Jonathan, A resulting limitation for the signal flow disciplines connecting to a conservative discipline would be that a signal flow node can have only one conservative instance connected to it, and that all signal-flow instances need to have the same port direction, i.e. all in or all out. Should an inout port direction not be allowed for signal flow models: it has to be either in or out. I can image a model where a signal-flow port is either read or driven, dependent on a parameter setting, but it cannot read and drive at the same time... Regards, Marq Marq Kole Competence Leader Analog Simulation, Philips ED&T Marq Kole/EHV/RESEARCH/PHILIPS wrote on 02-06-2006 16:08:32: > Jonathan, > > Your reply required some thinking before I could answer; I'll also > copy the reflector as I think this is relevant to our discussions. > > Regards, > Marq > > > Marq Kole > Competence Leader Analog Simulation, Philips ED&T > > Jonathan David <jb_david@yahoo.com> wrote on 31-05-2006 18:41:25: > > > Hi Marq, > > > > thanks for the reply. It looks like you missed part of > > my point. > > > > Let me ask a question; For a potential nature, do you > > expect KVL to be obeyed? I do, and I think you do > > also.. > > V(B) = V(A) + V(B,A) > > V(A,gnd) + V(B,A) + V(gnd,B) = 0; > This is not necessarily the KVL: in mathematics this is also known > as associativity. If you consider 0 to be the mathematical ground > i..e reference, then with V(B) = 2 and V(A) = 3 you say: > > 2 = 3 + (2 - 3) > (3 - 0) + (2 - 3) + (0 - 2) = 0 > > > therefor when I flip to the FLOW side, I expect KCL to > > be obeyed. > > KCL: Sum(I)@node = 0; > > > > In fact if it isn't, it wouldn't be possible to > > connect the flow type to the flow connection of the > > compatible conservative discipline. > > > > but your example doesn't show a violation. > > Without the context (how the block is connected) we > > can't talk about KCL. > > Your example has no context.. its not connected up > > with any thing else, and without the connection nodes, > > we have no nodes at which to sum the currents to 0. > > Yet the block itself is also a node, so the sum of currents flowing > into a block should equal the sum of currents flowing out of a > block. In a conservative system this would be solved by having the > missing current supplied by the ground. That is OK as the potential > of the ground stays 0: the energy conservation requirement of the > consevative system makes sure that each node adheres to the KCL and > each loop of branches to the KVL. > > However, in a signal flow environment the ground of a flow > discipline needs to be 0; you essentially give every flow a value > relative to the reference. > > The result is that Tellegen's Theorem (which says that the total > energy in a conservative system is equal to 0) does not hold for > signal flow disciplines. > > > As I read it, > > that model defines a second current in terms of a > > first. I(in,out) is not being defined as a branch > > relationship rather > > I(out,0) is being defined in terms of I(in,0). > > two separate branchs, neither having to do with each > > other.. so I don't see any violation of KCL.. > > Generally in the model I define the branch not the > > nodes.. > The KCL also applies to every possible collection of nodes in a > conservative lumped element system. > > > What I mean by flow signal_flow disciplines obeying > > the KCL, is that the sum of the current connections at > > a node will be 0. so you can have N current > > discipline sources into a node, as long as there are > > N+1 connections (only 1 load) > > without the electrical side to serve as a resolution > > function, I don't see how you could allow N+2 .. > > Unless we arbitrarily say that every undertermined > > branch gets an equal flow.. > Now I see what you're getting at: if I have three instances all > connected to the same node, > then if they are of a potential signal flow discipline, the value is > determined by just one of the three connections; if they are of a > flow signal flow discipline, the value for one of the three should > be determined from the other two. > > As there is no energy conservation in a signal flow system, there is > no possibillity to say how currents will be distributed if only one > of the three instances drives a current. It is an underdetermined > system (1 known, 3 equations). So here is a duality: in the > potential signal flow system there may be at most 1 source driving a > node, in the flow signal flow system there may be at most one sink > collecting from a node. > > Under these conditions I can agree that a flow signal-flow > discipline adheres to the KCL. Should we then also mandate that > directions be provided on all signal flow discipline ports so a > check on the above restrictions can be performed? > > The KCL does not apply to instances that contain sources in a signal > flow system: in a conservative system the KCL applies also in that case. > > > Most simulators I know don't allow this on the > > potential side.. > > if you have a loop of nodes, 0 ground, A, B, C, D, E, > > A > > and you define V(A,0), V(A,E) V(B,C) and V(C,D) > > (so V(A,B) and V(D,E) are undefined > > KVL requires that the sum of voltages around the loop > > be 0, but there are two unknowns.. and one equation. > > The simulator I use most will complain about "no path > > to ground and install a gmin to ground at B,C, of D. > > > > example.. If I define > > voltage A, B > > V(A) <+ 3.0; > > V(B,A) <+ 1.0; > > > > I expect V(B) {V(B,simulator ground)} = 4.0 > > > > I expect them to obey KVL, even though they are not > > conservative, but signal flow (potential) discipline. > > I don't expect KCL to be obeyed because the current's > > "don't exist".. > > > > I expect the same thing (KCL to work, KVL undefined) > > on the signal_flow (Flow) side. > > > > Here is a single model example that defines multiple > > branches between two nodes.. (giving us the connection > > network we need for KCL) > > > > > > current A, B > > branch one (A,B) > > branch two (A,B) > > branch three (A,B) > > I(one) <+ 1.0; > > I(two) <+ 1.0; > > Isum = I(three); > > will result in Isum = -2.0 > > > > defining a module with only 2 ports doesn't > > automatically make a branch between those two nodes if > > there are treated separately in the model.. > > (single node definitions always assume ground as the > > reference node for that branch ) > > > > In a "potential" situation, only 1 potential around a > > loop can be left undefined, determined by KVL. > > in a "flow" situation, only 1 flow into a node can be > > left undefined, determined by KCL. > > > > In fact, I think this is the behavior/constraint that > > allows the signal_flow disciplines to connect to the > > compatible conservative disciplines. > > > > I believe this is an accurate representation of what > > the signal flow guys are expecting for the behavior of > > "FLOW" type signal_flow behavior. > > > > does it make sense now? > > Jonathan > Yes, thanks for taking the time to help me understand. > > Cheers, > Marq > > > > > --- Marq Kole <marq.kole@philips.com> wrote: > > > > > Jonathan, > > > > > > In response to your email to Peter: I would not even > > > expect a signal flow > > > flow nature to follow the KCL. As an example: the > > > following signal flow > > > block does not obey the KCL: > > > > > > `include "disciplines.vams" > > > > > > discipline current; > > > flow Current; > > > enddiscipline; > > > > > > module current_mult (in, out); > > > inout in, out; > > > current in, out; > > > parameter real mult = 2; > > > > > > analog > > > I(out) <+ mult * I(in); > > > > > > endmodule > > > > > > In a conservative system the potential and the flow > > > are linked, where one > > > obeys the KCL, and the other the KVL. Because > > > conservation is absent in a > > > signal flow system, the actual distinction between a > > > potential and a flow > > > is also absent. The only relevant thing in such a > > > discipline is the value. > > > That is why limiting the nature in signal flow > > > disciplines to potential > > > only is a mistake. Both flow and potential would fit > > > equally well. > > > > > > To make a connection between a conservative system > > > and the above current > > > multiplier I assume a separate (connect)module would > > > be needed that > > > assures conservation on the conservative side. > > > > > > Marq > > > > > > > > > Marq Kole > > > Competence Leader Analog Simulation, Philips ED&T > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Jonathan David <jb_david@yahoo.com> > > > Sent by: > > > owner-verilog-ams@server.eda.org > > > 31-05-2006 01:36 > > > > > > To > > > Peter Liebmann <peterl@xpedion.com> > > > Sri Chandra <srikanth.chandrasekaran@freescale.com> > > > cc > > > Verilog-AMS LRM Committee > > > <verilog-ams@server.eda.org> > > > Subject > > > Re: Agenda for committee call - 30 May 2006 > > > Classification > > > > > > > > > > > > > > > > > > > > > > > > Resending my response to peter back to the list: > > > > > > I would expect both of those expressions to fail a > > > syntax check, due to using the output value on both > > > the left hand and right hand side of the equation.. > > > To do that I think you need to use the "IMPLICIT" > > > form.. > > > V(n1) : 2*V(n1)+6 = 0; > > > which I would read: > > > (the Voltage on n1 is defined such that 2*V(n1)+6 = > > > 0; > > > > > > You could model a resistor divider from n1 to n2 in > > > two ways: > > > conservative: > > > V(n1,n2) <+ R1* I(n1,n2); > > > V(n2) <+ R2*I(n2); // gnd is implicit reference > > > // handles non-zero current flow out of n2 into > > > other > > > circuitry > > > > > > signal flow potential > > > V(n2) <+ V(n1)*R2/(R1+R2); > > > //Assumes I(n2) ~0 > > > // but the voltage is the same even if its not.. > > > > > > But While I would expect a signal_flow (flow) nature > > > to follow KCL: without the accompanying potential we > > > can hardly call it conservative. > > > > > > its either CONSERVATIVE (Potential & FLOW) > > > or its SIGNAL FLOW (Potential or Flow).. never both. > > > > > > > > > an example: > > > --- > > > so if the SOURCE model has > > > > > > module top; > > > electrical extres; > > > voltage vbandgap; > > > current iref; > > > source REF (.n1(iref), .vbg(vbandgap) .res(extres)); > > > resistor #(.r(12K)) Rext (extres,gnd!); > > > load DUT (.ibias(iref)); > > > endmodule > > > > > > module source (n1, vbg, res); > > > output current n1; > > > output voltage vbg; > > > output electrical res; > > > analog begin > > > V(vbg) <+ 1.20; > > > V(res) <+ 1.20; // 1.2v/12K = 0.1m = 100uA > > > // out => -100mA > > > I(n1) <+ I(res)/2.0; // -50ua > > > end > > > > > > module load (ibias); > > > input current ibias; > > > real Ibias; > > > analog begin > > > @timer(0,10m) begin > > > $strobe("INFO: %M: Ibias = %g at %g\n", I(ibias), > > > $abstime); > > > end > > > end > > > endmodule > > > > > > I Should get > > > INFO: top.DUT: Ibias = 5.00e-5 at 0.000 > > > INFO: top.DUT: Ibias = 5.00e-5 at 1.00e-5 > > > ... > > > in the log file. > > > > > > Showing that the current OUT of the Source = the > > > current INTO the load (and "into" is the positive > > > current direction, even for output pins.. ) > > > > > > In my view, a single module in Verilog is useless.. > > > its the interconnection of multiple modules that is > > > useful.. > > > > > > > > > Jonathan > > > > > > --- Peter Liebmann <peterl@xpedion.com> wrote: > > > > > > > I have a question about signal flow with a flow > > > > nature. Is it conservative? > > > > The reason I ask if one has a signal flow > > > potential > > > > nature , the solution > > > > to a simple equation with only one source at n1, > > > > > > > > V(n1) <+ 2*V(n1) +6; > > > > > > > > is obviously -6. > > > > > > > > However, if n1 is a signal flow flow nature and is > > > > conservative, > > > > > > > > I(n1) <+ 2*I(n1) +6; > > > > > > > > has no solution since I(n1) must sum to 0 and > > > there > > > > is only one source > > > > at n1. > > > > > > > > Is this what we want? > > > > > > > > Peter Liebmann > > > > > > > > > > > > Sri Chandra wrote: > > > > > > > > > > Time & Date: 30 May 2006, 3pm Pacific > > > > > Dialin: 1-877-346-8823 (US - toll free) > > > > > 1-203-320-0407 (Intl) > > > > > Pin: 602538 > > > > > > > > > > > > > > > * Review of chapter 2 - lexical tokens with > > > > > === message truncated === > >Received on Fri Jun 2 07:51:15 2006
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