A capacitively coupled digital isolator with CMTI of 160 kV/μs and data rate of 230 Mbps

Abstract

—This paper presents a capacitively coupled digital isolator with superior Common Mode Transient Immunity (CMTI) and high performances. This work adopts the On-Off Keying (OOK) architecture to cancel the influence of Common Mode Transient (CMT) and increase the speed performances. In addition, it adopts a fast-transient-response architecture for the Schmitt trigger to further improving the speed performances. Besides, this work proposes a gate-cross-coupled common-gate pre-amplifier with an active zero load, amplifying the signal after the isolation capacitance. By applying the proposed technique, the high-frequency gain retains to high value, while the low-frequency gain is greatly attenuated. It employs an envelope-comparator, an integrator and a filter as demodulator to reduce the propagation delay and speed up the data rate. Fabricated in a 0.18 μm CMOS process, the chip achieves 160 kV/μs CMTI, 230 Mbps data rate, 6 ns propagation delay, 1.5 mA dynamic current and 14 kV isolation breakdown voltage with the area of the isolation capacitance of 2 × 104 μm2.