Opamp stability given in not inverting configuration The Next CEO of Stack OverflowWhat does it mean for amplifiers to be stable only down to N gain, where N > unity?How can you guarantee stability of an inverting opamp configuration amplifier?Cascaded vs. non-cascaded bridge-tied load circuits using opampsWhat is the typical error of a voltage follower opampTerminating unused unity-gain Unstable op-ampOpamp AB Class Current BufferDelay and Stablity in Negative Feedback Systems: ConfusionAPD Transimpedance amplifier stabilityWhat will be the output of opamp non inverting amplifier at 0v inputWhat is this opamp configuration?

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Opamp stability given in not inverting configuration



The Next CEO of Stack OverflowWhat does it mean for amplifiers to be stable only down to N gain, where N > unity?How can you guarantee stability of an inverting opamp configuration amplifier?Cascaded vs. non-cascaded bridge-tied load circuits using opampsWhat is the typical error of a voltage follower opampTerminating unused unity-gain Unstable op-ampOpamp AB Class Current BufferDelay and Stablity in Negative Feedback Systems: ConfusionAPD Transimpedance amplifier stabilityWhat will be the output of opamp non inverting amplifier at 0v inputWhat is this opamp configuration?










9












$begingroup$


If a datasheet (like AD828) says that an opamp is stable at Gain >2 (or reccomends to work with G>2, hence it is clearly not unity gain stable), what can we deduct about its stability in the inverting configuration at G=-1; G=-2 or G<<-2 (like in any transimpedance amplifier configuration)?
Is it always instable in the three above cases if not compensated?










share|improve this question











$endgroup$











  • $begingroup$
    Good question. The dynamic performance is also specified at G= -1, so it would seem that it is also stable below -1, but im not sure.
    $endgroup$
    – Linkyyy
    2 days ago






  • 1




    $begingroup$
    @Linkyyy Are you sure that you do not mean: so it would seem that it is also INstable at G = -1 The loopgain does not change for G = 1 vs G = -1. It is also the loopgain that determines (in)stability. G= -1 vs G = +1 only differs in the way where the input signal is applied.
    $endgroup$
    – Bimpelrekkie
    2 days ago






  • 1




    $begingroup$
    transimpedance amplifier configuration I think that the transimpedance amplifier is a bad example here as the ones I know all apply the input (current) at the - input so basically they're all inverting. I think we should only consider voltage amplifiers instead as these can be inverting and non inverting.
    $endgroup$
    – Bimpelrekkie
    2 days ago










  • $begingroup$
    It's a video amplifier so why are you even considering as a TIA?
    $endgroup$
    – Andy aka
    2 days ago






  • 1




    $begingroup$
    @Linkyyy the bandwidth at -1 is substantially lower than what is given at G=+2 You're comparing apples to pears. It is only fair to compare G = -1 vs G = 1 or G= 2 vs G = -2. The BW will be different between G = +/-1 and G=+/-2 because GBW product is constant.
    $endgroup$
    – Bimpelrekkie
    2 days ago















9












$begingroup$


If a datasheet (like AD828) says that an opamp is stable at Gain >2 (or reccomends to work with G>2, hence it is clearly not unity gain stable), what can we deduct about its stability in the inverting configuration at G=-1; G=-2 or G<<-2 (like in any transimpedance amplifier configuration)?
Is it always instable in the three above cases if not compensated?










share|improve this question











$endgroup$











  • $begingroup$
    Good question. The dynamic performance is also specified at G= -1, so it would seem that it is also stable below -1, but im not sure.
    $endgroup$
    – Linkyyy
    2 days ago






  • 1




    $begingroup$
    @Linkyyy Are you sure that you do not mean: so it would seem that it is also INstable at G = -1 The loopgain does not change for G = 1 vs G = -1. It is also the loopgain that determines (in)stability. G= -1 vs G = +1 only differs in the way where the input signal is applied.
    $endgroup$
    – Bimpelrekkie
    2 days ago






  • 1




    $begingroup$
    transimpedance amplifier configuration I think that the transimpedance amplifier is a bad example here as the ones I know all apply the input (current) at the - input so basically they're all inverting. I think we should only consider voltage amplifiers instead as these can be inverting and non inverting.
    $endgroup$
    – Bimpelrekkie
    2 days ago










  • $begingroup$
    It's a video amplifier so why are you even considering as a TIA?
    $endgroup$
    – Andy aka
    2 days ago






  • 1




    $begingroup$
    @Linkyyy the bandwidth at -1 is substantially lower than what is given at G=+2 You're comparing apples to pears. It is only fair to compare G = -1 vs G = 1 or G= 2 vs G = -2. The BW will be different between G = +/-1 and G=+/-2 because GBW product is constant.
    $endgroup$
    – Bimpelrekkie
    2 days ago













9












9








9


2



$begingroup$


If a datasheet (like AD828) says that an opamp is stable at Gain >2 (or reccomends to work with G>2, hence it is clearly not unity gain stable), what can we deduct about its stability in the inverting configuration at G=-1; G=-2 or G<<-2 (like in any transimpedance amplifier configuration)?
Is it always instable in the three above cases if not compensated?










share|improve this question











$endgroup$




If a datasheet (like AD828) says that an opamp is stable at Gain >2 (or reccomends to work with G>2, hence it is clearly not unity gain stable), what can we deduct about its stability in the inverting configuration at G=-1; G=-2 or G<<-2 (like in any transimpedance amplifier configuration)?
Is it always instable in the three above cases if not compensated?







operational-amplifier gain stability inverting-amplifier






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited 2 days ago









Linkyyy

54139




54139










asked 2 days ago









Gianluca GGianluca G

877




877











  • $begingroup$
    Good question. The dynamic performance is also specified at G= -1, so it would seem that it is also stable below -1, but im not sure.
    $endgroup$
    – Linkyyy
    2 days ago






  • 1




    $begingroup$
    @Linkyyy Are you sure that you do not mean: so it would seem that it is also INstable at G = -1 The loopgain does not change for G = 1 vs G = -1. It is also the loopgain that determines (in)stability. G= -1 vs G = +1 only differs in the way where the input signal is applied.
    $endgroup$
    – Bimpelrekkie
    2 days ago






  • 1




    $begingroup$
    transimpedance amplifier configuration I think that the transimpedance amplifier is a bad example here as the ones I know all apply the input (current) at the - input so basically they're all inverting. I think we should only consider voltage amplifiers instead as these can be inverting and non inverting.
    $endgroup$
    – Bimpelrekkie
    2 days ago










  • $begingroup$
    It's a video amplifier so why are you even considering as a TIA?
    $endgroup$
    – Andy aka
    2 days ago






  • 1




    $begingroup$
    @Linkyyy the bandwidth at -1 is substantially lower than what is given at G=+2 You're comparing apples to pears. It is only fair to compare G = -1 vs G = 1 or G= 2 vs G = -2. The BW will be different between G = +/-1 and G=+/-2 because GBW product is constant.
    $endgroup$
    – Bimpelrekkie
    2 days ago
















  • $begingroup$
    Good question. The dynamic performance is also specified at G= -1, so it would seem that it is also stable below -1, but im not sure.
    $endgroup$
    – Linkyyy
    2 days ago






  • 1




    $begingroup$
    @Linkyyy Are you sure that you do not mean: so it would seem that it is also INstable at G = -1 The loopgain does not change for G = 1 vs G = -1. It is also the loopgain that determines (in)stability. G= -1 vs G = +1 only differs in the way where the input signal is applied.
    $endgroup$
    – Bimpelrekkie
    2 days ago






  • 1




    $begingroup$
    transimpedance amplifier configuration I think that the transimpedance amplifier is a bad example here as the ones I know all apply the input (current) at the - input so basically they're all inverting. I think we should only consider voltage amplifiers instead as these can be inverting and non inverting.
    $endgroup$
    – Bimpelrekkie
    2 days ago










  • $begingroup$
    It's a video amplifier so why are you even considering as a TIA?
    $endgroup$
    – Andy aka
    2 days ago






  • 1




    $begingroup$
    @Linkyyy the bandwidth at -1 is substantially lower than what is given at G=+2 You're comparing apples to pears. It is only fair to compare G = -1 vs G = 1 or G= 2 vs G = -2. The BW will be different between G = +/-1 and G=+/-2 because GBW product is constant.
    $endgroup$
    – Bimpelrekkie
    2 days ago















$begingroup$
Good question. The dynamic performance is also specified at G= -1, so it would seem that it is also stable below -1, but im not sure.
$endgroup$
– Linkyyy
2 days ago




$begingroup$
Good question. The dynamic performance is also specified at G= -1, so it would seem that it is also stable below -1, but im not sure.
$endgroup$
– Linkyyy
2 days ago




1




1




$begingroup$
@Linkyyy Are you sure that you do not mean: so it would seem that it is also INstable at G = -1 The loopgain does not change for G = 1 vs G = -1. It is also the loopgain that determines (in)stability. G= -1 vs G = +1 only differs in the way where the input signal is applied.
$endgroup$
– Bimpelrekkie
2 days ago




$begingroup$
@Linkyyy Are you sure that you do not mean: so it would seem that it is also INstable at G = -1 The loopgain does not change for G = 1 vs G = -1. It is also the loopgain that determines (in)stability. G= -1 vs G = +1 only differs in the way where the input signal is applied.
$endgroup$
– Bimpelrekkie
2 days ago




1




1




$begingroup$
transimpedance amplifier configuration I think that the transimpedance amplifier is a bad example here as the ones I know all apply the input (current) at the - input so basically they're all inverting. I think we should only consider voltage amplifiers instead as these can be inverting and non inverting.
$endgroup$
– Bimpelrekkie
2 days ago




$begingroup$
transimpedance amplifier configuration I think that the transimpedance amplifier is a bad example here as the ones I know all apply the input (current) at the - input so basically they're all inverting. I think we should only consider voltage amplifiers instead as these can be inverting and non inverting.
$endgroup$
– Bimpelrekkie
2 days ago












$begingroup$
It's a video amplifier so why are you even considering as a TIA?
$endgroup$
– Andy aka
2 days ago




$begingroup$
It's a video amplifier so why are you even considering as a TIA?
$endgroup$
– Andy aka
2 days ago




1




1




$begingroup$
@Linkyyy the bandwidth at -1 is substantially lower than what is given at G=+2 You're comparing apples to pears. It is only fair to compare G = -1 vs G = 1 or G= 2 vs G = -2. The BW will be different between G = +/-1 and G=+/-2 because GBW product is constant.
$endgroup$
– Bimpelrekkie
2 days ago




$begingroup$
@Linkyyy the bandwidth at -1 is substantially lower than what is given at G=+2 You're comparing apples to pears. It is only fair to compare G = -1 vs G = 1 or G= 2 vs G = -2. The BW will be different between G = +/-1 and G=+/-2 because GBW product is constant.
$endgroup$
– Bimpelrekkie
2 days ago










3 Answers
3






active

oldest

votes


















5












$begingroup$

Stability is a function of NOISE GAIN, not strictly the same thing as gain...



Noise gain follows the formula for the gain of a non inverting stage $$NG = 1 + Rf/Rg$$



For an inverting unity gain stage this will be 2, making the part stable in this configuration.






share|improve this answer









$endgroup$








  • 3




    $begingroup$
    Although I've been an analog designer for 25 years, I didn't know about "noise gain" but looking up what it is, it is strongly related to loop gain which is what I use to evaluate loop stability. I like the term "noise gain" though as it emphasizes that there is no relation between stability and the input signal of the circuit. Good reading material: analog.com/media/en/training-seminars/tutorials/MT-033.pdf
    $endgroup$
    – Bimpelrekkie
    2 days ago











  • $begingroup$
    The classics are by Tobey, Graeme, Huelsman; two good books
    $endgroup$
    – analogsystemsrf
    2 days ago






  • 1




    $begingroup$
    What is NG for a TIA? Infinite (Rg=0)?
    $endgroup$
    – Gianluca G
    2 days ago


















0












$begingroup$

Loop gain is the stability determining factor.



Loop Gain = Beta * Ao where Beta = feedback fraction = R1/(R1+R2) and Ao = open loop gain.



1/Beta = Noise Gain.



So a non inverting amplifier with a closed loop gain of 2 (R1=R2, Beta = 0.5 and Noise Gain=2) has the same Beta and therefore the same noise gain as an inverting amplifier with a closed loop gain of -1 (R1=R2, Beta = 0.5 and Noise Gain = 2).



This means that an inverting amplifier with a gain of -1 is as stable as a non-inverting amplifier with a gain of 2.



In addition to Noise Gain being the stability determining factor, Noise Gain also determines the bandwidth of an amplifier.



Bandwidth = GBW/Noise Gain.



So a non-inverting amplifier with a gain of 2 (R1=R2) has the same bandwidth as an inverting amplifier with a gain of -1 (R1=R2).
If you make the closed loop gains of the two amplifiers both equal to 2 then the inverting amplifier will have a bandwidth equal to 2/3 the bandwidth of the non-inverting amplifier.



Non-Inverting amplifier with a closed loop gain of 2 has R1=R2 and a noise gain of 2.
Inverting amplifier with a closed loop gain of 2 has R2=2*R1 and a noise gain of 3.






share|improve this answer









$endgroup$








  • 1




    $begingroup$
    Take a look at the data sheet for the AD744 op amp which is stable for non-inverting gains of +2 or greater and also for inverting gains of -1 or greater. To be used as a unity gain follower this op amp requires extra compensation.
    $endgroup$
    – James
    2 days ago


















-1












$begingroup$

Stabilty is a function of the total feedback phaseshift.



1) Rout + Cload: 100 ohms and 100pf are 10,000 picosecond time constant, producing 45 degrees phaseshift at 100 MegaRadians/second of 16MHz. Many opamps have Rout (internal output resistance) near 100 ohms; some have Rout >>> 1Kohms.



2) phase margin beyond 90 degrees: a 60 degree phase margin opamp (Unity Gain phase margin) has 90+30 = 120 degrees phase shift



3) phase shift at the virtual_ground node: assume 10pF on that node, and resistive equivalent (Rin || Rfb, or Rg || Rfb) of 1,000 ohms; this produces 10,000 picosecond tme constant, or 45 degrees at 16MHz.



What rescues a feedback network? Usually the parasitic feedback capacitance in parallel with the feedback resistor. IMHO






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









    5












    $begingroup$

    Stability is a function of NOISE GAIN, not strictly the same thing as gain...



    Noise gain follows the formula for the gain of a non inverting stage $$NG = 1 + Rf/Rg$$



    For an inverting unity gain stage this will be 2, making the part stable in this configuration.






    share|improve this answer









    $endgroup$








    • 3




      $begingroup$
      Although I've been an analog designer for 25 years, I didn't know about "noise gain" but looking up what it is, it is strongly related to loop gain which is what I use to evaluate loop stability. I like the term "noise gain" though as it emphasizes that there is no relation between stability and the input signal of the circuit. Good reading material: analog.com/media/en/training-seminars/tutorials/MT-033.pdf
      $endgroup$
      – Bimpelrekkie
      2 days ago











    • $begingroup$
      The classics are by Tobey, Graeme, Huelsman; two good books
      $endgroup$
      – analogsystemsrf
      2 days ago






    • 1




      $begingroup$
      What is NG for a TIA? Infinite (Rg=0)?
      $endgroup$
      – Gianluca G
      2 days ago















    5












    $begingroup$

    Stability is a function of NOISE GAIN, not strictly the same thing as gain...



    Noise gain follows the formula for the gain of a non inverting stage $$NG = 1 + Rf/Rg$$



    For an inverting unity gain stage this will be 2, making the part stable in this configuration.






    share|improve this answer









    $endgroup$








    • 3




      $begingroup$
      Although I've been an analog designer for 25 years, I didn't know about "noise gain" but looking up what it is, it is strongly related to loop gain which is what I use to evaluate loop stability. I like the term "noise gain" though as it emphasizes that there is no relation between stability and the input signal of the circuit. Good reading material: analog.com/media/en/training-seminars/tutorials/MT-033.pdf
      $endgroup$
      – Bimpelrekkie
      2 days ago











    • $begingroup$
      The classics are by Tobey, Graeme, Huelsman; two good books
      $endgroup$
      – analogsystemsrf
      2 days ago






    • 1




      $begingroup$
      What is NG for a TIA? Infinite (Rg=0)?
      $endgroup$
      – Gianluca G
      2 days ago













    5












    5








    5





    $begingroup$

    Stability is a function of NOISE GAIN, not strictly the same thing as gain...



    Noise gain follows the formula for the gain of a non inverting stage $$NG = 1 + Rf/Rg$$



    For an inverting unity gain stage this will be 2, making the part stable in this configuration.






    share|improve this answer









    $endgroup$



    Stability is a function of NOISE GAIN, not strictly the same thing as gain...



    Noise gain follows the formula for the gain of a non inverting stage $$NG = 1 + Rf/Rg$$



    For an inverting unity gain stage this will be 2, making the part stable in this configuration.







    share|improve this answer












    share|improve this answer



    share|improve this answer










    answered 2 days ago









    Dan MillsDan Mills

    11.6k11124




    11.6k11124







    • 3




      $begingroup$
      Although I've been an analog designer for 25 years, I didn't know about "noise gain" but looking up what it is, it is strongly related to loop gain which is what I use to evaluate loop stability. I like the term "noise gain" though as it emphasizes that there is no relation between stability and the input signal of the circuit. Good reading material: analog.com/media/en/training-seminars/tutorials/MT-033.pdf
      $endgroup$
      – Bimpelrekkie
      2 days ago











    • $begingroup$
      The classics are by Tobey, Graeme, Huelsman; two good books
      $endgroup$
      – analogsystemsrf
      2 days ago






    • 1




      $begingroup$
      What is NG for a TIA? Infinite (Rg=0)?
      $endgroup$
      – Gianluca G
      2 days ago












    • 3




      $begingroup$
      Although I've been an analog designer for 25 years, I didn't know about "noise gain" but looking up what it is, it is strongly related to loop gain which is what I use to evaluate loop stability. I like the term "noise gain" though as it emphasizes that there is no relation between stability and the input signal of the circuit. Good reading material: analog.com/media/en/training-seminars/tutorials/MT-033.pdf
      $endgroup$
      – Bimpelrekkie
      2 days ago











    • $begingroup$
      The classics are by Tobey, Graeme, Huelsman; two good books
      $endgroup$
      – analogsystemsrf
      2 days ago






    • 1




      $begingroup$
      What is NG for a TIA? Infinite (Rg=0)?
      $endgroup$
      – Gianluca G
      2 days ago







    3




    3




    $begingroup$
    Although I've been an analog designer for 25 years, I didn't know about "noise gain" but looking up what it is, it is strongly related to loop gain which is what I use to evaluate loop stability. I like the term "noise gain" though as it emphasizes that there is no relation between stability and the input signal of the circuit. Good reading material: analog.com/media/en/training-seminars/tutorials/MT-033.pdf
    $endgroup$
    – Bimpelrekkie
    2 days ago





    $begingroup$
    Although I've been an analog designer for 25 years, I didn't know about "noise gain" but looking up what it is, it is strongly related to loop gain which is what I use to evaluate loop stability. I like the term "noise gain" though as it emphasizes that there is no relation between stability and the input signal of the circuit. Good reading material: analog.com/media/en/training-seminars/tutorials/MT-033.pdf
    $endgroup$
    – Bimpelrekkie
    2 days ago













    $begingroup$
    The classics are by Tobey, Graeme, Huelsman; two good books
    $endgroup$
    – analogsystemsrf
    2 days ago




    $begingroup$
    The classics are by Tobey, Graeme, Huelsman; two good books
    $endgroup$
    – analogsystemsrf
    2 days ago




    1




    1




    $begingroup$
    What is NG for a TIA? Infinite (Rg=0)?
    $endgroup$
    – Gianluca G
    2 days ago




    $begingroup$
    What is NG for a TIA? Infinite (Rg=0)?
    $endgroup$
    – Gianluca G
    2 days ago













    0












    $begingroup$

    Loop gain is the stability determining factor.



    Loop Gain = Beta * Ao where Beta = feedback fraction = R1/(R1+R2) and Ao = open loop gain.



    1/Beta = Noise Gain.



    So a non inverting amplifier with a closed loop gain of 2 (R1=R2, Beta = 0.5 and Noise Gain=2) has the same Beta and therefore the same noise gain as an inverting amplifier with a closed loop gain of -1 (R1=R2, Beta = 0.5 and Noise Gain = 2).



    This means that an inverting amplifier with a gain of -1 is as stable as a non-inverting amplifier with a gain of 2.



    In addition to Noise Gain being the stability determining factor, Noise Gain also determines the bandwidth of an amplifier.



    Bandwidth = GBW/Noise Gain.



    So a non-inverting amplifier with a gain of 2 (R1=R2) has the same bandwidth as an inverting amplifier with a gain of -1 (R1=R2).
    If you make the closed loop gains of the two amplifiers both equal to 2 then the inverting amplifier will have a bandwidth equal to 2/3 the bandwidth of the non-inverting amplifier.



    Non-Inverting amplifier with a closed loop gain of 2 has R1=R2 and a noise gain of 2.
    Inverting amplifier with a closed loop gain of 2 has R2=2*R1 and a noise gain of 3.






    share|improve this answer









    $endgroup$








    • 1




      $begingroup$
      Take a look at the data sheet for the AD744 op amp which is stable for non-inverting gains of +2 or greater and also for inverting gains of -1 or greater. To be used as a unity gain follower this op amp requires extra compensation.
      $endgroup$
      – James
      2 days ago















    0












    $begingroup$

    Loop gain is the stability determining factor.



    Loop Gain = Beta * Ao where Beta = feedback fraction = R1/(R1+R2) and Ao = open loop gain.



    1/Beta = Noise Gain.



    So a non inverting amplifier with a closed loop gain of 2 (R1=R2, Beta = 0.5 and Noise Gain=2) has the same Beta and therefore the same noise gain as an inverting amplifier with a closed loop gain of -1 (R1=R2, Beta = 0.5 and Noise Gain = 2).



    This means that an inverting amplifier with a gain of -1 is as stable as a non-inverting amplifier with a gain of 2.



    In addition to Noise Gain being the stability determining factor, Noise Gain also determines the bandwidth of an amplifier.



    Bandwidth = GBW/Noise Gain.



    So a non-inverting amplifier with a gain of 2 (R1=R2) has the same bandwidth as an inverting amplifier with a gain of -1 (R1=R2).
    If you make the closed loop gains of the two amplifiers both equal to 2 then the inverting amplifier will have a bandwidth equal to 2/3 the bandwidth of the non-inverting amplifier.



    Non-Inverting amplifier with a closed loop gain of 2 has R1=R2 and a noise gain of 2.
    Inverting amplifier with a closed loop gain of 2 has R2=2*R1 and a noise gain of 3.






    share|improve this answer









    $endgroup$








    • 1




      $begingroup$
      Take a look at the data sheet for the AD744 op amp which is stable for non-inverting gains of +2 or greater and also for inverting gains of -1 or greater. To be used as a unity gain follower this op amp requires extra compensation.
      $endgroup$
      – James
      2 days ago













    0












    0








    0





    $begingroup$

    Loop gain is the stability determining factor.



    Loop Gain = Beta * Ao where Beta = feedback fraction = R1/(R1+R2) and Ao = open loop gain.



    1/Beta = Noise Gain.



    So a non inverting amplifier with a closed loop gain of 2 (R1=R2, Beta = 0.5 and Noise Gain=2) has the same Beta and therefore the same noise gain as an inverting amplifier with a closed loop gain of -1 (R1=R2, Beta = 0.5 and Noise Gain = 2).



    This means that an inverting amplifier with a gain of -1 is as stable as a non-inverting amplifier with a gain of 2.



    In addition to Noise Gain being the stability determining factor, Noise Gain also determines the bandwidth of an amplifier.



    Bandwidth = GBW/Noise Gain.



    So a non-inverting amplifier with a gain of 2 (R1=R2) has the same bandwidth as an inverting amplifier with a gain of -1 (R1=R2).
    If you make the closed loop gains of the two amplifiers both equal to 2 then the inverting amplifier will have a bandwidth equal to 2/3 the bandwidth of the non-inverting amplifier.



    Non-Inverting amplifier with a closed loop gain of 2 has R1=R2 and a noise gain of 2.
    Inverting amplifier with a closed loop gain of 2 has R2=2*R1 and a noise gain of 3.






    share|improve this answer









    $endgroup$



    Loop gain is the stability determining factor.



    Loop Gain = Beta * Ao where Beta = feedback fraction = R1/(R1+R2) and Ao = open loop gain.



    1/Beta = Noise Gain.



    So a non inverting amplifier with a closed loop gain of 2 (R1=R2, Beta = 0.5 and Noise Gain=2) has the same Beta and therefore the same noise gain as an inverting amplifier with a closed loop gain of -1 (R1=R2, Beta = 0.5 and Noise Gain = 2).



    This means that an inverting amplifier with a gain of -1 is as stable as a non-inverting amplifier with a gain of 2.



    In addition to Noise Gain being the stability determining factor, Noise Gain also determines the bandwidth of an amplifier.



    Bandwidth = GBW/Noise Gain.



    So a non-inverting amplifier with a gain of 2 (R1=R2) has the same bandwidth as an inverting amplifier with a gain of -1 (R1=R2).
    If you make the closed loop gains of the two amplifiers both equal to 2 then the inverting amplifier will have a bandwidth equal to 2/3 the bandwidth of the non-inverting amplifier.



    Non-Inverting amplifier with a closed loop gain of 2 has R1=R2 and a noise gain of 2.
    Inverting amplifier with a closed loop gain of 2 has R2=2*R1 and a noise gain of 3.







    share|improve this answer












    share|improve this answer



    share|improve this answer










    answered 2 days ago









    JamesJames

    954




    954







    • 1




      $begingroup$
      Take a look at the data sheet for the AD744 op amp which is stable for non-inverting gains of +2 or greater and also for inverting gains of -1 or greater. To be used as a unity gain follower this op amp requires extra compensation.
      $endgroup$
      – James
      2 days ago












    • 1




      $begingroup$
      Take a look at the data sheet for the AD744 op amp which is stable for non-inverting gains of +2 or greater and also for inverting gains of -1 or greater. To be used as a unity gain follower this op amp requires extra compensation.
      $endgroup$
      – James
      2 days ago







    1




    1




    $begingroup$
    Take a look at the data sheet for the AD744 op amp which is stable for non-inverting gains of +2 or greater and also for inverting gains of -1 or greater. To be used as a unity gain follower this op amp requires extra compensation.
    $endgroup$
    – James
    2 days ago




    $begingroup$
    Take a look at the data sheet for the AD744 op amp which is stable for non-inverting gains of +2 or greater and also for inverting gains of -1 or greater. To be used as a unity gain follower this op amp requires extra compensation.
    $endgroup$
    – James
    2 days ago











    -1












    $begingroup$

    Stabilty is a function of the total feedback phaseshift.



    1) Rout + Cload: 100 ohms and 100pf are 10,000 picosecond time constant, producing 45 degrees phaseshift at 100 MegaRadians/second of 16MHz. Many opamps have Rout (internal output resistance) near 100 ohms; some have Rout >>> 1Kohms.



    2) phase margin beyond 90 degrees: a 60 degree phase margin opamp (Unity Gain phase margin) has 90+30 = 120 degrees phase shift



    3) phase shift at the virtual_ground node: assume 10pF on that node, and resistive equivalent (Rin || Rfb, or Rg || Rfb) of 1,000 ohms; this produces 10,000 picosecond tme constant, or 45 degrees at 16MHz.



    What rescues a feedback network? Usually the parasitic feedback capacitance in parallel with the feedback resistor. IMHO






    share|improve this answer









    $endgroup$

















      -1












      $begingroup$

      Stabilty is a function of the total feedback phaseshift.



      1) Rout + Cload: 100 ohms and 100pf are 10,000 picosecond time constant, producing 45 degrees phaseshift at 100 MegaRadians/second of 16MHz. Many opamps have Rout (internal output resistance) near 100 ohms; some have Rout >>> 1Kohms.



      2) phase margin beyond 90 degrees: a 60 degree phase margin opamp (Unity Gain phase margin) has 90+30 = 120 degrees phase shift



      3) phase shift at the virtual_ground node: assume 10pF on that node, and resistive equivalent (Rin || Rfb, or Rg || Rfb) of 1,000 ohms; this produces 10,000 picosecond tme constant, or 45 degrees at 16MHz.



      What rescues a feedback network? Usually the parasitic feedback capacitance in parallel with the feedback resistor. IMHO






      share|improve this answer









      $endgroup$















        -1












        -1








        -1





        $begingroup$

        Stabilty is a function of the total feedback phaseshift.



        1) Rout + Cload: 100 ohms and 100pf are 10,000 picosecond time constant, producing 45 degrees phaseshift at 100 MegaRadians/second of 16MHz. Many opamps have Rout (internal output resistance) near 100 ohms; some have Rout >>> 1Kohms.



        2) phase margin beyond 90 degrees: a 60 degree phase margin opamp (Unity Gain phase margin) has 90+30 = 120 degrees phase shift



        3) phase shift at the virtual_ground node: assume 10pF on that node, and resistive equivalent (Rin || Rfb, or Rg || Rfb) of 1,000 ohms; this produces 10,000 picosecond tme constant, or 45 degrees at 16MHz.



        What rescues a feedback network? Usually the parasitic feedback capacitance in parallel with the feedback resistor. IMHO






        share|improve this answer









        $endgroup$



        Stabilty is a function of the total feedback phaseshift.



        1) Rout + Cload: 100 ohms and 100pf are 10,000 picosecond time constant, producing 45 degrees phaseshift at 100 MegaRadians/second of 16MHz. Many opamps have Rout (internal output resistance) near 100 ohms; some have Rout >>> 1Kohms.



        2) phase margin beyond 90 degrees: a 60 degree phase margin opamp (Unity Gain phase margin) has 90+30 = 120 degrees phase shift



        3) phase shift at the virtual_ground node: assume 10pF on that node, and resistive equivalent (Rin || Rfb, or Rg || Rfb) of 1,000 ohms; this produces 10,000 picosecond tme constant, or 45 degrees at 16MHz.



        What rescues a feedback network? Usually the parasitic feedback capacitance in parallel with the feedback resistor. IMHO







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered 2 days ago









        analogsystemsrfanalogsystemsrf

        15.8k2822




        15.8k2822



























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