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8T49N205I - Block Diagram


FemtoClock® NG Universal FrequencyTranslator with Phase Build-Out

The IDT8T49N205I is a highly flexible FemtoClock® NG general purpose, low phase noise Frequency Translator / Synthesizer with Phase Build-Out (PBO) suitable for networking and communications applications. It is able to generate any output frequency in the 0.98MHz - 312.5MHz range and most output frequencies in the 312.5MHz - 1,300MHz range (see Table 3 for details). A wide range of input reference clocks and a range of low-cost fundamental mode crystal frequencies may be used as the source for the output frequency.

This device provides two factory-programmed default power-up configurations burned into One-Time Programmable (OTP) memory. The configuration to be used is selected by the CONFIG pin. The two configurations are specified by the customer and are programmed by IDT during the final test phase from an on-hand stock of blank devices. The two configurations may be completely independent of one another. One usage example might be to install the device on a line card with two optional daughter cards: an OC-12 option requiring a 622.08MHz LVDS clock translated from a 19.44MHz input and a Gigabit Ethernet option requiring a 125MHz LVPECL clock translated from the same 19.44MHz input reference.

To implement other configurations, these power-up default settings can be overwritten after power-up using the I2C interface and the device can be completely reconfigured. However, these settings would have to be re-written next time the device powers-up.



  • Fourth Generation FemtoClock® NG technology 
  • Universal Frequency Translator/Frequency Synthesizer
    • Zero ppm frequency translation
  • Two outputs, individually programmable as LVPECL or LVDS
  • Both outputs may be set to use 2.5V or 3.3V output levels
  • Programmable output frequency: 0.98MHz up to 1,300MHz
  • Two differential inputs support the following input types: LVPECL, LVDS, LVHSTL, HCSL
  • Input frequency range: 8kHz - 710MHz
  • Phase Build-Out minimizes output phase change on switchover
  • Crystal input frequency range: 16MHz - 40MHz
  • Two factory-set register configurations for power-up default state
  • Power-up default configuration pin or register selectable
  • Configurations customized via One-Time Programmable ROM
  • Settings may be overwritten after power-up via I2C
  • I2C Serial interface for register programming
  • RMS phase jitter at 155.52MHz, using a 40MHz crystal (12kHz - 20MHz): 378fs (typical), Low Bandwidth Mode (FracN)
  • Output supply voltage modes:
    • 3.3V/3.3V/3.3V
    • 3.3V/3.3V/2.5V
    • 2.5V/2.5V/2.5V
  •  -40°C to 85°C ambient operating temperature

Product Specification

Phase Jitter Typ RMS (ps)Inputs (#)Input TypeInput Freq (MHz)Outputs (#)Output TypeOutput Voltage (V)Output Freq Range (MHz)
0.3782LVPECL, LVDS, LVHSTL, HCSL, Crystal0.008000 - 710.0000002LVDS, LVPECL2.5, 3.30.980000 - 1300.000000

Product Options

Orderable Part IDPart StatusPkg. CodePkg. TypeLead Count (#)Temp. GradePb (Lead) FreeCarrier TypeSample & Buy
8T49N205A-000NLGIActiveNLG40P2VFQFPN40IYesTrayCheck Availability
8T49N205A-000NLGI8ActiveNLG40P2VFQFPN40IYesReelCheck Availability
8T49N205A-999NLGIActiveNLG40P2VFQFPN40IYesTrayCheck Availability
8T49N205A-999NLGI8ActiveNLG40P2VFQFPN40IYesReelCheck Availability


Technical Documentation

Title Type Format File Size Datesort icon
Datasheets & Errata
8T49N205I Data Sheet Datasheet PDF 723 KB Oct 10, 2012
User Guides & Manuals
FemtoNG Universal Frequency Translator Ordering Product Information Guide Manual - User Reference PDF 216 KB Sep 9, 2016
Apps Notes & White Papers
AN-828 Termination - LVPECL Application Note PDF 229 KB Jul 5, 2016
AN-831 The Crystal Load curve Application Note PDF 308 KB Sep 22, 2014
AN-844 Termination - AC Coupling Clock Receivers Application Note PDF 82 KB May 13, 2014
show all (22)
AN-846 Termination - LVDS Application Note PDF 50 KB May 13, 2014
AN-842 Thermal Considerations in Package Design and Selection Application Note PDF 403 KB May 12, 2014
AN-840 Jitter Specifications for Timing Signals Application Note PDF 349 KB May 8, 2014
AN-803 Crystal Timing Budget and Accuracy for IDT Timing Clock Products Application Note PDF 44 KB May 8, 2014
AN-839 RMS Phase Jitter Application Note PDF 149 KB May 7, 2014
AN-838 Peak-to-Peak Jitter Calculations Application Note PDF 32 KB May 7, 2014
AN-832 Timing Budget and Accuracy Application Note PDF 48 KB May 6, 2014
AN-834 Hot-Swap Recommendations Application Note PDF 67 KB May 6, 2014
AN-833 Differential Input Self Oscillation Prevention Application Note PDF 94 KB May 6, 2014
AN-837 Overdriving the Crystal Interface Application Note PDF 50 KB May 6, 2014
AN-835 Differential Input with VCMR being VIH Referenced Application Note PDF 77 KB May 6, 2014
AN-836 Differential Input to Accept Single-ended Levels Application Note PDF 37 KB May 6, 2014
AN-830 Quartz Crystal Drive Level Application Note PDF 59 KB May 5, 2014
AN-815 Understanding Jitter Units Application Note PDF 476 KB Apr 24, 2014
AN-827 Application Relevance of Clock Jitter Application Note PDF 1.06 MB Apr 24, 2014
AN-802 Crystal-Measuring Oscillator Negative Resistance Application Note PDF 52 KB Mar 12, 2014
AN-801 Crystal-High Drive Level Application Note PDF 109 KB Jan 15, 2014
AN-806 Power Supply Noise Rejection Application Note PDF 353 KB Jan 15, 2014
AN-805 Recommended Ferrite Beads Application Note PDF 38 KB Jan 15, 2014
PCN# : TB1311-01 New Carrier Tape on VFQFPN-28, VFQFPN-40, VFQFPN-48 Product Change Notice PDF 790 KB Apr 8, 2014
PCN# : N1307-01 Die Revision Change Product Change Notice PDF 71 KB Aug 14, 2013
Timing Fabric for Communications Equipment Overview Overview PDF 263 KB Dec 10, 2015
FemtoClockNG-UniversalFrequencyTranslators Product Brief PDF 1.06 MB Aug 8, 2011

Software & Tools

Title Type Format File Size Datesort icon
8T49N205I IBIS Model Model - IBIS ZIP 213 KB Nov 24, 2014