A Current Feedback Amplifier (CFA) is a type of amplifier that amplifies current instead of voltage, making it useful for high-speed and high-frequency applications such as in audio and video processing.
CFAs provide fast response times and are tolerant of capacitive loads, but are more challenging to design and require precise matching of input transistors.
Features of Current Feedback Amplifier
- High bandwidth
- High slew rate
- High linearity
- Fast response times
Working of Current Feedback Amplifier
Current Feedback Amplifiers (CFAs) work by converting an input voltage signal into a current signal, which is then amplified by a low-impedance current amplifier. The output signal is converted back to a voltage signal at the output stage. The amplifier’s gain is controlled by the difference in input currents, which can be adjusted through a feedback resistor.
Specifications of a current feedback amplifier:
- Input Impedance: CFAs typically have low input impedance, making them ideal for high-speed applications and for driving low-impedance loads.
- Voltage Gain: Unlike traditional voltage-feedback amplifiers, CFAs have a current gain, and their voltage gain is often unity (1). This means they maintain a constant voltage-to-current relationship.
- Bandwidth: CFAs are known for their wide bandwidth, which makes them suitable for high-frequency applications.
- High-Speed Operation: They excel in high-speed applications due to their low input capacitance and high bandwidth.
- Linearity: CFAs usually offer good linearity, which is important for accurate signal processing.
- Common-Mode Rejection Ratio (CMRR): CFAs have a high CMRR, allowing them to reject common-mode signals effectively.
- Slew Rate: CFAs often have high slew rates, enabling them to handle rapid changes in the input current.
- Input and Output Current Noise: These amplifiers may have different levels of current noise, which can impact their performance in low-noise applications.
Applications
- Transimpedance Amplifiers
- Audio and Video Processing
- Active Filters
- Instrumentation Amplifiers
- ADC Drivers