Hi guys,
I am currently trying to amplify 1mV analog signal to 1V.
What is the best way to do that?

 

Design an amplifier string with a combined gain of 1000.

 

Bandwidth of interest?

 

Hi guys,
I am currently trying to amplify 1mV analog signal to 1V.
What is the best way to do that?

What frequency? For most op amps it may be difficult to get a gain of 1,000 at a high frequency.

 

Hi guys,
I am currently trying to amplify 1mV analog signal to 1V.
What is the best way to do that?

Gain-Bandwidth
The standard LM741 gets less gain as frequency increases. Under ideal designs you might get a gain of 1,000 at a frequency of 1,000 Hz (1 MHz GBW). If your frequency is greater than 1 KHz you need more than one stage.
To get an overall gain of 1,000 you need two stages of about 32. You might get that gain of 32 at up to 100 KHz.
So, what is your frequency?

 

AC
DC
common mode rejection
source impedance
input impedance
output impedance
load impedance
anything

ak

 

Hi guys,
I am currently trying to amplify 1mV analog signal to 1V.
What is the best way to do that?

Crude and unfinished ideas, but just to give you an idea. Battery powered was assumed. Two 9 V batteries.
Below 1 KHz only one op amp is necessary. Two op amps gets you up to 100 KHz.
Better op amps may get you better results. Definitely needed for frequencies above 100 KHz. No filtering is shown, not knowing what your frequency is.

 

What frequency? For most op amps it may be difficult to get a gain of 1,000 at a high frequency.

Bandwidth is 100Hz- 1KHz.
Little more details on my project.
I am designing driver for BLDC motor and I am using IC with build in shut of 3 mOhm.
The motor is small and the current is 0.42A without load up to 20A with max load at voltage 14VDC

 

View attachment 111057 View attachment 111056

Crude and unfinished ideas, but just to give you an idea. Battery powered was assumed. Two 9 V batteries.
Below 1 KHz only one op amp is necessary. Two op amps gets you up to 100 KHz.
Better op amps may get you better results. Definitely needed for frequencies above 100 KHz. No filtering is shown, not knowing what your frequency is.

Thank you hp1729,
Looks like your ideas are what I am looking for

 

Note that the bandwidth of the single 741 op amp circuit gives a -3dB rolloff at 1KHz for a gain of 1000, since the op amp has a gain-bandwidth of about 1MHz.
For less rolloff at 1kHz, you would need a higher gain-bandwidth op amp or the two op amp circuit.

 

Help us out a bit more. What IC are you using?

 

Help us out a bit more. What IC are you using?

It is STK984-090A-E.
According to specs, this IC has current sensing resistor with min 2.91 mOhm, typ 3mOhm, and max 3.09 mOhm

 

Note that the bandwidth of the single 741 op amp circuit gives a -3dB rolloff at 1KHz for a gain of 1000, since the op amp has a gain-bandwidth of about 1MHz.
For less rolloff at 1kHz, you would need a higher gain-bandwidth op amp or the two op amp circuit.

Certainly agreeable on a better op amp (and circuit). Would a single supply op amp be better for him?

 

You probably want tot select a high side current amplifier. e.g. http://www.linear.com/product/LTC6101

or maybe http://www.linear.com/product/LTC4151 to get the values into a computer as well.

You have more issues than just amplifying 1 mV.

 

You probably want tot select a high side current amplifier. e.g. http://www.linear.com/product/LTC6101

or maybe http://www.linear.com/product/LTC4151 to get the values into a computer as well.

You have more issues than just amplifying 1 mV.

What do you mean by more issues ?
The current measurement is for speed control and that control does not have to be very precise.
Also, I can get rotor speed calculating it from current's frequency through windings but that calculation gives me possibility to miss unwanted rotor's slip. I mean that calculation is not enough.

 

It is STK984-090A-E.
According to specs, this IC has current sensing resistor with min 2.91 mOhm, typ 3mOhm, and max 3.09 mOhm

that is motor driver... what exactly you wish to accomplish? measure current draw using sense resistor in the IC? this resistor is on high side and you don't want AC coupling.

 

that is motor driver... what exactly you wish to accomplish? measure current draw using sense resistor in the IC? this resistor is on high side and you don't want AC coupling.

I know that is a BLDC driver. I wan to measure the current on the high side and there is no AC coupling.
Due to high frequency of switching the drawn current is AC not DC. BLDC has AC current trough windings

 

i agree with suggestion in post #14

 

There are OP-amp selection issues when the common mode range exceeds the power supply. Standard run of the mill OP-amps won't cut it. The second choice allows the micro to read the values with an EXTRA part.

 

There are OP-amp selection issues when the common mode range exceeds the power supply. Standard run of the mill OP-amps won't cut it. The second choice allows the micro to read the values with an EXTRA part.

I got it now.
Thank you for clarifying that issues