Analog verification layer for a 64-subcarrier OFDM PHY baseband. Full receive chain from antenna to ADC interface — LNA → Mixer → IF Filter — designed, simulated, and cascade-verified in Cadence Virtuoso + Spectre RF.
Antenna (2.4 GHz)
│
▼
┌─────────────┐ ┌──────────────────┐ ┌──────────────────┐ ┌──────────┐
│ Cascode │────▶│ Double-Balanced │────▶│ 4th-Order Gm-C │────▶│ ADC / │
│ LNA │ │ Gilbert Cell │ │ Bandpass Filter │ │ OFDM BB │
│ (2.4 GHz) │ │ Mixer → IF │ │ (200 MHz) │ │(Project 1│
└─────────────┘ └──────────────────┘ └──────────────────┘ └──────────┘
▲
│
┌───────────────┐
│ LO 2.2 GHz │
│ (PLL output) │
└───────────────┘
RF = 2.4 GHz │ LO = 2.2 GHz │ IF = 200 MHz │ BW = 20 MHz
Industry-standard inductive source degeneration topology for minimum noise at 2.4 GHz. Input matched to 50 Ω, cascode device for isolation and stability.
| Spec | Target |
|---|---|
| Gain (S21) | 15 dB |
| Noise Figure | < 2.5 dB |
| IIP3 | > −5 dBm |
| Input Match (S11) | < −10 dB |
| Power | < 10 mW |
Converts RF at 2.4 GHz down to 200 MHz IF using a 2.2 GHz LO. Differential topology suppresses LO feedthrough and even-order distortion.
| Spec | Target |
|---|---|
| Conversion Gain | > 6 dB |
| DSB Noise Figure | < 12 dB |
| IIP3 | > +5 dBm |
| LO–RF Isolation | > 30 dB |
| Power | < 15 mW |
Centred at 200 MHz IF, bandwidth matched exactly to the 20 MHz OFDM channel. Two cascaded Gm-C biquad sections (Butterworth response) — chosen over passive LC because on-chip inductors at 200 MHz are impractical.
| Spec | Target |
|---|---|
| Centre Frequency | 200 MHz |
| 3-dB Bandwidth | 20 MHz |
| Stopband Rejection | > 40 dB at ±40 MHz |
| Passband Ripple | < 0.5 dB |
| IIP3 | > +10 dBm |
All block specs were derived from the companion OFDM baseband project using Friis noise cascade and IIP3 cascade equations, then verified end-to-end via Spectre RF Pnoise simulation.
| Parameter | Result |
|---|---|
| Total Chain Gain | 19 dB |
| Cascade Noise Figure | 3.1 dB |
| Receiver Sensitivity | −97.9 dBm |
| SFDR | 55.6 dB |
| OFDM PAPR Margin | 44 dB |
| BER Target | QPSK < 10⁻³ ✓ |
The −97.9 dBm sensitivity meets the link budget required by the OFDM PHY baseband receiver for QPSK at BER < 10⁻³ (Eb/N0 = 6.8 dB, 20 MHz channel bandwidth).
| Analysis | Blocks | What It Extracts |
|---|---|---|
| DC operating point | All | Bias, saturation check |
| S-parameter sweep (1–6 GHz) | LNA | S21, S11, K-factor |
| Noise | LNA, cascade | NF vs frequency |
| PSS + PAC | Mixer, cascade | Conversion gain |
| Pnoise (periodic) | Mixer, cascade | DSB NF |
| Two-tone PSS + PAC | LNA, Mixer | IIP3 |
| AC sweep (50–400 MHz) | IF Filter | Frequency response, BW, ripple |
RF-IC-RX-FRONT-END/
│
├── netlists/
│ ├── 01_LNA.scs # Cascode LNA — schematic + all sim setups
│ ├── 02_Mixer.scs # Gilbert cell mixer
│ ├── 03_IF_Filter.scs # Gm-C bandpass filter (biquad subcircuits)
│ └── 04_Cascade_TB.scs # Full chain testbench
│
├── scripts/
│ ├── cascade_analysis.py # Friis NF + IIP3 + sensitivity calculator
│ ├── sizing_calculator.py # Transistor & component sizing equations
│ └── ocean_simulations.ocn # Cadence Ocean automation script
│
├── specs/
│ └── system_specs.md # Full specification table + blank results sheet
│
├── plots/
│ ├── cascade_iip3_extrapolation.png
│ └── cascade_nf_contribution.png
│
└── PROJECT_MANUAL.md # Step-by-step Virtuoso simulation guide
No Cadence licence needed for these. Pure Python.
# Install dependencies
pip install numpy matplotlib
# 1. Get analytical component values for all three blocks
python scripts/sizing_calculator.py
# 2. Run Friis cascade analysis — NF, IIP3, sensitivity, SFDR
python scripts/cascade_analysis.pycascade_analysis.py output:
Stage Gain(dB) CumGain(dB) NF(dB) CumNF(dB)
LNA 15.0 15.0 2.5 2.50
Mixer 6.0 21.0 12.0 3.52
IF Filter -2.0 19.0 3.0 3.53
Cascade NF : 3.53 dB
Sensitivity : -87.7 dBm (QPSK, BER=10⁻³, 20 MHz BW)
SFDR : 55.6 dB ✓ (> 11 dB OFDM PAPR)
| Tool | Purpose |
|---|---|
| Cadence Virtuoso | Schematic entry, testbench setup |
| Spectre RF | DC, SP, noise, PSS, PAC, Pnoise simulations |
| ADE L / ADE XL | Simulation management, waveform viewing |
| Ocean (SKILL) | Batch simulation automation |
| Python | Friis analysis, component sizing, plots |
| Process | 180 nm CMOS, 1.8 V supply |
This project is the analog front-end to a companion OFDM PHY baseband project. All receiver specifications were derived from baseband measurements:
- OFDM channel: 64 subcarriers, 20 MHz bandwidth, 312.5 kHz subcarrier spacing
- Modulation: QPSK (Eb/N0 = 6.8 dB) and 16-QAM (Eb/N0 = 10.5 dB)
- Measured PAPR: 11 dB → sets IIP3 requirement
- BER target: < 10⁻³ → sets sensitivity requirement
The front-end output (200 MHz IF, 20 MHz BW) feeds directly into the digital OFDM demodulator (FFT → channel equalisation → symbol detection).
Mayank Kumar Singh B.Tech Electronics & Communication Engineering