Nishant Kumar

Tips to clear any AMS Circuit Design Technical Interview? (1) Candidate should be thorough with what he or she has written in CV. What normally candidates do is they write more than what they have really done. This is not correct. If you do this you will be caught in interview and you will be in miserable situation during interview. e.g. If you have done Verification of some circuit, write clearly this. Don't write you have designed. (2) Remember, if you write too much that you have done so many things in short period, interviewer will not believe because it is not possible to do many things properly in short span. e.g. I have seen many CVs of RF Designers with five year experience mentioning too many things that they have done. In fact, some had mentioned they have done more than I have done in my more than 35 years of career in RF Design. (3) Be honest during interview. If you don't know please say I don't know. (4) Basically, in any AMS Circuit we use R, L, C, nMOS, pMOS. (In RF, other components are used. I will not discuss that now). You should be fully thorough with these components - how they work, types of these components, which parameters decide quality of these components, non-ideal model of these components, small-signal model, low-freq./high-frequency model of these components, etc.. If you don't know thoroughly about these components, you cannot become a good analog designer. (5) Connection of above components forms a circuit. To connect these components you use interconnects (different metal layers and vias). You should know these interconnect R, L, C models (transmission lines). Especially as frequency of operation of circuit increases this becomes very critical. (6) Thorough with writing Thevenin and Norton equivalent circuits. (7) Superposition theorem and control theory and network analysis. (8) Power Supply non idealities. (9) RLC Switching Circuits. (10) Remember, most of the circuits in analog and mixed-signal can be designed using switches and inverters. Be thorough with switches and inverters. (11) At least some basic knowledge in Analog Layout you must have so that you can mention how layout care to be taken in schematic itself. For example, which components need to be matched, where dummy devices should be placed, how much current major branches carry, where guard-rings to be placed, electro-migration, etc.. (12) Last but not least you should be thorough with use of at least one EDA tools, best is Cadence, for circuit simulation. You should know all possible simulations that can be done using Cadence. Best wishes! If you have any queries, please post here I will try to answer them or others may answer. 🙏🙏🙏🙏🙏

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🔹 𝗪𝗵𝗮𝘁 𝗶𝘀 𝗮 𝗣𝗨𝗟𝗦𝗘 𝘄𝗮𝘃𝗲𝗳𝗼𝗿𝗺 𝗶𝗻 𝗛𝗦𝗣𝗜𝗖𝗘? In HSPICE, the 𝗣𝗨𝗟𝗦𝗘 𝘀𝗼𝘂𝗿𝗰𝗲 is defined as: V1 node+ node- PULSE(Vinitial Vfinal Tdelay Trise Tfall Ton Tperiod) Example: Vclk in 0 PULSE(0 1.2 0 50p 50p 5n 10n) This means a clock-like signal swinging between 0 V and 1.2 V with rise/fall of 50ps, ON time 5ns, and period 10ns. 🔹 𝗪𝗵𝗲𝗿𝗲 𝗱𝗼 𝘄𝗲 𝘂𝘀𝗲 𝗶𝘁?  𝟭. 𝗖𝗹𝗼𝗰𝗸 𝗴𝗲𝗻𝗲𝗿𝗮𝘁𝗶𝗼𝗻 → to drive flip-flops, latches, and sequential circuits.  𝟮. 𝗜𝗻𝗽𝘂𝘁 𝘀𝘁𝗶𝗺𝘂𝗹𝘂𝘀 → applying test patterns to check timing behavior of combinational circuits.  𝟯. 𝗦𝗮𝗺𝗽𝗹𝗲-𝗮𝗻𝗱-𝗵𝗼𝗹𝗱 / Switch simulation → controlling the ON/OFF of MOSFET switches.  𝟰. 𝗧𝗿𝗮𝗻𝘀𝗶𝗲𝗻𝘁 𝗮𝗻𝗮𝗹𝘆𝘀𝗶𝘀 → verifying rise/fall delays, propagation delays, and switching speeds. 🔹 𝗪𝗵𝘆 𝗶𝘀 𝘂𝗻𝗱𝗲𝗿𝘀𝘁𝗮𝗻𝗱𝗶𝗻𝗴 𝗶𝘁 𝘀𝗼 𝗶𝗺𝗽𝗼𝗿𝘁𝗮𝗻𝘁?  • 𝗔𝗰𝗰𝘂𝗿𝗮𝗰𝘆 𝗼𝗳 𝘀𝗶𝗺𝘂𝗹𝗮𝘁𝗶𝗼𝗻: Wrong rise/fall time in PULSE will give unrealistic results (e.g., sharp ideal edges cause convergence issues, while realistic slopes show real delay).  • 𝗧𝗶𝗺𝗶𝗻𝗴 𝗮𝗻𝗮𝗹𝘆𝘀𝗶𝘀: Every setup/hold violation or glitch behavior depends on how your pulse is defined.  • 𝗕𝗿𝗶𝗱𝗴𝗶𝗻𝗴 𝗮𝗻𝗮𝗹𝗼𝗴 & 𝗱𝗶𝗴𝗶𝘁𝗮𝗹: The PULSE source is the foundation for modeling digital signals in an analog simulator like HSPICE.  • 𝗥𝗖 𝗶𝗺𝗽𝗮𝗰𝘁: In real circuits, interconnect parasitics stretch the pulse edges. Unless you define Trise/Tfall properly, you won’t see realistic RC delay effects. ✅ 𝗜𝗻𝘁𝗲𝗿𝘃𝗶𝗲𝘄 𝗔𝗻𝗴𝗹𝗲 𝗳𝗼𝗿 𝗙𝗿𝗲𝘀𝗵𝗲𝗿𝘀:  • 𝘉𝘦 𝘳𝘦𝘢𝘥𝘺 𝘵𝘰 𝘦𝘹𝘱𝘭𝘢𝘪𝘯 𝘩𝘰𝘸 𝘺𝘰𝘶’𝘥 𝘥𝘦𝘧𝘪𝘯𝘦 𝘢 𝘤𝘭𝘰𝘤𝘬 𝘴𝘪𝘨𝘯𝘢𝘭 𝘪𝘯 𝘏𝘚𝘗𝘐𝘊𝘌 𝘶𝘴𝘪𝘯𝘨 𝘗𝘜𝘓𝘚𝘌.  • 𝘞𝘩𝘺 𝘥𝘰 𝘸𝘦 𝘪𝘯𝘤𝘭𝘶𝘥𝘦 𝘧𝘪𝘯𝘪𝘵𝘦 𝘳𝘪𝘴𝘦/𝘧𝘢𝘭𝘭 𝘪𝘯𝘴𝘵𝘦𝘢𝘥 𝘰𝘧 𝘪𝘥𝘦𝘢𝘭?  • 𝘏𝘰𝘸 𝘛𝘰𝘯 𝘢𝘯𝘥 𝘛𝘱𝘦𝘳𝘪𝘰𝘥 𝘳𝘦𝘭𝘢𝘵𝘦 𝘵𝘰 𝘥𝘶𝘵𝘺 𝘤𝘺𝘤𝘭𝘦 𝘢𝘯𝘥 𝘴𝘺𝘴𝘵𝘦𝘮 𝘧𝘳𝘦𝘲𝘶𝘦𝘯𝘤𝘺. 👉 Without mastering the PULSE source, you can’t simulate even a basic inverter chain properly in HSPICE. 𝗜𝘁’𝘀 𝗹𝗶𝘁𝗲𝗿𝗮𝗹𝗹𝘆 𝘁𝗵𝗲 𝗵𝗲𝗮𝗿𝘁𝗯𝗲𝗮𝘁 𝗼𝗳 𝘁𝗲𝘀𝘁𝗯𝗲𝗻𝗰𝗵𝗲𝘀 for both analog and digital designs.

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𝗛𝗲𝗿𝗲 𝗶𝘀 𝗮 𝗾𝘂𝗶𝗰𝗸 𝗼𝘃𝗲𝗿𝘃𝗶𝗲𝘄 𝗼𝗳 𝗨𝗩𝗠 𝗽𝗵𝗮𝘀𝗲𝘀, 𝘄𝗵𝗲𝘁𝗵𝗲𝗿 𝘁𝗵𝗲𝘆 𝗮𝗿𝗲 𝘇𝗲𝗿𝗼-𝘁𝗶𝗺𝗲 𝗼𝗿 𝗻𝗼𝘁, 𝗵𝗼𝘄 𝘁𝗵𝗲𝘆 𝗮𝗿𝗲 𝗲𝘅𝗲𝗰𝘂𝘁𝗲𝗱, 𝗮𝗻𝗱 𝘁𝗵𝗲𝗶𝗿 𝗽𝘂𝗿𝗽𝗼𝘀𝗲. If you are just beginning your verification journey, stick this on your monitor or wall, and you will soon memorize it for life. I have always found it useful to have a quick reference like this when I need it. Here are some additional notes regarding the table. 𝙏𝙤𝙥-𝘿𝙤𝙬𝙣 𝙫𝙨. 𝘽𝙤𝙩𝙩𝙤𝙢-𝙐𝙥 🔵 In 𝘁𝗼𝗽-𝗱𝗼𝘄𝗻 phases (build, connect, etc.), each parent’s method runs before its children’s methods. 🔵 In 𝗯𝗼𝘁𝘁𝗼𝗺-𝘂𝗽 phases (extract, check, report, final), each child completes its method before the parent. 𝙕𝙚𝙧𝙤-𝙏𝙞𝙢𝙚 𝙫𝙨. 𝙏𝙞𝙢𝙚-𝘽𝙖𝙨𝙚𝙙 🔵  Except for run_phase, all other standard phases are zero-time—they happen 𝗶𝗻𝘀𝘁𝗮𝗻𝘁𝗮𝗻𝗲𝗼𝘂𝘀𝗹𝘆 in the UVM schedule. 🔵 𝗿𝘂𝗻_𝗽𝗵𝗮𝘀𝗲 is a 𝘁𝗮𝘀𝗸-𝗯𝗮𝘀𝗲𝗱 phase that consumes simulation time, allowing signals to be driven, monitors to observe, and sequences to execute. #uvm #verification #learning #cheatsheet #reference  

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Silicon Labs is extending our sub-GHz portfolio with the new FG23L SoC. This “Lite” variant is optimized for long-range, ultra-low-power IoT devices that need secure, cost-effective connectivity. Get the full details on FG23L here: https://lnkd.in/gMuHp6A4 

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𝐁𝐚𝐧𝐝𝐠𝐚𝐩 𝐑𝐞𝐟𝐞𝐫𝐞𝐧𝐜𝐞 𝐂𝐢𝐫𝐜𝐮𝐢𝐭𝐬: 𝐓𝐡𝐞 𝐒𝐢𝐥𝐞𝐧𝐭 𝐁𝐚𝐜𝐤𝐛𝐨𝐧𝐞 𝐨𝐟 𝐏𝐫𝐞𝐜𝐢𝐬𝐢𝐨𝐧 𝐀𝐧𝐚𝐥𝐨𝐠 𝐃𝐞𝐬𝐢𝐠𝐧 Whether you’re designing an LDO, ADC, PLL, or SoC power rail—your entire system’s reliability begins with a stable voltage reference. That’s where Bandgap Reference (BGR) circuits come in — the unsung heroes that quietly anchor your analog performance across temperature, supply, and process variations. 𝐖𝐡𝐚𝐭 𝐈𝐬 𝐚 𝐁𝐚𝐧𝐝𝐠𝐚𝐩 𝐑𝐞𝐟𝐞𝐫𝐞𝐧𝐜𝐞 (𝐁𝐆𝐑)? A Bandgap Reference is an analog circuit that generates a temperature-independent voltage, typically around 1.2V, by smartly combining two temperature-dependent voltages: PTAT (Proportional To Absolute Temperature) CTAT (Complementary To Absolute Temperature) When summed correctly, their temperature dependencies cancel out, producing a stable reference voltage over a wide temperature range. 𝐖𝐡𝐲 𝟏.𝟐𝐕? The value is derived from the silicon bandgap energy (~1.205V at 0K). Hence the name: Bandgap Reference. 𝐖𝐡𝐲 𝐈𝐬 𝐁𝐆𝐑 𝐒𝐨 𝐂𝐫𝐢𝐭𝐢𝐜𝐚𝐥? 1️⃣ Power Regulation: LDOs, SMPS, and charge pumps use BGR as their internal reference. A poor BGR = drifting output voltages. 2️⃣ Data Converters: Precision ADCs/DACs need stable reference voltages to preserve linearity and resolution. 3️⃣ Sensor Interfaces: Temperature, pressure, and current sensors calibrate based on fixed voltage rails. 4️⃣ PLL/VCO Stability: Reference voltages used in biasing affect frequency precision. 𝐂𝐡𝐚𝐥𝐥𝐞𝐧𝐠𝐞𝐬 𝐢𝐧 𝐁𝐆𝐑 𝐃𝐞𝐬𝐢𝐠𝐧 Mismatch & Layout Symmetry – causes offset Curvature Correction – for better temp stability across -40°C to 125°C Low Power vs. High PSRR – always a tradeoff Startup Circuit Design – must avoid latch-up or long settling times Process Corners Variations (PVT) – need robust bias generation  𝐁𝐆𝐑 𝐕𝐚𝐫𝐢𝐚𝐧𝐭𝐬 𝐘𝐨𝐮 𝐒𝐡𝐨𝐮𝐥𝐝 𝐊𝐧𝐨𝐰: 1. Brokaw Cell – Classic, robust, widely used 2. Widlar BGR – More layout compact 3. Sub-bandgap References – For ultra-low voltage systems 4. Curvature Corrected BGRs – For high-precision apps (±5 ppm/°C) 𝐋𝐚𝐲𝐨𝐮𝐭 𝐌𝐚𝐭𝐭𝐞𝐫𝐬 𝐢𝐧 𝐁𝐆𝐑 𝐃𝐞𝐬𝐢𝐠𝐧 Common Centroid Matching for BJTs and resistors Guard Rings to isolate substrate noise Thermal Symmetry to minimize temp gradients Metal Routing for kelvin connections 𝐖𝐚𝐧𝐭 𝐭𝐨 𝐒𝐰𝐢𝐭𝐜𝐡 𝐢𝐧𝐭𝐨 𝐀𝐧𝐚𝐥𝐨𝐠 𝐃𝐞𝐬𝐢𝐠𝐧? 📩 Apply here → https://lnkd.in/dZi8JDQA 📱 WhatsApp → https://lnkd.in/gaBkVDB2 📡 Join Telegram → https://t.me/AnalogIC_RFIC #BandgapReference #AnalogDesign #VoltageReference #LDO #AMSVerification #ADCDesign #SoCDesign #VLSICareer #PrecisionCircuits #SemiconductorJobs #GIICT #SiliconReady #Career2025 #AnalogIP

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The design of high-bandwidth PCB-RCs is discussed using the frequency response characteristics of the sensor, incorporating OP-AMP non-idealities. Continuous time-domain subtraction of the device currents is achieved with an instrumentation amplifier stage to reconstruct the AC node current. By virtue of the inherent isolation offered by PCB-RCs, the reconstructed current is directly coupled with an ADC channel of the microcontroller for subsequent closedloop current control. Further, using the developed PCB-RCs, ultrafast short-circuit protection for the GaN HEMTs is achieved under a DC bus fault at 400 V.

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🚀 STA Flow for SerDes: Timing Closure at High Speed Timing closure for SerDes is not STA as usual. Here’s the flow you need to visualize: 📌 Diagram Concept Core Logic → Serializer → TX Equalization → Channel → RX Equalization → CDR → Deserializer → Core Logic Key STA Points in Flow: 🔍 Model latency for Serializer & Deserializer ⏱ Include jitter uncertainty at CDR 📦 Apply IO delay for package + board 🎛 Validate adaptive EQ timing impact Checklist Recap: ✅ Model latency ⚡ Jitter budgeting 🔄 Clock domain handling 📐 Setup/Hold margins 🌡 Corner analysis 🔥 Question for you: Some Constraints to be taken care 🔍 Define IO Delays set_input_delay 0.8 -clock serdes_rx_clk [get_ports RX_DATA] set_output_delay 1.0 -clock serdes_tx_clk [get_ports TX_DATA] ⏱ Add Jitter Margin set_clock_uncertainty 0.05 [get_clocks serdes_tx_clk] 🔄 Handle Async Domains set_clock_groups -asynchronous \ -group {core_clk} \ -group {serdes_tx_clk serdes_rx_clk} 📐 Latency Constraints set_max_delay 2.5 -from [get_ports TX_DATA] -to [get_ports RX_DATA] 🌡 Corner Analysis Run STA across voltage, temperature, and channel loss conditions. How do you integrate SerDes timing into STA? Custom constraints or tool automation? #SerDes #STA #TimingClosure #PhysicalDesign #SignalIntegrity #VLSI #HighSpeedDesign

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Still splitting planes and ignoring return paths? That’s a recipe for EMI failures. Dive into our latest blog on grounding and return path best practices with Cadence Allegro X. Learn how to avoid power plane pitfalls and design for signal integrity from the start. 👉 https://ow.ly/wRnk50WEMgJ #PCBDesign #EMIFailures #ElectronicsDesign

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Clock jitter refers to the variation of a clock signal’s edge from its ideal position in time. It is critical in high-speed digital, mixed-signal, and communication systems because it affects timing margins, setup/hold requirements, and data integrity. ⸻ ✅ Types of Clock Jitter Here are the major types: 1. Period Jitter • Definition: Variation in the clock period from one cycle to the next. • Impact: • Causes frequency instability. • Can lead to setup/hold violations in synchronous systems. • Example: One clock cycle is 10.1 ns, the next is 9.9 ns instead of the ideal 10 ns. ⸻ 2. Cycle-to-Cycle Jitter • Definition: Difference in duration between two adjacent cycles. • Impact: • Critical in high-speed I/O and SerDes designs. • Affects PLL/DLL performance and data serialization/deserialization. ⸻ 3. Long-Term Jitter (or Accumulated Jitter) • Definition: Cumulative deviation of clock edges over a long time. • Impact: • Important in systems with multiple clock domains and data recovery. • Causes phase drift and synchronization issues. ⸻ 4. Random Jitter (RJ) • Definition: Caused by thermal noise and other stochastic processes. • Characteristics: • Unbounded, follows a Gaussian distribution. • Impact: • Dominates at very high frequencies. • Reduces timing margin for setup/hold. ⸻ 5. Deterministic Jitter (DJ) • Definition: Jitter that has a bounded, predictable cause. • Sources: • Crosstalk, power supply noise, EMI, clock interference. • Impact: • Can be analyzed and reduced by design improvements. ⸻ 6. Duty Cycle Distortion (DCD) • Definition: Variation in high and low times of the clock. • Impact: • Alters duty cycle, which can affect latch/flip-flop operation. • Critical in DDR memory and high-speed buses. ⸻ 7. Phase Jitter • Definition: Short-term variations in the phase of the clock signal. • Impact: • Affects PLL lock stability and clock data recovery (CDR). ⸻ ✅ Impact on Design 1. Timing Violations • Jitter reduces the effective setup and hold margins. • In STA (Static Timing Analysis), jitter is modeled as clock uncertainty. 2. Signal Integrity • High jitter increases bit error rate (BER) in high-speed links (e.g., PCIe, DDR, SerDes). 3. PLL/DLL Design • Jitter tolerance is key in clock generation and recovery circuits. 4. Synchronous System Stability • More jitter → skew variations, synchronization failures. ⸻ How It’s Handled in Design • Clock uncertainty in STA = Jitter + Skew. • Jitter budget allocation among PLL, clock tree, and data paths. • Low-noise power supply design (reduce supply-induced jitter). • Use of spread-spectrum clocking to minimize EMI-based jitter. • Filtering (PLL bandwidth) to suppress high-frequency jitter.

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💡 Post-Silicon Failures: Where Design Meets Reality You taped out the chip. Coverage metrics look great. Patterns passed validation. But in bring-up lab or production test, reality hits: 🔴 Common post-silicon failures: 1. Scan chain failures Shift path timing issues Chain ordering or stitching bugs IR drop causing intermittent shifts 2. Capture fails Clock skew across capture domains Power droop during mass launch Tester setup vs design assumptions 3. Functional fails Incorrect test mode configurations Reset or isolation cell misbehaviour ECO-induced logic escapes 4. Parametric fails Marginal paths not flagged by STA Variation-induced leakage or delay Process corner drifts unseen in pre-silicon sims 5. Yield-related systemic fails Lithography hotspots Cross-wafer systematic defects Packaging-induced stress failures 🔍 Why does this happen despite “good coverage”? Because: Fault models ≠ physical defects ATPG does not model tester loading Sign-off checks have assumptions Variation, noise, and real environment effects rarely match simulations ✅ Post-silicon debug is critical: Scan diagnosis to pinpoint chain or logic defects Volume diagnosis to identify systemic issues Correlating test fails with layout, process, and design data Effective ECO planning to patch without new risks 🔄 Silicon validates assumptions. Failures teach truths. 💭 What was your toughest post-silicon debug that changed your design approach forever? --- #DFT #PostSilicon #ATPG #ScanDiagnosis #VolumeDiagnosis #YieldEngineering #SiliconDebug #Semiconductor #VLSI #ChipDesign #FailureAnalysis #TestEngineering #VibhuayaTechnologies

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