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Low Voltage DC Amplification

Ahsan Noor Khan
Prodigy 180 points
Other Parts Discussed in Thread: INA333

Hi,

I am a Doctoral student and working on Human Bio Sensors. The sensor is converting body temperature in to an Electrical Signal (DC Voltages). The range of DC voltages is between 2 - 5 mV with 1 nW of Power. I have to amplify these voltages to 3 V. Is there any amplifier  which can solve my purpose ?

In addition, the output voltages are not PURE DC. There are probably AC components. So what other component I require to get Pure DC Amplified Voltages at the output ?

Thanking you in anticipation.

Best Regards,

Ahsan

  • 0
    TI__Guru*** 140136 points
    Ahsan,

    5mV to 3V is a voltage gain of 600
    Having a 1% max error on a 2mV input requires an input offset error less than 20uV

    While this can be done with a signal op-amp, I suggest a two amplifier design. The first amplifier should have very low offset voltage and low noise. The second amplifier can have more offset and noise. Each stage would amplify by 24.5; 24.5^2 = 600

    First, you must decide how much error is acceptable and how much bandwidth is needed.
  • 0
    TI__Guru* 93105 points
    Hello Ahsan,

    Ron's points are well stated. A low noise, low offset op amp or instrumentation amplifier should be selected for the input amplifier stage(s) depending on the bio sensor output, single-ended or differential. Since you are ultimately interested in pure dc the ac waveform components would need to be rectified - converted to dc. An op amp based precision rectifier could be employed after the input amplifier stage(s). The precision rectification can be accomplished using an absolute value circuit such as this one covered in a TI Precision Design:

    www.ti.com/.../tidu030.pdf

    A nice feature of the absolute value circuit is a dc level applied to the input will be replicated at the output; +10 mV at the input will be seen as +10 mV at the circuit's output. Since it is an absolute value function a negative dc level such as -10 mV will be seen as +10 mV at the output as well. AC signals, up to about 1 kHz, would be rectified and converted to full-wave, pulsating dc signal.

    Since full-wave pulsating dc has significant ac ripple, the ripple would have to be smoothed to achieve a pure dc level at the output of the signal path. An active low-pass filter could be applied after the absolute value circuit to remove the ripple.

    Regards, Thomas
    Precision Amplifiers Applications Engineering
  • 0 in reply to Thomas Kuehl
    TI__Guru*** 140136 points
    Ahsan,

    If you want to keep the DC component and remove AC component use low pass filters. If you want to rectify and use the AC signal use Thomas' advice.
  • 0 in reply to Ron Michallick
    Prodigy 180 points
    Hi Ron,



    I need to know the type of Amplifiers which will be helpful to amplify my low voltages.

    Can you please refer me any amplifiers from TI ? I am unable to find amplifiers which can amplify such low voltages. (3-5 mV)

    Thanking you in anticipation.

    Best Regards
  • 0 in reply to Ahsan Noor Khan
    TI__Guru*** 140136 points
    Ahsan,

    An instrument amplifier would be best.
    www.ti.com/.../products.html
    INA333 is my suggestion for its low power