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110dB gain

Hi,
I design an amplifier circuit with a very high gain for ultrasonic flaw detector. Modern flaw detectors (http://www.olympus-ims.com/en/epoch600/) have gain up to 110dB and a bandwidth from 0.2MHz to 20MHz. My calculations show that if I will use an amplifier with gain 110dB, with a noise density 0,7nV/rtHz, 1MHz bandwidth, then the noise will be equal to ~2Vp-p and will be more then input span of the ADC. This calculation for ideal conditions, taking into account only the noise of the amplifier.

How do they do it? How to achieve this amplification?

  • Hi Maksim,

    I know very little about ultrasound fault detectors.

    However, one way to reduce the equivalent input noise is by using "active feedback", similar to the scheme used in the LM96511.

    Also, off-the-shelf broadband (including DC) op amps may not be a good comparison as the dedicated / ASIC amplifier used for these applications may be able to take advantage of optimization techniques (e.g. lowering the base resistance, tuning, lowered temperature, high power biasing, etc.) to achieve the ultimate low noise.

    May be somebody with first-hand expertise in this area can chime in with specifics?

    Regards,

    Hooman