A 10-b 75-MSPS subranging A/D converter with integrated sample and hold

The design of a fully differential two-step analog-to-digital converter (ADC) is presented. A sample-and-hold (S/H) circuit based on a unity-gain feedback amplifier, flash ADCs driven by differential resistor ladders, and a differential digital-to-analog converter (DAC) combined with the subtractor are described. The chip has been fabricated in a standard high-speed bipolar process and, by extensively utilizing compensation techniques, achieves +or-1 LSB integral nonlinearity and low harmonic distortion. A 75 Msample/s conversion rate not yet exceeded even by full-flash 10-b ADCs, has been achieved with a power consumption of 2 W. Due to the S/H circuit, the input bandwidth of 250 MHz; the effective resolution of 9 b at 5 MHz exhibits a gradual decrease over input frequency but still remains above 8 b up to 50 MHz. >

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