# how can i bode plot this low pass filter?

i am not an expert by any means in matlab but i am asked to plot this transfer function which reflects an active low pass filter but i can't seem to get it right ... can you point out where is the error in this command please? ( the error shows a graph with straight lines)

```
num=9.18;
den=[(10e3)*(5e-9)];
lowpass= tf(num,den)
bode (lowpass)
```

I think i have missed up with the brackets but can't tell unfortunately, and i know another command which is easier to generate the required graph , but i have been ask to do this one as it shows the correct form of the transform function.

## Answers:

This is not a MATLAB issue. You have defined the transfer function `9.18/(10e3*5e-9)`

=`9.18/5.0000e-05`

. This results in a transfer function representing a static gain of `183600`

. So you defined only one numerator and one denominator coefficient.

You probably mean: `den=[ 10e3, 5e-9 ];`

giving you two denominator coefficients.

```
>> lowpass
lowpass =
9.18
---------------
10000 s + 5e-09
Continuous-time transfer function.
```

This results in lowpass characteristics:

```
bode(lowpass)
```