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Simulators >> RF Simulators >> Problem in simulating a Diff.  Switching PA in SpectreRF
https://designers-guide.org/forum/YaBB.pl?num=1240534227

Message started by AnalogAroma on Apr 23rd, 2009, 5:50pm

Title: Problem in simulating a Diff.  Switching PA in SpectreRF
Post by AnalogAroma on Apr 23rd, 2009, 5:50pm

Hi  Everybody,

      I am facing some problems in simulating a differential switching power amplifier where  the tail current is modulated by the baseband signal.  I mean, the baseband signal will generate a ref current which will linearly control the tail current which will be  up-converted to the RF frequency  using a LO signal. Similar to a single balanced mixer. The attached pic further clarfies the PA.

Typical simulation techiniques in SpectreRF are suitable for a PA succeeding a mixer where RF input is coming from the mixer.

But, in my case,  LO osc input  does not have any baseband envelope .
And the low freq baseband input cannot use RF port symbol !!!

So, typical way of calculating  1dB compression  point is not suitable.

Is there any way to overcome this problem in SpectreRF ?
Any trick ?

Title: Re: Problem in simulating a Diff.  Switching PA in SpectreRF
Post by pancho_hideboo on Apr 23rd, 2009, 7:25pm

I can't find out any Design Issue in your questions.  Your questions are simple measurement issue of RF block.

I can't understand what you are confusing.
Your "Switching PA???" is no more than TX-UpMixer or AM-Modulator which have two inputs, LO and BB.
So there is no problem in treating your case by two-tones(LO, BB) or one-tone(LO) steady state analysis.

I don't think your circuit is Switching PA. http://www.designers-guide.org/Forum/YaBB.pl?num=1214811603


AnalogAroma wrote on Apr 23rd, 2009, 5:50pm:
Typical simulation techiniques in SpectreRF are suitable for a PA succeeding a mixer where RF input is coming from the mixer.
But, in my case,  LO osc input  does not have any baseband envelope.
And the low freq baseband input cannot use RF port symbol !!!
What do you mean ?


AnalogAroma wrote on Apr 23rd, 2009, 5:50pm:
So, typical way of calculating  1dB compression  point is not suitable.
How do you define 1dB compression  point ?
"LO_Input_Level v.s. Output_Level with BB_Input=Constant Level(DC or Sine)"
 or
"BB_Input_Level v.s. Output_Level with LO_Input=Constant Level(Sine)" ?

How do you define output power for modulation output ?
"Averaged Power" or "PEP(Peak Envelope Power)" ?

Usually I simulate simply non-modulation case where BB is DC.
Here I use swept BB of DC source with one-tone(LO) steady state analysis.

If I use sinusoidal signal for BB, I invoke two-tones(LO, BB) steady state analysis.
Here you have to choose which output power you should evaluate. "Averaged Power" or "PEP(Peak Envelope Power)".
This selection is dependent on your needs or interests.

Attached figure is Instantaneous Envelope Power of ASK signal.
http://www.designers-guide.org/Forum/YaBB.pl?num=1209812189


AnalogAroma wrote on Apr 23rd, 2009, 5:50pm:
Is there any way to overcome this problem in SpectreRF ?
Is there any problem in treating your case by Cadence Spectre ?, although I don't use Cadence Spectre.

Title: Re: Problem in simulating a Diff.  Switching PA in SpectreRF
Post by Ken Kundert on Apr 23rd, 2009, 11:53pm

SpectreRF does not require the use of ports as sources. It works just as well with voltage sources and current sources.

-Ken

Title: Re: Problem in simulating a Diff.  Switching PA in SpectreRF
Post by pancho_hideboo on Apr 24th, 2009, 4:30am


Ken Kundert wrote on Apr 23rd, 2009, 11:53pm:
SpectreRF does not require the use of ports as sources. It works just as well with voltage sources and current sources.
Any vendor's RF simulator except for very old one such as "SuperCOMPACT" does not require the use of ports as sources.

Title: Re: Problem in simulating a Diff.  Switching PA in SpectreRF
Post by Andrew Beckett on Apr 24th, 2009, 6:39am

Correct, but it's a common misperception amongst users of RF simulators, perhaps because examples are often using ports, and so there is sometimes a mistaken assumption that you must use them.

Title: Re: Problem in simulating a Diff.  Switching PA in SpectreRF
Post by AnalogAroma on May 6th, 2009, 10:55am

Tape out date is over. So far, I could not respond to  all the feedback.
Within several days I will try to describe the problems
encountered in the recent tape-out of power amplifier in greater detail.

Title: Re: Problem in simulating a Diff.  Switching PA in SpectreRF
Post by AnalogAroma on May 11th, 2009, 10:38am

Although I had attached a CMOS  based PA image, in reality SiGe HBT based PA   was designed.

Title: Re: Problem in simulating a Diff.  Switching PA in SpectreRF
Post by pancho_hideboo on May 12th, 2009, 3:54am


AnalogAroma wrote on May 11th, 2009, 10:38am:
Although I had attached a CMOS based PA image, in reality SiGe HBT based PA was designed.
What do you want to say ?

Whatever process you use for designing your PA, simulation methods are same.

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