrors can be used to compensate for temperature variations in certain circuits, ensuring that the output currents are relatively unaffected by temperature changes.
Digital-to-Analog Converters (DACs): In some DAC architectures, current steering techniques are used, and current mirrors are employed to precisely generate and control the currents flowing through the DAC's output resistors.
Analog Multipliers and Dividers: Current mirrors are utilized in building analog multiplier and divider circuits, where the output current is proportional to the product or quotient of two input currents.
Overall, current mirrors play a vital role in ensuring accurate and consistent current replication, which is crucial for numerous analog and mixed-signal applications in electronic circuits.