The op amps typically used in instrumentation amplifier designs are low power precision op amps without much drive capability, so values at least in the kΩ range are typically needed so the op amps can drive them. Note that the ratios for the gain stage are independent of the ratios for the difference amplifier stage. Matt
Could I get your help? I need to amplify a ground referenced input voltage (range = 1mV to 150mV) by a gain factor of 10X (i.e to get 10mV to 1500mV)out for an A2D converter. My problem is, trying to do this in the most cost efficient manner. Since this needs to be accurate, linearity and near ground performance are mandatory. I have wondered in the past how chips like the ICL-7107 3-1/2 digit DVM on a chip accomplished this without a negative supply. The system utilizes a single supply but I have made small negative converters before but need to try and stay simple for cost. Would you know how the DVM chip did this or what I can do? Thanks for any help you might have.
@izan009 You are welcome... we are working on more whiteboard videos. P.S. Thanks also for your comment on the Noise of an Instrumentation Amplifier Circuit video
Hi Matt. Do you prefer using AD620 IC (Instrumentation amplifier IC) for measuring PT100 RTD from 10 degrees Celsius up to 90 degrees celsius to amplify its millivolts to 0 to 5 volts? If not, then what would you prefer? BTW, great lecture. Thanx
Hello, The first stage’s purpose is to provide high input impedance and gain. The 2nd stage’s purpose is to remove the common mode voltage; in other words, change from a differential signal to a voltage referred to the voltage on the reference pin.
Resistor values were drawn without units to emphasize that the resistor ratios set the gain. So the 1 and 1.5 values could be 1 kΩ and 1.5 kΩ, or could be 10 kΩ and 15 kΩ, or could be 3 kΩ and 4.5 kohm. The values depend on the tradeoff you want to make between power consumption vs. noise and bias current error.
How are you calculating the 2.5V and the -1.5V???? Will this amp work if you connect the reference to the -Vin pin.... just to get output voltage progressing upwards from 0V, from a bridge sensor??
pat60606 Start with 0.5V common mode and 1V differential. Gain differential by 4. Signals at outputs of first stage op amps are 0.5V - 4V/2 = -1.5V and 0.5V + 4V/2 =2.5V. Because our first stage op amp does not have a negative supply it can’t drive the -1.5V, regardless of the reference pin voltage.
@pat60606 an easier way to understand the 2.5V and -1.5V is considering each amplifier for IN - and IN+ independently. In this way you have non-inverting configurations where the output is just [(1+1.5/1)*Vp] - [(1.5/1)*Vn). For the top amplifier (IN-) Vp = 0V and Vn = 1V, then Vo = -1.5V. Similarly for the bottom amplifier (IN+) Vp = 1V and Vn = 0V, therefore Vo = 2.5V. In the video I think he just got them switched but the rest of the explanation is correct. @AnalogDevices could you confirm?
Hello.. it was a really informative lesson. This is more like the circuit I have to design for a project. Could please help. I am connecting a Wheatstone bridge with 350 ohm resistors, to an instrumentation amplifier. Could you please explain more on the gain stage and differential amplifier stage? What are the exact tasks done by these stages and so on. Thanks in advance.
How do you become an applications engineer? Seems like the kind of thing you'd need a careers worth of industry experience to do. Great videos, thanks.
Typically this should be given in the instrumentation amplifier datasheet, but in common mode and differential. If not given, you can measure cm impedance, by applying a common mode voltage, and then changing it and measuring the current difference. Or to measure diff impedance, apply a differential voltage with common mode of 0, and then apply a different differential voltage and measure the change in current. You must make two measurements - if you only make one, you won't be able to cancel out the effect of the bias current.
Hey Luis, You don't have to calculate it. Generally it's listed in the datasheet for the instrumentation amplifiers. For example the AD8421 datasheet lists an input impedance of 30 Gohms in parallels with 3 pF.
+ANTALIFE thank you :) its been a while. I implemented this circuit and it was so much fun to do that.We call Vs as Vcc most of the time thats why i confused. Thank you
Great lesson, very clear and informative! At TMD Technologies, we are one of the world's leading manufacturers of microwave tubes, high voltage power supplies, and transmitters for Radar, EW, Communications, EMC RF testing, and other Laboratory applications. You can find out more about our products and the technologies behind them at tmd.co.uk
Introduced in a lecture on sensors at a Japanese university.It was easy to understand.
Hello elnocho3, I can adjust the order of the videos. What order/arrangement would you like? Thanks
The op amps typically used in instrumentation amplifier designs are low power precision op amps without much drive capability, so values at least in the kΩ range are typically needed so the op amps can drive them. Note that the ratios for the gain stage are independent of the ratios for the difference amplifier stage.
Matt
Could I get your help?
I need to amplify a ground referenced input voltage (range = 1mV to 150mV) by a gain factor of 10X (i.e to get 10mV to 1500mV)out for an A2D converter. My problem is, trying to do this in the most cost efficient manner. Since this needs to be accurate, linearity and near ground performance are mandatory. I have wondered in the past how chips like the ICL-7107 3-1/2 digit DVM on a chip accomplished this without a negative supply. The system utilizes a single supply but I have made small negative converters before but need to try and stay simple for cost. Would you know how the DVM chip did this or what I can do?
Thanks for any help you might have.
Learned something new thank you sir
@izan009 You are welcome... we are working on more whiteboard videos. P.S. Thanks also for your comment on the Noise of an Instrumentation Amplifier Circuit video
Hi Matt. Do you prefer using AD620 IC (Instrumentation amplifier IC) for measuring PT100 RTD from 10 degrees Celsius up to 90 degrees celsius to amplify its millivolts to 0 to 5 volts? If not, then what would you prefer? BTW, great lecture. Thanx
Hello, The first stage’s purpose is to provide high input impedance and gain. The 2nd stage’s purpose is to remove the common mode voltage; in other words, change from a differential signal to a voltage referred to the voltage on the reference pin.
Resistor values were drawn without units to emphasize that the resistor ratios set the gain. So the 1 and 1.5 values could be 1 kΩ and 1.5 kΩ, or could be 10 kΩ and 15 kΩ, or could be 3 kΩ and 4.5 kohm. The values depend on the tradeoff you want to make between power consumption vs. noise and bias current error.
How are you calculating the 2.5V and the -1.5V???? Will this amp work if you connect the reference to the -Vin pin.... just to get output voltage progressing upwards from 0V, from a bridge sensor??
pat60606 Start with 0.5V common mode and 1V differential. Gain differential by 4. Signals at outputs of first stage op amps are 0.5V - 4V/2 = -1.5V and 0.5V + 4V/2 =2.5V. Because our first stage op amp does not have a negative supply it can’t drive the -1.5V, regardless of the reference pin voltage.
but the formula for V1 is V1=(Vcm +( Vd/2)).
and not (Vcm + Gain/2)
@pat60606 an easier way to understand the 2.5V and -1.5V is considering each amplifier for IN - and IN+ independently. In this way you have non-inverting configurations where the output is just [(1+1.5/1)*Vp] - [(1.5/1)*Vn). For the top amplifier (IN-) Vp = 0V and Vn = 1V, then Vo = -1.5V. Similarly for the bottom amplifier (IN+) Vp = 1V and Vn = 0V, therefore Vo = 2.5V. In the video I think he just got them switched but the rest of the explanation is correct.
@AnalogDevices could you confirm?
mr.matt duff i need a project video based on amplifiers using only IC741 and IC555
Hello.. it was a really informative lesson. This is more like the circuit I have to design for a project. Could please help. I am connecting a Wheatstone bridge with 350 ohm resistors, to an instrumentation amplifier. Could you please explain more on the gain stage and differential amplifier stage? What are the exact tasks done by these stages and so on. Thanks in advance.
How do you become an applications engineer? Seems like the kind of thing you'd need a careers worth of industry experience to do. Great videos, thanks.
Are your resistor values in ohms or kohms?
Hi Matt. I love your videos. Dont you think you should interchange voltages you write at time 2:57?
Yes. I think I figured this out around 3:22. I'll see if we can add a note or something.
So nice thanks
So nice
can you explain how to solve this problem with more details ?
Hello Hassan, please visit ez.analog.com/community/amplifiers to ask additional questions. Thanks
Greetings, i have a question? How do we calculate the input impedance of an Instrumentation Amplifier?
Typically this should be given in the instrumentation amplifier datasheet, but in common mode and differential. If not given, you can measure cm impedance, by applying a common mode voltage, and then changing it and measuring the current difference. Or to measure diff impedance, apply a differential voltage with common mode of 0, and then apply a different differential voltage and measure the change in current. You must make two measurements - if you only make one, you won't be able to cancel out the effect of the bias current.
Thank you very much. I am making Bioinstrumentation amplifiers using TL084s, i did not know how to measure impedance. They work pretty well!
Hi Matt how would you calculate input impedance for the circuit you are talking about "Instrumentation Amplifier" Thanks in advanced
Hey Luis, You don't have to calculate it. Generally it's listed in the datasheet for the instrumentation amplifiers. For example the AD8421 datasheet lists an input impedance of 30 Gohms in parallels with 3 pF.
0.5v common mode signal?
Hi, i am an electrical eng student, what is that Vs?
+Vs is +ve rail supply voltage e.g. +5V
-Vs is -ve rail supply voltage e.g. -5V or GND
+ANTALIFE thank you :) its been a while. I implemented this circuit and it was so much fun to do that.We call Vs as Vcc most of the time thats why i confused. Thank you
Nice, am in the process of learning about instrumentation amps myself. Can't wait to get something put together :D
Great lesson, very clear and informative! At TMD Technologies, we are one of the world's leading manufacturers of microwave tubes, high voltage power supplies, and transmitters for Radar, EW, Communications, EMC RF testing, and other Laboratory applications.
You can find out more about our products and the technologies behind them at tmd.co.uk