Help me with an amplifier

[collinjie]

Hello! I need an amplifer that can be used to amplify a voltage range from 10mV to 200mV. Because the voltage is quite low i can not find a suitable amplifer.
At the beginning, i choose MAX4190, but i find it is not suitable.

 

[Kral]

collinjie,
What are your gain, accuracy, bandwidth requirements?
Regards,
Kral

 

[collinjie]

to kral:
Gain=1.775, accuracy is ±0.01 and the bandwidth is not very important

 

[Kral]

collinjie,
Is the accuracy an absolute ratio or a %? In other words are you saying that the gain must be
1.775 +/- .01775
or
1.775 +/- .0001775
The reason I ask is that the op-amp offset parameters and bias current will affect the accuracy. The required tolerance will determine the quality of op-amp required in terms of offset voltage, offset current.
Regards,
Kral

 

[collinjie]

to kral :
thank you and you are absolutely correct.
The gain is 1.775±0.01 is acceptable. i am a greenhand thanks again

 

[Kral]

collinjie,
You are right. The MAX41490 is a video amplifier, not suitable for your application.
~
I would suggest using any Op-Amp that has a low input offset voltage spec, such as the Analog Devices AD8677.
~
If you need a non inverting amplifier, connect a feedback resistor RF from the output to the inverting input. Connect an input resistor Ri from the inverting input to ground. Use the non-inverting input to the OP-Amp as your amplifier input. The feedback resistor must be 0.775 X the input resistor.
~
For an inverting amplifier, connect the feedback resistor Rf from the Op-Amp output to the inverting input. Connect the input resistor Ri to the inverting input of the Op-Amp. The other end of the input resistor is your amplifier input. The feedback resistor must be 1.775 X the input resistor.
~
An instrumentation Amplifier, such as the Analog Devices AD8230 would also work, but it would be a more expensive solution. Most IAs have the capability of setting the gain with a single resistor. Again, you would have to use series or parallel combinations of resistors to get the correct resistor value
~
You won't be able to find standard resistor values that meet your resistor value requirements. You will have to use series or parallel combinations of resistors to get the correct value for either Rf or Ri, or the gain setting resistor, if you decide to use an IA. In addition, the resistor tolerances must be on the order of 0.5% to meet your accuracy requirements.
Regards,
Kral

 

[Miguel Gaspar]

Another excellent opamp is the LT1012 from linear technologies it is widely used in instrumentation circuits, like logaritmic amplifiers where precition is very important.
Youmust especify if you will use Pin In Hole or SMT tehcnology.
For SMT you can get 0.01% resistors.
For PIH you can use multiturns potentiometers.