Body-Driven Enhanced-Impedance Current Source: An Approach to the Implementation of Low-Voltage Current-Steering D/A Converters

Regular Current-Steering D/A Converters (CS-DACs) using high-swing cascode current-source structures fail to operate with very-low supply voltages. In this paper, body-driven enhanced-impedance current cells have been employed to satisfy required characteristics of CS-DAC in low headroom voltage. In this technique, a body-driven amplifier increases the output impedance of a cascode current source without degrading its high-frequency behavior. A 1-V 10-bit 100MHz CS-DAC using the proposed current source structure has been designed and simulated in a 0.18um CMOS technology. Monte-Carlo simulations show that the probability of Spurious Free Dynamic Range (SFDR) of more than 60 dB is more than 90% for input frequencies up to Nyquist frequency, which confirms the proper operation of the converter in very low supply voltages.