A CMOS-only R-2R ladder D/A converter for image sensor applications

This paper presents a monotonic CMOS-only R-2R ladder D/A converter to be used in a single-slope A/D converter for image sensor applications. It employs complementary switches with dummy transistors in the ladder to reduce the glitch energy of the output. This does not affect the monotonicity of the ladder and adds less than 0.5% to the total mismatch variations. The estimate of the mismatch variations results in 99.5% of probability for monotonic behavior of the fabricated chips. The complete D/A converter was implemented in a standard 0.35 ¿m CMOS process and occupies an area of only 0.03 mm
²
. Post-layout simulations showed that the DNL graph does not exceed the range of ± 1 LSB, which indicates a monotonic behavior of the D/A converter. The average power consumption for the conversion of a full digital cycle is 0.55 mW.