For an inverting opamp, is inverting the same thing as an 180 degree phase shift?












5












$begingroup$


Many texts talk about 180 degree phase shift as a function of the inverting opamp.



Is that correct? It seems to me inverting is happening almost immediately but phase is related to time and period and time delay between the input and output.






op-amp







share|improve this question











$endgroup$








  • 1




    $begingroup$
    Phase is making sense for periodical sinusoidal signals, where phase shift of 180 degrees is equivalent to multiplication by -1. For other signals it is not the same.
    $endgroup$
    – Eugene Sh.
    2 days ago








  • 2




    $begingroup$
    But thats an illusion for the sine case, it just “looks like” phase shifted. Correct?
    $endgroup$
    – Genzo
    2 days ago








  • 1




    $begingroup$
    Yes it is an "illusion" but if it is a pure sinewave, you will be unable to tell the difference so it does not matter, the resulting signal is the same whether you invert of phase-delay.
    $endgroup$
    – Bimpelrekkie
    2 days ago
















5












$begingroup$


Many texts talk about 180 degree phase shift as a function of the inverting opamp.



Is that correct? It seems to me inverting is happening almost immediately but phase is related to time and period and time delay between the input and output.






op-amp







share|improve this question











$endgroup$








  • 1




    $begingroup$
    Phase is making sense for periodical sinusoidal signals, where phase shift of 180 degrees is equivalent to multiplication by -1. For other signals it is not the same.
    $endgroup$
    – Eugene Sh.
    2 days ago








  • 2




    $begingroup$
    But thats an illusion for the sine case, it just “looks like” phase shifted. Correct?
    $endgroup$
    – Genzo
    2 days ago








  • 1




    $begingroup$
    Yes it is an "illusion" but if it is a pure sinewave, you will be unable to tell the difference so it does not matter, the resulting signal is the same whether you invert of phase-delay.
    $endgroup$
    – Bimpelrekkie
    2 days ago














5












5








5





$begingroup$


Many texts talk about 180 degree phase shift as a function of the inverting opamp.



Is that correct? It seems to me inverting is happening almost immediately but phase is related to time and period and time delay between the input and output.






op-amp







share|improve this question











$endgroup$




Many texts talk about 180 degree phase shift as a function of the inverting opamp.



Is that correct? It seems to me inverting is happening almost immediately but phase is related to time and period and time delay between the input and output.






op-amp




op-amp






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited 2 days ago









Acccumulation

1133




1133










asked 2 days ago









GenzoGenzo

376218




376218








  • 1




    $begingroup$
    Phase is making sense for periodical sinusoidal signals, where phase shift of 180 degrees is equivalent to multiplication by -1. For other signals it is not the same.
    $endgroup$
    – Eugene Sh.
    2 days ago








  • 2




    $begingroup$
    But thats an illusion for the sine case, it just “looks like” phase shifted. Correct?
    $endgroup$
    – Genzo
    2 days ago








  • 1




    $begingroup$
    Yes it is an "illusion" but if it is a pure sinewave, you will be unable to tell the difference so it does not matter, the resulting signal is the same whether you invert of phase-delay.
    $endgroup$
    – Bimpelrekkie
    2 days ago














  • 1




    $begingroup$
    Phase is making sense for periodical sinusoidal signals, where phase shift of 180 degrees is equivalent to multiplication by -1. For other signals it is not the same.
    $endgroup$
    – Eugene Sh.
    2 days ago








  • 2




    $begingroup$
    But thats an illusion for the sine case, it just “looks like” phase shifted. Correct?
    $endgroup$
    – Genzo
    2 days ago








  • 1




    $begingroup$
    Yes it is an "illusion" but if it is a pure sinewave, you will be unable to tell the difference so it does not matter, the resulting signal is the same whether you invert of phase-delay.
    $endgroup$
    – Bimpelrekkie
    2 days ago








1




1




$begingroup$
Phase is making sense for periodical sinusoidal signals, where phase shift of 180 degrees is equivalent to multiplication by -1. For other signals it is not the same.
$endgroup$
– Eugene Sh.
2 days ago






$begingroup$
Phase is making sense for periodical sinusoidal signals, where phase shift of 180 degrees is equivalent to multiplication by -1. For other signals it is not the same.
$endgroup$
– Eugene Sh.
2 days ago






2




2




$begingroup$
But thats an illusion for the sine case, it just “looks like” phase shifted. Correct?
$endgroup$
– Genzo
2 days ago






$begingroup$
But thats an illusion for the sine case, it just “looks like” phase shifted. Correct?
$endgroup$
– Genzo
2 days ago






1




1




$begingroup$
Yes it is an "illusion" but if it is a pure sinewave, you will be unable to tell the difference so it does not matter, the resulting signal is the same whether you invert of phase-delay.
$endgroup$
– Bimpelrekkie
2 days ago




$begingroup$
Yes it is an "illusion" but if it is a pure sinewave, you will be unable to tell the difference so it does not matter, the resulting signal is the same whether you invert of phase-delay.
$endgroup$
– Bimpelrekkie
2 days ago










3 Answers
3






active

oldest

votes


















13












$begingroup$

An inverting op-amp inverts the signal; it does not phase change the signal at the output by 180 degrees although, if the input waveform were a sinewave, then it would look like 180 degrees of phase shift.






share|improve this answer









$endgroup$













  • $begingroup$
    So it “looks like” as if it is phase shifted but actually it is not. There is a nuance here.
    $endgroup$
    – Genzo
    2 days ago










  • $begingroup$
    @Genzo indeed and a lot of EEs will use the terms interchangeably (including me but I always try and correct these bad habits of mine).
    $endgroup$
    – Andy aka
    2 days ago






  • 1




    $begingroup$
    More specifically inverting is equivalent to phase shifting every constituent sine wave in the Fourier representation of the signal by 180 degrees. So in that sense it is equivalent, but potentially miselading in cases where there are other "phases" of interest, such as modulated signals where "invert" is not necessarily the same as phase shifting the modulation by 180 degrees. This is where people get tripped up, phase actually means slightly different things in different contexts.
    $endgroup$
    – Evan
    2 days ago












  • $begingroup$
    Filters have phase shift and group delay. Inverters have 180 deg inversion
    $endgroup$
    – Sunnyskyguy EE75
    2 days ago










  • $begingroup$
    Another situation where it matters is if the voltage and current are out of phase.
    $endgroup$
    – Acccumulation
    2 days ago



















5












$begingroup$

How an opamp behaves depends on how you configure it in a circuit.



But the opamp is actually irrelevant to your actual question.



I think that your actual question is:



Is inverting a signal the same as phase shifting it by 180 degrees



What we mean by inverting a signal is multiplying the signal by -1, so +33mV becomes -33 mV
and -0.5 V becomes +0.5 V.



A 180 degree phase shift is indeed related to time but since phase is also coupled to frequency we only tend to use phase when talking about a single frequency. The only signal that contains a single frequency is a sinewave. Now for a sinewave inverting it (multiply it by -1) or phase shifting it 180 degrees will result in the same signal.



So yes, for sinusoidal signals, inverting and phase shifting with 180 degrees is the same thing.



Also for periodic signals like square waves and sawtooth signals, which consist of a base frequency and harmonics, inverting and phase shifting with 180 degrees is the same thing. Then the phase is only related to the base (lowest) frequency.



For non-periodic signals (these do not have a base-frequency) this isn't the case.






share|improve this answer











$endgroup$









  • 1




    $begingroup$
    "Also for periodic signals like square waves and sawtooth signals, which consist of a base frequency and harmonics, inverting and phase shifting with 180 degrees is the same thing." That makes it sound like it's true of all periodic waves. It's only true of odd waves (i.e. nothing but odd harmonics).
    $endgroup$
    – Acccumulation
    2 days ago



















0












$begingroup$

Inverting a signal is the same as a phase shift of 180 degrees at all frequencies.



If you take the Fourier transform of a signal, and compare it to the Fourier transform of the inverted version of the signal, you will see that the latter has the phase shifted by 180 degrees at every frequency.



This means if you invert a sine wave you get a shifted sine wave, but also if you invert the sum of two sine waves, for example, you get the sum of two sine waves that are each shifted by 180 degrees.



You can describe this in either the time domain or the frequency domain. Obviously it is more intuitive in the time domain ("it multiplies the signal by -1").



You are correct that the frequency at a single point in time doesn't make sense to talk about - but we are not talking about inverting a single point in time, because the circuit will invert the signal at all points in time. Or at least, all the points between turning it on and turning it off.






share|improve this answer









$endgroup$













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    3 Answers
    3






    active

    oldest

    votes








    3 Answers
    3






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    13












    $begingroup$

    An inverting op-amp inverts the signal; it does not phase change the signal at the output by 180 degrees although, if the input waveform were a sinewave, then it would look like 180 degrees of phase shift.






    share|improve this answer









    $endgroup$













    • $begingroup$
      So it “looks like” as if it is phase shifted but actually it is not. There is a nuance here.
      $endgroup$
      – Genzo
      2 days ago










    • $begingroup$
      @Genzo indeed and a lot of EEs will use the terms interchangeably (including me but I always try and correct these bad habits of mine).
      $endgroup$
      – Andy aka
      2 days ago






    • 1




      $begingroup$
      More specifically inverting is equivalent to phase shifting every constituent sine wave in the Fourier representation of the signal by 180 degrees. So in that sense it is equivalent, but potentially miselading in cases where there are other "phases" of interest, such as modulated signals where "invert" is not necessarily the same as phase shifting the modulation by 180 degrees. This is where people get tripped up, phase actually means slightly different things in different contexts.
      $endgroup$
      – Evan
      2 days ago












    • $begingroup$
      Filters have phase shift and group delay. Inverters have 180 deg inversion
      $endgroup$
      – Sunnyskyguy EE75
      2 days ago










    • $begingroup$
      Another situation where it matters is if the voltage and current are out of phase.
      $endgroup$
      – Acccumulation
      2 days ago
















    13












    $begingroup$

    An inverting op-amp inverts the signal; it does not phase change the signal at the output by 180 degrees although, if the input waveform were a sinewave, then it would look like 180 degrees of phase shift.






    share|improve this answer









    $endgroup$













    • $begingroup$
      So it “looks like” as if it is phase shifted but actually it is not. There is a nuance here.
      $endgroup$
      – Genzo
      2 days ago










    • $begingroup$
      @Genzo indeed and a lot of EEs will use the terms interchangeably (including me but I always try and correct these bad habits of mine).
      $endgroup$
      – Andy aka
      2 days ago






    • 1




      $begingroup$
      More specifically inverting is equivalent to phase shifting every constituent sine wave in the Fourier representation of the signal by 180 degrees. So in that sense it is equivalent, but potentially miselading in cases where there are other "phases" of interest, such as modulated signals where "invert" is not necessarily the same as phase shifting the modulation by 180 degrees. This is where people get tripped up, phase actually means slightly different things in different contexts.
      $endgroup$
      – Evan
      2 days ago












    • $begingroup$
      Filters have phase shift and group delay. Inverters have 180 deg inversion
      $endgroup$
      – Sunnyskyguy EE75
      2 days ago










    • $begingroup$
      Another situation where it matters is if the voltage and current are out of phase.
      $endgroup$
      – Acccumulation
      2 days ago














    13












    13








    13





    $begingroup$

    An inverting op-amp inverts the signal; it does not phase change the signal at the output by 180 degrees although, if the input waveform were a sinewave, then it would look like 180 degrees of phase shift.






    share|improve this answer









    $endgroup$



    An inverting op-amp inverts the signal; it does not phase change the signal at the output by 180 degrees although, if the input waveform were a sinewave, then it would look like 180 degrees of phase shift.







    share|improve this answer












    share|improve this answer



    share|improve this answer










    answered 2 days ago









    Andy akaAndy aka

    240k11179412




    240k11179412












    • $begingroup$
      So it “looks like” as if it is phase shifted but actually it is not. There is a nuance here.
      $endgroup$
      – Genzo
      2 days ago










    • $begingroup$
      @Genzo indeed and a lot of EEs will use the terms interchangeably (including me but I always try and correct these bad habits of mine).
      $endgroup$
      – Andy aka
      2 days ago






    • 1




      $begingroup$
      More specifically inverting is equivalent to phase shifting every constituent sine wave in the Fourier representation of the signal by 180 degrees. So in that sense it is equivalent, but potentially miselading in cases where there are other "phases" of interest, such as modulated signals where "invert" is not necessarily the same as phase shifting the modulation by 180 degrees. This is where people get tripped up, phase actually means slightly different things in different contexts.
      $endgroup$
      – Evan
      2 days ago












    • $begingroup$
      Filters have phase shift and group delay. Inverters have 180 deg inversion
      $endgroup$
      – Sunnyskyguy EE75
      2 days ago










    • $begingroup$
      Another situation where it matters is if the voltage and current are out of phase.
      $endgroup$
      – Acccumulation
      2 days ago


















    • $begingroup$
      So it “looks like” as if it is phase shifted but actually it is not. There is a nuance here.
      $endgroup$
      – Genzo
      2 days ago










    • $begingroup$
      @Genzo indeed and a lot of EEs will use the terms interchangeably (including me but I always try and correct these bad habits of mine).
      $endgroup$
      – Andy aka
      2 days ago






    • 1




      $begingroup$
      More specifically inverting is equivalent to phase shifting every constituent sine wave in the Fourier representation of the signal by 180 degrees. So in that sense it is equivalent, but potentially miselading in cases where there are other "phases" of interest, such as modulated signals where "invert" is not necessarily the same as phase shifting the modulation by 180 degrees. This is where people get tripped up, phase actually means slightly different things in different contexts.
      $endgroup$
      – Evan
      2 days ago












    • $begingroup$
      Filters have phase shift and group delay. Inverters have 180 deg inversion
      $endgroup$
      – Sunnyskyguy EE75
      2 days ago










    • $begingroup$
      Another situation where it matters is if the voltage and current are out of phase.
      $endgroup$
      – Acccumulation
      2 days ago
















    $begingroup$
    So it “looks like” as if it is phase shifted but actually it is not. There is a nuance here.
    $endgroup$
    – Genzo
    2 days ago




    $begingroup$
    So it “looks like” as if it is phase shifted but actually it is not. There is a nuance here.
    $endgroup$
    – Genzo
    2 days ago












    $begingroup$
    @Genzo indeed and a lot of EEs will use the terms interchangeably (including me but I always try and correct these bad habits of mine).
    $endgroup$
    – Andy aka
    2 days ago




    $begingroup$
    @Genzo indeed and a lot of EEs will use the terms interchangeably (including me but I always try and correct these bad habits of mine).
    $endgroup$
    – Andy aka
    2 days ago




    1




    1




    $begingroup$
    More specifically inverting is equivalent to phase shifting every constituent sine wave in the Fourier representation of the signal by 180 degrees. So in that sense it is equivalent, but potentially miselading in cases where there are other "phases" of interest, such as modulated signals where "invert" is not necessarily the same as phase shifting the modulation by 180 degrees. This is where people get tripped up, phase actually means slightly different things in different contexts.
    $endgroup$
    – Evan
    2 days ago






    $begingroup$
    More specifically inverting is equivalent to phase shifting every constituent sine wave in the Fourier representation of the signal by 180 degrees. So in that sense it is equivalent, but potentially miselading in cases where there are other "phases" of interest, such as modulated signals where "invert" is not necessarily the same as phase shifting the modulation by 180 degrees. This is where people get tripped up, phase actually means slightly different things in different contexts.
    $endgroup$
    – Evan
    2 days ago














    $begingroup$
    Filters have phase shift and group delay. Inverters have 180 deg inversion
    $endgroup$
    – Sunnyskyguy EE75
    2 days ago




    $begingroup$
    Filters have phase shift and group delay. Inverters have 180 deg inversion
    $endgroup$
    – Sunnyskyguy EE75
    2 days ago












    $begingroup$
    Another situation where it matters is if the voltage and current are out of phase.
    $endgroup$
    – Acccumulation
    2 days ago




    $begingroup$
    Another situation where it matters is if the voltage and current are out of phase.
    $endgroup$
    – Acccumulation
    2 days ago













    5












    $begingroup$

    How an opamp behaves depends on how you configure it in a circuit.



    But the opamp is actually irrelevant to your actual question.



    I think that your actual question is:



    Is inverting a signal the same as phase shifting it by 180 degrees



    What we mean by inverting a signal is multiplying the signal by -1, so +33mV becomes -33 mV
    and -0.5 V becomes +0.5 V.



    A 180 degree phase shift is indeed related to time but since phase is also coupled to frequency we only tend to use phase when talking about a single frequency. The only signal that contains a single frequency is a sinewave. Now for a sinewave inverting it (multiply it by -1) or phase shifting it 180 degrees will result in the same signal.



    So yes, for sinusoidal signals, inverting and phase shifting with 180 degrees is the same thing.



    Also for periodic signals like square waves and sawtooth signals, which consist of a base frequency and harmonics, inverting and phase shifting with 180 degrees is the same thing. Then the phase is only related to the base (lowest) frequency.



    For non-periodic signals (these do not have a base-frequency) this isn't the case.






    share|improve this answer











    $endgroup$









    • 1




      $begingroup$
      "Also for periodic signals like square waves and sawtooth signals, which consist of a base frequency and harmonics, inverting and phase shifting with 180 degrees is the same thing." That makes it sound like it's true of all periodic waves. It's only true of odd waves (i.e. nothing but odd harmonics).
      $endgroup$
      – Acccumulation
      2 days ago
















    5












    $begingroup$

    How an opamp behaves depends on how you configure it in a circuit.



    But the opamp is actually irrelevant to your actual question.



    I think that your actual question is:



    Is inverting a signal the same as phase shifting it by 180 degrees



    What we mean by inverting a signal is multiplying the signal by -1, so +33mV becomes -33 mV
    and -0.5 V becomes +0.5 V.



    A 180 degree phase shift is indeed related to time but since phase is also coupled to frequency we only tend to use phase when talking about a single frequency. The only signal that contains a single frequency is a sinewave. Now for a sinewave inverting it (multiply it by -1) or phase shifting it 180 degrees will result in the same signal.



    So yes, for sinusoidal signals, inverting and phase shifting with 180 degrees is the same thing.



    Also for periodic signals like square waves and sawtooth signals, which consist of a base frequency and harmonics, inverting and phase shifting with 180 degrees is the same thing. Then the phase is only related to the base (lowest) frequency.



    For non-periodic signals (these do not have a base-frequency) this isn't the case.






    share|improve this answer











    $endgroup$









    • 1




      $begingroup$
      "Also for periodic signals like square waves and sawtooth signals, which consist of a base frequency and harmonics, inverting and phase shifting with 180 degrees is the same thing." That makes it sound like it's true of all periodic waves. It's only true of odd waves (i.e. nothing but odd harmonics).
      $endgroup$
      – Acccumulation
      2 days ago














    5












    5








    5





    $begingroup$

    How an opamp behaves depends on how you configure it in a circuit.



    But the opamp is actually irrelevant to your actual question.



    I think that your actual question is:



    Is inverting a signal the same as phase shifting it by 180 degrees



    What we mean by inverting a signal is multiplying the signal by -1, so +33mV becomes -33 mV
    and -0.5 V becomes +0.5 V.



    A 180 degree phase shift is indeed related to time but since phase is also coupled to frequency we only tend to use phase when talking about a single frequency. The only signal that contains a single frequency is a sinewave. Now for a sinewave inverting it (multiply it by -1) or phase shifting it 180 degrees will result in the same signal.



    So yes, for sinusoidal signals, inverting and phase shifting with 180 degrees is the same thing.



    Also for periodic signals like square waves and sawtooth signals, which consist of a base frequency and harmonics, inverting and phase shifting with 180 degrees is the same thing. Then the phase is only related to the base (lowest) frequency.



    For non-periodic signals (these do not have a base-frequency) this isn't the case.






    share|improve this answer











    $endgroup$



    How an opamp behaves depends on how you configure it in a circuit.



    But the opamp is actually irrelevant to your actual question.



    I think that your actual question is:



    Is inverting a signal the same as phase shifting it by 180 degrees



    What we mean by inverting a signal is multiplying the signal by -1, so +33mV becomes -33 mV
    and -0.5 V becomes +0.5 V.



    A 180 degree phase shift is indeed related to time but since phase is also coupled to frequency we only tend to use phase when talking about a single frequency. The only signal that contains a single frequency is a sinewave. Now for a sinewave inverting it (multiply it by -1) or phase shifting it 180 degrees will result in the same signal.



    So yes, for sinusoidal signals, inverting and phase shifting with 180 degrees is the same thing.



    Also for periodic signals like square waves and sawtooth signals, which consist of a base frequency and harmonics, inverting and phase shifting with 180 degrees is the same thing. Then the phase is only related to the base (lowest) frequency.



    For non-periodic signals (these do not have a base-frequency) this isn't the case.







    share|improve this answer














    share|improve this answer



    share|improve this answer








    edited 2 days ago

























    answered 2 days ago









    BimpelrekkieBimpelrekkie

    48.2k240107




    48.2k240107








    • 1




      $begingroup$
      "Also for periodic signals like square waves and sawtooth signals, which consist of a base frequency and harmonics, inverting and phase shifting with 180 degrees is the same thing." That makes it sound like it's true of all periodic waves. It's only true of odd waves (i.e. nothing but odd harmonics).
      $endgroup$
      – Acccumulation
      2 days ago














    • 1




      $begingroup$
      "Also for periodic signals like square waves and sawtooth signals, which consist of a base frequency and harmonics, inverting and phase shifting with 180 degrees is the same thing." That makes it sound like it's true of all periodic waves. It's only true of odd waves (i.e. nothing but odd harmonics).
      $endgroup$
      – Acccumulation
      2 days ago








    1




    1




    $begingroup$
    "Also for periodic signals like square waves and sawtooth signals, which consist of a base frequency and harmonics, inverting and phase shifting with 180 degrees is the same thing." That makes it sound like it's true of all periodic waves. It's only true of odd waves (i.e. nothing but odd harmonics).
    $endgroup$
    – Acccumulation
    2 days ago




    $begingroup$
    "Also for periodic signals like square waves and sawtooth signals, which consist of a base frequency and harmonics, inverting and phase shifting with 180 degrees is the same thing." That makes it sound like it's true of all periodic waves. It's only true of odd waves (i.e. nothing but odd harmonics).
    $endgroup$
    – Acccumulation
    2 days ago











    0












    $begingroup$

    Inverting a signal is the same as a phase shift of 180 degrees at all frequencies.



    If you take the Fourier transform of a signal, and compare it to the Fourier transform of the inverted version of the signal, you will see that the latter has the phase shifted by 180 degrees at every frequency.



    This means if you invert a sine wave you get a shifted sine wave, but also if you invert the sum of two sine waves, for example, you get the sum of two sine waves that are each shifted by 180 degrees.



    You can describe this in either the time domain or the frequency domain. Obviously it is more intuitive in the time domain ("it multiplies the signal by -1").



    You are correct that the frequency at a single point in time doesn't make sense to talk about - but we are not talking about inverting a single point in time, because the circuit will invert the signal at all points in time. Or at least, all the points between turning it on and turning it off.






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      0












      $begingroup$

      Inverting a signal is the same as a phase shift of 180 degrees at all frequencies.



      If you take the Fourier transform of a signal, and compare it to the Fourier transform of the inverted version of the signal, you will see that the latter has the phase shifted by 180 degrees at every frequency.



      This means if you invert a sine wave you get a shifted sine wave, but also if you invert the sum of two sine waves, for example, you get the sum of two sine waves that are each shifted by 180 degrees.



      You can describe this in either the time domain or the frequency domain. Obviously it is more intuitive in the time domain ("it multiplies the signal by -1").



      You are correct that the frequency at a single point in time doesn't make sense to talk about - but we are not talking about inverting a single point in time, because the circuit will invert the signal at all points in time. Or at least, all the points between turning it on and turning it off.






      share|improve this answer









      $endgroup$
















        0












        0








        0





        $begingroup$

        Inverting a signal is the same as a phase shift of 180 degrees at all frequencies.



        If you take the Fourier transform of a signal, and compare it to the Fourier transform of the inverted version of the signal, you will see that the latter has the phase shifted by 180 degrees at every frequency.



        This means if you invert a sine wave you get a shifted sine wave, but also if you invert the sum of two sine waves, for example, you get the sum of two sine waves that are each shifted by 180 degrees.



        You can describe this in either the time domain or the frequency domain. Obviously it is more intuitive in the time domain ("it multiplies the signal by -1").



        You are correct that the frequency at a single point in time doesn't make sense to talk about - but we are not talking about inverting a single point in time, because the circuit will invert the signal at all points in time. Or at least, all the points between turning it on and turning it off.






        share|improve this answer









        $endgroup$



        Inverting a signal is the same as a phase shift of 180 degrees at all frequencies.



        If you take the Fourier transform of a signal, and compare it to the Fourier transform of the inverted version of the signal, you will see that the latter has the phase shifted by 180 degrees at every frequency.



        This means if you invert a sine wave you get a shifted sine wave, but also if you invert the sum of two sine waves, for example, you get the sum of two sine waves that are each shifted by 180 degrees.



        You can describe this in either the time domain or the frequency domain. Obviously it is more intuitive in the time domain ("it multiplies the signal by -1").



        You are correct that the frequency at a single point in time doesn't make sense to talk about - but we are not talking about inverting a single point in time, because the circuit will invert the signal at all points in time. Or at least, all the points between turning it on and turning it off.







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered yesterday









        immibisimmibis

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