spice3 simulation of VCO

[ICguy]

Why can not I see the result of AC analysis of the VCO in spice3? I can
observe that there is an oscilation in transient anaylisis.

Thank you

 

[Charlie Edmondson]

ICguy wrote:

Why can not I see the result of AC analysis of the VCO in spice3? I can
observe that there is an oscilation in transient anaylisis.

Thank you

Basically, because your VCO model is not modeled, as such, in the AC

domain. AC analysis doesn't do that sort of 'stuff'!

Charlie

 

[Jim Thompson]

On Tue, 12 Jul 2005 13:39:30 -0700, Charlie Edmondson
<edmondson@ieee.org> wrote:

ICguy wrote:
Why can not I see the result of AC analysis of the VCO in spice3? I can
observe that there is an oscilation in transient anaylisis.

Thank you

Basically, because your VCO model is not modeled, as such, in the AC
domain. AC analysis doesn't do that sort of 'stuff'!

Charlie

Sure it does, Charlie. Just do a loop gain (.AC) analysis.

Best performed using my LoopGain technique, as described on my website
;-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[ICguy]

Thank you both for your reply. I will try the loop gain analysis...

 

[Jim Thompson]

On 13 Jul 2005 13:10:40 -0700, "ICguy" <wangllu@gmail.com> wrote:

Thank you both for your reply. I will try the loop gain analysis...

Make sure you use enough steps per octave/decade/whatever in your .AC
analysis. Otherwise you'll completely sail right over the resonances
of the crystal.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[ICguy]

I tried the .AC analysis on VCO, the output is still zero. However, if
some noise is added to the VCO, then I can observe an nonzero output of
the VCO in AC analysis. Does this mean that the VCO is not oscilating
at all? if so, why I can observe an oscilltion in .TRAN analysis?

Thank you

 

[Jim Thompson]

On 14 Jul 2005 10:16:00 -0700, "ICguy" <wangllu@gmail.com> wrote:

I tried the .AC analysis on VCO, the output is still zero. However, if
some noise is added to the VCO, then I can observe an nonzero output of
the VCO in AC analysis. Does this mean that the VCO is not oscilating
at all? if so, why I can observe an oscilltion in .TRAN analysis?

Thank you

Do you know how to do a .AC analysis? Maybe post your schematic to

<alt.binaries.schematics.electronic>

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[ICguy]

Isn't . AC analysis like the following?

..AC dec No. fstar fstop


I couldn't find <alt.binaries.schematics.electronic>.

 

[Jim Thompson]

On 14 Jul 2005 11:01:58 -0700, "ICguy" <wangllu@gmail.com> wrote:

Isn't . AC analysis like the following?

.AC dec No. fstar fstop


I couldn't find <alt.binaries.schematics.electronic>.

Go to my website and E-mail me a schematic, PDF preferred but an
LTspice listing will also work, and I'll take a look.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.