Up-converted 1/f PM and AM noise in linear HBT amplifiers

Area of Science:

• Electronics
• Semiconductor Devices
• Radio Frequency Engineering

Background:

• 1/f noise is a significant factor in electronic amplifier performance.
• Up-conversion of baseband current noise impacts phase modulation (PM) and amplitude modulation (AM) in amplifiers.
• Heterojunction bipolar transistors (HBTs) are widely used in microwave applications.

Purpose of the Study:

• To develop a technique for predicting 1/f PM and AM noise in HBT amplifiers.
• To provide an accurate model for HBT amplifier voltage gain.
• To enable optimization of amplifier design for reduced noise.

Main Methods:

• Developed an accurate model for microwave HBT amplifiers.
• Derived expressions for voltage gain based on DC bias, transistor parameters, and circuit components.
• Applied definitions of PM and AM noise to the gain expression to determine noise sensitivities.

Main Results:

• Accurate theoretical predictions of 1/f PM and AM noise sensitivities were obtained.
• Experimental measurements at 500 MHz and 1 GHz validated the theoretical predictions.
• Demonstrated a 9 dB reduction in PM noise by adjusting the input coupling capacitor.

Conclusions:

• The developed technique accurately predicts 1/f PM and AM noise in HBT amplifiers.
• The method provides a valuable tool for optimizing amplifier design to minimize noise.
• Specific design adjustments, like input coupling capacitor tuning, can significantly reduce PM noise.