A CMOS 8-bit, 40 MS/s, folding and Interpolation A/D converter with single 5V power supply has been designed for ultrasound imaging system. Owing to output interpolating technique in the pre-amplifier used in the flash type ADC, the number of pre-amp was reduced by half. As a result, the low power consumption and low input capacitance are obtained. To make insensitive to the influence of the input differential pair offset, resistive averaging technique was used. In the interpolation block, buffer with positive feedback loop was substituted for conventional source follower type buffer. By doing this, the gain of the interpolation circuit approaches unity. In addition, the comparator kick-back noise is reduced by locating switch properly in latch structure. This A/D converter achieves a clock frequency of 100MHz with an analog power dissipation of 40mW, and 0.5pF low input capacitance. In designing this ADC, 0.8um ETRI CMOS model was used.
