We present the design of a low-power 4-bit 1GS/s folding-flash ADC with a folding factor of two in standard 65nm CMOS technology. The design of a new unbalanced double-tail dynamic comparator affords an ultra-low power operation and a high dynamic range. Unlike the conventional approaches, this design uses a fully matched input stage, an unbalanced latch stage, and a two-clock operation scheme. A combination of these features yields significant reduction of the kick-back noise, while allowing the design flexibility for adjusting the trip points of the comparators. As a result, the ADC achieves SNDR of 22.3 dB at 100MHz and 21.8 dB at 500MHz (i.e. the Nyquist frequency). The maximum INL and DNL are about 0.2 LSB. The converter consumes about 700μW from a 1-V supply yielding a figure of merit of 65fJ/conversion step. These attributes make the proposed folding-flash ADC attractive for the next-generation wireless applications.