I design an amplifier circuit with a very high gain for ultrasonic flaw detector. Modern flaw detectors 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?