Q1: How to choose an EDA tool?
A: The choice depends on the specific needs. For general circuit design, options like PADS or Cadence offer good performance-to-price ratios. Beginners in PLD design can start with integrated environments provided by chip manufacturers and transition to single-point tools for designs above a million gates.
Q2: Recommended EDA software for high-speed signal processing and transmission?
A: For conventional circuit design, Professional PCB manufacturer EASHUB believes that INNOVEDA’s PADS is excellent, especially for 70% of applications. However, for high-speed, mixed-signal circuits, Cadence solutions offer good performance-to-price ratios. Mentor’s capabilities, especially in design process management, are noteworthy.
Q3: Explanation of PCB layer meanings?
A: Layers like Topoverlay display top component names. Multilayer defines pads or vias across multiple layers if specified. For instance, defining it as multilay on a 4-layer board will place the pad on all layers, while defining it for the top layer limits it to that layer.
Q4: Key considerations for high-frequency PCB design (2G or higher)?
A: High-frequency PCB design, like RF circuits, involves layout and routing considerations due to distributed effects. Tools like Mentor’s board station offer specialized RF design modules. Additionally, RF designs often require specific RF circuit analysis tools like Agilent’s eesoft with good interfaces to Mentor’s tools.
Q5: Rules for designing microstrip lines in high-frequency PCBs (2G or higher)?
A: RF microstrip line design requires extracting transmission line parameters using 3D field analysis tools, where all rules should be defined.
Q6: Protection and driving capability considerations for an 80MHz clock source on an all-digital signal PCB?
A: Ensuring clock driving capability often involves using a clock driver chip rather than protection circuits. Clock driver chips divide a clock signal among multiple loads, addressing concerns about driving capacity caused by multiple clock loads.
Q7: Interface recommendations for a separate clock signal board to minimize signal transmission effects?
A: Shorter clock signals experience fewer transmission line effects. For longer distances, differential signaling is advised. However, for slower clocks like 27MHz, it might not be necessary.
Q8: Addressing interference caused by harmonics (second and third) of clock lines (27M, SDRAM clock at 80M-90M) in the VHF band?
A: Modifying the duty cycle might help manage harmonics. For unidirectional clock signals, source-end series matching could suppress second reflections without affecting clock edge rates.
Q9: What is the topology of routing in PCB design?
A: Topology or routing order refers to the sequence of connections for multi-port networks.
Q10: How does adjusting routing topology enhance signal integrity?
A: The impact of topology on network signal quality varies with signal direction, type, and levels. Identifying which topology suits signal integrity requires a deep understanding of circuit principles, signal types, and routing complexity during pre-simulation.
Q1: How can layer arrangement reduce EMI issues?
A: Layer arrangement primarily provides short signal return paths, reduces coupling areas, and suppresses common-mode interference. Coupling ground and power layers tightly, extending the power layer slightly, aids in suppressing common-mode interference.
Q2: Why is copper pouring used?
A: Copper pouring serves several purposes: electromagnetic compatibility (EMC) shielding, meeting PCB process requirements, ensuring signal integrity, providing complete return paths for high-frequency digital signals, and catering to heat dissipation and specific device installation requirements.
Q3: What considerations should be made when routing a system containing DSP and PLD?
A: Consider the ratio of signal speed to routing length. If the signal’s transmission delay and its temporal signal changes are comparable, signal integrity issues need consideration. Additionally, routing topology for multiple DSPs, clocks, and data signals can impact signal quality and timing.
Q4: Apart from Protel, are there other good tools for routing?
A: Besides Protel, other routing tools like Mentor’s WG2000, EN2000 series, and PowerPCB, Cadence’s Allegro, Zuken’s Cadstar, CR5000, among others, each have their strengths.
Q5: What is a “signal return path”?
A: A signal return path, or return current, refers to the current path flowing back along the ground or power plane from the load to the driver in high-speed digital signal transmission. This involves charging the dielectric capacitance sandwiched between the transmission line and the DC plane.
Q6: How to perform SI analysis on connectors?
A: In the IBIS3.2 standard, connector models are described using EBD models. Special boards like backplanes might require SPICE models. Multi-board simulation software (like HyperLynx or IS_multiboard) can establish a multi-board system using distributed parameters from the connector manual.
Q7: What are the methods of termination?
A: Termination involves active and terminal matching. Active termination typically uses series resistors, while terminal termination usually involves parallel matching using various methods such as pull-up resistors, pull-down resistors, Thevenin matching, AC matching, and Schottky diode matching.
Q8: What factors determine the choice of termination method?
A: The choice of termination method generally depends on buffer characteristics, topology, signal types, decision-making methods, signal duty cycle, and system power consumption, aiming to improve signal quality at the decision-making moment.
Q9: Are there rules for employing termination methods?
A: Signal integrity is crucial in digital circuits for deterministic signal quality. The goal of termination is to achieve stable signal quality while ensuring setup and hold times for level-sensitive signals and monotonic signal change rates for edge-sensitive signals.
Q10: Can IBIS models simulate the logical function of devices? If not, how to simulate circuit-level and system-level electronics?
A: IBIS models are behavior-level and cannot simulate functional behavior. For functional simulation, SPICE models or other structural-level models are required to perform circuit-level and system-level simulations.
Q1: In systems with coexistence of digital and analog components, are there differences between separating digital and analog grounds versus uniting power and ground for each?
A: The fundamental principle is similar because power and ground are equivalent for high-frequency signals. The separation aims to combat interference, primarily digital circuits interfering with analog ones. However, division may impact the integrity of signal return paths, affecting digital signal quality and overall EMC quality. Hybrid designs now integrate both approaches, segregating layout and wiring based on digital and analog components, avoiding cross-domain signals.
Q2: What do FCC and EMC stand for?
A: FCC stands for Federal Communication Commission, a regulatory body. EMC stands for Electromagnetic Compatibility, representing a standard in the field. Both have specific reasons, standards, and test methods.
Q3: What defines differential traces?
A: Differential signals, also known as differential pairs, transmit two identical signals with opposite polarity, relying on the difference in their signal levels for detection. In layout, they require parallelism, maintaining consistent trace width and spacing.
Q4: What are some PCB simulation software available?
A: Various software caters to high-speed digital signal integrity analysis, including ICX, SignalVision, HyperLynx, XTK, SpectraQuest, and sometimes Hspice for certain aspects of simulations.
Q5: How do PCB simulation software conduct layout simulations?
A: In high-speed digital circuits, multi-layered boards with dedicated power and ground layers are used to enhance signal quality and reduce wiring complexity.
Q6: How to ensure stability for signals above 50MHz during layout and routing?
A: Layout for high-speed digital signals demands short transmission lines to minimize their impact. Signal speed defines high-speed signals, and different signal types (TTL, GTL, LVTTL) require distinct approaches to ensure signal quality.
Q7: What material requirements exist for a PCB hosting RF, IF, and low-frequency circuits, and how to prevent interference between these circuits?
A: Combining various circuits on a single PCB poses challenges. RF circuits typically have dedicated layouts or even shielding to minimize distributed parameter effects. Materials with a lower dielectric constant are preferred for RF circuits. Separating areas for RF and digital circuits, using ground vias, and shielded enclosures help mitigate interference.
Q8: What solutions does Mentor provide for integrating RF, IF, and low-frequency circuits on a single PCB?
A: Mentor’s board-level system design software includes specialized RF design modules that facilitate parameterized component models and interfaces with RF analysis tools. These tools assist in layout, pattern editing, and offer bidirectional interfaces with RF simulation tools, enhancing design management for hybrid circuits.
Q9: What’s the product structure of Mentor?
A: Mentor Graphics’ PCB tools include the WG (originally Veribest) series and the Enterprise (BoardStation) series.
