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?
$begingroup$
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 12 hours ago
Linkyyy
54139
asked 15 hours ago
Gianluca GGianluca G
756
$endgroup$
|
show 3 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 12 hours ago
Linkyyy
54139
asked 15 hours ago
Gianluca GGianluca G
756
$endgroup$
$begingroup$
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
15 hours 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
14 hours 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
14 hours ago
$begingroup$
It's a video amplifier so why are you even considering as a TIA?
$endgroup$
– Andy aka
14 hours 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
14 hours ago
|
show 3 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 12 hours ago
Linkyyy
54139
asked 15 hours ago
Gianluca GGianluca G
756
$endgroup$
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 12 hours ago
Linkyyy
54139
asked 15 hours ago
Gianluca GGianluca G
756
edited 12 hours ago
Linkyyy
54139
asked 15 hours ago
Gianluca GGianluca G
756
edited 12 hours ago
Linkyyy
54139
edited 12 hours ago
Linkyyy
54139
edited 12 hours ago
Linkyyy
54139
54139
asked 15 hours ago
Gianluca GGianluca G
756
asked 15 hours ago
Gianluca GGianluca G
756
asked 15 hours ago
Gianluca GGianluca G
756
756
$begingroup$
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
15 hours 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
14 hours 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
14 hours ago
$begingroup$
It's a video amplifier so why are you even considering as a TIA?
$endgroup$
– Andy aka
14 hours 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
14 hours ago
|
show 3 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
15 hours 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
14 hours 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
14 hours ago
$begingroup$
It's a video amplifier so why are you even considering as a TIA?
$endgroup$
– Andy aka
14 hours 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
14 hours 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
15 hours 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
15 hours 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
14 hours 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
14 hours 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
14 hours 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
14 hours ago
$begingroup$
It's a video amplifier so why are you even considering as a TIA?
$endgroup$
– Andy aka
14 hours ago
$begingroup$
It's a video amplifier so why are you even considering as a TIA?
$endgroup$
– Andy aka
14 hours 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
14 hours 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
14 hours ago
|
show 3 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 14 hours ago
Dan MillsDan Mills
11.6k11124
$endgroup$
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
14 hours ago
$begingroup$
The classics are by Tobey, Graeme, Huelsman; two good books
$endgroup$
– analogsystemsrf
11 hours ago
$begingroup$
What is NG for a TIA? Infinite (Rg=0)?
$endgroup$
– Gianluca G
7 hours ago
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 14 hours ago
analogsystemsrfanalogsystemsrf
15.7k2822
$endgroup$
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 12 hours ago
JamesJames
703
$endgroup$
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
11 hours ago
add a comment |
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3 Answers
3
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 14 hours ago
Dan MillsDan Mills
11.6k11124
$endgroup$
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
14 hours ago
$begingroup$
The classics are by Tobey, Graeme, Huelsman; two good books
$endgroup$
– analogsystemsrf
11 hours ago
$begingroup$
What is NG for a TIA? Infinite (Rg=0)?
$endgroup$
– Gianluca G
7 hours ago
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 14 hours ago
Dan MillsDan Mills
11.6k11124
$endgroup$
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
14 hours ago
$begingroup$
The classics are by Tobey, Graeme, Huelsman; two good books
$endgroup$
– analogsystemsrf
11 hours ago
$begingroup$
What is NG for a TIA? Infinite (Rg=0)?
$endgroup$
– Gianluca G
7 hours ago
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 14 hours ago
Dan MillsDan Mills
11.6k11124
$endgroup$
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 14 hours ago
Dan MillsDan Mills
11.6k11124
answered 14 hours ago
Dan MillsDan Mills
11.6k11124
answered 14 hours ago
Dan MillsDan Mills
11.6k11124
answered 14 hours 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
14 hours ago
$begingroup$
The classics are by Tobey, Graeme, Huelsman; two good books
$endgroup$
– analogsystemsrf
11 hours ago
$begingroup$
What is NG for a TIA? Infinite (Rg=0)?
$endgroup$
– Gianluca G
7 hours ago
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
14 hours ago
$begingroup$
The classics are by Tobey, Graeme, Huelsman; two good books
$endgroup$
– analogsystemsrf
11 hours ago
$begingroup$
What is NG for a TIA? Infinite (Rg=0)?
$endgroup$
– Gianluca G
7 hours 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
14 hours 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
14 hours ago
$begingroup$
The classics are by Tobey, Graeme, Huelsman; two good books
$endgroup$
– analogsystemsrf
11 hours ago
$begingroup$
The classics are by Tobey, Graeme, Huelsman; two good books
$endgroup$
– analogsystemsrf
11 hours ago
$begingroup$
What is NG for a TIA? Infinite (Rg=0)?
$endgroup$
– Gianluca G
7 hours ago
$begingroup$
What is NG for a TIA? Infinite (Rg=0)?
$endgroup$
– Gianluca G
7 hours ago
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 14 hours ago
analogsystemsrfanalogsystemsrf
15.7k2822
$endgroup$
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 14 hours ago
analogsystemsrfanalogsystemsrf
15.7k2822
$endgroup$
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 14 hours ago
analogsystemsrfanalogsystemsrf
15.7k2822
$endgroup$
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 14 hours ago
analogsystemsrfanalogsystemsrf
15.7k2822
answered 14 hours ago
analogsystemsrfanalogsystemsrf
15.7k2822
answered 14 hours ago
analogsystemsrfanalogsystemsrf
15.7k2822
answered 14 hours ago
analogsystemsrfanalogsystemsrf
15.7k2822
15.7k2822
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$begingroup$
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 12 hours ago
JamesJames
703
$endgroup$
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
11 hours ago
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 12 hours ago
JamesJames
703
$endgroup$
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
11 hours ago
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 12 hours ago
JamesJames
703
$endgroup$
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 12 hours ago
JamesJames
703
answered 12 hours ago
JamesJames
703
answered 12 hours ago
JamesJames
703
answered 12 hours ago
JamesJames
703
703
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
11 hours ago
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
11 hours 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
11 hours 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
11 hours ago
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
15 hours 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
14 hours 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
14 hours ago
$begingroup$
It's a video amplifier so why are you even considering as a TIA?
$endgroup$
– Andy aka
14 hours 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
14 hours ago