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Design >> RF Design >> Differential Inductor design/simulation in ADS Momentum
https://designers-guide.org/forum/YaBB.pl?num=1217521760

Message started by tkhan on Jul 31^st, 2008, 9:29am

Title: Differential Inductor design/simulation in ADS Momentum
Post by tkhan on Jul 31^st, 2008, 9:29am

Hi, I am new to EM softwares and I want to use ADS Momentum to design structures which are not in our PDK pcell library. I have designed a differential inductor but I'm not sure how to simulate it properly, specifically what type of ports to use so i can determine the inductance and quality factor. I put differential ports on the two terminals, but i am not getting 2port s-parameters. any help would be greatly appreciated. thanks.

Title: Re: Differential Inductor design/simulation in ADS Momentum
Post by tkhan on Jul 31^st, 2008, 1:44pm

i forgot to add a center tap to the inductor, and i put the port as common mode, associated with the differential port. now i am getting 2port sparameters but i'm not sure if this is the correct simulation setup...

Title: Re: Differential Inductor design/simulation in ADS Momentum
Post by pancho_hideboo on Jul 31^st, 2008, 4:40pm

See the following.
http://www.designers-guide.org/Forum/YaBB.pl?num=1205240723/0#9

Title: Re: Differential Inductor design/simulation in ADS Momentum
Post by tkhan on Aug 4^th, 2008, 6:20pm

hi. thank you for your reply, but i am still not clear what kind of ports to use. differential for the two input terminals and common mode for center tap? thanks.

Title: Re: Differential Inductor design/simulation in ADS Momentum
Post by pancho_hideboo on Aug 4^th, 2008, 8:24pm

tkhan wrote on Aug 4^th, 2008, 6:20pm:

but i am still not clear what kind of ports to use.

See ADS's momentum manual and text book on microwave engineering basic.

tkhan wrote on Aug 4^th, 2008, 6:20pm:

differential for the two input terminals and common mode for center tap?

Use Single Port for all three ports(pins).
Then you can calculate any mode S-parameter from three port S-parameter.

In native ADS's momentum, there are many port types we can choose.
But if we use momentum in RFDE, only two port types, single and differential are options we can choose.

Title: Re: Differential Inductor design/simulation in ADS Momentum
Post by tkhan on Aug 5^th, 2008, 10:37am

hi, i have looked at chapter 4 of momentum documentation before. the inductor is intended to be used in a LC VCO so it makes sense to me for it to be driven differentially. ok then i will use single ended and give it a shot. i am not using RFDE, just ADS.

Title: Re: Differential Inductor design/simulation in ADS Momentum
Post by pancho_hideboo on Aug 7^th, 2008, 1:02am

tkhan wrote on Aug 5^th, 2008, 10:37am:

Consider actual situation when you characterize a center tapped inductor using network analyzer.
How to connect port to inductor ?

You have to learn measurements using actual instruments. Not "EDA Tool Play".

Title: Re: Differential Inductor design/simulation in ADS Momentum
Post by tkhan on Aug 7^th, 2008, 9:15am

well in canada IC is not so big in university level, only a few schools with proper rf labs. our school is just getting into the field and we don't have so much equipment, we have to rent from other places and we have not done many fab yet. personally i havent done. so i have to rely on tools to learn these things until i can get my hands on equipment...

Title: Re: Differential Inductor design/simulation in ADS Momentum
Post by tkhan on Aug 9^th, 2008, 9:45pm

ok i have done some reading from cascade application notes, and i am more clear than before but still a bit unclear. i am not expert in RF measurement so help would be appreciated.

1. to test a differential, centre tapped inductor w/ PGS, is this a correct probe configuration?

2. why are the input terminals both single ports and not differential? it seems this way, both ports have same polarity.

3. the ground ports should be referenced to a port that is on the same reference plane as itself. then all the signals should be applied to same layer as ground and ground should be associated with signal?

4. in general, how are the ports configured using ads momentum? in cadence spectre, it was possible to define the parameters of the port such as excitation signal, frequency, amplitude, etc. in ads i can only change the type of port (single, internal, differential, coplanar, ground reference).

5. my understanding of 'port' and 'probe' is a bit off i think. for example, GSG probe configuration. each G/S/G is referred to as 'probe' and 'port' is the entire GSG configuration? see http://www.ndl.org.tw/old/equip/highways/lrfowm.pdf pg 2. how does this concept apply in ads? to design GSG i should have 3 PORTS? one signal and two ground PORTS?

thanks.

Title: Re: Differential Inductor design/simulation in ADS Momentum
Post by pancho_hideboo on Aug 10^th, 2008, 5:44pm

tkhan wrote on Aug 9^th, 2008, 9:45pm:

ok i have done some reading from cascade application notes,

You mean "Cascade Microtech Inc" ?

tkhan wrote on Aug 9^th, 2008, 9:45pm:

1. to test a differential, centre tapped inductor w/ PGS, is this a correct probe configuration?

I don't know what you mean by "PGS".
If you have two "GS" probes and one "GSG" probe, it is correct configuration.

But Probe configulation is dependent on what probes you have.
http://www.cmicro.com/go/engineering-products-division/product-portfolio/probes/rf-probes/infinity/

For example, "GSG" probe is for center tapped pin and "GSGSG" probe is for other pins of inductor.

Quote:

2. why are the input terminals both single ports and not differential? it seems this way, both ports have same polarity.

You don't seem to understand S-parameter.
Again you should read text book on microwave engineering basic.

Quote:

3. the ground ports should be referenced to a port that is on the same reference plane as itself. then all the signals should be applied to same layer as ground and ground should be associated with signal?

I can't understand what you mean.

Quote:

4. in general, how are the ports configured using ads momentum? in cadence spectre, it was possible to define the parameters of the port such as excitation signal, frequency, amplitude, etc. in ads i can only change the type of port (single, internal, differential, coplanar, ground reference).

I can't understand what you mean.
If you want to drive differetially, excecute AC analysis not SP analysis.
But even though you excecute SP analysis, you can derive any mode S-parameter.
Again you should read text book on microwave engineering basic.

Quote:

5. my understanding of 'port' and 'probe' is a bit off i think. for example, GSG probe configuration. each G/S/G is referred to as 'probe' and 'port' is the entire GSG configuration?

You can consider like the above.

Title: Re: Differential Inductor design/simulation in ADS Momentum
Post by tkhan on Aug 10^th, 2008, 6:59pm

thanks for the reply. yes, i got app notes from cascade microtech.

1. PGS = patterened ground shield.

the probe pad configuration is just based on what i read and what made sense to me, and i realize different configurations are available. i just chose this since i am only characterizing a structure in software, not sending for fab (yet). we do not have direct relationship with ibm foundry, we go through a 3rd party. as well we borrow equipment and obtain software licenses through them. so whatever they have available is what we design around - in this case, probes. we are in the process of obtaining our own equipment, we already have a used probe station but the probe tips are damaged. we don't have the money to just call up hp/agilent and order a $200k VNA...

2. currently i'm reading "Introduction to microwave circuits : radio frequency and design applications / Robert J. Weber" chapters on SP and SP measurement. i think i am getting mixed up by different terminology in ADS and elsewhere :-?.

3.

details about ports in ads are here: http://72.14.205.104/search?q=cache:aE8Nah2kuysJ:edocs.soco.agilent.com/display/ads2008/Ports%2Bin%2BMomentum+ADS+momentum+documentation+ports&hl=en&ct=clnk&cd=6&gl=ca&client=firefox-a

the terminology in ADS may be confusing. it is my understanding that a SINGLE PORT is equivalent to a Signal probe, and GROUND REFERENCE PORT is equivalnet to Ground probe. in order to have a GS configuration, you make one instance of each then ASSOCIATE them with eachother so they are simulated as 1 port.

4. well i am thinking of how i did it in Cadence Spectre Schematic. i did a single ended LNA using PSIN to obtain SP, NF, etc.. unfortunately our cadence license does not have the inductor extraction or inductor modeler tool, so i have to work outside cadence to characterize a structure, then import it (SPICE model and layout). so i use ads since our ibm pdk came with substrate/layer definitions for momentum... but now it seems i have problems due to virtual memory, so i must speak with our department lead eng'g to resolve this :-/

Title: Re: Differential Inductor design/simulation in ADS Momentum
Post by pancho_hideboo on Aug 10^th, 2008, 7:09pm

tkhan wrote on Aug 10^th, 2008, 6:59pm:

the terminology in ADS may be confusing. it is my understanding that a SINGLE PORT is equivalent to a Signal probe, and GROUND REFERENCE PORT is equivalnet to Ground probe. in order to have a GS configuration, you make one instance of each then ASSOCIATE them with eachother so they are simulated as 1 port.

I can't understand what you mean.
What do you mean by Ground probe ?

tkhan wrote on Aug 10^th, 2008, 6:59pm:

4. well i am thinking of how i did it in Cadence Spectre Schematic. i did a single ended LNA using PSIN to obtain SP, NF, etc.. unfortunately our cadence license does not have the inductor extraction or inductor modeler tool,

If you have SpectreRF license, you can use VPCD(Virtuso Passive Component Designer) to build PDK of inductor.

tkhan wrote on Aug 10^th, 2008, 6:59pm:

but now it seems i have problems due to virtual memory, so i must speak with our department lead eng'g to resolve this :-/

If you analyze inductor with PGS(Patterened Ground Shield), you have to reduce contact number or simplify contact, for example, merge as large contact.
Anyway it takes much time and memory if you analyze inductor with PGS(Patterened Ground Shield).

Title: Re: Differential Inductor design/simulation in ADS Momentum
Post by tkhan on Aug 10^th, 2008, 8:28pm

well i dont know why we can't use the passive device modeler, since we can use rf and special functions in calculator then we must have spectrerf license... transmission line, transformer and inductor modeler are there in analog environment, but after entering all your data at the end it gives a license error :-?

in regards to ports/probes in ADS: back to my example in 2 previous posts, a PORT with GSG configuration has 3 PROBES: 1xSignal and 2xGround, yes? in ADS, the signal conductor is the SINGLE PORT, and ground conductors are GROUND REFERENCE PORTs. the ground refs (return path) should be associated (a function in ADS) with the single port to complete the transmission line. to do this, create three ports: P1=SINGLE PORT, P2,P3=GROUND REFERENCE, in the options for P2/3, they are associated with P1. in the end, P1/2/3 will just simulated as "P1". at least, this is my understanding.

in regards to patterned ground shield: the "X" that goes from corner to corner does not break the shield into 4 pieces, the corners are still contacted. is this what you mean? i should read what are the environment variables related to solver parameters and memory allocation also.

Title: Re: Differential Inductor design/simulation in ADS Momentum
Post by pancho_hideboo on Aug 10^th, 2008, 8:47pm

tkhan wrote on Aug 10^th, 2008, 8:28pm:

since we can use rf and special functions in calculator then we must have spectrerf license

SP and NF analyses are ability of Spectre not SpectreRF.
Also you can use "rf and special functions in calculator" without SpectreRF license.

tkhan wrote on Aug 10^th, 2008, 8:28pm:

P1=SINGLE PORT, P2,P3=GROUND REFERENCE, in the options for P2/3, they are associated with P1. in the end, P1/2/3 will just simulated as "P1".
at least, this is my understanding.

Usually coplanar ground pattern is enough far from inductor, so I don't include coplanar ground pattern in momentum analysis.
Here coplanar ground pattern is connected to substrate by contact vias.
I use implicit ground reference.

tkhan wrote on Aug 10^th, 2008, 8:28pm:

in regards to patterned ground shield: the "X" that goes from corner to corner does not break the shield into 4 pieces,
the corners are still contacted. is this what you mean?

I can't understand what you mean.
If you use many small contact vias, you have to reduce or simplify.
This is true for inductor vias.

Title: Re: Differential Inductor design/simulation in ADS Momentum
Post by tkhan on Aug 11^th, 2008, 6:19am

This is similar to what I'm using, except around the outer edges there is 1um border of M1 to connect all the strips. For the inductor crossovers, I have one lumped via rather than an array of minimum sized vias to reduce complexity for simulation.