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Ultra High Speed Digital Circuits Brandon Ravenscroft 12/03/2015 How Fast Is Ultra High Speed? • Speeds which require special materials, cables, connectors or severely restrictive board layouts • Fastest commercially available parts (clock speed and rise/fall time) • Clock rates and rise times faster than we saw in class material Ultra High Speed Considerations • • • • • • • Alternate Logic Types Dielectric Materials Connectors and Cables Voltage and Power Measurement Techniques Ultra High Speed IC Examples Ultra High Speed Layout Challenges Ultra High Speed Considerations • • • • • • • Alternate Logic Types Dielectric Materials Connectors and Cables Voltage and Power Measurement Techniques Ultra High Speed IC Examples Ultra High Speed Layout Challenges Current Mode Logic (CML) • No official standardization. Typically vendor specific [3] • Used for high speed, point to point signaling only (Typically Differential) • Needs termination resistors for current flow • Input stage has 2 emitterfollowers • Output stage is a BJT differential pair • AC or DC Coupling • Used up to 10 Gbps+[2, 3] Maxim Integrated CML Implementation [2] Current Mode Logic (CML) • Maxim Integrated Implementation [2]: • On chip 50 Ω Input and Output Terminations • Typical 16 mA Current Source • Vcc: +3.3 V Single Supply • Single ended or differential mode. • Typical 800 mV output differential voltage • Common mode output voltage of Vcc – 0.2 V Maxim Integrated CML Implementation [2] Low Voltage Differential Signaling (LVDS) • Developed by National Semiconductor • Standardized as ANSI/TIA/EIA-644-A [3] • Used for point-to-point or multi-drop transmission of low voltage differential signals (Typically Differential) • Input Voltage from 0 to 2.4 V • 350 mV differential output voltage • Used up to 2.5 Gbps • Requires 100 Ω termination • Very low power consumption (load current must be < 3.5 mA) – less than ECL or CML • DC Coupling only [2, 3] Maxim Integrated LVDS Implementation Output Stage [2] Low Voltage Differential Signaling (LVDS) • Maxim Integrated Implementation • Differential input and output terminated in 100 Ω Maxim Integrated LVDS Implementation Input Stage [2] Maxim Integrated LVDS Implementation Output Stage [2] Comparison of Fast Logic Families ECL LVDS CML Bus P-P or Multi-Drop P-P or Multi-Drop P-P only Relative Power High Low Medium Coupling DC or AC DC Only DC or AC Termination 50 Ω 100Ω 50 Ω Semiconductor Transistor Type BJT CMOS, BiCMOS BJT, CMOS Speed > 10 Gbps 2 Gbps >10 Gbps Fast Logic Families Comparison Data Provided by [3] These three logic families can be interfaced with proper design. Ultra High Speed Considerations • • • • • • • Alternate Logic Types Dielectric Materials Connectors and Cables Voltage and Power Measurement Techniques Ultra High Speed IC Examples Ultra High Speed Layout Challenges High Speed Dielectric Materials Motivations: 𝑐 • 𝑣𝑝 = → lower dielectric constant allows faster 𝜖𝑟 signal propagation. • Consider a high speed square wave as sine waves with fundamental and higher order harmonic frequencies. • High frequency harmonics must be preserved to avoid dispersion and signal distortion. • Stability over temperature and frequency is desired. High Speed Dielectric Materials Material Examples: • PTFE Resin [4]: • 𝜖𝑟 = 2.1 • Small change in dielectric constant over large frequency and temperature range. • DF ≤ 0.0004 up to 1 GHz. Increases slightly with temperature • RT/duroid 5880 (PTFE Composite) [5]: • 𝜖𝑟 = 2.2 • Used in Ku band and above (12-18 GHz) • 125 ppm/◦C change in 𝜖𝑟 • DF = 0.0009 at 10 GHz Ultra High Speed Considerations • • • • • • • Alternate Logic Types Dielectric Materials Connectors and Cables Voltage and Power Measurement Techniques Ultra High Speed IC Examples Ultra High Speed Layout Challenges High Speed Connectors • BNC (Bayonet Navy or British Naval Connector) • Originated in military use – quick to connect/disconnect • Used for frequencies up to 4 GHz. Slots radiate above this frequency. • Common in 50 Ω and 75 Ω ohm impedance • Threaded version (TNC) usable up to 12 GHz • PTFE Dielectric [7, 8] BNC Male Connector [6] High Speed Connectors • SMA (Sub-miniature type-A) • Very widely used in RF/Microwave • Operates up to 25 GHz • PTFE Dielectric • Designed by Bendix Scintilla [7, 8] SMA Male (left) and Female (right) connectors [9] High Speed Connectors • K Connector • Operates in all K band regions (1840 GHz) • Developed by Wiltron • Advancement of 2.92 mm connector • Air Dielectric [7,8] Various K connectors [10] High Speed Connectors • 1 mm Connector • Developed by Hewlett-Packard • Supports frequencies up to 110 [GHz] • Air Dielectric Male (left) and Female (right) 1 mm connectors [11] High Speed Coaxial Cable • Gore Precision Cable • ePTFE Dielectric with 𝜖 𝑟 = 1.3 • Measured 1.15 ns/ft propagation delay (87% of C) • Conductor sizes down to AWG 42 (2.5 mils) • DF < 0.0002 Gore Coaxial Cable [12] Ultra High Speed Considerations • • • • • • • Alternate Logic Types Dielectric Materials Connectors and Cables Voltage and Power Measurement Techniques Ultra High Speed IC Examples Ultra High Speed Layout Challenges Voltage and Power • • CPU Clock Frequency vs. Power • For CMOS devices: 𝑃𝐷𝑦𝑛 = 𝑓 ∗ 𝑉 2 ∗ 𝐶 • Reducing voltage logic level in processor reduces power dissipation • Intel 8080 Processor (1974) had clock speed of 4 MHz and voltage levels of +12V and -5V [13] • Intel Core i7 (2013) has a clock speed of 2.66 GHz and voltage level from 800 mV – 1.375 V [14] CPU Load vs. Power • 𝑃𝐷 = 𝑉 ∗ 𝐼 • More load devices requires high current sourcing capabilities. Lowering voltage decreases power • Intel Core i7 (2013) has thermal design power dissipation of 130 W. [14] Ultra High Speed Considerations • • • • • • • Alternate Logic Types Dielectric Materials Connectors and Cables Voltage and Power Measurement Techniques Ultra High Speed IC Examples Ultra High Speed Layout Challenges Ultra High Speed Measurement • Lower inductance in measurement path to reduce effect on measurement • Don’t use ground wire on scope probe • Remove clip from probe tip and apply tip directly to test point • Connect ground shield directly to circuit ground if possible or place ground wire as close to measurement point as possible • Shunt probe capacitance can alter circuit performance Ultra High Speed Measurement Test Point Ground Curlycue Ultra High Speed Considerations • • • • • • • Alternate Logic Types Dielectric Materials Connectors and Cables Voltage and Power Measurement Techniques Ultra High Speed IC Examples Ultra High Speed Layout Challenges Hittite HMC841 D Flip-Flop • CML design (single-ended or differential) • -3.3 V Supply • Max clock rate: 43 GHz • Rise/Fall time: 12 ps → Fknee = 41.7 GHz • Propagation delay: 10 ps • 630 mW power consumption • Package: 24 lead 4 mm x 4 mm SMT (Area of a dime is ~ 250 mm2) • Adjustable output voltage between 200 -850 mVpp [15] HMC841 Diagram [15] Micrel SY55851(A) Any Gate • Programmable to perform any Boolean function of two bits • Clock frequency up to 3 GHz • 100 Ω or 50 Ω CML output on board termination • Inputs compatible with differential PECL and CML • 2.3 - 6.0 V supply voltage • 350 ps propagation delay • 110 ps rise/fall time → Fknee = 4.5 GHz • 10 Pin 3 mm x 3 mm leaded package [16] Micrel SY55851 Functional Block Diagram [16] Ultra High Speed Considerations • • • • • • • Alternate Logic Types Dielectric Materials Connectors and Cables Voltage and Power Measurement Techniques Ultra High Speed IC Examples Ultra High Speed Layout Challenges Simple High Speed Layout • Clock divider circuit fA = ½ * fClk fB = ¼ * fClk Source: [17] • HMC841 D flip-flops will be used. Tr= 12 ps, fClk = 43 GHz max, Td = 10 ps. Setup time not given, assume negligible. Simple High Speed Layout • Ignoring Trace Delays fA = ½ * fClk fB = ¼ * fClk 1 2 Source: [17] • Time for clock to stable signal 1: 10 ps • Time for clock to stable signal 2: 10 ps + 10 ps = 20 ps Simple High Speed Layout • Allowable time for trace and other delays fA = ½ * fClk fB = ¼ * fClk 1 2 Source: [17] • 43 GHz clocks requires maximum path delay of 23.3 ps • Only 23.3 ps - 20 ps = 300 fs is left for trace and all other delays to achieve maximum clock frequency! • At 180 ps/in (FR-4 ) only 1.7 mils are left for traces Simple High Speed Layout • Challenge: Design a layout to implement this circuit with the maximum possible clock frequency. fA = ½ * fClk fB = ¼ * fClk 1 2 Source: [17] References [1] Title Photo: "Circuit, Circle, Circulation." Digital Media Theory. N.p., 31 Oct. 2013. Web. 02 Dec. 2015. <https://digitalmediatheory.wordpress.com/2013/10/31/circuit-circle-circulation/>. [2] "Introduction to LVDS, PECL, and CML." Maxim Integrated (2008): 1-14. Web. 27 Nov. 2015. <http://pdfserv.maximintegrated.com/en/an/AN291.pdf>. [3] Goldie, John. "LVDS, CML, ECL-differential Interfaces with Odd Voltages." EETimes. EETimes, 21 Jan. 2003. Web. 02 Dec. 2015. <http://www.eetimes.com/document.asp?doc_id=1225744>. [4] "Teflon PTFE Properties Handbook." (n.d.): n. pag. Web. 01 Dec. 2015. <http://www.rjchase.com/ptfe_handbook.pdf>. [5] "RT/duroid® 5870 /5880 High Frequency Laminates." (n.d.): n. pag. 2015. Web. 01 Dec. 2015. <https://www.rogerscorp.com/documents/606/acs/RT-duroid-5870-5880-Data-Sheet.pdf>. [6] "BNC." Telco Antennas BNC. Telco Antennas, n.d. Web. 02 Dec. 2015. <https://www.telcoantennas.com.au/site/category/products/bnc-connectors>. [7] "Microwave Connectors." Microwaves101. N.p., n.d. Web. 02 Dec. 2015. <http://www.microwaves101.com/encyclopedias/microwave-connectors>. [8] Agilent RF and Microwave Test Accessories. Agilent Technologies, 2003. Web. 01 Dec. 2015. <http://www.keysight.com/upload/cmc_upload/All/CoaxialConnectorOverview.pdf?&cc=US&lc=eng>. References [9] What Is an SMA Connector? Moton Industrial, n.d. Web. 01 Dec. 2015. <http://www.mtrf.com/shownews.asp?id=212>. [10] "K Connectors." K Connectors. Carlisle Interconnect Technologies, n.d. Web. 02 Dec. 2015. <http://www.carlisleit.com/product/k-connectors>. [11] Wikipedia Commons. N.p., n.d. Web. 01 Dec. 2015. <https://commons.wikimedia.org/wiki/File:1mm_connector_male_female.jpg>. [12] "Precision Coaxial Cable." Precision Coaxial Cable. Gore, n.d. Web. 02 Dec. 2015. <http://www.gore.com/en_xx/products/cables/coaxialmicrowave/aircraft/precision_coaxial_cable.html> [13] "Intel 8080 Family." Intel 8080 Family. CPU World, n.d. Web. 02 Dec. 2015. <http://www.cpuworld.com/CPUs/8080/>. [14] "Intel® Core I7-920 Processor (8M Cache, 2.66 GHz, 4.80 GT/s Intel® QPI) Specifications." ARK Product Launch. Intel, n.d. Web. 02 Dec. 2015. <http://ark.intel.com/products/37147/Intel-Core-i7-920Processor-8M-Cache-2_66-GHz-4_80-GTs-Intel-QPI>. [15] "HMC841." (n.d.): n. pag. HMC841. Hittite. Web. 02 Dec. 2015. <http://www.analog.com/media/en/technical-documentation/data-sheets/hmc841.pdf>. References [16] "Micrel SY55851(A) Any Gate." (n.d.): n. pag. Micrel SY55851(A) Any Gate. Micrel. Web. 02 Dec. 2012. <http://www.micrel.com/_PDF/HBW/sy55851-51a.pdf>. [17] "How to Make Frequency Divider?" Digital Logic. N.p., n.d. Web. 02 Dec. 2015. <http://electronics.stackexchange.com/questions/73722/how-to-make-frequency-divider>. [18] Slide Template: http://identity.ku.edu/powerpoint/index.shtml Thank you! Questions?