A 7 mW 20 MHz BW Time-Encoding Oversampling Converter Implemented in a 0.08 mm$^{2}$ 65 nm CMOS Circuit

This work presents an area- and power-efficient realization of a new time-encoding oversampling converter (TEOC) consisting of a third-order continuous time (CT) loop filter and a self-oscillating pulse-width modulator (PWM). The modulator displays similar performance to that of a standard multibit CT-ΣΔ modulator but has the complexity of a single bit design. The time-encoding quantizer (TEQ) is implemented inside a ΣΔ modulator by replacing a multibit quantizer. An innovative TEQ is used to overcome design issues in a 1.0 V supply-voltage 65 nm digital CMOS technology. The TEQ allows an exchange of amplitude-resolution by time-resolution. The approach of time-resolution alleviates the scaling difficulties of mixed-signal circuits in nano-scale technologies. The TEOC features a 63 dB dynamic-range and a peak-SNDR of 61 dB over a 20 MHz signal bandwidth. Clocked at 2.5 GHz, the complete ADC consumes 7 mW from a single 1.0 V supply, including also the reference buffers. The ADC core results in an attractively small area of 0.08 mm
²
and in a figure-of-merit (FoM=Pwr/2 · BW · 2
^ENOB
) of 0.17 pJ/conversion-step.