Transfer Function Implementation with s and sqrt

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Anastasios 2023-12-4

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https://ww2.mathworks.cn/matlabcentral/answers/2056104-transfer-function-implementation-with-s-and-sqrt

编辑： Dyuman Joshi 2023-12-5

I am trying to implement the following transfer function:

H = ((2*(acos(sqrt((Vout*(1+(s*TIA_Cf*TIA_Rf)))/(TIA_Rf*Pin*0.9)))))-(3*pi/2))/((2e-7)*(7.8e-3));

However I am getting the error:

Incorrect number or types of inputs or outputs for function 'sqrt'.

Is it because the sqrt() cannot be always a positive number?

How may I handle a situation like this?

Thank you.

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Anastasios 2023-12-4

Sam Chak 2023-12-4

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Hi @Anastasios, I'll explain what happened to your code. If you look into the documentation of sqrt(), you will find that the function only accepts inputs of data types such as single, double, table, and timetable. However, 's' is a tf-class data, and thus it threw the "Incorrect number of types of inputs..." error message.

Vout   = 300e-9;
TIA_Cf = 1e-12;
TIA_Rf = 1e3;
Pin    = 1e-3;
whos Vout TIA_Cf TIA_Rf Pin
  Name        Size            Bytes  Class     Attributes

  Pin         1x1                 8  double              
  TIA_Cf      1x1                 8  double              
  TIA_Rf      1x1                 8  double              
  Vout        1x1                 8  double              
s      = tf('s');
whos s
  Name      Size            Bytes  Class    Attributes

  s         1x1              1281  tf                 
%% OP's "transfer function"
H = ((2*(acos(sqrt((Vout*(1+(s*TIA_Cf*TIA_Rf)))/(TIA_Rf*Pin*0.9)))))-(3*pi/2))/((2e-7)*(7.8e-3));
Incorrect number or types of inputs or outputs for function sqrt.

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回答（1 个）

Sam Chak 2023-12-5

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https://ww2.mathworks.cn/matlabcentral/answers/2056104-transfer-function-implementation-with-s-and-sqrt#answer_1365849

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Hi @Anastasios

The transfer function that describes the mapping from the input (input Current) to the output (output Voltage) appears to be the one shown in the image. However, this may not be truly what you are looking for. What exactly is "a [ng]"?