# Shared Flashcard Set

## Details

ECE 481 Topic 1
ECE 481 Topic 1
36
Computer Science
05/09/2012

Term
 What is sampled-data system?
Definition
 system which has both discrete and continuous time signals
Term
 What does it mean by stable if system is open loop?
Definition
 transfer function has all poles in open left half plane
Term
 what does it mean by stable if system is close loop?
Definition
 every possible closed-loop transfer function is stable
Term
 is G(S)= 10 stable?
Definition
 yes, because the output is always bounded
Term
 why is it impossible to build a controller that's improper?
Definition
Term
 what's the difference between stable and stablizing?
Definition
 stable is for when open loop, stablizing is for when closed loop
Term
 what does it mean by a function is linear?
Definition
 super position principal holds
Term
 what are steps of designing process?
Definition
 1. Get the requirement2. Model the plant (System identification)3. Get transfer function for the plan4. Design a controller5. Simulate controller6. implement the controller
Term
 what is system identification?
Definition
 given input and output, find model
Term
 what's the main difference between discrete time systems and continuous time systems?
Definition
 discrete time signal has a maximum frequency that can be exhibited, W <= 0.5 Ws
Term
 describe ADC by giving a system that has input and output. Draw the behavior of input and output
Definition
Term
 describe DAC by giving a system that has input and output. Draw the behavior of input and output.
Definition
Term
 what's the condition for an ideal sampler?
Definition
 no time shift, no error
Term
 what's the condition for an ideal hold?
Definition
 no time shift
Term
 in ece 481, what do we assume regarding S and H?
Definition
 1. S and H are synchronized2. sampling period is constant3. no signal quantization
Term
 are S and H linear?
Definition
 yes, so they can be moved around
Term
 do S and H commute?
Definition
 no, they are not transfer functions because they are not time invariant
Term
 describe an SH and HS system.
Definition
Term
 What are some causes of non-linearity?
Definition
 1. on and off switch (relay)2. saturator3. static friction
Term
 What are some solutions to non-linearity?
Definition
 1. cancel out the non-linearity2. approximate by linearization3. use limit cycles
Term
 Why does higher frequency mapped into lower frequency?
Definition
 because all signals can be decomposed into cos and sin which have property of higher frequency mapped to lower frequency
Term
 what are two ways to deal with aliasing?
Definition
 1. sample really fast2. use an anti-aliasing filter
Term
 what is a rule of thumb for cutoff frequency for AA filter?
Definition
 Wcutoff < Ws/5
Term
 what are two disadvantage of sampling really fast to avoid aliasing?
Definition
 1. noise might be also included2. money issue
Term
 what are two disadvantage of using AA filter?
Definition
 1. money issue2. phase lag
Term
 what are three advantages to gain from fast sampling rate?
Definition
 1. good at tracking and reject disturbances2. sometimes you can only get good output by sampling fast3. if AA is used, want cutoff for AA to be big, so sampling rate has to be big as well
Term
 what are rule of thumb when sampling using sampling really fast and when using AA filter?
Definition
 1. sampling fast: 10Ws2. AA: 25Ws
Term
 what are disadvantages to sample that fast?
Definition
 1. economy 2. numerical issues
Term
 what are three ways to design controllers for sampled-data systems?
Definition
 1. design by emulation2. direct design3. true sampled-data design
Term
Definition
 1. easy because don't need to iterate designing C(s), only need to change sample frequency
Term
Definition
 economy issue (might not be able to sample that fast)
Term
 what are design steps in emulation?
Definition
 1. find C(S) 2. find D[Z] by approximation 3. implement C[Z]
Term
 will emulation work for large T?
Definition
 no
Term
 What are design steps of designing in discrete time?
Definition
 1. get Pd[z]2. get C[z]3. implement C[z]
Term
 What are advantages of doing direct design?
Definition
 it works on any T
Term
 what are disadvantages of doing direct design?
Definition
 1. Sometimes final performance is not that good2. inter-sample behavior is ignored3. have to redo if T is changed
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