PLLATINUMSIM-SW: Phase margin from bode plot

Toshihiro Watanabe

Genius 10235 points

Part Number: PLLATINUMSIM-SW

Hello,

There are phase margin plot in bode plot graph. How should we read the graph?

Or Phase-Margin of Loop Characteristics in bode plot tab is only needed to pay attention for stability?

Best regards,

Toshihiro Watanabe

over 7 years ago

0 Dean Banerjee over 7 years ago

TI__Mastermind 28031 points

Toshiro-san,

The phase margin is equal to 180 degrees minus the phase of the open loop response. In the plot, the "Open loop gain" is G(s)*N. So when the magnitude of the open loop gain is 20*log(N), you read the phase margin from the graph, and this is the value. Sometimes others may use forward gain, which differs by a factor of 20*log(N).

The phase margin is the main thing to pay attention to.
The gain margin also has some value and has an explanation if you click on the ? for filter characteristics.

Regards,
Dean

0 Toshihiro Watanabe over 7 years ago in reply to Dean Banerjee

TI__Genius 10235 points

Hello Dan-san,

I think G(s) is transfer function of loop filter which include charge pump and Kpd and N is N divider value. Is my understanding correct?

We can know the phase margin from bode plot below steps.

1. Calculate 20 log(N) value

2. Find the frequency Open loop gain = 20log (N)

3. look at the phase margin plot at the frequency of above.

It seems we don't need this process because PLLatinum show this in Loop Filter Characteristic in bode plot tab, right?

Best regards,

Toshihiro Watanabe

0 Dean Banerjee over 7 years ago in reply to Toshihiro Watanabe

TI__Mastermind 28031 points

Yes, this is true

Regards,
Dean

Clock & timing

Clock & timing forum

PLLATINUMSIM-SW: Phase margin from bode plot