Filter Design Toolbox

zplane

Compute a zero-pole plot for quantized filters

Syntax

• zplane(Hq)
  zplane(Hq,'plotoption')
  zplane(Hq,'plotoption','plotoption2')
  [zq,pq,kq] = zplane(Hq)
  [zq,pq,kq,zr,pr,kr] = zplane(Hq)
  

Description

This function displays the poles and zeros of quantized filters, as well as the poles and zeros of the associated unquantized reference filter.

zplane(Hq) plots the zeros and poles of a quantized filter Hq in the current figure window. The poles and zeros of the quantized and unquantized filters are plotted by default. The symbol o represents a zero of the unquantized reference filter, and the symbol x represents a pole of that filter. The symbols and + are used to plot the zeros and poles of the quantized filter Hq. The plot includes the unit circle for reference.

zplane(Hq,'plotoption') plots the poles and zeros associated with the quantized filter Hq according to one specified plot option. The string 'plotoption' can be either of the following reference filter display options:

• 'on' to display the poles and zeros of both the quantized filter and the associated reference filter (default)
• 'off' to display the poles and zeros of only the quantized filter

zplane(Hq,'plotoption','plotoption2') plots the poles and zeros associated with the quantized filter Hq according to two specified plot options. The string 'plotoption' can be selected from the reference filter display options listed in the previous syntax. The string 'plotoption2' can be selected from the section-by-section plotting style options described below:

• 'individual' to display the poles and zeros of each section of the filter in a separate figure window
• 'overlay' to display the poles and zeros of all sections of the filter on the same plot
• 'tile' to display the poles and zeros of each section of the filter in a separate plot in the same figure window

[zq,pq,kq] = zplane(Hq) returns the vectors of zeros zq, poles pq, and gains kq. If Hq has n sections, zq, pq, and kq are returned as 1-by-n cell arrays. If there are no zeros (or no poles), zq (or pq) is set to the empty matrix [].

[zq,pq,kq,zr,pr,kr] = zplane(Hq) returns the vectors of zeros zr, poles pr, and gains kr of the reference filter associated with the quantized filter Hq, and returns the vectors of zeros zq, poles pq, and gains kq for the quantized filter Hq.

Examples

Create a quantized filter Hq from a fourth-order digital filter with cutoff frequency of 0.6. Scale the transfer function parameters to avoid overflows due to coefficient quantization. Plot the quantized and unquantized poles and zeros associated with this quantized filter.

• [b,a] = ellip(4,.5,20,.6);
  Hq = qfilt('df2',{b/2 a/2});
  zplane(Hq);
  
  
  
  

See Also
freqz, impz

zpkshiftc

Bibliography