Designer’s Guide Community

essam

Junior Member

Offline

Posts: 15

ADS HB: Oscillator + Divider
May 07^th, 2009, 4:22pm

Hello All,

I am trying to simulate 1.8GHz CMOS oscillator + divide-by-2 circuits. Both circuits are working fine separately (taking loading into account). When I put them together, the simulation does not converge at the divider output, but does converge at the oscillator output.

My simulation settings for HB:
Frequency: 1/2 oscillator frequency
Enable Oscillator: Yes

I also tried the Transient Assisted HB (TAHB), but still divider output is dead.

The following is the message I get from TAHB:
-------------------------------------------------------------------------
TAHB conversion started at t=1.105e-007 without reaching steady state.
The circuit did not reach steady state; the worst node was MOSFET44.d.
� �Final �transient �frequency = 1.799496029 GHz
t=1.111e-007 �100%
---------------------------------------------------------------------------

Does anybody have a clue?

Thanks,
Essam

Back to top

IP Logged

Ken Kundert Global Moderator Offline Posts: 2384 Silicon Valley	Re: ADS HB: Oscillator + Divider Reply #1 - May 7^th, 2009, 5:39pm Quote: the simulation does not converge at the divider output, but does converge at the oscillator output. What does that mean? What do you mean when you say that the output either does or does not converge. Perhaps you can try describing the problem using different words. -Ken
Back to top	IP Logged

essam

Junior Member

Offline

Posts: 15

Re: ADS HB: Oscillator + Divider
Reply #2 - May 7^th, 2009, 5:43pm

Hi Ken,

I mean that I am monitoring two output nodes. The output at the oscillator is good (I can see the waveforms). However, the output at the divider is dead, although I am sure that the oscillator can drive it properly. I tried that in a separate sim replacing the oscillator with a source that has similar output impedance and output swing.

I hope this is more clear now.

Thanks,
Essam

Back to top

IP Logged

pancho_hideboo

Senior Fellow

Offline

Posts: 1424
Real Homeless

Re: ADS HB: Oscillator + Divider
Reply #3 - May 7^th, 2009, 7:27pm

essam wrote on May 7^th, 2009, 4:22pm:

When I put them together, the simulation does not converge at the divider output, but does converge at the oscillator output.

Partial covergence is never possible in simulator.
So if the divider output does not converge, simulation itself results in fail with convergence error.

essam wrote on May 7^th, 2009, 5:43pm:

I mean that I am monitoring two output nodes.
The output at the oscillator is good (I can see the waveforms).
However, the output at the divider is dead, although I am sure that the oscillator can drive it properly.

So your simulation itself does not fail with convergence error. Right ?

Show me version of ADS you use.
Show me netlist of ADS and full logfile.

Show me your Frequency setting for Fund[1].
Show me your HB_Order.
Show me your HB_Oversample.

Do you set "Convergence Mode" as "Advanced(Robust)" ?

Which method do you use for Oscillation Analysis using HB, "Specify Nodes" or "Use Oscport" ?

If you use "Specify Nodes", where do you specify in circuits ?

If you use "Use Oscport", where do you insert "OscPort" or "OscPort2" in circuits ?

Show me "Harmonic Number" in your setting for "Use Oscport" or "Specify Nodes".

Back to top

OSC_HB.rar

« Last Edit: May 7^th, 2009, 8:37pm by pancho_hideboo »

Kita━━━━━━(ﾟ∀ﾟ)━━━━━━ !!!!!
http://www7.plala.or.jp/ungeromeppa/flash/kita.html
http://www.youtube.com/watch?v=mjIxGh55bMM&feature=related

IP Logged

Ken Kundert Global Moderator Offline Posts: 2384 Silicon Valley	Re: ADS HB: Oscillator + Divider Reply #4 - May 7^th, 2009, 8:40pm This seems like a signal tracing exercise. The signal goes into the divider and does not come out. Can't you just follow the signal until it stops, and then determine why the signal stops? -Ken
Back to top	IP Logged

essam

Junior Member

Offline

Posts: 15

Re: ADS HB: Oscillator + Divider
Reply #5 - May 7^th, 2009, 8:49pm

HI,

Thank you for your help.

I am using the following:

Show me version of ADS you use: (ADS 2008 Update 2)

Show me netlist of ADS and full logfile.

Show me your Frequency setting for Fund[1]: 1/2*FRF where FRF is the oscillation frequency (I have divide-by-2 circuit)

Show me your HB_Order. (I tried 12, 20,31)

Show me your HB_Oversample. (4)

Do you set "Convergence Mode" as "Advanced(Robust)" ? (I tried auto and Advanced Robust)

Which method do you use for Oscillation Analysis using HB, "Specify Nodes" or "Use Oscport" ? (Oscport)

(I put it in the feedback path of the cross-coupled MOS diff-pair)

Thanks,
Essam

Back to top

IP Logged

pancho_hideboo

Senior Fellow

Offline

Posts: 1424
Real Homeless

Re: ADS HB: Oscillator + Divider
Reply #6 - May 7^th, 2009, 8:52pm

Answer my question.

Your simulation itself does not fail with convergence error. Right ?

Show me full logfile.

essam wrote on May 7^th, 2009, 8:49pm:

pancho_hideboo wrote on May 7^th, 2009, 7:27pm:

Which method do you use for Oscillation Analysis using HB, "Specify Nodes" or "Use Oscport" ?

(Oscport)
(I put it in the feedback path of the cross-coupled MOS diff-pair)

Show me "Harmonic Number" in your setting for "OscPort".

Back to top

Kita━━━━━━(ﾟ∀ﾟ)━━━━━━ !!!!!
http://www7.plala.or.jp/ungeromeppa/flash/kita.html
http://www.youtube.com/watch?v=mjIxGh55bMM&feature=related

IP Logged

essam Junior Member Offline Posts: 15	Re: ADS HB: Oscillator + Divider Reply #7 - May 8^th, 2009, 1:36pm Thanks, you pointed out the problem. i was using Harm=1 in OscPort although I should use harm=2 because the oscillator oscillates at twice the HB frequency. Thank you so much for your help. I really appreciate it. Essam
Back to top	IP Logged

pancho_hideboo

Senior Fellow

Offline

Posts: 1424
Real Homeless

Re: ADS HB: Oscillator + Divider
Reply #8 - May 8^th, 2009, 10:42pm

essam wrote on May 7^th, 2009, 8:49pm:

pancho_hideboo wrote on May 7^th, 2009, 7:27pm:

Show me your HB_Order.

(I tried 12,20,31)

In Agilent ADSsim(RFDE), you should increase HB_Order as 2**N-1, N=1,2,3,4,5,...
HB_Order=3,7,15,31,63,.....

So your HB_Order=12 is treated as HB_Order=15 internally.
Your HB_Order=20 is treated as HB_Order=31 internally.

essam wrote on May 7^th, 2009, 8:49pm:

pancho_hideboo wrote on May 7^th, 2009, 7:27pm:

Show me your HB_Oversample.

(4)

HB_Oversample=2**N, N=1,2,3,4,5,...
HB_Oversample=2,4,8,16,.....

See http://www.designers-guide.org/Forum/YaBB.pl?num=1237890768/10#10

Back to top

Kita━━━━━━(ﾟ∀ﾟ)━━━━━━ !!!!!
http://www7.plala.or.jp/ungeromeppa/flash/kita.html
http://www.youtube.com/watch?v=mjIxGh55bMM&feature=related

IP Logged