Integration Challenges in Single-Chip Radios Adil Kidwai Intel Corporation, Hillsboro Outline • Motivation – product targets • Architecture overview – Single-chip WiFi • Issues and Mitigation Techniques • Multi-standard coexistence in Single-chip • Issues and Mitigation techniques • Conclusions ASP Integration Why Integrate? Cost Pressure Innovation Double Sided Solution More Functionality $ BOM Time Need to push the BOM down Multi-Comm ASP = Average Sales Price BOM = Bill of Material (Cost) Why not to integrate? • Technology – It places extra dependence on RF design – To get to single-chip, the RF must migrate technologies at same pace as digital flow • Sku variation – How easy will it be to create different die for different markets and applications? – Multi-com becomes more complex to make silicon changes Single chip defined (or not) Antennas FEM FEM RFIC RFIC MAC MAC • What is single-chip? – If you have a FEM, is it still single-chip? – How many devices should be combined to achieve the goal? What is the Goal? Integration and Single-chip dc-dc LVR LVR LVR Ant 1 Analog interface FEM Radio Ant 2 MAC/PHY Digital interface FEM Ref clock VCO Xtal EEPROM Specific Example Single-chip WiFi – Top Down Design • Start with final board target • Determine expected BOM • Dive into package • Only then, into the silicon J.C.Jensen, A.A. Kidwai et al. RFIC 2010 Issues in single-chip radios • Package coupling • Board coupling • Silicon coupling • Thermal issues Package Modeling • Modeling is important part of predicting, understanding, and mitigating package impacts QFN and flip chip technologies presented here Pin placement • Generic wirebond • Dual row • Depopulated inner row • Frame, bondwires, paddle, … all couple signals • Placement is key The Periphery • The periphery design (pads, ESD and IO driver cells) is integral to the design of single chip products • IOs drive signals off chip… or around the chip to sensitive circuits ESD Isolation Silicon Floor plan vco PA dc2dc PCIe • The IO periphery was cut into two separate domains • Local subsectors exist for further separation • Distance is #1 factor for isolation • Main aggressors are placed as far apart as possible Isolation basics • Taps typically reduce coupling by 20-30dB • Deep nwell can double that if used appropriately – Appropriately means separate and quiet ground (see next slide) epi RX tap Large tap substrate tap TX Silicon Technology • Deep nwell must be tied to quiet supply and usually they are hard to come by • Must provide a very low impedance path to that ground Clean ground A nwell tap n+ gate p+ n+ iso-pw gateClean ground B source iso-pwell tap n+ p+ n+ iso-pwell drain n+ Any old drain supply n+ p+ deep nwell p+ drain p+ n+ psub substrate gate Iso-pwell to nwell diode n+ n+ p+ iso-pw Lossy substrate dnw dnw nwell to psub diode Power Delivery and isolation IO power First step to protecting circuits is to isolate power domains Isolation between supplies depends on: – Regulator PSRR – Board decoupling methods VCO CP Pres buffer LOG RX RF TX RF Domain XO Synthesizer RF dc2dc Digital dc2dc Analog Digital Host PLL ADC/ DAC Bias BG Power Delivery and Isolation Vssp Vcc_core1 Vcc_phy Vss Vss Vccp Vcc3 Vccp Domain2 Vssp Vss VDDOD Vss Vss Vssp Vcc2 Vccp Vssp Vcc IO Vccp Vssp ` Vss Vccp Vss Vcc1 Vcc5 Domain 3 Vssp Domain1 Analog Vcc4 Vss • Generally… what works for ESD performance, increases the potential for coupling signals Vcc_IO Vccp Vss Vccp Vssp Vcc4 Vcc Vcc_core Board coupling issue: Example Aggressor Victim Aggressor Victim Aggressor Victim PMU noise coupling issue: Example • Noise from the on-chip dc-dc is well below spec for on soldered parts; but can be seen in ADC SNR (through power supply) in socketed parts • The ground connection for a the package will affect the impact of the dc-dc on circuits and the ability to couple to other parts of the product Ant 1 Ant 1 LVR LVR ADC Radio dc-dc supply MAC/PHY Host LVR Xtal EEPROM DC-DC impact on receiver performance Thermal issues in single-chip: Example DC-DC • Overall dissipation may remain unchanged; but the thermal density increases • This is one of the biggest limitations in integrating products • Concurrent mode operation of multi-com products becomes challenging Power Amplifier PCIe Spurs in single-chip: Example • 40MHz spurs from the charge pump travel from loop filter into RX on board by proximity • Board and pin location issue, not chip or package issue LVR LVR LVR dc-dc supply LVR LF LF Ant 1 FEM Radio MAC/PHY Radio AntAnt11 Host FEM FEM Xtal EEPROM WiFi-BT coupling: Example Balun Balun iTR SP3T Chain A RX / TX WiFi BT (leaked to WiFi port) Mirror (2BT – WiFi) WiFi 1x2 RFIC Chain B RX only BT chain RX / TX BT WiFi Transmitter Chain WiFi-BT coupling: Example continued Q I BB 45o VDD Pre-Driver Driver Power Amplifier I Q BB VSS 2*BT couples to the driver ground With default pre-driver current (18mA) With default pre-driver current (31mA) Linearize the pre-driver device by degeneration Coupling through Internal Switch Second Harmonic Balun Balun Balun Balun External switch iTR SP3T iTR Internal switch 6-7dB better performance: Internal switch solution is differential Chain A RX / TX WiFi 1x2 RFIC Chain B RX only BT chain RX / TX BT Specifications achieved for WiFi single-chip This Work (measured at the antenna connector) Standard 802.11b/g/n S. Khorram et al. JSSC-05 (measured at the antenna connector) M.Zargari et al. JSSC-08 (Measured at Soc) P.B.Leong et al. ISIC-07 (Measured at Soc) 802.11b 802.11a/b/g/n 802.11a/b/g & BT Receiver Specifications Receiver Sensitivity 6Mbps/54Mbps (dBm) -89/-73 -93 @ 2Mbps -88 @ 11Mbps -92/-74 -75 @54Mbps Receiver Noise Figure (dB) 5.5 6-7 4.0 n/a Power consumption in 54Mbps (Legacy 802.11g) (mW) 663 (RF Rx/Synth/BB Filter= 264 MAC/PHY/PCIE/ADC =399 ) 525 mW @ 11Mbps 802.11b n/a 315 (RFRx/Synth/Filter/ADC) excluding PMU efficiency Power consumption in 300Mbps ( MIMO 802.11n mode) (mW) 818 (RF Rx/Synth/BB Filter= 352 MAC/PHY/PCIE/ADC =466 ) n/a 800 n/a n/a 11 -8 @-31dB EVM 0 @ -35dB EVM Transmitter Specifications Output 1dB Compression point (dBm) 19.3 Output power to meet EVM 25dB (dBm) 15.5 @ -25dB EVM (with digital pre-disortion) Power consumption in 54Mbps transmit rate (Legacy 802.11g) (mW) 878 @ 15dBm output power (RF Tx /Synth/BB Filter= 600 MAC/PHY/PCIE/DAC = 278) Power consumption in 150Mbps transmit rate (802.11n mode) (mW) [email protected] output power (RF Tx/Synth/Filter = 600 MAC/PHY/PCIE/DAC = 407) Technology Die Area Package 90nm CMOS with 3V I/O 33 sq. mm 10x10 QFN dual row 86pin 18 [email protected] Output power 802.11b 11Mbps Other Specifications 180nm CMOS 32.2 sq. mm 144 pin BGA 251 (RFTx/Synth/Filter/DAC) excluding PMU efficiency 630 @ -5 dBm output power n/a 130nm, CMOS 36 sq. mm 88pin leadless 90nm CMOS n/a n/a Conclusions • Integration, isolation, and coexistence begins from the beginning of chip planning • One must take into account all aspects of the final product before work begins • Many low level decisions can only be answered in the context of the high level environment Acknowledgements • I would like to thank the Intel Mobile Wireless Group team for all the design and testing to support this talk • I want to especially thank Jonathan Jensen, Rob Derania, Ram Sadhwani, Ryan Collins and Lei Feng for their time, testing and input.