RF Budget Analysis
Understanding RF Budget Analysis
RF budget analysis is the system engineer's primary tool for predicting receiver sensitivity, dynamic range, and overall system performance before hardware is built. Every component in the chain is characterized and its contribution tracked.
Budget Components
- Gain budget: Sum of all gains and losses: antenna gain + cable loss + LNA gain + filter loss + mixer conversion loss + IF gain + ... = total gain.
- Noise budget: Cascaded NF = NF1 + (NF2-1)/G1 + (NF3-1)/(G1*G2) + ... (Friis equation). The first stage dominates if it has sufficient gain.
- Linearity budget: 1/IP3_sys = 1/IP3_1 + G1/IP3_2 + G1*G2/IP3_3 + ... The last stage typically dominates.
Key Results
- Sensitivity: MDS = -174 + NF_sys + 10log(BW) dBm.
- Dynamic range (SFDR): 2/3 x (IIP3_sys - MDS) dB.
- Compression point: Determines maximum input signal before saturation.
Frequently Asked Questions
What is RF budget analysis?
RF budget analysis tracks signal power, noise, and linearity through every stage. Gain budget gives signal levels. Noise budget gives system NF. Linearity budget gives IP3. Together they predict sensitivity and dynamic range.
What is the Friis noise equation?
NF_sys = NF1 + (NF2-1)/G1 + (NF3-1)/(G1*G2). The first stage NF dominates if its gain is sufficient (15-20 dB). This is why the LNA is the most critical component for receiver sensitivity.
How do you create a budget?
List every component from antenna to ADC. For each: gain (or loss), NF, and IP3. Calculate running totals of gain, cascaded NF, and cascaded IP3. Verify sensitivity and dynamic range meet requirements.