Scicos Block
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Second order Loop Filter for PLL type 2 block

Contents

• Second order Loop Filter for PLL type 2 block
  • Palette
  • Description
  • Dialog box
  • Default properties
  • Interfacing function
  • See also
  • Authors

Palette

• Pll - Phase Locked Loop palette

Description

This block realizes a continuous second order loop filter defined by the following electrical circuit :

Figure 1: Passive second order loop filter

Because this circuit can be explicitly expressed with linear ordinary differential equations, it is able to be described by a tranfert function.
The transfer function of this filter is :

$$\begin{eqnarray} F(s)=\dfrac{1+\tau_{1}s}{\tau s\left(1+\tau_{2}s\right)}, \end{eqnarray}$$

where the zero $\tau_{1}$ and the poles $\tau\,\tau_{2}$ are computed according to the dialogue parameters and with the hep of the Scilab macro calcul_3eme_ordre.

The interfacing function of this block also allows to plot the different Bode diagrams of the linear model of a third order type 2 PLL.
This can be useful for the calibration of the the attenuation at cut-off frequency of the closed-loop transfert function.

Dialog box

• Natural loop frequency (Hz)
  The cut-off frequency of the closed-loop transfert function.
  Type 'vec' of size 1.

• Phase Margin (rad)
  The phase margin at the cut-off frequency.
  Type 'vec' of size 1.

• Linear VCO gain (Hz/V)
  The local sensitivity of the VCO when loop is in lock.
  Type 'vec' of size 1.

• Charge pump current (A)
  The maximal output current of the charge pump.
  Type 'vec' of size 1.

• Nominal divider value (integer)
  The value of the feed-back frequency divider of the loop.
  Type 'vec' of size 1.

• Plot open loop transfert function (0=No) ?
  Plot the Bode diagram of the open loop transfert function in a scilab window.
  Type 'vec' of size 1.

• Plot closed loop transfert function (0=No) ?
  Plot the Bode diagram of the closed loop transfert function in a scilab window.
  Type 'vec' of size 1.

• Plot fm response transfert function (0=No) ?
  Plot the Bode diagram of the the frequency modulation response transfert function (viewed as the input of the VCO) in a scilab window.
  Type 'vec' of size 1.

Default properties

• always active: yes
• direct-feedthrough: no
• zero-crossing: no
• mode: no
• regular inputs:
  - port 1 : size [1,1] / type 1
  
• regular outputs:
  - port 1 : size [1,1] / type 1
  
• number/sizes of activation inputs: 0
• number/sizes of activation outputs: 0
• continuous-time state: yes
• discrete-time state: no
• object discrete-time state: no
• name of computational function: csslti

Interfacing function

• MODNUMCOS/macros/scicos_blocks/Pll/SOLOOPFILTER_f.sci [view code]

See also

• calcul_3eme_ordre - return the zeros and the pole of a third order digital PLL type 2 (Scilab Function)

Authors

A. Layec