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A small-size on-chip transformer-based digital isolator for power control systems is proposed. With a proposed pulse generation and detection scheme that enables a 5 V standard CMOS transistor to utilize GHz-band signals, transformer area is reduced to 1/4-1/8 that of conventional transformers. A test chip achieves a 2.5 kV isolation voltage, a 35 kV/us CMR, a 1.6 mA static current and a 250 Mbps data rate, all which are equal to or superior to those of optocouplers or conventional digital isolators. The developed technology greatly reduces the number of chips in power control systems by allowing integration of multiple isolators in a CMOS chip together with microcontrollers or gate drivers. Moreover, the high-speed low-power capability expands the application potential to include isolated serial links, controller area network (CAN), FlexRay, medical devices, displays, sensors, etc.