Opamp stability given in not inverting configurationWhat 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
What 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?
$begingroup$
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?
operational-amplifier gain stability inverting-amplifier
edited Mar 28 at 14:40
Linkyyy
54139
asked Mar 28 at 11:57
Gianluca GGianluca G
877
$endgroup$
|
show 2 more comments
$begingroup$
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?
operational-amplifier gain stability inverting-amplifier
edited Mar 28 at 14:40
Linkyyy
54139
asked Mar 28 at 11:57
Gianluca GGianluca G
877
$endgroup$
$begingroup$
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
Mar 28 at 12:34
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
Mar 28 at 12:40
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
Mar 28 at 12:43
$begingroup$
It's a video amplifier so why are you even considering as a TIA?
$endgroup$
– Andy aka
Mar 28 at 12:45
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
Mar 28 at 12:52
|
show 2 more comments
$begingroup$
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?
operational-amplifier gain stability inverting-amplifier
edited Mar 28 at 14:40
Linkyyy
54139
asked Mar 28 at 11:57
Gianluca GGianluca G
877
$endgroup$
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
operational-amplifier gain stability inverting-amplifier
edited Mar 28 at 14:40
Linkyyy
54139
asked Mar 28 at 11:57
Gianluca GGianluca G
877
edited Mar 28 at 14:40
Linkyyy
54139
asked Mar 28 at 11:57
Gianluca GGianluca G
877
edited Mar 28 at 14:40
Linkyyy
54139
edited Mar 28 at 14:40
Linkyyy
54139
edited Mar 28 at 14:40
Linkyyy
54139
54139
asked Mar 28 at 11:57
Gianluca GGianluca G
877
asked Mar 28 at 11:57
Gianluca GGianluca G
877
asked Mar 28 at 11:57
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
Mar 28 at 12:34
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
Mar 28 at 12:40
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
Mar 28 at 12:43
$begingroup$
It's a video amplifier so why are you even considering as a TIA?
$endgroup$
– Andy aka
Mar 28 at 12:45
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
Mar 28 at 12:52
|
show 2 more comments
$begingroup$
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
Mar 28 at 12:34
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
Mar 28 at 12:40
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
Mar 28 at 12:43
$begingroup$
It's a video amplifier so why are you even considering as a TIA?
$endgroup$
– Andy aka
Mar 28 at 12:45
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
Mar 28 at 12:52
$begingroup$
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
Mar 28 at 12:34
$begingroup$
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
Mar 28 at 12:34
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
Mar 28 at 12:40
$begingroup$
@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
Mar 28 at 12:40
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
Mar 28 at 12:43
$begingroup$
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
Mar 28 at 12:43
$begingroup$
It's a video amplifier so why are you even considering as a TIA?
$endgroup$
– Andy aka
Mar 28 at 12:45
$begingroup$
It's a video amplifier so why are you even considering as a TIA?
$endgroup$
– Andy aka
Mar 28 at 12:45
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
Mar 28 at 12:52
$begingroup$
@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
Mar 28 at 12:52
|
show 2 more comments
3 Answers
3
active
oldest
votes
$begingroup$
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.
answered Mar 28 at 12:57
Dan MillsDan Mills
11.7k11124
$endgroup$
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
Mar 28 at 13:11
$begingroup$
The classics are by Tobey, Graeme, Huelsman; two good books
$endgroup$
– analogsystemsrf
Mar 28 at 16:23
1
$begingroup$
What is NG for a TIA? Infinite (Rg=0)?
$endgroup$
– Gianluca G
Mar 28 at 20:28
add a comment |
$begingroup$
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.
answered Mar 28 at 14:53
JamesJames
934
$endgroup$
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
Mar 28 at 15:56
add a comment |
$begingroup$
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
answered Mar 28 at 13:11
analogsystemsrfanalogsystemsrf
15.9k2822
$endgroup$
add a comment |
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3 Answers
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active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
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.
answered Mar 28 at 12:57
Dan MillsDan Mills
11.7k11124
$endgroup$
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
Mar 28 at 13:11
$begingroup$
The classics are by Tobey, Graeme, Huelsman; two good books
$endgroup$
– analogsystemsrf
Mar 28 at 16:23
1
$begingroup$
What is NG for a TIA? Infinite (Rg=0)?
$endgroup$
– Gianluca G
Mar 28 at 20:28
add a comment |
$begingroup$
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.
answered Mar 28 at 12:57
Dan MillsDan Mills
11.7k11124
$endgroup$
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
Mar 28 at 13:11
$begingroup$
The classics are by Tobey, Graeme, Huelsman; two good books
$endgroup$
– analogsystemsrf
Mar 28 at 16:23
1
$begingroup$
What is NG for a TIA? Infinite (Rg=0)?
$endgroup$
– Gianluca G
Mar 28 at 20:28
add a comment |
$begingroup$
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.
answered Mar 28 at 12:57
Dan MillsDan Mills
11.7k11124
$endgroup$
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.
answered Mar 28 at 12:57
Dan MillsDan Mills
11.7k11124
answered Mar 28 at 12:57
Dan MillsDan Mills
11.7k11124
answered Mar 28 at 12:57
Dan MillsDan Mills
11.7k11124
answered Mar 28 at 12:57
Dan MillsDan Mills
11.7k11124
11.7k11124
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
Mar 28 at 13:11
$begingroup$
The classics are by Tobey, Graeme, Huelsman; two good books
$endgroup$
– analogsystemsrf
Mar 28 at 16:23
1
$begingroup$
What is NG for a TIA? Infinite (Rg=0)?
$endgroup$
– Gianluca G
Mar 28 at 20:28
add a comment |
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
Mar 28 at 13:11
$begingroup$
The classics are by Tobey, Graeme, Huelsman; two good books
$endgroup$
– analogsystemsrf
Mar 28 at 16:23
1
$begingroup$
What is NG for a TIA? Infinite (Rg=0)?
$endgroup$
– Gianluca G
Mar 28 at 20:28
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
Mar 28 at 13:11
$begingroup$
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
Mar 28 at 13:11
$begingroup$
The classics are by Tobey, Graeme, Huelsman; two good books
$endgroup$
– analogsystemsrf
Mar 28 at 16:23
$begingroup$
The classics are by Tobey, Graeme, Huelsman; two good books
$endgroup$
– analogsystemsrf
Mar 28 at 16:23
1
1
$begingroup$
What is NG for a TIA? Infinite (Rg=0)?
$endgroup$
– Gianluca G
Mar 28 at 20:28
$begingroup$
What is NG for a TIA? Infinite (Rg=0)?
$endgroup$
– Gianluca G
Mar 28 at 20:28
add a comment |
$begingroup$
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.
answered Mar 28 at 14:53
JamesJames
934
$endgroup$
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
Mar 28 at 15:56
add a comment |
$begingroup$
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.
answered Mar 28 at 14:53
JamesJames
934
$endgroup$
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
Mar 28 at 15:56
add a comment |
$begingroup$
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.
answered Mar 28 at 14:53
JamesJames
934
$endgroup$
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.
answered Mar 28 at 14:53
JamesJames
934
answered Mar 28 at 14:53
JamesJames
934
answered Mar 28 at 14:53
JamesJames
934
answered Mar 28 at 14:53
JamesJames
934
934
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
Mar 28 at 15:56
add a comment |
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
Mar 28 at 15:56
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
Mar 28 at 15:56
$begingroup$
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
Mar 28 at 15:56
add a comment |
$begingroup$
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
answered Mar 28 at 13:11
analogsystemsrfanalogsystemsrf
15.9k2822
$endgroup$
add a comment |
$begingroup$
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
answered Mar 28 at 13:11
analogsystemsrfanalogsystemsrf
15.9k2822
$endgroup$
add a comment |
$begingroup$
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
answered Mar 28 at 13:11
analogsystemsrfanalogsystemsrf
15.9k2822
$endgroup$
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
answered Mar 28 at 13:11
analogsystemsrfanalogsystemsrf
15.9k2822
answered Mar 28 at 13:11
analogsystemsrfanalogsystemsrf
15.9k2822
answered Mar 28 at 13:11
analogsystemsrfanalogsystemsrf
15.9k2822
answered Mar 28 at 13:11
analogsystemsrfanalogsystemsrf
15.9k2822
15.9k2822
add a comment |
add a comment |
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$begingroup$
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
Mar 28 at 12:34
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
Mar 28 at 12:40
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
Mar 28 at 12:43
$begingroup$
It's a video amplifier so why are you even considering as a TIA?
$endgroup$
– Andy aka
Mar 28 at 12:45
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
Mar 28 at 12:52