RF Low Noise Amplifier

Essential Principles for Accurate Noise Figure Measurement & Characterization

1. Core Definition of Noise Figure

The noise figure (NF) is fundamentally defined as the ratio of the input signal-to-noise ratio (SNR) to the output SNR of the RF Low Noise Amplifier.
It quantifies how much the amplifier's internal noise degrades the signal quality. An ideal amplifier adds no noise, resulting in a perfect NF.
In practice, inherent component noise lowers the output SNR compared to the input, increasing the measured noise figure.
Grasping this core logic is essential for all subsequent measurement and analysis of the RF LNA.

2. Fundamental Measurement Principles

The core method involves precise calculation of both input and output SNR using professional test equipment.
Measure the signal and noise power at the amplifier input to calculate the input SNR.
With the same source, measure the output power and total noise power (signal + amplifier noise) to find the output SNR.
The noise figure is derived from the ratio of these two SNRs. Source stability and equipment accuracy are critical for reliable results.

3. Key Influencing Factors

Measurements must account for real-world operational conditions to ensure practical relevance for the RF Low Noise Amplifier.
Operating Frequency: NF performance varies significantly across bands due to component noise characteristics.
Temperature: Increased temperature typically raises internal noise levels, adversely affecting the noise figure.
Bias Settings: Proper DC bias configuration is crucial to maintain the NF within an optimal range.

4. Practical Calibration Implementation

Enhance measurement accuracy through systematic calibration procedures.
First, calibrate the test system itself to remove the noise contribution of the measurement equipment.
Select calibration methods appropriate for the RF LNA's structure and target application scenario.
Perform multiple measurements, compare data, exclude outliers, and use stable results as the final noise figure reference value.