[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
standard?
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?
regards,
Scott
--
Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax
http://www.teraspeed.com
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