voltage regulator on chip
**On-Chip Voltage Regulators** are **integrated power management circuits generating stable supply voltages directly on-die or in companion PMICs**, providing point-of-load regulation with fast transient response that external VRMs cannot achieve.
**Regulator Topologies**:
| Topology | Efficiency | Area | Noise | Response | Use Case |
|----------|-----------|------|-------|----------|----------|
| **LDO** | Low (Vout/Vin) | Small | Very low | <1ns | Analog, fine-grain DVFS |
| **Switched-Cap** | Medium | Medium | Medium | ~10ns | On-die conversion |
| **Buck** | High (>85%) | Large | Higher | ~100ns | Main supply |
| **Hybrid** | High | Medium | Low | Fast | Modern SoC |
**LDO Design**: Pass transistor (PMOS) controlled by error amplifier comparing output against bandgap reference. Challenges: **dropout voltage** (sub-100mV for modern designs), **transient response** (100mA load steps in 1ns need 100+ MHz loop BW), **PSRR** (>40dB rejection), **quiescent current** (<1uA for IoT).
**Digital LDO**: Digital comparator + shift-register-controlled PMOS array. Fully synthesizable, PVT-robust. Challenges: limit-cycle oscillation, quantization noise, slower transient response.
**Switched-Capacitor**: Flying capacitors for voltage conversion. No inductor needed. **Multi-phase interleaving** reduces ripple, **reconfigurable ratios** (gear shifting 3:1 to 2:1), **soft charging** reduces losses. Achieves 80-90% efficiency.
**Integrated Buck**: On-package air-core inductors at 100-400 MHz switching frequency. Intel FIVR achieves 85-90% efficiency. High frequency enables small inductors but creates EMI.
**Per-Core DVFS**: On-chip regulators enable each core at independently optimized voltage/frequency. Requirements: multiple independent outputs, fast transitions (<100ns), minimal cross-regulation.
**On-chip regulation delivers 20-40% energy savings over board-level regulation, making it essential for modern processor efficiency.**