Analyzing Power Distribution Networks (PDN)

When to Use

• Analyzing DC voltage and current distribution on PCB power rails
• Checking design rules (max current density, voltage margins, via current limits)
• Discovering and listing power nets on an imported PCB layout
• Assigning source/load/sense topology for PDN analysis
• Running batch analysis across multiple power rails on a board
• Inferring nominal voltage from standard PCB net naming conventions

When NOT to Use

• Importing PCB layouts (Gerber, ODB++, Allegro) — use matlab-read-pcb-layout
• Analyzing S-parameters, fields, or EM performance — use matlab-analyze-em
• Analyzing crosstalk between signal traces — use matlab-design-pcb-txline
• Defining dielectric or conductor materials — use matlab-manage-pcb-material
• Modeling via structures — use matlab-model-via

Typical Workflow

1. Before: matlab-read-pcb-layout — import the PCB layout from Gerber/ODB++/Allegro
2. This skill: Run DC analysis, check IR drop, evaluate design rules, batch-analyze nets
3. After: Iterate on the physical design in CAD and re-import, or use results to inform stackup changes via matlab-manage-pcb-material

Quick Reference

PCB Import and Net Discovery

Importing a PCB Layout

pcbFileRead imports a PCB file and returns an object for hierarchical inspection. Supported formats: native directory (CSV files), ODB++ (zipped or unzipped), and Cadence Allegro .brd (requires one-time extractaSetup()).

% Native format (directory containing CSV files)
pcb = pcbFileRead(fullfile(boardDir, 'pcie5_native'));

% ODB++ format
pcb = pcbFileRead(fullfile(boardDir, 'myboard.zip'));

% Allegro .brd (run extractaSetup() once first)
extractaSetup();  % one-time setup for Allegro support
pcb = pcbFileRead(fullfile(boardDir, 'myboard.brd'));

The returned object exposes: NumLayers, NumCadnets, NumPadStacks, NumComponents, NumParts, LayerHeight.

Listing All Nets

NetList = cadnetList(pcb);
disp(NetList);

Returns a table with columns: CadnetIdx, CadnetName, NumPins, Length. A real board may have 3000+ nets.

Finding Power Nets

There is no built-in findPowerNets function. Filter the cadnetList output using regex to identify power and ground nets by name:

netList = cadnetList(pcb);

% Define naming patterns (case-insensitive)
powerPatterns = ["^P\d+V", "^VDD", "^VCC", "^AVDD", "^DVDD", "^VDDO"];
groundPatterns = ["^GND", "^AGND", "^DGND", "^PGND", "^VSS", "^AVSS", "^DVSS"];

% Match power nets
isPower = false(height(netList), 1);
for p = powerPatterns
    isPower = isPower | ~cellfun(@isempty, regexpi(netList.CadnetName, p));
end
powerNets = sortrows(netList(isPower, :), 'NumPins', 'descend');

% Match ground nets
isGround = false(height(netList), 1);
for g = groundPatterns
    isGround = isGround | ~cellfun(@isempty, regexpi(netList.CadnetName, g));
end
groundNets = sortrows(netList(isGround, :), 'NumPins', 'descend');

% Filter by minimum pin count
minPins = 5;
powerNets = powerNets(powerNets.NumPins >= minPins, :);

% Search for a specific pattern (e.g., 0.8V rails)
idx = ~cellfun(@isempty, regexpi(powerNets.CadnetName, "P0V8"));
rails_0v8 = powerNets(idx, :);

Common power net naming conventions (case-insensitive):

• Power rails: P<digit>V<digit> (P0V8, P3V3_AUX, P12V), VDD*, VCC*, AVDD*, DVDD*, VDDO*
• Ground nets: GND*, AGND*, DGND*, PGND*, VSS*, AVSS*, DVSS*

Inferring Rail Voltage from Net Name

There is no built-in inferRailVoltage function. Parse voltage from net names using regex:

function nomV = parseNetVoltage(netName)
    netName = string(netName);
    % Pattern: P<int>V<frac> (e.g., P0V8 → 0.8, P3V3 → 3.3, P12V → 12.0)
    tok = regexp(netName, '(?i)P(\d+)V(\d*)', 'tokens');
    if ~isempty(tok)
        intPart = str2double(tok{1}{1});
        fracStr = tok{1}{2};
        if isempty(fracStr)
            nomV = intPart;
        else
            nomV = intPart + str2double(fracStr) / 10^numel(fracStr);
        end
        return;
    end
    % Pattern: explicit decimal (e.g., 3.3V, 1.8V)
    tok = regexp(netName, '(\d+\.\d+)\s*V', 'tokens');
    if ~isempty(tok)
        nomV = str2double(tok{1}{1});
        return;
    end
    % Pattern: millivolt (e.g., 800MV → 0.8)
    tok = regexp(netName, '(\d+)\s*MV', 'tokens', 'ignorecase');
    if ~isempty(tok)
        nomV = str2double(tok{1}{1}) / 1000;
        return;
    end
    nomV = NaN;
end

Usage in a loop:

for k = 1:height(powerNets)
    netName = powerNets.CadnetName{k};
    nomV = parseNetVoltage(netName);
    fprintf('%s → %.2f V\n', netName, nomV);
end

cadnet Object

Creating a Cadnet

cnet = cadnet(pcb, 'P0V8');

Properties:

Visualizing a Cadnet

show(cnet);

Finding Connected Components

findComponents returns a table with columns: Refdes, PinList, ComponentType, Part.

% All components on the net
allComps = findComponents(cnet);

% Filter by component type
inductors = findComponents(cnet, "ComponentType", "Inductor");
ics       = findComponents(cnet, "ComponentType", "IC");
resistors = findComponents(cnet, "ComponentType", "Resistor");
caps      = findComponents(cnet, "ComponentType", "Capacitor");

The Refdes values are strings -- use them directly for Source/Load/Sense assignment in setNetworkParameters.

Getting Detailed Cadnet Data

data = cadnetData(cnet);
s = shapes(cnet);

powerDistributionNetwork Object

Creating a PDN Model

PDN = powerDistributionNetwork(cnet);

Properties:

PDN Configuration

setNetworkParameters -- Assign Source, Load, Sense, Plating

Use findComponents output to assign topology:

% Manual assignment using RefDes from findComponents
setNetworkParameters(PDN, ...
    Source=sourceRefDes, ...
    Load=sinkRefDes, ...
    Sense=senseRefDes, ...
    PlatingThickness=0.002);

% Auto-assign defaults (fallback when topology is unclear)
setNetworkParameters(PDN, AutoAssignDefault='True');

• Source -- RefDes of the power source (typically an inductor). Use all inductors for multiphase rails.
• Load -- RefDes of the load (typically an IC). Use all ICs on the net.
• Sense -- RefDes of the sense component (typically a resistor or test point).
• PlatingThickness -- Via barrel plating thickness in inches (e.g., 0.002 = 2 mil ≈ 1.4 oz copper).

#### Sense Component Resolution

The Sense parameter is required. When no test point is available on the net, use a resistor as the sense component:

tp = findComponents(cnet, 'ComponentType', 'Test Point');
if ~isempty(tp)
    senseRef = tp.Refdes;
else
    res = findComponents(cnet, 'ComponentType', 'Resistor');
    senseRef = res.Refdes(1);  % use first resistor as sense fallback
end
setNetworkParameters(PDN, Source=src, Load=load, Sense=senseRef, ...
    PlatingThickness=0.002);

#### Multiphase Rails

For multiphase VRM designs, multiple inductors feed the same rail. Always use all inductors as Source, not just the first:

inductors = findComponents(cnet, "ComponentType", "Inductor");
setNetworkParameters(PDN, Source=inductors.Refdes);  % handles multiphase

setDCParameters -- Set Electrical Parameters

setDCParameters(PDN, "NominalVoltage", 0.8, "LoadCurrent", 1);  % placeholder — ask user for actual value

setDCRules -- Set DC Design Rules

setDCRules(PDN, ...
    "MaxCurrentDensity", 0.5, ...
    "MaxVoltage", 0.816, ...
    "MinVoltage", 0.784, ...
    "MaxViaCurrent", 500);

DC rules units (mixed — specific to this API):

Voltage tolerance guidelines:

DC Analysis

Voltage Distribution

voltage(PDN);

% Show design rule violations
voltage(PDN, ShowViolation=true);

Current Distribution

current(PDN);

% Show current direction arrows
current(PDN, Direction='on');

Inspecting PDN Configuration Before Analysis

Check the PDN model properties after setup to verify assignments:

PDN.Source
PDN.Load
PDN.Sense
PDN.NominalVoltage
PDN.LoadCurrent

Workflow: Single-Net PDN Analysis

Interactive workflow for analyzing one power net end-to-end:

%% Step 1: Import the board
pcb = pcbFileRead(fullfile(boardDir, 'pcie5_native'));

%% Step 2: Identify power nets
netList = cadnetList(pcb);
powerPatterns = ["^P\d+V", "^VDD", "^VCC", "^AVDD", "^DVDD"];
isPower = false(height(netList), 1);
for p = powerPatterns
    isPower = isPower | ~cellfun(@isempty, regexpi(netList.CadnetName, p));
end
powerNets = sortrows(netList(isPower, :), 'NumPins', 'descend');
disp(powerNets);

%% Step 3: Create cadnet and inspect
cnet = cadnet(pcb, 'P0V8');
show(cnet);

%% Step 4: Discover components for topology assignment
allComps = findComponents(cnet);
inductors = findComponents(cnet, "ComponentType", "Inductor");
ics       = findComponents(cnet, "ComponentType", "IC");
resistors = findComponents(cnet, "ComponentType", "Resistor");

%% Step 5: Resolve voltage from net name
nomV = parseNetVoltage('P0V8');  % 0.8 V (see helper function above)

%% Step 6: Create and configure PDN
PDN = powerDistributionNetwork(cnet);

setNetworkParameters(PDN, ...
    Source=inductors.Refdes, ...
    Load=ics.Refdes, ...
    Sense=resistors.Refdes(1), ...
    PlatingThickness=0.002);

setDCParameters(PDN, "NominalVoltage", nomV, "LoadCurrent", 1);  % placeholder — ask user for actual value

tolerancePct = 0.02;  % 2% for <1V rails
setDCRules(PDN, ...
    "MaxCurrentDensity", 0.5, ...
    "MaxVoltage", nomV * (1 + tolerancePct), ...
    "MinVoltage", nomV * (1 - tolerancePct), ...
    "MaxViaCurrent", 500);

%% Step 7: Run analysis
voltage(PDN, ShowViolation=true);
current(PDN, Direction='on');

Workflow: Multi-Net Batch Analysis

For batch analysis of all power rails on a board (loop with skip logic, per-rail spec tables), see references/batch-analysis.md.

Common Patterns

Component Refdes Usage

findComponents returns Refdes as a string -- use directly in setNetworkParameters. Use all matching components, not just the first:

inductors = findComponents(cnet, "ComponentType", "Inductor");
setNetworkParameters(PDN, Source=inductors.Refdes);  % all inductors

When to Use AutoAssignDefault

Use AutoAssignDefault='True' only when:

• No inductors found on the net (LDO rails, connector-fed rails)
• User explicitly requests automatic topology assignment
• Quick screening mode where accuracy is secondary

Always prefer explicit findComponents-based assignment.

Z-Axis Visualization

Use daspect to see Z-axis detail in 3D views:

ax = gca;
daspect(ax, [1, 1, 0.05]);

Pitfalls

1. `inferRailVoltage` returns `NaN` for unrecognized nets. Guard with isnan() before using the result in calculations or display (e.g., string(NaN) produces "NaN", not missing).

1. `Sense` parameter is required in `setNetworkParameters`. When no test point exists on the net, use a resistor as the sense component. Omitting Sense will cause errors during analysis.

1. `AutoAssignDefault` is a fallback, not a first choice. It may produce incorrect topology assignments on complex rails (LDO, connector-fed). Prefer explicit assignment via findComponents output.

1. `LoadCurrent` cannot be inferred from board data — STOP and ask. Unlike NominalVoltage (which can be parsed from net names), load current must come from IC datasheets or system power budgets. Before calling setDCParameters, ask the user for the actual load current and STOP execution — do not proceed until the user responds. Do NOT assume 1 A or any default without explicit user confirmation. Once the user responds that they don't have it or asks you to proceed, present these estimation options and let them choose:

• Per-pin heuristic: 0.5 A × number of load pins (e.g., 130 pins → 65 A)
• TDP-based: total power budget ÷ rail voltage (e.g., 40 W ÷ 0.8 V = 50 A)
• Fixed conservative: 10 A per load IC (quick screening)
• 1 A token: minimal value to verify the workflow runs end-to-end

Only after the user selects an option or provides a value, proceed with setDCParameters.

1. `LoadCurrent` must be a vector, not a scalar total. When multiple load ICs exist on a rail, setDCParameters requires one current value per load. For example, with loads U1 (4.8 A) and U9 (0.2 A): setDCParameters(PDN, LoadCurrent=[4.8, 0.2]). Passing a scalar (e.g., LoadCurrent=5) errors when the topology has more than one load.

1. PDN units are mixed — not all SI. PlatingThickness is in inches (not meters): 0.002 = 2 mil ≈ 1.4 oz copper. MaxCurrentDensity is mA/mil² (not A/mm²). MaxViaCurrent is mA (not A). MinVoltage/MaxVoltage are absolute volts. Using meters for plating (e.g., 35e-6) or amps for via current (e.g., 1) produces wildly incorrect results.

1. Batch mode: skip rather than block. When a rail is missing voltage, source, or load information, skip it and report which rails were skipped and why. Do not halt the entire batch for one incomplete rail.

1. Large boards have 3000+ nets. cadnetList returns all nets. Filter with regex on CadnetName to narrow to power/ground nets, then further filter by NumPins or specific patterns.

1. `cnet.Voltage` is unreliable. The Voltage property on the cadnet object is populated heuristically from the PCB file and often returns '0.000' even for valid power rails. Always parse the voltage from the net name using regex instead of relying on this property.

1. No built-in `findPowerNets` or `inferRailVoltage`. These do not exist as MATLAB functions. Use cadnetList(pcb) + regexpi filtering for net discovery, and the parseNetVoltage helper (defined in this skill) for voltage inference from net names.

1. `.brd` files require extracta — STOP if unavailable. If the user only has a .brd file and extractaSetup() returns [] or errors, STOP and inform the user: extracta (from a Cadence install) is required. Offer alternatives: (a) provide the path to extracta.exe, (b) export from Allegro as ODB++ or native CSV format, (c) use a colleague's Cadence install to convert. Do not attempt workarounds.

Related Skills

• matlab-read-pcb-layout -- Importing PCB/package layouts for PDN analysis
• matlab-manage-pcb-material -- Substrate and conductor material setup
• matlab-model-via -- Via modeling for power delivery paths
• matlab-analyze-em -- EM analysis fundamentals

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