Slide 1: How to Measure Clock Jitter – Part 3
SiTime University Turbo Seminar Series How to Measure Clock Jitter – Part 3 C2C Jitter and Long Term Jitter May 13, 2013
Slide 2: What is Clock Jitter
What is Clock Jitter • Jitter is, “The deviation of an event timing relative to its ideal value” • Event? - defined by specific type of jitter • Ideal value? - event timing on an ideal clock, often estimated from average value of the event • Jitter definitions: • Period Jitter (Covered in Part 1) •
Slide 3: Cycle-to-cycle Jitter (C2C) Definitions and Terminology
Jitter Definitions and Terminology Cycle-to-cycle Jitter (C2C) t0 t1 t2 t3 t k 1 tk T1 T2 T3 Tk • Cycle-to-cycle jitter: the difference of one period and its adjacent one • Event: Three consecutive rising or falling edges • Ideal value = average C2C J CC (k ) Tk Tk 1 J CC (k ) Tk 1 Tk
Slide 4: About C2C Jitter
About C2C Jitter • C2C jitter is the difference of two adjacent clock period and it dominated by the high frequency jitter • Can be measure by real-time oscilloscope • C2C jitter is not sensitive to low frequency jitter or slow frequency modulation of oscillator frequency • Often Used to specify jit
Slide 5: C2C Jitter in a Spread Spectrum Clock
C2C Jitter in a Spread Spectrum Clock • C2C jitter changes little with spread spectrum clock (SSC) mode enabled or disabled • C2C jitter is not sensitive to low frequency phase noise SiT9001-125MHz SSXO with 2% down spread Spread Spectrum Disabled Spread Spectrum Enabled C2C jitter 17ps max C2C jitt
Slide 6: Period Jitter in a Spread Spectrum Clock
Period Jitter in a Spread Spectrum Clock • Period jitter changes significantly when SSC enabled • C2C jitter is the difference of two adjacent periods and it remains steady with slow SSC frequency modulation. SiT9001-125MHz SSXO with 2% down spread Spread Spectrum Disabled Spread Spectrum Enabled Pe
Slide 7: Long Term Jitter (LTJ) Definitions and Terminology
Jitter Definitions and Terminology Long Term Jitter (LTJ) 1 2 N+1 N+2 2N 2N+1 t0 t1 tN tN+1 t2N-1 t2N T N-cycle (0) T N-cycle (1) LTJ N-cycle (i) = T N-cycle (i+1) - T N-cycle (i) • Long term jitter: variations of timing intervals between the first edge and the last edge of N consecutive clock cycle
Slide 8: Long Term Jitter (LTJ) Definitions and Terminology
Jitter Definitions and Terminology Long Term Jitter (LTJ) Ideal value = Number of cycles (N) * average period (TC) TimeJ (i N ) TimeJ (i ) Relate LTJ to TIE or Timing Jitter N i 1 J j i PerJ (i ) Relate LTJ to Period Jitter • Long term jitter: sensitive to low frequency phase noise inte
Slide 9: Observe LTJ on Real Time Scope
Observe LTJ on Real Time Scope • Set “Trigger Delay” to observe 100 s LTJ of a 125 MHz clock Trigger Delay 0 s Trigger Delay 100 s Jitter increases with accumulation time SiT9001-125 MHz SSXO with spread spectrum disabled
Slide 10: LTJ Measurement Setup with Real-Time Oscilloscope
LTJ Measurement Setup with Real-Time Oscilloscope Setup: Direct connection to oscilloscope 50Ω loading to the oscillator output 50 Ω • Measure LTJ with Real Time Oscilloscope • Use oscilloscope with low time base error (< 0.5 ps rms) • Optimize oscilloscope settings to reduce measurement error • Hig
Slide 11: LTJ Measurement Setup with Time Interval Analyzer (TIA)
LTJ Measurement Setup with Time Interval Analyzer (TIA) Setup: Time Interval Direct connection to TIA Analyzer 50Ω loading to the oscillator output SiTime jitter measurement setup 50 Ω • Measure LTJ with TIA • Based on counter-timer approach • Can achieve high equivalent time base resolution in sub-
Slide 12: Measure LTJ on TIA
Measure LTJ on TIA • Set N = 2500 to measure LTJ@100 s on a SiT8208-25 MHz clock 25 MHz Clock Period N x TC RMS and P-P LTJ@100s = 2500 x (1/25E6) = 100 s Accumulation Time for N-cycle TIA Model: Wavecrest SIA-4000
Slide 13: Who cares about LTJ
Who cares about LTJ • Applications that require synchronization of timing events over relatively long time interval or many clock cycles • Analog and digital video • DDR for achieving phase locking in DDR interface Processing frame start LTJ www.sitime.com 13
Slide 14: Summary
Summary • C2C jitter reflects the high frequency jitter of the clock signal and is not sensitive to slow frequency modulation of a spread spectrum XO • Long term jitter, defined by accumulation time or N-cycle, is sensitive to low frequency phase noise • Applications care about LTJ when multiple tim
Slide 15: Contact Information
Contact Information • For Questions, contact SiTime Technical Support Technicalsupport@sitime.com • For Turbo Webinar pdf Downloads on SiTime’s Web Site www.sitime.com/support/sitime-u/turbo-webinars •All new webinars will be posted within 24-hours • For app notes and other info, visit http://www.si