Electronics Guide

Basic Principles

In a single-point ground system, each circuit or subsystem has a dedicated ground conductor that runs directly to the central grounding point. No ground currents from one circuit flow through another circuit's ground conductor. The central point is typically located at the power supply, where the main power return provides a low-impedance connection to the primary reference.

Key characteristics of single-point grounding:

• Current isolation: High-current return paths are physically separate from sensitive signal returns
• Predictable voltage drops: Each circuit experiences only its own ground current effects
• Systematic design: The ground topology is explicit and easily analyzed
• Scalability: Additional circuits can be added without affecting existing ground connections

Series vs. Parallel Star

Two variations of single-point grounding address different requirements:

• Series connection (daisy chain): Ground conductors connect to each circuit in sequence, with a single return to the star point. This minimizes wiring, but each segment carries the return current of every circuit beyond it, so each circuit's ground is offset by the other circuits' currents. Where it must be used, place the most sensitive circuit nearest the star point, where that accumulated drop is smallest, and reserve the arrangement for circuits that can tolerate the coupling
• Parallel connection (true star): Each circuit has an independent ground conductor running directly to the star point. This provides maximum isolation but requires more wiring. It is essential for precision analog systems where any ground contamination is unacceptable

In practice, hybrid approaches often prove most practical, with true star connections for sensitive analog circuits and series connections for less critical functions.

Frequency Limitations

Single-point grounding is inherently a low-frequency technique. As frequency increases, the inductance of the ground conductors becomes significant:

• A typical wire has inductance of approximately 1 microhenry per meter
• At 1 MHz, this inductance presents an impedance of about 6 ohms per meter
• At 100 MHz, the impedance rises to about 600 ohms per meter, and a 1 meter conductor, a third of a wavelength long, no longer behaves as a simple inductance at all

These high impedances make long star-point connections ineffective at high frequencies, where ground planes become necessary. Where the changeover falls depends on conductor length and on how much ground impedance the circuit can tolerate. Henry Ott's widely quoted rule of thumb, from Noise Reduction Techniques in Electronic Systems, prefers a single-point ground below about 1 MHz and a multipoint ground above about 10 MHz; between the two, the usual test is whether the longest ground conductor is shorter than about one-twentieth of a wavelength. For a precision circuit the limit can fall well below 1 MHz: through the 6 ohms that a meter of wire presents at that frequency, a ground current of just 1 milliampere develops about 6 millivolts, thousands of times a microvolt-level signal.

Implementing Single-Point Grounds

Practical implementation requires attention to several details:

• Star point location: Place at the power supply output, where the main filter capacitors provide a low-impedance reference
• Conductor sizing: Size ground conductors for low resistance; high-current returns may need substantial cross-section
• Connection quality: Use crimped or welded connections at the star point; avoid creating additional resistance or thermoelectric junctions
• Physical arrangement: Route ground conductors to minimize loop areas and keep them away from noise sources
• Documentation: Clearly mark the ground topology in schematics and assembly drawings to ensure correct implementation

Electrical Characteristics

A ground plane's effectiveness derives from several properties:

• Low DC resistance: The wide cross-section provides very low resistance for DC and low-frequency currents
• Low inductance: Current can flow in many parallel paths, dramatically reducing effective inductance
• Return current concentration: High-frequency return currents naturally flow in the plane directly beneath the signal trace, minimizing loop area
• Shield effect: The plane provides electrostatic shielding between layers and from external fields

At high frequencies, return current flows in a narrow strip directly under the signal trace, with current density falling off with distance. For a narrow trace at height h above the plane, the return current per unit width of plane at a lateral distance D from the trace centerline is approximately

J(D) = (I/πh) × 1/[1 + (D/h)²]

where I is the signal current. Half of the return current flows within one trace height of the centerline on either side, and about 80 percent within three heights. This natural current concentration minimizes the loop area formed by the signal and return paths, reducing both radiated emissions and susceptibility to external fields.

PCB Ground Plane Design

Printed circuit board ground planes require careful design to achieve their potential benefits:

• Solid copper pour: Use uninterrupted copper on one or more layers; avoid unnecessary cuts, slots, or split planes
• Via stitching: Connect ground planes on multiple layers with frequent vias to maintain low impedance at high frequencies
• Component placement: Position components to minimize return current path lengths and avoid forcing return currents around obstacles
• Slot avoidance: Never route signals across slots in the ground plane; the interrupted return path increases inductance and radiates

When signals must transition between layers, place ground vias adjacent to signal vias to provide a low-inductance return current path through the plane transition.

Ground Plane Partitioning

In some systems, designers partition the ground plane to steer return currents while keeping impedance low elsewhere. Because any cut forces return current to detour around it, these techniques are a considered exception rather than a default:

• Moat and bridge: Cut a gap in the plane with a narrow bridge at one point, forcing ground current through a defined path
• Separate planes with single connection: Use physically distinct planes for analog and digital, connected at one carefully chosen point
• Partial cuts: Interrupt the plane over part of its width to guide return currents while maintaining low impedance for other currents

Partitioning must be done thoughtfully; an improperly placed gap forces return currents into long detours that increase both noise and radiation. Every signal that crosses a gap must have an adjacent ground path at the crossing point. For most boards a solid, unbroken plane combined with careful component placement outperforms a cut plane.

Multi-Layer Considerations

Multi-layer PCBs offer additional ground plane options:

• Internal ground plane: A ground plane on an internal layer gives the surface traces above it a close, continuous reference and shields them from circuitry on the far side of the plane
• Multiple ground planes: Additional ground layers, stitched together with vias, lower the reference impedance further and give each signal layer an adjacent return plane
• Ground-power pairs: Adjacent ground and power planes form a distributed bypass capacitor that improves high-frequency power integrity

The stackup design significantly affects both signal integrity and power delivery. Symmetric stackups help prevent board warping during manufacturing and provide predictable impedances for controlled-impedance traces.

Hierarchical Ground Structure

Complex systems benefit from a multi-level star topology:

• System star: The main grounding point where power supply return, chassis ground, and subsystem grounds meet
• Subsystem stars: Secondary star points that collect grounds within each major subsystem
• Local grounds: Individual circuit ground returns within subsystems

This hierarchy allows high-current returns to reach the system star through dedicated conductors while sensitive circuits within subsystems remain isolated from each other and from high-current effects.

Current Magnitude Ordering

When designing star ground systems, arrange the returns by current magnitude:

• Highest currents closest to power return: Power supply filter capacitors, power stage returns, and motor drives connect with the shortest, lowest-impedance paths, so that their large currents develop the smallest possible drops
• Medium currents next: Digital logic, interface circuits, and moderate-power analog stages
• Lowest currents on dedicated conductors: Precision analog front ends, reference circuits, and sensitive measurement inputs each return to the star point on a conductor that carries no other circuit's current

This arrangement keeps the voltage drops of high currents out of the conductors that sensitive circuits use. Where returns must instead share a conductor in series, the series rule applies: the most sensitive circuit goes nearest the star point, where the accumulated drop of the other circuits' currents is smallest.

Grounding Point Selection

The location of the star point significantly affects system performance:

• At the power supply: Provides a solid reference tied to the main filter capacitors and power return
• At the ADC: In mixed-signal systems, placing the star at the analog-to-digital converter keeps ground potential differences out of the critical conversion
• At the signal source: For remote sensing applications, grounding at the sensor minimizes errors from ground potential differences

The optimal location depends on the specific application and which ground relationships are most critical for system accuracy.

Bus Bar Implementation

For high-current systems, a ground bus bar can serve as the star point:

• Material: Heavy copper or aluminum bar stock provides very low resistance
• Connection hardware: Use bolted or welded connections to maintain low contact resistance
• Surface treatment: Keep connection surfaces clean and use anti-oxidation compounds
• Mounting: Insulate the bus bar from the chassis if needed to prevent unintended current paths

A bus bar approximates a single point because the impedance between its connections is small, though not zero: a copper bar 25 by 6 millimeters still has about 0.11 milliohm of resistance per meter, so 100 amperes flowing along 10 centimeters of it develops about 1.1 millivolts, enough to matter beside a microvolt-level measurement. Its low impedance makes connection ordering less critical than with wire connections, but it does not make it irrelevant.

Ground Loop Formation

Ground loops typically form when:

• Multiple equipment grounds: Two pieces of equipment, each with safety ground connections, linked by a signal cable create a loop through the power system
• Redundant ground connections: Connecting grounds at multiple points within a system creates parallel paths
• Cable shields grounded at both ends: Shield current can flow in a loop formed by the shield and the ground system

The loop acts as a single-turn transformer that couples magnetic fields from nearby power wiring, motors, or other sources into the signal path. Even small magnetic flux changes induce voltages that can overwhelm microvolt-level signals. Just as often, nothing needs to be induced: leakage current from the line-filter capacitors and power-transformer capacitance of the connected equipment flows in the building's safety-ground conductors and leaves the two equipment grounds at slightly different potentials, which then drive current through the signal cable's shield or return conductor. Either way, the noise appears as a voltage drop along that shared conductor, in series with the signal of an unbalanced connection.

Identifying Ground Loops

Ground loop symptoms include:

• Power line frequency hum: 50 or 60 Hz interference, often with significant harmonic content
• Noise that varies with nearby equipment: Interference that changes when motors, transformers, or other equipment operates
• Noise that disappears when the interconnection is isolated: Inserting an isolation transformer or isolator in the signal path, or temporarily running one unit from batteries, removes the noise (a diagnostic, not by itself a solution)
• Position-dependent noise: Moving cables or equipment changes the interference level

Systematic testing can identify ground loops by temporarily disconnecting signal cables and shields one at a time and observing which change affects the noise. Never lift a safety ground to run the test: a unit whose protective earth has been removed can carry a lethal fault voltage on its chassis.

Prevention Techniques

Preventing ground loops requires systematic design:

• Single-point grounding: Ensure only one ground connection between any two subsystems
• Differential signaling: Transmit signals as voltage differences that are independent of ground potential variations
• Signal isolation: Use transformers, optocouplers, or capacitive isolators to break ground connections in signal paths
• Ground equalization: Bond the equipment grounds together with a heavy conductor, ideally run alongside the signal cable. It cannot reduce the voltage that a changing magnetic field induces in the loop, but it lowers the ground potential difference that a given ground current develops between the two ends, and it carries most of that current in place of the cable's shield or return conductor

Cable Shield Grounding

Shield grounding requires careful consideration:

• Single-end grounding: Ground the shield at one end only, so that no ground-loop current can flow in it. Connect it at the end where the signal circuit itself is grounded: at the source when the source is grounded, and at the receiver when the source floats. The shield stops electric-field (capacitive) pickup at low frequencies but, carrying no current, does nothing against magnetic fields; those are countered by keeping the signal loop small, as a twisted pair does
• Both-end grounding: Ground the shield at both ends, ideally with a 360-degree bond at each connector. This keeps the shield effective at radio frequencies, where a shield grounded at one end loses its effectiveness once the cable approaches a twentieth of a wavelength, but it lets ground-loop current flow in the shield at power-line frequencies
• Hybrid grounding: Ground the shield directly at one end and through a capacitor at the other, so that it is grounded at one end at power-line frequencies and at both ends at radio frequencies

For audio frequencies, single-end grounding usually provides the best results. At radio frequencies, both-end grounding is necessary for effective shielding.

Breaking Ground Loops

When ground loops cannot be prevented by topology, they can be broken or mitigated:

• Isolation transformers: Audio and signal transformers provide galvanic isolation while passing the signal
• Optical isolation: Optocouplers and fiber optics completely eliminate electrical connection
• Balanced connections: Balanced (differential) connections reject common-mode voltage differences
• Ground lift switches: Many audio and instrument units provide a switch that disconnects the signal ground or cable shield from the chassis; never substitute an adapter that lifts the protective earth of a power plug

The choice of solution depends on frequency range, signal type, and the magnitude of the ground potential difference.

Digital Ground Noise

Digital circuits create ground noise through several mechanisms:

• Switching current spikes: CMOS logic draws current pulses during transitions, creating voltage drops across ground inductance
• Simultaneous switching output noise: Multiple outputs switching together create large current transients
• Power supply ringing: LC resonances in the power distribution network create oscillatory noise
• Clock distribution: Clock signals and their harmonics couple to ground through parasitic capacitance

How much ground noise results depends on the layout as much as on the logic. A single fast output charging 15 picofarads through 3.3 volts in 1 nanosecond draws about 50 milliamperes. Even if that current takes a full nanosecond to rise, it develops 100 millivolts across just 2 nanohenries of shared ground inductance, by the ground-bounce relation V = L di/dt described below. That is far more than the microvolt-level signals that precision analog circuits resolve.

Separation Strategies

Historically, designers managed analog-digital interaction by physically splitting the ground plane into separate analog and digital regions joined at a single point. Current best practice, reflected in the application notes of the major data-converter manufacturers, instead favors a single unbroken ground plane with the board partitioned by component placement. High-frequency return current naturally flows in the plane directly beneath its signal trace, so digital return current has little incentive to stray into the analog region as long as digital and analog components and traces are kept in their own areas.

• Unified plane with partitioned layout (preferred): Keep one solid ground plane and separate the analog and digital components and traces into distinct board regions, letting return currents stay beneath their own signals
• Split plane with bridge: Divide the plane and join the halves at one point near the converter. This can help in specific cases but risks impedance discontinuities, enlarged return loops, and slot-antenna radiation if any signal crosses the gap; use it with caution
• Separate power supplies: Independent regulators or filtered rails for the analog and digital sections eliminate shared supply impedance
• Ferrite separation: Ferrite beads between supply rails provide high-frequency isolation while maintaining a DC connection

The optimal strategy depends on the system architecture and the specific conversion devices used, but a single continuous ground plane is the safer default for most mixed-signal boards.

Data Converter Grounding

Analog-to-digital and digital-to-analog converters require special attention as the interface between domains:

• Manufacturer recommendations: Follow the specific grounding guidance in the converter datasheet; devices vary significantly
• AGND and DGND pins: These labels denote the converter's internal analog and digital sections, not a mandate to split the board ground; most datasheets direct that both pins connect to the same low-impedance ground plane
• Ground connection point: The analog-digital ground connection often works best directly at the converter, making it the effective star point for ground domains
• Return current paths: Ensure digital return currents do not flow through analog ground areas

Many high-resolution ADC data sheets direct that AGND and DGND be tied together immediately at the device and connected to the analog ground plane, with each supply pin decoupled locally. The reasoning is that a converter is an analog component, and the digital current through its DGND pin stays small as long as its outputs drive only a light load.

Routing Across Ground Boundaries

Signals crossing between the analog and digital regions require care, whether the two regions share one plane or sit on split planes:

• Cross at the bridge: Where the plane is split, route crossing signals over the bridge, where both grounds are at the same potential and the return current has a continuous path
• Provide return paths: Include ground connections adjacent to signals crossing the boundary
• Avoid high-frequency crossings: Keep fast digital signals away from analog regions; use level shifters or buffers at the boundary if needed
• Consider isolation: For very sensitive systems, use digital isolators at the boundary

Safety Ground Requirements

Safety ground, also called protective earth, serves to protect users from electrical shock:

• Fault current path: Provides a low-impedance path for fault currents to trip protective devices
• Touch potential limiting: Maintains accessible metal surfaces at safe potentials relative to earth
• Regulatory requirements: Must meet applicable safety standards (for example, IEC 62368-1 for audio/video, information and communication technology equipment, which has replaced the withdrawn IEC 60950-1, or IEC 61010-1 for measurement, control, and laboratory equipment)
• Never interrupt: Safety ground connections must be permanent and reliable

Safety ground must never be compromised for noise reduction or any other purpose. Alternative techniques must be used to address noise issues while maintaining safety.

Chassis Ground Functions

The chassis or enclosure provides several electrical functions:

• Electromagnetic shielding: A conductive enclosure shields internal circuits from external fields and contains internally generated emissions
• Electrostatic reference: Provides a local ground reference for cable shields and external connections
• Thermal management: Conducts heat from internal components to the environment
• Mechanical protection: Protects circuits from physical damage and contamination

These functions may or may not require direct connection to signal ground, depending on the application.

Chassis-to-Circuit Ground Connection

The connection between chassis and circuit ground requires careful consideration:

• Single-point connection: Connect chassis to circuit ground at one point to avoid ground loops through the chassis
• Connection location: Typically at the power entry point where safety ground enters the equipment
• High-frequency bonding: Additional capacitive connections may be needed for RF shielding while avoiding low-frequency ground loops
• Isolated systems: Some systems intentionally isolate circuit ground from chassis, requiring careful management of the potential difference

Grounding Conductor Specifications

Safety grounding conductors must meet specific requirements:

• Current capacity: Must carry expected fault currents without excessive temperature rise
• Low impedance: Must ensure fault currents are large enough to trip protective devices quickly
• Mechanical integrity: Must remain connected under fault conditions including mechanical stress
• Color coding: Green or green/yellow striped wire is reserved for safety ground

Never use the safety ground conductor as a signal return path, as fault conditions or ground potential differences could damage equipment or corrupt signals.

Surface Leakage Protection

PCB surfaces accumulate contamination that creates conductive paths between traces. At high impedances, these leakage currents can cause significant errors:

• Contamination sources: Flux residue, humidity, dust, and handling contamination
• Leakage currents: Surface resistance of 10¹⁰ ohms (not uncommon) creates 1 nanoampere of leakage per 10 volts of potential difference
• Error magnitudes: 1 nanoampere into 10 megohms creates a 10 millivolt error

Guard rings address this by intercepting leakage currents before they reach the sensitive node.

Guard Ring Implementation

A guard ring is a conductive trace that completely surrounds the sensitive node:

• Physical design: Continuous ring with no gaps, on the same PCB layer as the protected node
• Voltage driving: The guard is driven to the same potential as the protected node, eliminating any voltage difference that would drive leakage current
• Buffer requirements: Any offset between guard and node drives leakage across the gap between them, so the guard driver needs very low offset voltage and noise; a 1 millivolt offset across the same 10¹⁰ ohms of surface resistance still drives 0.1 picoampere, which matters in electrometer work
• Multiple layers: Extend guards through all PCB layers beneath the sensitive node

With the guard at the same potential as the protected node, any surface leakage flows from external points to the guard, not to the protected node.

Driven Shields

Driven shields extend the guard concept to cables and connectors:

• Coaxial cable shields: Driving the shield to follow the center conductor voltage largely removes the effect of cable capacitance and leakage
• Triaxial cables: Inner shield serves as a driven guard; outer shield provides electrostatic protection and safety ground
• Connector guards: Guard rings in connector bodies protect high-impedance pins

Driven shields are essential for measuring high-impedance sources through cables, where cable capacitance and leakage would otherwise dominate the measurement.

Guard Driver Circuits

The guard driver must track the protected node accurately:

• Unity gain buffer: The simplest configuration uses a voltage follower driving the guard
• Low offset: Offset voltage appears as an equivalent input error; chopper-stabilized amplifiers may be needed
• Bandwidth considerations: The guard must track signal changes; inadequate bandwidth allows transient leakage
• Stability: The capacitive load of the guard can cause oscillation; compensation may be required

Faraday Shields

Faraday shields provide electrostatic isolation between circuit elements:

• Transformer shields: Conductive foil between primary and secondary windings blocks capacitive coupling while allowing magnetic coupling; its overlapping ends are insulated from each other so that the foil does not form a shorted turn
• Amplifier shields: Metal cans or PCB copper pours around sensitive amplifiers block external electric fields
• Ground connection: The shield must connect to the appropriate ground reference, typically the signal ground of the protected circuit

Faraday shields differ from guards in being grounded rather than driven, providing protection against external fields rather than leakage.

Resistance at DC and Low Frequencies

At DC and low frequencies, ground impedance is dominated by resistance:

• Conductor resistance: Determined by material resistivity, length, and cross-sectional area
• Contact resistance: Connections add resistance that can exceed conductor resistance if poorly made
• Temperature effects: Conductor resistance increases with temperature; copper increases approximately 0.4% per degree Celsius

For copper conductors, resistance is approximately 17 milliohms per meter for 1 square millimeter cross-section. Doubling the cross-section halves the resistance.

Inductance at High Frequencies

At higher frequencies, inductance dominates ground impedance:

• Self-inductance: Round wire has approximately 1 microhenry per meter; flat conductors have lower inductance
• Mutual inductance: Parallel conductors couple magnetically, affecting total inductance
• Skin effect: At high frequencies, current crowds toward the conductor surface, within about 66 micrometers of it in copper at 1 MHz, increasing effective resistance

Inductive reactance is X_L = 2πfL, where f is the frequency and L the inductance. At 10 MHz, 1 microhenry presents 63 ohms, far exceeding the DC resistance of practical conductors.

Minimizing Ground Inductance

Several techniques reduce ground inductance:

• Wide, flat conductors: For the same cross-section, a wide, thin strap has less inductance than a round wire, and keeping a strap short relative to its width lowers it further
• Ground planes: Continuous copper provides the lowest inductance by offering multiple parallel paths
• Short connections: Inductance grows roughly in proportion to length; minimize the distance to the ground reference
• Multiple vias: Parallel vias reduce inductance when transitioning between layers
• Adjacent return paths: Keeping signal and return conductors close reduces loop inductance

Ground Bounce

Ground bounce occurs when fast current changes through ground inductance create voltage transients:

• Mechanism: V = L di/dt, where L is the inductance of the ground path and di/dt the rate of change of the current through it; fast switching creates high di/dt and significant voltage spikes
• Effects: Ground reference shifts relative to other circuits, causing noise and potentially false logic transitions
• Mitigation: Reduce inductance, slow edge rates where possible, use multiple ground pins on ICs, place bypass capacitors close to current sources

Ground bounce is particularly problematic in digital systems where many gates switch simultaneously, but the resulting noise affects analog circuits as well.

Measuring Ground Impedance

Characterizing ground impedance helps validate design assumptions:

• DC resistance: Measure with a four-wire ohmmeter to exclude lead resistance
• AC impedance: Inject a known current and measure the resulting voltage across the ground path
• Network analyzer: Directly measures impedance versus frequency
• Time domain reflectometry: Reveals impedance discontinuities along ground paths

Actual measurements often reveal higher impedances than calculations predict due to contact resistances and unexpected current paths.

Design Process

A methodical approach to grounding design includes:

1. Identify all current sources and sinks: Map out where currents flow, including power, signal, and parasitic currents
2. Characterize current magnitudes and frequencies: Understanding the spectrum of ground currents guides topology choices
3. Define sensitivity requirements: Determine acceptable noise levels for each circuit
4. Select grounding topology: Choose single-point, multi-point, or hybrid based on frequency range and isolation needs
5. Design current paths: Route conductors to minimize coupling between high-current and sensitive circuits
6. Specify connections: Define connection points, conductor sizes, and hardware
7. Verify design: Calculate or simulate voltage drops and coupling to confirm requirements are met

Documentation

Ground system documentation ensures correct implementation and maintainability:

• Grounding diagram: Schematic showing all ground connections and their relationships
• Current flow paths: Indication of expected current magnitudes and directions
• Connection specifications: Hardware, torque values, and surface preparation requirements
• Test points: Locations for verifying ground integrity and impedance

Clear documentation prevents well-intentioned but misguided modifications during production or maintenance.

Common Mistakes

Grounding problems often result from these common errors:

• Assuming grounds are at the same potential: All grounds have impedance; never assume two ground points are at identical voltage
• Sharing return paths: Current flows in the lowest-impedance path, which may include sensitive circuits
• Ignoring high-frequency effects: Designs that work at low frequencies may fail when high-frequency components are present
• Multiple ground connections: Redundant, unplanned connections between units or subsystems create ground loops
• Underestimating parasitic currents: Capacitive coupling creates currents that must return through the ground system

Troubleshooting Ground Problems

When ground-related noise appears, systematic troubleshooting identifies the source:

• Characterize the noise: Measure frequency content, amplitude, and correlation with system activity
• Trace current paths: Use a current probe to follow ground currents and identify unexpected paths
• Measure voltage differences: Check potential between ground points that should be at the same voltage
• Isolate sections: Disconnect subsystems to identify which contributes the noise
• Test modifications: Try alternative grounding connections to understand the sensitivity

Patience and systematic investigation eventually reveal the cause, which is often different from initial assumptions.

Precision Measurement Systems

High-resolution data acquisition requires careful grounding:

• Single-point ground at the ADC reference
• One unbroken ground plane beneath the converter, with the analog and digital circuitry kept to their own regions
• Guarded inputs for high-impedance sensors
• Shielded cables with single-end shield grounding
• A separate low-noise supply for the analog section, galvanically isolated where the measurement must float

Audio Systems

Professional audio equipment uses specific grounding practices:

• Balanced (differential) connections between equipment
• Star ground topology within each unit
• Careful shield management to prevent ground loops
• Transformer isolation for challenging environments
• Single technical ground reference for the entire system

Mixed-Signal Systems

Systems combining analog and digital require careful ground management:

• A single continuous ground plane under both sections in most designs
• Analog and digital components and traces partitioned into separate board regions
• Data converters straddling the boundary, with AGND and DGND tied together at the device
• Routing that keeps digital return currents out of analog areas
• Adequate bypass capacitance at each supply pin and across the analog-digital boundary