Wideband Amplifier
Understanding Wideband Amplifiers
Wideband amplifiers are essential whenever the system must operate across a wide frequency range simultaneously. Unlike narrowband amplifiers (which can use reactive matching for optimal performance at one frequency), wideband amplifiers use resistive or distributed techniques that sacrifice some performance for bandwidth.
Wideband Amplifier Architectures
- Distributed (traveling-wave): Artificial transmission lines formed by the transistor capacitances and added inductors. Extremely wideband (DC-40+ GHz). Moderate gain (5-15 dB).
- Feedback: Resistive feedback flattens gain across frequency. Moderate bandwidth (2-3 octaves). Good match and stability.
- Balanced: Two amplifiers with 90-degree hybrids. Wideband match. Doubled power. Common for octave-band products.
Frequently Asked Questions
What is a wideband amplifier?
A wideband amplifier provides gain over a very wide band (2:1 to 20:1 frequency ratio). Architectures include distributed (DC-40+ GHz), feedback (2-3 octaves), and balanced (octave+). Used in test equipment, EW, SIGINT, and broadband communications.
What are the trade-offs of wideband vs narrowband?
Wideband: gain flatness over wide range but lower peak gain, higher noise figure, and lower efficiency than optimized narrowband. Narrowband: best performance at one frequency but useless outside the design band.
How do distributed amplifiers work?
Distributed amplifiers connect multiple transistors between input and output artificial transmission lines. Each transistor adds a small amount of gain. The gain contributions add in-phase along the output line. This achieves flat gain from DC to the cutoff frequency of the artificial lines.