Design and Analysis of 1.8V-to-1.2V LDO Regulator

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Create a PhD/Industry-level technical presentation titled "Design and Analysis of a 1.8V to 1.2V Low Dropout Regulator (LDO)". Specifications: - Input Voltage: 1.8V - Output Voltage: 1.2V - Maximum Load Current: 10mA - Output Capacitor: 3pF - With output capacitor (not capacitor-less) - No simulation slides - No layout/area slides Include ~30 professional slides with strong theoretical depth and equations. Slide Outline: 1. Title Slide 2. Problem Statement 3. Applications in SoCs and Mixed-Signal Systems 4. System-Level Specifications 5. LDO Architecture Overview 6. Detailed Block Diagram Amplifier Section: 7. Error Amplifier Requirements (Gain, BW, Offset) 8. Common Source Amplifier Analysis (Gain equation) 9. Differential Amplifier (CMRR, ICMR) 10. Folded Cascode Op-Amp Architecture 11. DC Gain Derivation 12. ICMR and OCMR Analysis 13. Input Offset Impact on Output Accuracy Pass Device Section: 14. Pass Transistor Operation Regions 15. PMOS vs NMOS Trade-offs (justify PMOS choice) 16. Pass Device Sizing for 10mA Load 17. Dropout Voltage Derivation Stability & Control: 18. Small-Signal Model of LDO 19. Loop Gain Derivation 20. Pole-Zero Locations 21. Phase Margin and Gain Margin Targets (>60°, >10dB) 22. Compensation Strategy with 3pF Output Capacitor Performance Metrics: 23. PSRR (Low-Frequency and High-Frequency Behavior) 24. Slew Rate (SR = I/C) 25. Transient Response and Settling Time (Ts) 26. Line Regulation (ΔVout/ΔVin) 27. Load Regulation (ΔVout/ΔIload) 28. Load Current Limitation and Power Dissipation Final Section: 29. Design Trade-offs (Area, Stability, Speed, PSRR) 30. Performance Summary Table 31. Conclusion Use a professional dark-theme style with clean equations and technical formatting suitable for PhD defense or industry review.

Technical review of a low-dropout regulator (LDO) design for low-voltage SoCs: from problem statement and specs to error amplifier, PMOS pass device, stability analysis, and performance metrics like PSRR >60dB, PM >60°, for Vin=1.8V, Vout=1.2V, Imax=

February 22, 202620 slides

Slide 1 of 20

Slide 1 - Design and Analysis of a 1.8V to 1.2V Low Dropout Regulator (LDO)

Design and Analysis of a 1.8V to 1.2V Low Dropout Regulator (LDO)

Vin = 1.8V, Vout = 1.2V, Imax = 10mA, Cout = 3pF PhD/Industry Technical Review

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Slide 1 - Design and Analysis of a 1.8V to 1.2V Low Dropout Regulator (LDO)

Slide 2 of 20

Slide 2 - Presentation Agenda

Problem Statement & Applications
System-Level Specifications
LDO Architecture Overview
Error Amplifier Section
Pass Device Section
Stability & Control
Performance Metrics
Design Trade-offs & Conclusion

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Slide 3 of 20

Slide 3 - Section 1: Introduction

Problem Statement

Motivation for LDOs in Low-Voltage SoCs

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Slide 4 of 20

Slide 4 - Problem Statement

LDO enables regulation when Vin ≈ Vout (dropout = 0.6V here)
Advantages over switching regs:
• No switching noise
• Smaller size: no inductors/transformers
• Simpler design: reference + amplifier + pass element
Disadvantage: Power dissipation = (1.8-1.2V)×I_L = 6μW at 10mA

Source: Wikipedia: Low-dropout regulator

Slide 5 of 20

Slide 5 - Applications in SoCs & Mixed-Signal Systems

SoC Integration: Local regulation reduces off-chip passives
Mixed-Signal: Supplies clean Vout=1.2V to ADCs, DACs, PLLs
Low dropout ideal for stacked power domains (1.8V digital → 1.2V analog)
Battery-powered IoT: Efficient at low Vin-Vout differential

Slide 6 of 20

Slide 6 - System-Level Specifications

Parameter	Symbol	Value	Unit
Input Voltage	Vin	1.8	V
Output Voltage	Vout	1.2	V
Maximum Load Current	ILmax	10	mA
Output Capacitor	Cout	3	pF
Dropout Voltage	VDrop	0.6	V
Target PSRR (DC)	PSRR	>60	dB
Target Phase Margin	PM	>60	°
Target Settling Time	Ts	<1	μs

Slide 7 of 20

Slide 7 - Architecture Overview

LDO Architecture Overview

Reference, Error Amplifier, Pass Device & Feedback

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Slide 8 of 20

Slide 8 - Detailed LDO Block Diagram

Bandgap reference generates Vref (e.g., 0.6V)
Error amplifier: Vout/2 → Vfb vs Vref
PMOS pass transistor Mp controls Iout
Feedback divider R1-R2 sets Vout=1.2V
Cout=3pF stabilizes dominant pole

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Slide 9 of 20

Slide 9 - Amplifier Section

Error Amplifier Design

Gain, Bandwidth, Offset, CMRR Requirements

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Slide 10 of 20

Slide 10 - Error Amplifier Requirements

DC Gain: A0 > 60 dB (Vout accuracy < 0.1%)
GBW > 10 MHz (transient response)
Input Offset: Vos < 1 mV
CMRR > 80 dB, PSRR > 60 dB (@DC)
Slew Rate SR > 1 V/μs
Low input bias current for R_feedback

Slide 11 of 20

Slide 11 - Amplifier Architectures: CS vs Differential

Common Source Amplifier Gain: Av = -g{m1} (r{o2} || r{o4}) ~40 dB typical in 180nm High GBW but poor PSRR/CMRR Simple but insufficient for LDO

Differential Amplifier CMRR = 20 log{10} (Ad / Acm) ICMR: V{SS} + V{DSsat} to V{DD} - |V{GS}| - V{DSsat} High gain with current mirror load PSRR improves with matching

Slide 11 - Amplifier Architectures: CS vs Differential

Slide 12 of 20

Slide 12 - Folded Cascode Op-Amp Architecture

High DC gain: >80 dB
Improved ICMR for 1.8V supply
Single pole dominant response
Low power suitable for LDO
Compensation via output cap

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Slide 12 - Folded Cascode Op-Amp Architecture

Slide 13 of 20

Slide 13 - DC Gain Derivation - Folded Cascode

Input pair gain: A1 = g{m1} (r{o1} || r{o3})
Cascode gain: A2 = g{mc} (r{oc1} || r{oc2}) (1 + g{mc} r{oc2})
Total Av = A1 × A2 ≈ gm r_o ^2 > 80 dB (90 dB typ.)
High Rout enhances loop gain

Slide 14 of 20

Slide 14 - ICMR, OCMR & Offset Analysis

ICMRmin = V{GS1} + V{DSsat,tail} + V{DSsat,fold}
ICMRmax = VDD - |V{GS,fold}| + V{DSsat}
OCMR: V{SS} + V{DSsat} to VDD - V{DSsat}
Offset impact: ΔVout ≈ V{os} / (1 + A0 β) < 1mV / 1000 = 1μV

Slide 15 of 20

Slide 15 - Pass Device

Pass Transistor Design

PMOS vs NMOS Trade-offs & Sizing for 10mA

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Slide 16 of 20

Slide 16 - PMOS vs NMOS Pass Device Trade-offs

PMOS Pass Transistor (Chosen)

Low V{GS} sufficient (V{GS} = Vout - V{gate} ≈ 0.6V)
No bootstrap circuit needed
Good for dropout < V{TH}
Ron ∝ 1/(W/L μp Cox (V{GS}-V{TH}))

NMOS Pass Transistor

Higher mobility μn > μp → lower Ron
Requires V{GS} > Vin (bootstrap/driver needed)
Complex for low dropout
Poor for Vin ≈ Vout + small dropout

Slide 16 - PMOS vs NMOS Pass Device Trade-offs

Slide 17 of 20

Slide 17 - Pass Device Sizing & Dropout Derivation

Target Ron < V{drop}/I{Lmax} = 0.6V/10mA = 60 Ω
PMOS (W/L) ≈ μn Cox (V{GS}-V{TH}) Ron ^{-1} → W/L ≈ 200/0.18 μm
Dropout V{drop} = IL R{on} + I_Q (negligible)
Operation: Saturation (fast transient) → Triode (steady-state regulation)
Max Pdiss = 6 mW

Slide 18 of 20

Slide 18 - Stability Analysis

Stability & Control Loop

Small-Signal Model, Pole-Zero, Phase/Gain Margin

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Slide 19 of 20

Slide 19 - Small-Signal Model of LDO

Loop gain T(s) = A(s) β Rout / (Rout + 1/sCout)
Dominant pole fp1 ≈ 1/(2π Rout Cout)
Non-dominant poles from amp, pass device
Zero from ESR (negligible at 3pF)
Target PM >60°, GM >10dB

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Photo by Ludovico Ceroseis on Unsplash

Slide 20 of 20

Slide 20 - Key Performance Metrics & Targets

Metric	Target	Equation/Notes
PSRR (DC)	>60 dB	PSRR = 20 log (ΔVsupply / ΔVout)	Slew Rate	>1 V/μs	SR = Itail / Ccomp	Settling Time	<1 μs	Ts = 4 / (GBW × ln(1/ε))	Line Reg.	<1 mV/V	ΔVout/ΔVin	Load Reg.	<1 mV/mA	ΔVout/ΔIL × R_on	Phase Margin	>60°	Stability criterion	Gain Margin	>10 dB

Source: Wikipedia: Power supply rejection ratio

Slide 20 - Key Performance Metrics & Targets

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