Forum Discussion

Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
16 years ago

Maximum Frequency Input on Cyclone 3 device

Hi,

I have to realise a frequency divisor from 320 MHz to 40 Mhz. I read from datasheet of cyclone 3 that maximum frequency input on clock pin (LVDS in single ended mode) is about 400MHz. Could you confirm it ? I'm not sure about the result for this range of frequency.

I would like also to use general purpose pin to do this (TTL), is it possible ?

Mb it's better to use arria FPGA for this kind of application?

Thanx

Remi

4 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    16 years ago

    By Cyclone III specification, input toggle rates above 250 MHz are only supported for the LVDS standard. If you want to keep the specification strictly, an external LVDS driver could convert a single ended signal to LVDS. That's obviously more economic than using Arria or similar only to support 320 MHz single ended clock.

    In any case, you'll have difficulties to find a driver supporting 320 MHz with a single ended standard. Single ended driven "LVDS", e.g. a low voltage signal from a clock oscillator should most likely work with Cyclone III.

    If clock quality is critical, you'll get less jitter with an external LVDS repeater or differential output high speed comparator, that's not affected by the interfering signals present in a FPGA.
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    16 years ago

    Ok,

    Thanx for the reply. I'll do test and see the result.

    In Cyclone 3 device data sheet :

    .altera.com./literature./hb./cyc3./cyc3_ciii52001.pdf

    P21 Cyclone III Devices LVDS Receiver Timing Specifications

    They classify Max input clock frequency according to "Modes" *1, *2, *4, *7.....

    What is a Mode ?

    Is it a kind of protocol for LVDS transmittion ?

    Thx

    Remi
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    16 years ago

    --- Quote Start ---

    They classify Max input clock frequency according to "Modes" *1, *2, *4, *7.....

    What is a Mode ? Is it a kind of protocol for LVDS transmittion ?

    --- Quote End ---

    modes is referring to serialization factor. Cyclone III SERDES uses software SERDES only, so you are not limited to the Modes provided by the altlvds MegaFunction.

    LVDS implies no particular protocol, it's a synchronous raw binary data transmission.