mjhjmtu

I'm wondering how can I avoid excessive white space under equation.
This happens only a time in the entire document; in the other pages there are not this problem (I wrote the equation and the text in the same way everywhere).

poi saranno applicate quando si collegherà solo il sensore:
beginequation*
H(j omega) = Z_Known(j omega) fracV^ZK_ADC1(j omega)V_IN(j omega)
endequation*
dove $V^ZK_ADC1$ è la tensione letta dall'ADC quando tra il WE1 ed il CE è collegata solo la $Z_Known$ (footnoteNotare che, quando $V^ZC_ADC1(j omega) = V^ZK_ADC1(j omega)$, si ha: beginequation*
Z_S(j omega) = Z_Known(j omega) fracV^ZK_ADC1(j omega)V_IN(j omega) fracV_IN(j omega)V^ZS_ADC1(j omega) = Z_Known(j omega)
endequation*).
L'impedenza $Z_Known$ ha la seguente espressione:

EDIT: I'm using classicthesis template. The documentclass is:

documentclass[oneside,titlepage,numbers=noenddot,%1headlines,
 headinclude,footinclude,cleardoublepage=empty,abstract=on,
 BCOR=5mm,paper=a4,fontsize=11pt
 ]scrreprt

https://ctan.org/tex-archive/macros/latex/contrib/classicthesis?lang=en

Thank you so much in advance.

As @egreg has already pointed out in a comment, the big gap at the bottom of page 23 is caused by the fact that the material that follows the first displayed equation contains a lengthy footnote. This material -- including footnote 19 -- just won't fit at the bottom of page 23 and hence gets pushed to the top of page 24.

The following screenshot shows how this can happen (the code is given at the end of this answer):

There are several possible remedies:

• Make footnote 19 take up less space. E.g., is it essential to include a displayed equation in that footnote? Alternatively, if the footnote material truly is sufficiently important to warrant a displayed equation, it may be sufficiently important to be include in the main text, rather than being relegated to a footnote.




• Shorten the material earlier on page 23 (or page 22, or ...).




• Insert an instruction such as enlargethispage0.75baselineskip (or whatever vertical skip may be necessary...) just before the paragraph that contains the displayed equation.

Any visual fine-tuning should be performed only at the very end of the editing process, i.e., once the paper is truly done from a content perspective.

For the sake of completeness, here's the code that gave rise to the screenshot shown above; note that I would use upright Roman lettering for acronyms and full words, such as 'Known' and 'ADC', that occur in a math context.

documentclass[oneside,titlepage,numbers=noenddot,
 headinclude,footinclude,cleardoublepage=empty,abstract=on,
 BCOR=5mm,paper=a4,fontsize=11pt]scrreprt
usepackageamsmath
usepackage[dottedtoc]classicthesis
usepackagelipsum
newcommandvn[1]mathrm#1 
newcommandmyfootnote[1]%
 textsuperscript(%
 footnote#1%
 textsuperscript)
begindocument
setcounterpage23
setcounterfootnote17
setcounterchapter2
setcountersection3
sectionConfronto tra il biosensore ed un bipotenziostato da banco

lipsum[1-2] % filler text
myfootnoteCalibrare significa sollecitare con ingressi noti e misurare 
le correspondenti uscite. In questo caso gli ingressi noti dots
lipsum[2] % more filler text

% Check out what happens if the following line is uncommented.
%enlargethispage0.75baselineskip 
bigskip
noindent
poi saranno applicate quando si collegherà solo il sensore:
beginequation*
H(jomega) = Z_vnKnown(jomega) fracV^vnZK_vnADC1(jomega)V_vnIN(jomega)
endequation*
dove $V^vnZK_vnADC1$ è la tensione letta dall'ADC quando tra il WE1 ed il~CE è collegata solo la $Z_vnKnown$.%
myfootnoteNotare che, quando $V^vnZC_vnADC1(jomega) = V^vnZK_vnADC1(jomega)$, si ha: 
[
Z_S(jomega) = Z_vnKnown(jomega) 
fracV^vnZK_vnADC1(jomega)V_vnIN(jomega) 
fracV_vnIN(jomega)V^vnZS_vnADC1(jomega) 
= Z_vnKnown(jomega),.
]
L'impedenza $Z_vnKnown$ ha la seguente espressione: dots

bigskip
lipsum[4-7] % still more filler texxt
enddocument