Cascade Plant or Parallel Plant (串聯或並聯)
在一般控制系統或信號處理中，有串聯式或並聯式。What’s the pros and cons?
What’s the problem of using parallel?
Why not multi-integrator?
two pole is fundamental, right? polynomial factoring (one pole or two conjugated poles) => cascaded plants
But multi-poles plant/filter/controller do exist (e.g. sigma delta): always decompose to cascaded one pole or two poles plant?
cascaded plant (串聯). How about parallel plant (並聯) for two poles or multi-poles?
cons: matching! amplitude matching; phase (delay) matching ==> very difficult to analyze stability !
no signal multiplication but signal addition or selection/switching (not good for small signal)
Cons: distortion at cross-over point (class B)
How about Pros?
* Robust: in cascaded system, one plant fails mean all fails. Sometimes, not even fail, just saturation causes the entire system fail. (e.g. CIFB vs. CIFF in sigma delta modulator)
* High dynamic range: (i) no cascaded gain, each plant has the same dynamic range; (ii) control some plant (high Q) to saturate first to increase dynamic range)
* Most attractive: noise cancellation (but be careful not signal cancellation: by out of frequency or operation band (hmos or pmos only for positive/negative signal), or inner loop (like chopper or cross coupling feedback)); offset cancellation (chopper)
* Stability seems to be better if control each path 2nd pole.
* Low latency; fast response