Typical RF Receive Frontend Architecture
Antenna → Antenna Switch → Pre-select Filter → LNA → IF Filter → Mixer Each block must be specified and verified with S-parameters. System NF and sensitivity determine success.
Step 1: Define System Requirements
Example: LTE Band 3 Receiver (1805–1880 MHz DL) Minimum sensitivity: −100 dBm (10 MHz channel) Maximum blocker level: −43 dBm at 900 MHz (3GPP test) Operating temperature: −40 to +85°C TX power: +33 dBm (FDD, duplexer required)
Step 2: Component Specification
| Block | Key Spec | Typical Component |
|---|---|---|
| Antenna switch | IL <0.5 dB, isolation >30 dB | SP6T switch IC |
| Duplexer (FDD) | RX IL <2 dB, TX→RX >52 dB | SAW duplexer |
| LNA | NF <1.5 dB, Gain >15 dB | SiGe LNA IC |
| IF filter | IL <2 dB, BW ≥ 75 MHz | BAW bandpass filter |
Step 3: System NF Calculation (Friis)
Chain: Switch (IL=0.5dB) → Duplexer RX (IL=1.8dB) → LNA (NF=1.5dB, G=18dB) → ...
F_system = F_switch + (F_dup-1)/G_switch + (F_LNA-1)/(G_sw×G_dup) + ...
= 1.12 + (1.51-1)/0.89 + (1.41-1)/(0.89×0.66) + ...
≈ 1.12 + 0.57 + 0.70 + small ≈ 2.39
NF_system ≈ 3.8 dB
Sensitivity = −174 + 3.8 + 70 + (−1) = −101.2 dBm → meets −100 dBm spec ✓
Step 4: Simulate with RF View
- Download .s2p for each component from manufacturer website
- Load each as S2P block in RF View Circuit Simulator
- Add matching elements between blocks as needed
- Simulate complete chain S11 (input match) and S21 (total gain)
- Verify NF using noise figure cascade calculator
RF View Frontend Design: Cascade all frontend S2P blocks in RF View's Circuit Simulator. Simulate total gain, input match, and use NF Cascade Calculator for sensitivity. Design matching networks between stages. Free on Android.