A low power impulse radio ultra-wideband (IR-UWB) receiver for DC-960MHz band is proposed in this paper. The proposed receiver employs multiple DC power-free charge-domain sampling correlators to eliminate the need for phase synchronization. To alleviate BER degradation due to an increased charge injection in a subtraction operation in the sampling correlator than that of an addition operation, a comparator with variable threshold (=offset) voltage is used, which enables an addition-only operation. The developed receiver fabricated in 1.2V 65nm CMOS achieves the lowest energy consumption of 17.6pJ/bit at 100Mbps in state-of-the-art correlation-based UWB receivers.