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# open loop system analysis

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#### rainman.cn

##### Member level 2
open loop system

how can we analysis the open-loop system(eg.:comparator)?
thx,

#### hung_wai_ming@hotmail.com

##### Full Member level 6
open loop stability analysis

Do u mean linear comparator or non-linear comparator?
If linear, then the analysis is just like an OTP
If non-linear, you need to do .dc analysis or .tran to have two inputs at slightly different values to have output changed and from there to determine the gain.

### rainman.cn

Points: 2

#### pfd001

transient simulation for the comparator.

### rainman.cn

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#### rainman.cn

##### Member level 2
thx,
but i want to know the stability of the open loop system,
the comparator work in open loop condition, even have no feedback, so the loop gain is small, we have no need to analysis the stability of it? (i refer linear comparator)

#### surianova

rainman.cn said:
thx,
but i want to know the stability of the open loop system,
the comparator work in open loop condition, even have no feedback, so the loop gain is small, we have no need to analysis the stability of it? (i refer linear comparator)

yes,comparator is a open loop system and no feedback.. u can't check the phase margin or stability.

### rainman.cn

Points: 2

#### gingerjiang

##### Full Member level 3
for a comparator, you need consider the speed, offset, resolution, hysteresis, etc., not stability

### rainman.cn

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#### qutang

##### Full Member level 5
I think dc will be good.

### rainman.cn

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#### jinnose

##### Junior Member level 1
Speed, offset and power consumption.

### rainman.cn

Points: 2

#### hung_wai_ming@hotmail.com

##### Full Member level 6
Hi rainman.cn

We concern stability analysis only for open loop system. Why, since the output or intermediate node fed back to input will cause changes in input signal that results in phase change. That phase change will create stability concern.
For open loop, no signals fed back to input, no matter output changes, it won't affect the input. As it won't affect input, there's no way for input to be changed except itself from the source, so you need not do any stability analysis

### rainman.cn

Points: 2

#### jeffsky520

##### Member level 4
amplifier can work in open-loop when its gain is low and while stability is not problem. but high gain amplifier must be used in closed loop stable, or it will be a comparator.

### rainman.cn

Points: 2

#### rainman.cn

##### Member level 2
thanks very much.
i get it .

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