172 SAMPLED-DATA CONTROL SYSTEMS 
Again it is pointed out that the complexity of the digital controller is 
no greater with this approach than with the approach using minimal 
prototypes or staleness factor. 
In applying the ripple-free design criterion, it is seen that A(z) must 
contain as many zeros as does the plant pulse transfer function G(z). 
This means that the settling time at sampling instants will generally be 
Output 

Time, sec. 
Fic. 7.15. Response of system in example using ripple-free design to unit ramp input. 

Time, sec. 
Fic. 7.16. Response of system in example using ripple-free design to a unit step input. 
ereater than that of minimal systems which have over-all pulse transfer 
functions containing only those zeros of the pulse transfer function which 
lie outside of the unit circle in the z plane. Whether or not this is a dis- 
advantage depends on the application. If intersample ripple is con- 
