[ibis-macro] Ibis Serdes Transmitters

  • From: Scott McMorrow <scott@xxxxxxxxxxxxx>
  • To: IBIS-ATM <ibis-macro@xxxxxxxxxxxxx>
  • Date: Tue, 25 May 2010 19:42:26 -0400

I have several questions regarding Transmitters in IBIS Serdes modeling

1) How does the EDA platform know that a model is a Transmitter or a Receiver?

   * It appears that the *.ibs model would indicate this, since there
     is nothing required in the ami or algorithmic model to delineate
     between Tx and Rx
   * If the ibs model is the only place where this occurs, what is the
     meaning of a model with a Model Type other then Input or Output,
     such as Series, 3-state, or I/O?

2) Where is the beginning, center, and end of a Tx stimulus bit?

   * according to the spec, the input waveform is differential and
     centered around 0 Volts.  Otherwise, there is no additional
     information regarding the input waveform.
   * how should a Tx GetWave determine the bit center, in order to
     clock any algorithmic processing?
   * how can the EDA platform inject DCD or deterministic jitter?
   * how does one vary the bit width input to the Tx on a dynamic basis?
   * how does the Tx clock PLL, and it's stochastics fit into the
     modeling?  Is this just encapsulated in GetWave and unavailable to
     the EDA platform?

3) Is the EDA platform or the ami dll responsible for providing the impulse response of the analog driver?

   * Since the dll is in the algorithmic domain, it would appear that
     this function is provided by the EDA platform, which seems to be
     evidenced by the following steps in the reference flow:
         o   Step 1. The simulation platform obtains the impulse
           response for the
           |          analog channel.  This represents the combined
           impulse response
           |          of the transmitter's analog output, the channel
           and the
           |          receiver's analog front end.  This impulse
           response represents
           |          the transmitter's output characteristics without
           filtering, for
           |          example, equalization.
           |  Step 2. The output of Step 1 is presented to the TX
           model's AMI_Init
           |          call.  If Use_Init_Output for the TX model is set
           to True, the
           |          impulse response returned by the TX AMI_Init call
           is passed
           |          onto Step 3.  If Use_Init_Output for the TX model
           is set to
           |          False, the same impulse response passed into Step
           2 is passed
           |          on to step 3.
   * The following paragraph would agree, since it differentiates
     filtered from the previous un-filtered response
         o | The AMI_Init function may return a modified impulse
           response by modifying
           | the first column of impulse_matrix.  If the impulse
           response is modified,
           | the new impulse response is expected to represent the
           filtered response.
   * However, clearly the IBIS analog buffer model is insufficient for
     creating a realistic Tx impulse response that incorporates
     frequency dependent effects.  So, in real implementations does
     part of the output driver filtering get moved into the AMI_Init
     filtering? Are additional S-parameter models required for the
     frequency dependent die effects that are not included in the IBIS

4) Given the above, how in the world are Tx_Jitter and Tx_DCD used, given that they are of Usage Info and Out? I assume that a Tx GetWave must perform an edge detect on a bit, and then use this to perform the associated Jitter and DCD functions, since these parameters are only informational to the EDA platform, and the Tx needs to synthesize its own internal clock. Or does everyone just statistically process the Tx?



Scott McMorrow
Teraspeed Consulting Group LLC
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Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax


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