The Effect of Substrate-Coupled Noise on the Design of SiGe BICMOS Circuits for RF/Mixed-Signal Applications

1. The Effect of Substrate-Coupled Noise on the Design of SiGe BICMOS Circuits for RF/Mixed-Signal Applications • SC913 EE Design Project Description (summer 2002) • “Substrate Noise Characterization Test Site” • Background on Substrate-Coupled Noise • MOSIS SiGe BICMOS Technology Options – IBM 5HP/6HP • Models and Layout Design Rules - SiGe Design Kit • Circuit Design in Cadence SpectreRF • Test Site Floorplan • Progress to Date • New Course in the Fall: RF/Analog IC Design Fundamentals (SC500) • Conclusions R. W. Knepper BBTalk, slide 1

2. SC913 EE Design Project: Substrate Noise Characterization Test Site for SiGe BICMOS • Project Description: • Design a test chip in SiGe BICMOS technology to characterize substrate-coupled noise in a RF/analog/digital mixed-signal environment • Digital CMOS drivers and/or NPN bipolar drivers to generate a controlled amount of substrate bounce • Sensitive RF and analog circuit behavior (failure and/or degradation) based on the number of drivers switching at one time • Study various substrate contact and guard ring structures at different distances to isolate analog circuits from digital noise sources • Single devices, transmission lines, wire coupling, and substrate contact structures for S parameter measurements using on-chip probing • Utilize MOSIS facility and IBM’s 6HP SiGe process to fabricate the test site via an unfunded research MEP proposal • Characterize chip in Fall or Spring semester when hardware is received • Obtain RF probe station and network analyzer setup for on-chip testing • Utilize high frequency scopes and bench test equipment for PGA packaged chips • Students: • 12-13 ECE graduate students with various levels of participation R. W. Knepper BBTalk, slide 2

3. Students Participating on SC913 Project • Aspiyan Gazder • Yuchun (Justin) Liao • Andrew McKnight • Marianne Nourzad • Jing Wu • Raman Mathur • Sulakshana Pasnoor • Chien-Chih Huang • Soma Ghosh • Zibing Yang • Christian Karl • Fangyi Chen • Duk Joung Kim R. W. Knepper BBTalk, slide 3

4. IBM PRML Magnetic Recording Channel IC • IBM PRML magnetic recording chip, circa 1991, shown at top-left • P+ substrate with P- epi layer • All necessary analog and digital circuitry except for read head pre-amp (27 MHz) • Digital CMOS logic coupled noise into 6-bit A/D converter on chip • 6-bit Flash A/D converter shown at bottom-right • Resistor ladder network • Differential noise problem on the ladder network experienced Verghese, Schmerbeck, and Allstot, “Simulation Techniques and Solutions For Mixed-Signal Coupling in Integrated Circuits”, Kluwer, 1995 Also, Verghese’ PhD Thesis, CMU, 1995 R. W. Knepper BBTalk, slide 4

5. IBM PRML Magnetic Recording Channel IC • Common mode noise observed on PRML magnetic disk head chip in A/D converter resistor ladder network (left-top) • AGC output with (right) and without (left) digital logic switching • Circuit techniques were used to reduce the ADC error to less than ½ LSB Verghese, Schmerbeck, and Allstot, “Simulation Techniques and Solutions For Mixed-Signal Coupling in Integrated Circuits”, Kluwer, 1995 Also, Verghese’ PhD Thesis, CMU, 1995 R. W. Knepper BBTalk, slide 5

6. Texas Instruments A/D Converter TVP5700 • Triple 8-bit semiflash pipelined video A/D converter by TI (left-top) continued to have substrate noise problem after 3 design attempts • Severe sparkle code error causing DNL error above +/- 1 LSB • Twelve output buffer cells switching simultaneously coupled excessive noise into the P+ substrate • Verghese’s PhD substrate modeling methodology was used to extract substrate model • Circuit schematic of one output buffer and ESD circuitry shown (bottom-left) • Coupling through bonding pad capacitance and M12 transistor • Separate Digital VSS and Analog VSS with wire/pin inductance values shown • Extracted substrate resistances shown TVP5700 – Triple 8-bit Video analog-to-Digital Converter, Product Review, Texas Instruments Inc., April 1994. Also, Nishath Verghese’ PhD Thesis, CMU, 1995 R. W. Knepper BBTalk, slide 6

7. Texas Instruments A/D Converter TVP5700 • Simulation of ADC output and coupled substrate noise shown at top-left (prior to design fixes) • Use of extracted substrate model allowed design choices to be made to alleviate the noise problem • Routing N-wells under bonding pads and clock lines • Reducing lead inductance of DVSS and DVDD lines • Resistively damped DVSS and DVDD lines • Stagger the driver switching times to reduce delta-I noise • Simulation of ADC output and coupled substrate noise after the design fixes were made is shown at bottom-left • Tremendous improvement in noise TVP5700 – Triple 8-bit Video analog-to-Digital Converter, Product Review, Texas Instruments Inc., April 1994. Also, Nishath Verghese’ PhD Thesis, CMU, 1995 R. W. Knepper BBTalk, slide 7

8. Verghese PhD Thesis (CMU – August 1995) • Development of substrate circuit model: • Using Poisson’s equation and continuity equations for electrons and holes we can derive an equation for the substrate analysis   (/t)(E) + (E) = 0 where  is a relaxation time constant • Same equation can be derived from Maxwell’s equations • Substrate model (below left) was used to study effect of digital gate coupling noise into substrate and affecting analog transistor tied into same substrate model • Figure (below right) shows admittance coupling (magnitude of Y12) between two different nodal points of the substrate model versus frequency • For 15 ohm-cm material, the frequency dependence starts to become important above about 4-5 GHz; for more heavily doped substrates, the roll-off moves to higher frequencies Nishath Verghese’ PhD Thesis, CMU, 1995 R. W. Knepper BBTalk, slide 8

9. Comparison of Device Medici Simulation with Circuit SPICE Mesh Simulation: P+ Substrate • A comparison was done between Medici device simulation and SPICE circuit simulation with the mesh substrate model for the case of a heavily-doped P+ substrate with a lightly-doped P- epi layer on top. • The circuit schematic is shown at the bottom left figure with parasitic inductors added to account for wire. • Results are shown bottom right for peak-to-peak noise voltage at the sensitive node for various cases of guard ring, no guard ring, n-well, backside contact, etc. • Good agreement between Medici Device Simulation and SPICE circuit simulation with substrate model! Nishath Verghese PhD Thesis, CMU, 1995 R. W. Knepper BBTalk, slide 9

10. Comparison of Device Medici Simulation with Circuit SPICE Mesh Simulation: P- Substrate • A comparison was done between Medici device simulation and SPICE circuit simulation with the mesh substrate model for the case of a lightly-doped P- substrate. • The circuit schematic is shown with parasitic inductors added to account for wire. • Results are shown bottom right for peak-to-peak noise voltage at the sensitive node for various cases of guard ring, no guard ring, n-well, backside contact, etc. • Good agreement between Medici Device Simulation and SPICE circuit simulation • P+ guard ring is more effective in reducing noise than in P+ substrate case • Backside contact ineffective Nishath Verghese PhD Thesis, CMU, 1995 R. W. Knepper BBTalk, slide 10

11. Discussions with IBM Engineer Robert Barry Phone conversation with Bob Barry on June 5, 2002 • Suggest we read the following books on substrate noise, modeling and coupling • Signal Integrity Effects in Custom IC and ASIC Designs, Raminderpal Singh, IEEE Press and Wiley & Sons, Nov. 2001 • Analysis and Solutions for Switching Noise Coupling in Mixed-Signal IC’s, X. Aragones, et al., Kluwer Academic Publishers, 1999. • Put capacitor across each resistor in substrate model to compute substrate relaxation time accurately • C = o/R where R is the resistance of the substrate region (cube) • If R = l/A = /l = 13.5 ohm-cm / 0.01 cm = 1.35 K, and • C = oA/l = ol = 8.85E-14 F/cm x 11.9 x 0.01 cm = 10 fF, then • RC = substrate relaxation time constant = o = 13.5 ps • For fast risetime pulses with spectral components in the 12-20 GHz range, we will need to add the capacitors to our substrate model • Suggest we put some structures on the chip for S-parameter measurement using three pad input and output ports (ground-signal-ground) • Substrate contacts and guard ring structures • Collector to substrate capacitor • Transistors • Suggest to use bipolar drivers in addition to CMOS drivers due ability to induce large current spikes into the substrate R. W. Knepper BBTalk, slide 11

12. Substrate Modeling Vendor Code (SeismIC) • Marketed by Cadence Design Systems • Nishath Verghese was a principal at startup Apres Technologies – acquired by CadMOS Design Technology in Oct 1998 – acquired by Cadence in April 2001 • SeismIC Methodology • Complete physical design of the chip • Solves the equation   (/t)(E) + (E) = 0 • integral form using Green’s function for large multi-layered substrates (for greater speed) • differential form for the top layer with wells, trenches, and devices (for greater accuracy) • Extracts an RC network from the substrate matrix • Simulate circuit to determine coupled noise injection points • Perform transient simulation including all noise sources and devices • Noise sources can be studied one at a time • Modify design as required using new results and repeat process • Cost is excessive ( > $100K/seat) “Preventing a NoiseQuake”, IEEE Circuits and Devices Magazine, Ponnapalli, Verghese, Chu, and Coram, Nov. 2001 R. W. Knepper BBTalk, slide 12

13. “0.13 um 210 GHz Ft SiGe HBTs – Expanding the Horizons of SiGe BICMOS”, Joseph, et al, IBM, IEEE ISSCC, Paper 11.1, Feb. 2002 R. W. Knepper BBTalk, slide 13

14. IBM SiGe Technology Comparison “0.13 um 210 GHz Ft SiGe HBTs – Expanding the Horizons of SiGe BICMOS”, Joseph, et al, IBM, IEEE ISSCC, Paper 11.1, Feb. 2002 R. W. Knepper BBTalk, slide 14

15. 6HP SiGe Process: Base-after-Gate Integration • SiGe Bipolar is integrated into CMOS process • SiGe film deposited with Low Temperature Epi (LTE) tool with Ge atomically graded from 0% to about 10% and back to 0% within the (<500A) base film • NPN built after CMOS is structurally completed • Minimize NPN thermal budget • Utilized in technologies 0.25 um and beyond “0.13 um 210 GHz Ft SiGe HBTs – Expanding the Horizons of SiGe BICMOS”, Joseph, et al, IBM, IEEE ISSCC, Paper 11.1, Feb. 2002 R. W. Knepper BBTalk, slide 15

16. IBM 0.18um SiGe NPN Vertical Cross-section • Shallow and Deep trench isolations • Buried N+ subcollector with epi layer • Carbon-doped SiGe LTE base region • Min WE = 0.2 um • CoSi2 collector and base contacts “0.13 um 210 GHz Ft SiGe HBTs – Expanding the Horizons of SiGe BICMOS”, Joseph, et al, IBM, IEEE ISSCC, Paper 11.1, Feb. 2002 R. W. Knepper BBTalk, slide 16

17. HBT Performance Trend - fT • Cutoff frequency quadrupled over 4 generations of SiGe HBTs “0.13 um 210 GHz Ft SiGe HBTs – Expanding the Horizons of SiGe BICMOS”, Joseph, et al, IBM, IEEE ISSCC, Paper 11.1, Feb. 2002 R. W. Knepper BBTalk, slide 17

18. HBT Performance Trend - fmax • Rbb and Ccb reduced simultaneously with transit time to improve speeds > 200 GHz “0.13 um 210 GHz Ft SiGe HBTs – Expanding the Horizons of SiGe BICMOS”, Joseph, et al, IBM, IEEE ISSCC, Paper 11.1, Feb. 2002 R. W. Knepper BBTalk, slide 18

19. IBM SiGe NPN Operating Voltage • BVCEO has been reducing with technology scaling (higher doping, narrower base) • Avalanche does not create degradation • Designers may readily design above BVCEO (using BVCER) with low base resistance RB • Modeling reverse base current is the key “0.13 um 210 GHz Ft SiGe HBTs – Expanding the Horizons of SiGe BICMOS”, Joseph, et al, IBM, IEEE ISSCC, Paper 11.1, Feb. 2002 R. W. Knepper BBTalk, slide 19

20. 6HP BICMOS Models and Layout Design Rules • Obtain SiGe 6HP Design Kit from IBM via MOSIS (USC) • License agreement must be signed by Boston University legal dept • IBM Microelectronics conducts training sessions on use of models and design kit • Runs in Cadence SpectreRF CAD tool • Device specs at left R. W. Knepper BBTalk, slide 20

21. Circuit Design in Cadence SpectreRF • Cadence Affirma RF Simulator (SpectraRF) is already installed in ECE VLSI Lab running on new SUN Blade 100 workstations • SC913 students have completed tutorials on simulation of a mixer, an oscillator with transmission delay line, a low noise amplifier, and transmission line • SpectreRF capability • Periodic Steady State analysis (PSS) – large signal • Periodic AC analysis (PAC) • Periodic S Parameter analysis (PSP) • Periodic Transfer Function analysis (PXF) • Periodic Noise analysis (PNoise) • Quasi-periodic noise analysis (QNoise) • Periodic Distortion analysis (Pdisto) • Standard methodology • Design (schematic) in Composer • Layout in Virtuoso • Checking with DRC and LVS • Extract models and simulate in Analog Environment with SpectreRF model library R. W. Knepper BBTalk, slide 21

22. Noise Characterization Test Site Preliminary Floorplan • Allowed chip area = 10 mm2 max • CMOS and NPN drivers • Utilize to generate capacitive noise coupling to the P- substrate from switching drains and collectors • Selectable in groups of 4 to 32 simultaneously switching • Analog and RF circuits • Design in a way to observe behavior (or failure) with increasing numbers of switching digital drivers • Utilize different types of substrate contacts and guard ring protection • To be designed by teams of 2 or 3 students each • On-chip probe-able structures for S-parameter and simple dc measurements • Single devices and capacitors • Interconnect wire and transmission lines • Substrate contact and guard ring exp’s R. W. Knepper BBTalk, slide 22

23. Progress To Date • Students completed SpectreRF tutorials • Assigned reading and reports on selected IEEE papers on substrate modeling research results • Study of Nishath Verghese PhD thesis, CMU, 1995, on substrate modeling • Started development of three-layer substrate resistive model for 700 um thick P- substrate with digital and analog circuits tied-in to demonstrate effects of substrate noise • Top layer schematic sketch shown at left with arbitrary points to hook in circuits • CMOS driver NFET device node N2 (& output pad capacitance) • Current mirror and diff amp tie-in via N1 • BICMOS mixer circuit tie-in via N3 • Initial Cadence simulation complete • Waiting for license signing to receive SiGe 6HP design kit R. W. Knepper BBTalk, slide 23

24. Progress To Date (continued) • Resistive substrate model (top layer only) show below at left • Cadence simulation results show severe noise spikes coupled into differential outputs of CMOS diff amp with current mirror current source – somewhat independent of location • Bottom two traces show mixer output (NPN collectors) - seems immune to substrate noise R. W. Knepper BBTalk, slide 24 Chien-Chih Huang, Raman Mathur

25. SC500: RF/Analog IC Design Fundamentals Course Description: • This course will teach the fundamentals of CMOS and SiGe HBT BICMOS RF and analog circuit technology used in the design of a single chip radio. Topics to be covered include low noise amplifiers, switched capacitor circuits, A/D and D/A converters, phase locked loops, oscillators, mixers, active filters, low power design, RF design techniques, and mixed-signal circuitry typical of modern telecommunications technology. The course will include VLSI laboratory exercises involving the design, layout, and simulation of RF and analog integrated circuits using Cadence CAD software tools. • Textbook(s): • Design of CMOS Radio Frequency Integrated Circuits, Thomas Lee, Cambridge Univ Press, 1998 • Low-Power CMOS Radio Receivers, Shaeffer and Lee, Kluwer, 1999 • Analog Integrated Circuit Design, Johns and Martin, Wiley, 1997 • Prerequisites: • SC410, SC412, SC571, or permission of instructor • Professor: Ron Knepper, ECE Dept. • Meets: M/W 2-4 PM R. W. Knepper BBTalk, slide 25

26. SC500 RF/Analog IC Design Fundamentals TopicWeeks • Compact analog/RF circuit models for BICMOS devices 1 • SiGe BICMOS Technology: process, layout, and design rules 1 • Operational amplifiers, comparators, current mirrors 1 • Switched capacitor circuits 0.5 • A/D and D/A Converters 1 • Active Filters 0.5 • Noise analysis/low noise amplifier design 1 • RF techniques on-chip 1 • Mixers 1 • Oscillators 1 • RF Power Amplifiers 0.5 • Phase-Locked Loop 1 • Low power design techniques 0.5 • Radio receiver architectures 0.5 • Design of a single chip radio 1.5 Total: 13 R. W. Knepper BBTalk, slide 26