In this episode, we delve into two fascinating VLSI domains: Analog Design and Analog Mixed Signal (AMS) Design. While their names might sound similar, these domains require distinctly different skill sets. If you're curious about the differences and the expertise needed for each, stick around until the end!
Setting the Stage:
This episode is part of our ongoing series answering a question from our viewer. As previously mentioned, the detailed answer spans multiple episodes. In this second installment, we'll be focusing on the Analog Design and AMS Design domains. Let's get started!
Domains Inside Analog Design:
Analog design is rooted in concepts many of you may have encountered during your college days. If you've worked with SPICE or explored circuits like operational amplifiers (op-amps), phase-locked loops (PLLs), or oscillators, you're already on familiar ground.
Let's break down the key aspects:
1.Schematic Design :
- Why It Matters: In the industry, manual SPICE-based node labeling isn't practical for complex designs. Instead, schematic capture tools like Cadence Virtuoso and Synopsys Custom Compiler streamline the process. These tools provide graphical interfaces to design and simulate circuits efficiently.
- Skills Needed:
- Strong foundation in analog electronics.
- Familiarity with schematic capture tools like Virtuoso and LTspice (a free option to start with).
- Knowledge of analysis methods such as transient, AC, DC, and noise analysis.
2. Layout Design
- Process: Analog layout design often employs semi-custom or full-custom techniques, particularly for unique blocks. Tools like Virtuoso and Custom Compiler are essential for this stage.
- Skills Needed: Expertise in analog layout methodologies. Ability to optimize for performance metrics like noise, power and parasitics.
3. Physical Verification
- Verification Steps:
- Using tools like Calibre DRC, LVS, and ICV to ensure design rule compliance and layout correctness.
- DSPF Extraction with tools like StarRC to check parasitic effects.
- Running EMIR (Electromigration and IR drop) checks and making necessary corrections.
- Skills Needed:
- Mastery of verification tools and scripting languages like Tcl for custom rule coding.
4. Post-Layout Functional Verification
- Objective: Incorporating parasitic effects into the design and ensuring performance remains within permissible limits.
- Tools Used: Industry-standard SPICE simulators like HSPICE, Spectre, and CustomSim for efficient simulations.
Domains Inside AMS Design:
AMS design combines analog and digital blocks, leveraging the best of both worlds. The scaling down of technology nodes below 10nm has made AMS designs increasingly relevant.
1. System-Level Modeling
- Approach: Design begins with a top-down or bottom-up methodology. Tools like C++, Simulink, and SystemVerilog are used for system-level modeling.
- Skills Needed: Proficiency in system-level modeling and simulation tools.
2. Behavioral Design
- Analog Behavioral Modeling:
- Verilog-A is used for analog components.
- Verilog-AMS allows seamless integration of analog and digital components.
- Digital Behavioral Modeling: Verilog or SystemVerilog.
- Skills Needed: Expertise in Verilog, Verilog-A, and Verilog-AMS.
3. Mixed-Signal Verification
- Process: Concurrent simulation of analog and digital blocks using SPICE (for analog) and Verilog (for digital). Proper configuration of A-to-D and D-to-A converters to facilitate smooth signal transactions.
- Tools Used: Virtuoso AMS, CustomSim AMS, and Vista IDMS simulators.
4. AMS Layout and Physical Verification
- Layout Tools: AMS-specific layout capabilities in tools like Virtuoso AMS and Custom Compiler AMS Layout.
- Verification: Standard DRC, LVS, ERC checks, and EMIR analysis.
- Additional Skills:
- Coding DRC rules with Tcl or tool-specific languages.
- Deep understanding of silicon fabrication processes.
Conclusion:
The Analog and AMS domains offer exciting opportunities, but they require dedicated learning and practice. From foundational tools like SPICE to advanced simulators like HSPICE and Virtuoso AMS, mastering these skills can open doors to rewarding VLSI careers.
Watch the video here:
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