UPF Supply Sets

12 min read | Intermediate Level

What You'll Learn

• Understand what supply sets are and why they're needed
• Create supply sets with function assignments using create_supply_set
• Associate supply sets with power domains
• Work with multiple supply sets for different power states

What is a Supply Set?

A supply set is a collection of supply nets grouped by their functional roles. Instead of treating power and ground as separate entities, a supply set bundles them together to represent a complete power delivery configuration.

Each supply set defines:

• Power Supply: The primary power net (e.g., VDD)
• Ground Supply: The ground reference (e.g., VSS)
• Optional Supplies: Nwell, pwell, or other specialized supplies

Supply sets answer the question: "What complete set of power connections does this domain need to operate?" Rather than saying "this domain uses VDD and VSS separately," you say "this domain uses supply set SS_TOP, which provides both power and ground."

Why Supply Sets?

Supply sets provide several benefits:

• Logical Grouping: Power and ground are naturally paired—supply sets reflect this relationship
• State Management: Different power states can use different supply sets (active vs retention)
• Cleaner Association: One command associates complete power delivery with a domain
• Advanced Features: Enable nwell/pwell biasing and multi-threshold designs

Syntax: create_supply_set

The create_supply_set command creates a named group of supply nets with functional roles.

Basic Form

create_supply_set set_name -function {role net_name} [additional_functions]

Parameters

• set_name - Unique identifier for the supply set (required)
• -function {role net_name} - Assign a supply net to a functional role (required, repeatable)

Standard Function Roles

Usage Variations

1. Basic Supply Set (Power + Ground):

create_supply_set SS_TOP \
  -function {power VDD_TOP} \
  -function {ground VSS}

2. Supply Set with Well Biasing:

create_supply_set SS_CPU \
  -function {power VDD_CPU} \
  -function {ground VSS} \
  -function {nwell VDD_CPU} \
  -function {pwell VSS}

3. Retention Supply Set:

create_supply_set SS_RET \
  -function {power VDD_RET} \
  -function {ground VSS}

Creating Basic Supply Sets

Every power domain requires at least one supply set defining its power and ground.

Single-Domain Example

# Create power domain
create_power_domain PD_TOP -include_scope

# Create supply nets
create_supply_net VDD -domain PD_TOP
create_supply_net VSS -domain PD_TOP

# Create supply set grouping power and ground
create_supply_set SS_TOP \
  -function {power VDD} \
  -function {ground VSS}

# Associate supply set with domain (next section)
associate_supply_set SS_TOP -handle PD_TOP

This creates a complete power delivery specification: PD_TOP uses SS_TOP, which provides VDD (power) and VSS (ground).

Multi-Domain Supply Sets

Each power domain typically has its own supply set reflecting its unique voltage and power delivery.

# ===================================================================
# Multi-Domain Supply Sets Example
# ===================================================================

# Top-level domain (1.2V, always-on)
create_power_domain PD_TOP -include_scope
create_supply_net VDD_TOP -domain PD_TOP
create_supply_net VSS -domain PD_TOP

create_supply_set SS_TOP \
  -function {power VDD_TOP} \
  -function {ground VSS}

associate_supply_set SS_TOP -handle PD_TOP

# CPU domain (1.0V, switchable)
create_power_domain PD_CPU -elements {cpu_inst}
create_supply_net VDD_CPU -domain PD_CPU
create_supply_net VSS -domain PD_CPU

create_supply_set SS_CPU \
  -function {power VDD_CPU} \
  -function {ground VSS}

associate_supply_set SS_CPU -handle PD_CPU

# GPU domain (0.9V, switchable)
create_power_domain PD_GPU -elements {gpu_inst}
create_supply_net VDD_GPU -domain PD_GPU
create_supply_net VSS -domain PD_GPU

create_supply_set SS_GPU \
  -function {power VDD_GPU} \
  -function {ground VSS}

associate_supply_set SS_GPU -handle PD_GPU

# ===================================================================
# Result: Each domain has its own supply set
#   - PD_TOP uses SS_TOP (1.2V)
#   - PD_CPU uses SS_CPU (1.0V)
#   - PD_GPU uses SS_GPU (0.9V)
# ===================================================================

Naming convention: Use "SS_" prefix for supply sets matching the domain name. If PD_CPU is your domain, name its supply set SS_CPU. This makes the association obvious when reading UPF.

Associating Supply Sets with Domains

After creating a supply set, associate it with a power domain using associate_supply_set.

Syntax

associate_supply_set set_name -handle domain_name

Parameters

• set_name - Name of the supply set to associate
• -handle domain_name - Power domain receiving this supply set

Example

# Create supply set
create_supply_set SS_CPU \
  -function {power VDD_CPU} \
  -function {ground VSS}

# Associate with domain
associate_supply_set SS_CPU -handle PD_CPU

This tells UPF: "PD_CPU gets its power from the supplies defined in SS_CPU."

The associate_supply_set command is what actually connects the abstract supply set definition to the concrete power domain. Without this association, the supply set exists but isn't used.

Multiple Supply Sets per Domain

A single domain can have multiple supply sets for different operating states.

Active vs Retention Example

# ===================================================================
# Power-Gated Domain with Retention
# ===================================================================

create_power_domain PD_GPU -elements {gpu_inst}

# Supply nets
create_supply_net VDD_GPU -domain PD_GPU      # Main power (switchable)
create_supply_net VDD_RET -domain PD_GPU      # Retention power (always-on)
create_supply_net VSS -domain PD_GPU

# Active supply set: Used during normal operation
create_supply_set SS_GPU_ACTIVE \
  -function {power VDD_GPU} \
  -function {ground VSS}

# Retention supply set: Used during power-down to preserve state
create_supply_set SS_GPU_RET \
  -function {power VDD_RET} \
  -function {ground VSS}

# Primary association: Active mode
associate_supply_set SS_GPU_ACTIVE -handle PD_GPU

# ===================================================================
# Note: Retention strategy (later module) will specify using
# SS_GPU_RET for retention cells during power-down
# ===================================================================

Well Biasing with Supply Sets

Advanced process nodes may require explicit nwell and pwell supply specifications for body biasing techniques.

Standard Well Biasing

# Typical case: Nwell tied to VDD, Pwell tied to VSS
create_supply_set SS_CPU \
  -function {power VDD_CPU} \
  -function {ground VSS} \
  -function {nwell VDD_CPU} \
  -function {pwell VSS}

Advanced Body Biasing

For designs using adaptive body biasing (ABB) or reverse body biasing (RBB):

# Create separate well bias supplies
create_supply_net VDDN -domain PD_CPU   # N-well supply (can be > VDD_CPU)
create_supply_net VDDP -domain PD_CPU   # P-well supply (can be < VSS)

create_supply_set SS_CPU_ABB \
  -function {power VDD_CPU} \
  -function {ground VSS} \
  -function {nwell VDDN} \      # Forward body bias: VDDN > VDD_CPU
  -function {pwell VDDP}        # Reverse body bias: VDDP < VSS (negative)

# Isolation strategy (covered in later module)
set_isolation ISO_GPU -domain PD_GPU \
  -isolation_supply_set SS_TOP \   # Use always-on supply, not GPU supply
  -clamp_value 0

# Level shifter crossing from low-voltage to high-voltage
# Typically uses supplies from destination domain
set_level_shifter LS_CPU_TO_TOP -domain PD_CPU \
  -location parent
  # Implicitly uses SS_TOP supplies (parent domain)

# ===================================================================
# Complete UPF: Domains + Supply Nets + Supply Sets
# ===================================================================

# ===================================================================
# TOP DOMAIN (Always-on, 1.2V)
# ===================================================================
create_power_domain PD_TOP -include_scope

create_supply_net VDD_TOP -domain PD_TOP
create_supply_net VSS -domain PD_TOP

create_supply_set SS_TOP \
  -function {power VDD_TOP} \
  -function {ground VSS}

associate_supply_set SS_TOP -handle PD_TOP

# ===================================================================
# CPU DOMAIN (Power-gated, 1.0V, with retention)
# ===================================================================
create_power_domain PD_CPU -elements {cpu_inst}

create_supply_net VDD_CPU -domain PD_CPU
create_supply_net VDD_RET -domain PD_CPU
create_supply_net VSS -domain PD_CPU

# Active mode supply set
create_supply_set SS_CPU_ACTIVE \
  -function {power VDD_CPU} \
  -function {ground VSS}

# Retention mode supply set
create_supply_set SS_CPU_RET \
  -function {power VDD_RET} \
  -function {ground VSS}

associate_supply_set SS_CPU_ACTIVE -handle PD_CPU

# ===================================================================
# GPU DOMAIN (Power-gated, 0.9V)
# ===================================================================
create_power_domain PD_GPU -elements {gpu_inst}

create_supply_net VDD_GPU -domain PD_GPU
create_supply_net VSS -domain PD_GPU

create_supply_set SS_GPU \
  -function {power VDD_GPU} \
  -function {ground VSS}

associate_supply_set SS_GPU -handle PD_GPU

# ===================================================================
# Summary:
# - 3 domains: PD_TOP (always-on), PD_CPU (gatable), PD_GPU (gatable)
# - 4 supply sets: SS_TOP, SS_CPU_ACTIVE, SS_CPU_RET, SS_GPU
# - PD_CPU has 2 sets (active + retention), others have 1
# ===================================================================

# INCOMPLETE: Supply set created but not associated
create_supply_set SS_CPU \
  -function {power VDD_CPU} \
  -function {ground VSS}
# Missing: associate_supply_set SS_CPU -handle PD_CPU

# COMPLETE:
create_supply_set SS_CPU \
  -function {power VDD_CPU} \
  -function {ground VSS}
associate_supply_set SS_CPU -handle PD_CPU

# WRONG: Missing ground function
create_supply_set SS_CPU \
  -function {power VDD_CPU}

# CORRECT: Include both power and ground
create_supply_set SS_CPU \
  -function {power VDD_CPU} \
  -function {ground VSS}

# WRONG: VDD_CPU not created yet
create_supply_set SS_CPU \
  -function {power VDD_CPU} \
  -function {ground VSS}

# CORRECT: Create nets before referencing them
create_supply_net VDD_CPU -domain PD_CPU
create_supply_net VSS -domain PD_CPU

create_supply_set SS_CPU \
  -function {power VDD_CPU} \
  -function {ground VSS}

# ===================================================================
# Complete Supply Hierarchy Exercise Solution
# ===================================================================

# TOP DOMAIN: Always-on, 1.2V
create_power_domain PD_TOP -include_scope
create_supply_net VDD_AON -domain PD_TOP
create_supply_net VSS -domain PD_TOP

create_supply_set SS_TOP \
  -function {power VDD_AON} \
  -function {ground VSS}

associate_supply_set SS_TOP -handle PD_TOP

# MODEM DOMAIN: Power-gated, 1.0V, with retention
create_power_domain PD_MODEM -elements {modem_inst}
create_supply_net VDD_MDM -domain PD_MODEM
create_supply_net VDD_RET -domain PD_MODEM
create_supply_net VSS -domain PD_MODEM

# Active mode supply set
create_supply_set SS_MDM_ACTIVE \
  -function {power VDD_MDM} \
  -function {ground VSS}

# Retention mode supply set
create_supply_set SS_MDM_RET \
  -function {power VDD_RET} \
  -function {ground VSS}

associate_supply_set SS_MDM_ACTIVE -handle PD_MODEM

# SENSOR DOMAIN: Always-on, 0.9V
create_power_domain PD_SENSOR -elements {sensor_hub}
create_supply_net VDD_SENSOR -domain PD_SENSOR
create_supply_net VSS -domain PD_SENSOR

create_supply_set SS_SENSOR \
  -function {power VDD_SENSOR} \
  -function {ground VSS}

associate_supply_set SS_SENSOR -handle PD_SENSOR

# ===================================================================
# Result Summary:
# - PD_TOP: SS_TOP (VDD_AON 1.2V, always-on)
# - PD_MODEM: SS_MDM_ACTIVE (VDD_MDM 1.0V) and SS_MDM_RET (VDD_RET)
# - PD_SENSOR: SS_SENSOR (VDD_SENSOR 0.9V, always-on)
# ===================================================================