In the case of ECL and CMOS I suspect there might be DC blocking capacitors. Except for proprietary interfaces, I see very few serial interfaces with direct DC connections.
-- Scott McMorrow Teraspeed Consulting Group LLC 16 Stormy Brook Road Falmouth, ME 04105 (401) 284-1827 Business (401) 284-1840 Fax http://www.teraspeed.com Teraspeed® is the registered service mark of Teraspeed Consulting Group LLC On 6/5/2013 1:28 PM, Muranyi, Arpad wrote:
Radek, I am not quite sure what exactly our interoperability statement is, but I doubt that it guarantees absurd things like an ECL Tx (working in the negative voltages) being interoperable with a CMOS Rx (working in the positive voltages), and the like... Thanks, Arpad ================================================================= *From:*radek_biernacki@xxxxxxxxxxx [mailto:radek_biernacki@xxxxxxxxxxx] *Sent:* Wednesday, June 05, 2013 12:21 PM *To:* Muranyi, Arpad; ibis-macro@xxxxxxxxxxxxx *Subject:* RE: [ibis-macro] Re: BIRD 158.3 - 2 Arpad,While there is some rationale in what you are saying, this is not what we state about interoperability.Radek*From:*ibis-macro-bounce@xxxxxxxxxxxxx <mailto:ibis-macro-bounce@xxxxxxxxxxxxx> [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] *On Behalf Of *Muranyi, Arpad*Sent:* Wednesday, June 05, 2013 10:15 AM *To:* ibis-macro@xxxxxxxxxxxxx <mailto:ibis-macro@xxxxxxxxxxxxx> *Subject:* [ibis-macro] Re: BIRD 158.3 - 2 Radek, You are correct, we cannot guarantee that a Tx model will know what the linear operating region of the Rx is, but most channels are following some sort of a standard which usually specify the signal levels one way or another. I would think that a Tx vendor's product will be compatible with any other Rx vendor's product for a given communication protocol, which also implies that the common mode component of the signal coming from the Tx will be in the range where the Rx products are designed to function. Regarding the initial condition topic, please explain how I misunderstood Fangyi's statement. Thanks, Arpad =======================================================*From:*ibis-macro-bounce@xxxxxxxxxxxxx <mailto:ibis-macro-bounce@xxxxxxxxxxxxx> [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] *On Behalf Of *radek_biernacki@xxxxxxxxxxx <mailto:radek_biernacki@xxxxxxxxxxx>*Sent:* Wednesday, June 05, 2013 11:59 AM*To:* Muranyi, Arpad; ibis-macro@xxxxxxxxxxxxx <mailto:ibis-macro@xxxxxxxxxxxxx>*Subject:* [ibis-macro] Re: BIRD 158.3 - 2 Hi Arpad, (I am replying to an earlier message in this thread.)Regarding the common mode issue, how can you guarantee that Tx_Vol and Tx_Voh specified on TX AMI model are -- in your words -- " the appropriate common mode component" for any user selected RX model. Is it possible that for given and fixed Tx_Vol and Tx_Voh the independently user-selected RX will be driven into a strongly nonlinear operation?In other words, by specifying those parameters, aren't we imposing conditions that could otherwise be left to the user for a proper setting?Second, regarding the initial conditions, there are several ways to address this issue but what you say is consistent with what I was trying to convey yesterday and you probably misinterpreted what Fangyi was saying. However, I would avoid new terms like "AMI Impulse response" as it does not seem necessary to introduce them.Radek*From:*ibis-macro-bounce@xxxxxxxxxxxxx <mailto:ibis-macro-bounce@xxxxxxxxxxxxx> [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] *On Behalf Of *Muranyi, Arpad*Sent:* Tuesday, June 04, 2013 9:39 PM *To:* ibis-macro@xxxxxxxxxxxxx <mailto:ibis-macro@xxxxxxxxxxxxx> *Subject:* [ibis-macro] Re: BIRD 158.3 - 2 Correction about the initial condition text below: I should have used Tx_Voh and Tx_Vol for the source voltages, not Tx_V and 0, but the concept of what I was trying to say remains the same... Sorry for the confusion, Arpad =====================================================*From:*ibis-macro-bounce@xxxxxxxxxxxxx <mailto:ibis-macro-bounce@xxxxxxxxxxxxx> [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] *On Behalf Of *Muranyi, Arpad*Sent:* Tuesday, June 04, 2013 11:27 PM *To:* ibis-macro@xxxxxxxxxxxxx <mailto:ibis-macro@xxxxxxxxxxxxx> *Subject:* [ibis-macro] Re: BIRD 158.3 - 2 Radek, I agree that "AMI technology does not handle the common mode" but during the channel characterization simulation the models must include the appropriate common mode component if the differential response depends on what the common mode component is. As an analogy, consider the SPICE small signal .AC simulation. The DC component is irrelevant for the frequency sweep, yet the simulator will start with a DC operating point calculation because the circuit's behavior might vary quite a bit for different bias conditions. We can have the same situation in IBIS-AMI with certain types of non-linear Rx models which can still be considered linear devices for AMI purposes if the signaling range falls into their linear region. In situations like this, the channel characterization simulation will only give the correct results if the differential signal contains the correct DC "bias" or common mode component. Now that you mentioned the initial conditions, after thinking about Fangyi's statement in the ATM meeting today that in LTI systems the initial conditions do not make a difference, I tend to disagree. Let's consider a simple RC filter with (a) zero initial charge on the capacitor and (b) 1 V initial voltage across the capacitor. By applying a 1 V step, you will get exponential rise in case (a) but a flat 1 volt output in case (b). Also, in the circuit proposed in the BIRD, the voltage sources are essentially non-zero for time<0. We should state in the BIRD that: It is assumed that before transition, the circuit remains sufficiently long under inputs SRC1 = 0 and SRC2 = Tx_V, so that the steady state is achieved. After time=0, SRC1 changes to Tx_V and SRC2 to 0. We measure the voltage difference between ports 2 and 4, subtract the initial value (in steady state this difference is not zero), and divide the result by 2. This gives us the 'edge response' which starts from zero. Then, find its time difference and get "AMI Impulse response". It is important to understand that the difference voltage was non-zero before transition and at time=0 started to change to another steady state. The derivative should be taken by considering that non-zero voltage prior to zero. Otherwise, when finding the derivative (for impulse response), we'll get incorrect results. Thanks, Arpad =================================================================*From:*radek_biernacki@xxxxxxxxxxx <mailto:radek_biernacki@xxxxxxxxxxx> [mailto:radek_biernacki@xxxxxxxxxxx]*Sent:* Tuesday, June 04, 2013 7:24 PM*To:* Dmitriev-Zdorov, Vladimir; bob@xxxxxxxxxxxxx <mailto:bob@xxxxxxxxxxxxx>; wkatz@xxxxxxxxxx <mailto:wkatz@xxxxxxxxxx>; Muranyi, Arpad; ibis-macro@xxxxxxxxxxxxx <mailto:ibis-macro@xxxxxxxxxxxxx>*Subject:* RE: [ibis-macro] Re: BIRD 158.3 - 2 Hi Walter,I am still not convinced that specifying Vol and Voh for a specific TX AMI is of any particular value in the context of an arbitrary RX to interact with. AMI technology does not handle the common mode and we should not make an impression it does. If, in the future, handling of the common mode becomes necessary, there will be ways to enhance this methodology, and it should be done in a complete way.Second, the BIRD still needs to clarify the following three items: (a) that the "step response" of interest (to determine the impulse response) represents the response to a unit step function at the input, (b) the sources in the diagram do not represent that input, and (c) following Vladimir's comments, handling of non-zero initial conditions (if taking place) -- it needs to be stated how their impact is removed.Radek*From:*Dmitriev-Zdorov, Vladimir [mailto:vladimir_dmitriev-zdorov@xxxxxxxxxx]*Sent:* Friday, May 24, 2013 12:39 PM*To:* BIERNACKI,RADEK (A-Sonoma,ex1); bob@xxxxxxxxxxxxx <mailto:bob@xxxxxxxxxxxxx>; wkatz@xxxxxxxxxx <mailto:wkatz@xxxxxxxxxx>; Muranyi, Arpad; ibis-macro@xxxxxxxxxxxxx <mailto:ibis-macro@xxxxxxxxxxxxx>*Subject:* RE: [ibis-macro] Re: BIRD 158.3 - 2 Radek,I agree with your comments on redundancy of the input characterization: one parameter is enough since the common mode input is constant (with defined stimulus) hence no conversion of time varying common mode into differential is possible.Regarding step response, the definition in fact should be even more stringent. The step response is a response of a circuit to a certain unit size step-wise excitation, assuming no independent sources (i.e. non-autonomous circuit only) and also zero initial conditions! If we measure the response as a transition from prolonged '0' (lasted for many bits, to allow initial steady state) to '1' state, it is not a response with zero initial conditions, and for a linear circuit it gives us doubled step response. Then, EDA platform has to account for this fact by applying a factor 0.5. Another problem with 'step response' is that it is defined for one excitation only.Vladimir ------------------------------------------------------------------------*From:*ibis-macro-bounce@xxxxxxxxxxxxx <mailto:ibis-macro-bounce@xxxxxxxxxxxxx> [ibis-macro-bounce@xxxxxxxxxxxxx] on behalf of radek_biernacki@xxxxxxxxxxx <mailto:radek_biernacki@xxxxxxxxxxx> [radek_biernacki@xxxxxxxxxxx]*Sent:* Friday, May 24, 2013 12:30 PM*To:* bob@xxxxxxxxxxxxx <mailto:bob@xxxxxxxxxxxxx>; wkatz@xxxxxxxxxx <mailto:wkatz@xxxxxxxxxx>; Muranyi, Arpad; ibis-macro@xxxxxxxxxxxxx <mailto:ibis-macro@xxxxxxxxxxxxx>*Subject:* [ibis-macro] Re: BIRD 158.3 - 2 Hi All,In my opinion the latest changes made the proposal somewhat more confusing. The common-mode input is introduced quite unnecessarily. All that is needed is the difference of Tx_Vol and Tx_Voh and the proposal asks for two numbers where just one number is needed. The one number needed could be either half of the differential voltage swing or the full differential voltage swing. (That would correspond to either Tx_Vol = -Tx_V and Tx_Voh = Tx_V, or Tx_Vol = -Tx_V/2 and Tx_Voh = Tx_V/2, and specifying just Tx_V as before.)Furthermore, the use of inherent common-mode concept associated with specifying two (could be arbitrary) numbers will be more confusing to the users of the AMI technology, and model developers in particular.Arpad: your comment about the unit excitation was quite incorrect. By definition, the step response of a circuit is the output signal (here the output differential voltage) when a unit step signal (the input differential voltage) is applied to the input. The circuit inside must not have independent sources in it. The framework in which this BIRD is written does not follow this convention, and suggests independent sources being part of the circuit. In fact these sources should properly be described as voltage-controlled voltage sources that are controlled by an input signal that is not shown. A unit excitation (Dirac delta, or unit step function) must be applied to that input to determine the impulse response needed for AMI simulation. In the context of the picture in the BIRD that unit excitation *will result* in the voltages of the sources as described. Those voltages are poorly termed in the BIRD as "step response stimulus". In fact the picture does not reflect an input-output model of the actual circuit, but shows a schematic for impulse response calculation -- that should be explicitly stated.Radek*From:*ibis-macro-bounce@xxxxxxxxxxxxx <mailto:ibis-macro-bounce@xxxxxxxxxxxxx> [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] *On Behalf Of *Bob Ross*Sent:* Friday, May 24, 2013 8:44 AM*To:* wkatz@xxxxxxxxxx <mailto:wkatz@xxxxxxxxxx>; Arpad_Muranyi@xxxxxxxxxx <mailto:Arpad_Muranyi@xxxxxxxxxx>; 'IBIS-ATM'*Subject:* [ibis-macro] Re: BIRD 158.3 - 2 All: Looks good enough to me for submission. Bob*From:*ibis-macro-bounce@xxxxxxxxxxxxx <mailto:ibis-macro-bounce@xxxxxxxxxxxxx> [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] *On Behalf Of *Walter Katz*Sent:* Friday, May 24, 2013 7:43 AM*To:* Arpad_Muranyi@xxxxxxxxxx <mailto:Arpad_Muranyi@xxxxxxxxxx>; 'IBIS-ATM'*Subject:* [ibis-macro] Re: BIRD 158.3 - 2 All,I have made the changes requested by Bob and Arpad (enclosed). Any additional comments before I send the formal version to Michael this afternoon would be appreciated.Walter*From:*ibis-macro-bounce@xxxxxxxxxxxxx <mailto:ibis-macro-bounce@xxxxxxxxxxxxx> [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] *On Behalf Of *Muranyi, Arpad*Sent:* Friday, May 24, 2013 10:03 AM *To:* IBIS-ATM *Subject:* [ibis-macro] Re: BIRD 158.3 Walter, Here are my comments on this BIRD draft. What does "differential transmission" mean in this sentence:"This Impulse Response characterizes the differential transmission of the Tx analog buffer model,"?Could you make this clearer with better wording? In the following sentence you are talking about the "die side of the package":"For a Tx buffer, the Transmitter Circuit defines the analog buffer model between the zero impedance stimulus input voltage source and the die side of the package model. For an Rx buffer, the Receiver Circuit defines the analog buffer model between the die side of the package model and a high impedance probe at the input to the Rx Algorithmic model."However, it is not clear whether this means that the buffer model described by the data in the Touchstone file can/should also include the on-die interconnect or not. I think this should be clearly stated otherwise different people will make different assumptions to model on-die interconnects. This sentence:"Note that this Touchstone analog model only represent the on-die model between the die pad and buffer interface to the algorithmic model"is somewhat misleading, because it can be interpreted as if the Touchstone model is **the** on-die interconnect model between the pad and the buffer's terminals ("buffer interface"). You use the words "unit excitation". This sentence:"This BIRD defines what that unit excitation is when the Tsonefile parameter is present."really doesn't make sense, because by definition a unit = 1, i.e. the "unit excitation" would have to have a fixed and predefined magnitude of 1 volt, yet in this BIRD you define Tx_Voh and Tx_Vol, which is not "unit" anymore. Also, please correct the spelling of "Tsonefile" in this sentence (missing "t"). You mention in the discussion of the Impulse Response generation that the Tstonefile parameter is a Reserved Parameter, but you don't say anywhere in the document whether the rest of the parameters in this BIRD are Reserved or Model_Specific. Please specify what you want them to be. I would also like to request to put a "0" before and after each decimal point for properness. For example, instead of "(Range 1. .5 1.)"please write "(Range 1.0 0.5 1.0)", it is much more readable that way...Thanks, Arpad ======================================================================*From:*ibis-macro-bounce@xxxxxxxxxxxxx <mailto:ibis-macro-bounce@xxxxxxxxxxxxx> [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] *On Behalf Of *Walter Katz*Sent:* Thursday, May 23, 2013 9:04 PM *To:* IBIS-ATM *Subject:* [ibis-macro] BIRD 158.3 All,Please review version 158.3 (Tstonefile AMI models) before I send the final version to Michael tomorrow afternoon.The major change is that there are now two Tx voltage levels (Tx_Vol and Tx_Voh) that determine the differential step response stimulus that is assumed for generating the Impulse Response of the channel. This make BIRD158 Tstonefile models directly convertible to BIRD 160 external models, and gives the model maker the ability to determine the common mode voltage when generating the Impulse Response of a channel.Walter Walter Katz wkatz@xxxxxxxxxx <mailto:wkatz@xxxxxxxxxx> Phone 303.449-2308 Mobile 303.335-6156
