An ultra-low noise linear-in-dB variable gain amplifier for medical ultrasound applications

Medical ultrasound is an imaging technique that uses high-frequency (0.5 to 30 MHz) sound waves to allow noninvasive examination of many different body parts like the heart, blood vessels, liver, kidneys, and developing fetuses. The latter is the most widely known use of medical ultrasound applications in the general public. Ultrasound waves are generated by a piezoelectric transducer, which is held against the patient´s body. By applying a voltage the transducer is mechanically deformed and acoustic sound waves are generated which then travel through the tissue of the body. In the process many reflections are being created while the waves are bouncing off various tissue interfaces. Since the transducers are bi-directional elements, they also function as the detectors for the returning sound waves. These returning waves are converted by the transducers into electrical signals that are propagated via a cable to the imaging system for all the signal processing. The amplifier presented here represents the state-of-the-art in low noise variable gain amplifiers. It took the already widely regarded original X-AMP design and improved on it by: eliminating the offset ripple; stabilizing the gain ripple verses temperature; adding a preamplifier to reduce source loading; significantly lowering the noise; making the X-AMP single supply allowing for a fully differential input