J. Fan, J. Talman, A. Fleischman, and S.L. Garverick (USA)
Low noise, high-voltage, limiter, ultrasonic imaging
An ultrasonic preamplifier with integrated active limiter circuit and high-voltage coupling capacitor was designed for a high-frequency, intravascular ultrasonic imaging (IVUS) system. The preamplifier provides modest gain, while the active limiter circuit protects the amplifier from the high-voltage transmit pulse, 100 Vp with 25-ns width. The high-voltage coupling capacitor was also integrated to achieve a total size of 0.95 mm by 1.25 mm. The chip was fabricated using a standard 0.35-m CMOS process. The input-referred noise for the amplifier was measured to be 1.9 nV/Hz1/2 , which was optimized for the 2-mm transducer capacitance. The 3-dB cutoff frequen cies of the amplifier are 6 MHz and 95 MHz. The com plete circuit was pulsed repeatedly with a 100-Vp pulse generator, with no observed effect on the amplifier. The recovery settling time from this transmit pulse is less than 1 s. Total power consumption, including preamplifier and 50-ohm buffer, is just 35 mW from a dual current supply.
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