Simulation with bbspice file or spectre file created from touchstone/citi file

Amit,

The spectre format for s-parameter files is just an alternative format to Touchstone. It's still in terms of real/imaginary or phase/magnitude for the matrices of s-parameters at each frequency; it does not just mean you can use a spectre sub circuit instance.

You could use RFM if coming from an external rational model creation tool such as ADS broadband spice, or if including a spectre subckt model as you have here, that can't be done with an n-port. You need to create a component which has the right pins and netlists in the right order - maybe the Keysight integration can take care of that (that's a question for Keysight, not us).

Regards,

Andrew

Andrew thanks. 

So I understand you correctly, you are saying that we can't directly use a bbspice file in the nport for simulations. 

It is also not possible to use the .scs file generated by ADS with the nport, like shown below.

Correct? 

Regards,

Amit

Hi Amit,

It rather depends what you mean by a "bbspice file". If the Keysight Broadband SPICE tool produces an RFM file, then you can use it with nport. The nport cannot however use a spectre netlist (i.e. a spectre subckt). The "spectre" format is  (as I said earlier) a spectre syntax file for s-parameters, and looks like this - it does NOT mean a spectre netlist:

; S-parameter data file spectre.s8p.
;
; Thu Jul  7 14:09:19 2022
; Number of ports is 8

reference resistance 
		 port8 = 50.000000 
		 port7 = 50.000000 
		 port6 = 50.000000 
		 port5 = 50.000000 
		 port4 = 50.000000 
		 port3 = 50.000000 
		 port2 = 50.000000 
		 port1 = 50.000000 

format freq:  s1:1(real,imag) 	 s1:2(real,imag) 	 
	      s1:3(real,imag) 	 s1:4(real,imag) 	 
	      s1:5(real,imag) 	 s1:6(real,imag) 	 
	      s1:7(real,imag) 	 s1:8(real,imag) 	 
	      s2:1(real,imag) 	 s2:2(real,imag) 	 
	      s2:3(real,imag) 	 s2:4(real,imag) 	 
	      s2:5(real,imag) 	 s2:6(real,imag) 	 
	      s2:7(real,imag) 	 s2:8(real,imag) 	 
	      s3:1(real,imag) 	 s3:2(real,imag) 	 
	      s3:3(real,imag) 	 s3:4(real,imag) 	 
	      s3:5(real,imag) 	 s3:6(real,imag) 	 
	      s3:7(real,imag) 	 s3:8(real,imag) 	 
	      s4:1(real,imag) 	 s4:2(real,imag) 	 
	      s4:3(real,imag) 	 s4:4(real,imag) 	 
	      s4:5(real,imag) 	 s4:6(real,imag) 	 
	      s4:7(real,imag) 	 s4:8(real,imag) 	 
	      s5:1(real,imag) 	 s5:2(real,imag) 	 
	      s5:3(real,imag) 	 s5:4(real,imag) 	 
	      s5:5(real,imag) 	 s5:6(real,imag) 	 
	      s5:7(real,imag) 	 s5:8(real,imag) 	 
	      s6:1(real,imag) 	 s6:2(real,imag) 	 
	      s6:3(real,imag) 	 s6:4(real,imag) 	 
	      s6:5(real,imag) 	 s6:6(real,imag) 	 
	      s6:7(real,imag) 	 s6:8(real,imag) 	 
	      s7:1(real,imag) 	 s7:2(real,imag) 	 
	      s7:3(real,imag) 	 s7:4(real,imag) 	 
	      s7:5(real,imag) 	 s7:6(real,imag) 	 
	      s7:7(real,imag) 	 s7:8(real,imag) 	 
	      s8:1(real,imag) 	 s8:2(real,imag) 	 
	      s8:3(real,imag) 	 s8:4(real,imag) 	 
	      s8:5(real,imag) 	 s8:6(real,imag) 	 
	      s8:7(real,imag) 	 s8:8(real,imag) 	 
	      

0.00000000e+00:       0.0952347,              0          0.904765,              0     
 		    6.09073e-18,              0       4.73637e-18,              0     
 		    6.56501e-18,              0       6.89042e-18,              0     
 		   -2.57966e-17,    3.15917e-33      -2.54298e-17,    3.11425e-33     
 		       0.904765,              0         0.0952347,              0     
 		    4.80646e-18,              0       3.65391e-18,              0     
 		    7.50038e-18,              0       8.04044e-18,              0     
 		   -2.43549e-17,   -2.98261e-33      -2.38638e-17,   -2.92247e-33     
 		    6.09073e-18,              0       4.80646e-18,              0     
 		      0.0952347,              0          0.904765,              0     
 		   -1.19384e-17,    1.46203e-33      -1.11698e-17,    1.36791e-33     
 		   -4.53054e-17,    5.54831e-33      -4.51132e-17,    5.52477e-33     
 		    4.73637e-18,              0       3.65391e-18,              0     
 		       0.904765,              0         0.0952347,              0     
 		   -1.05454e-17,    1.29143e-33      -9.69719e-18,    1.18756e-33     
 		   -4.48846e-17,    5.49678e-33      -4.45961e-17,    5.46145e-33     
 		    6.56501e-18,              0       7.50038e-18,              0     
 		   -1.19384e-17,    1.46203e-33      -1.05454e-17,    1.29143e-33     
 		      0.0952347,              0          0.904765,              0     
 		   -2.69002e-17,    3.29432e-33      -2.73924e-17,     3.3546e-33     
 		    6.89042e-18,              0       8.04044e-18,              0     
 		   -1.11698e-17,    1.36791e-33      -9.69719e-18,    1.18756e-33     
 		       0.904765,              0         0.0952347,              0     
 		   -2.81865e-17,    3.45185e-33      -2.85554e-17,    3.49703e-33     
 		   -3.30526e-17,    4.04778e-33      -3.11881e-17,    3.81944e-33     
 		   -3.60507e-17,    4.41494e-33      -3.62503e-17,    4.43939e-33     
 		   -2.53231e-17,    3.10118e-33      -2.19563e-17,    2.68887e-33     
 		      0.0111921,              0          0.988808,              0     
 		   -1.81738e-17,    2.22564e-33      -1.70305e-17,    2.08563e-33     
 		   -5.43679e-17,    6.65815e-33      -5.32304e-17,    6.51885e-33     
 		   -2.89695e-17,    3.54774e-33      -3.47856e-17,    4.26001e-33     
 		       0.988808,              0         0.0111921,              0     
1.00000000e+07:        0.095235,    0.000166635          0.904765,   -0.000485411     
 		    3.35158e-07,    0.000324742      -2.95556e-07,   -0.000191771     
 		    3.31927e-07,    0.000324743      -2.92301e-07,   -0.000191769     
 		    2.73369e-07,    0.000254719      -2.79749e-07,   -0.000208871     
 		       0.904765,   -0.000485411          0.095235,    0.000166636     
 		   -2.94364e-07,   -0.000191776       3.34661e-07,    0.000324746     
 		   -2.94614e-07,   -0.000191765        3.3401e-07,     0.00032474     
 		   -2.83248e-07,   -0.000208868       2.70455e-07,    0.000254722     
 		    3.35158e-07,    0.000324742      -2.94364e-07,   -0.000191776     
 		       0.095235,    0.000162908          0.904765,     -0.0004892     
 		    2.63366e-07,    0.000227881      -2.85141e-07,   -0.000219015     
 		    3.05974e-07,    0.000323221      -2.26308e-07,   -0.000145197     
 		   -2.95556e-07,   -0.000191771       3.34661e-07,    0.000324746     
 		       0.904765,     -0.0004892          0.095235,    0.000162899     
 		   -2.83792e-07,   -0.000219018       2.60768e-07,    0.000227887     
 		   -2.29735e-07,   -0.000145186       3.03962e-07,    0.000323232     
 		    3.31927e-07,    0.000324743      -2.94614e-07,   -0.000191765     
 		    2.63366e-07,    0.000227881      -2.83792e-07,   -0.000219018     
 		       0.095235,    0.000162897          0.904765,   -0.000489209     
 		    3.07694e-07,    0.000323227      -2.25929e-07,    -0.00014519     
 		   -2.92301e-07,   -0.000191769        3.3401e-07,     0.00032474     
 		   -2.85141e-07,   -0.000219015       2.60768e-07,    0.000227887     
 		       0.904765,   -0.000489209          0.095235,    0.000162897     
 		   -2.30516e-07,   -0.000145193       3.02943e-07,    0.000323223     
 		    2.73369e-07,    0.000254719      -2.83248e-07,   -0.000208868     
 		    3.05974e-07,    0.000323221      -2.29735e-07,   -0.000145186     
 		    3.07694e-07,    0.000323227      -2.30516e-07,   -0.000145193     
 		      0.0111921,   -4.81561e-05          0.988807,   -0.000597269     
 		   -2.79749e-07,   -0.000208871       2.70455e-07,    0.000254722     
 		   -2.26308e-07,   -0.000145197       3.03962e-07,    0.000323232     
 		   -2.25929e-07,    -0.00014519       3.02943e-07,    0.000323223     
 		       0.988807,   -0.000597269         0.0111921,   -4.81568e-05     

(the example above is truncated - it's to show the principle).

I can't answer as to what the available output formats are from the Keysight tool are.

Andrew

Hi Amit,

Everything you ever wanted to know about the nport is here:  7 Habits of Highly Successful S-Parameters, Spectre 21.1   (note that this is a more recent version than what Andrew mentioned) or in Spectre Classic Simulator, Spectre APS, Spectre X, and Spectre XPS User Guide -- Modeling for Signal Integrity 

The nport takes the following types of s-parameter data format:

• spectre (spectre's own s-parameter format as an alternative to the touchstone format)
• touchstone (industry recognized s-parameter format)
• citi ( Common Instrumentation Transfer and Interchange file format.  Used by many test and measure equipment tools - See Keysight for more info) 
• bnp (Broadband Network Parameter, a binary format of Touchstone generated (only) by the Sigrity tools.) 

• rfm (an HSPICE format).    It will contain a header (first 5 lines) which contains information on the number of ports, and the matrix type (S or Y for example).  The data fields consist of rational function coefficients. 

As Andrew mentioned, this is really a question for Customer Support https://support.cadence.com .   Do not label any of these files with the suffix .scs

Best regards,

Tawna

Thanks Tawna. I have already gone through your "7 habits ... " pdf some time back. Although I believe it was an earlier version,not the 21.1. 

As to the suffix of .scs, it is how ADS generates this spectre version of the sp file. To me it made sense as spectre does use .scs file extension. Anyways, below is a snapshot of all the different files ADS can generate from a touchstone file. 



The suffix .bbn is the broadband spice file that I was trying to use. Tried the other file formats as well but nport can't read them. 

Unfortunately ADS cant generate a RFM file. We have to use a separate tool for that and there are very few licenses available for it. It's a nightmare to get transient simulations run for RF designers :D :P 

As I've now said several times, nport is designed to read s-parameter-like data; it also support RFM (Rational Function Matrix) which is a rational model format. If you have a SPICE or Spectre sub-circuit, then the nport would be superfluous - all you need to do is instantiate the subckt.

If you don't want to create your own symbol (which could easily be done by creating a spectre text view and pasting in the generated SCS file contents; you'll be prompted to create a symbol afterwards), you could use this approach: How to create pcell symbol with variable pins and write custom netlist procedure for spectre and then you can reference the file as a model file.

Andrew

Hi AmitG22,

Read the latest version of the Appnote.  It's been updated.   Seriously - a Customer Support AE can assist you with this.  Please file a case on https://support.cadence.com .  Andrew and I answer questions in our "off work hours".  You'll get consistent, trackable support for the Customer Support team.  If it's past my dinner time, you'll get cranky responses from me. 

Thanks. This is interesting, I have never used the spectreText view before. I gave it a try. Had a small issue and Customer support helped me. Could run the simulation with spectreText view, the output looks really patchy (more than the touchstone data), but that is probably another issue. 



Thanks for all the support.  

Since that's just a spectre netlist and Spectre is not having to do any modelling of that, this would most likely be reflecting the quality/accuracy of the Spectre/SPICE model produced by the Keysight tools, or the input s-parameter data used to produce it.

Andrew

Since that's just a spectre netlist and Spectre is not having to do any modelling of that, this would most likely be reflecting the quality/accuracy of the Spectre/SPICE model produced by the Keysight tools, or the input s-parameter data used to produce it.

Andrew

I agree Andrew. I will need to spend some more time on reviewing the touchstone file and try to create a few variants by following Tawna's guidelines. 

I don't want to post the entire spectreText here but its attached to the case 46629498. It seems to be described in terms of real and complex poles for each port. Seems quite elaborate to me but I have no experience with this sort of a view. Will try to generate a couple of more variants and check the difference visually.

Hi AmitG22,

Thank you for posting the Case number.   Having said that, you really need to be working with your Customer Support AE on this, rather than posting to the Community Forum.  Your questions go beyond the scope of the forum.    The Customer Support team is a dedicated group of expert AEs whose "day job" is helping out customers like you.    If your questions aren't getting answered in a timely fashion, you can escalate it through the Case.   You can post follow-on questions if your Case is closed.  I know the Customer Support AEs - trust me, they'll pull in me (or Andrew) and R&D when they need help.  :-) 

best regards

Tawna

Edit:  You can post follow on questions by filing a new Case on https://support.cadence.com .

I will but before that I want to do a brief check myself.