Asynchronous circuit design has been long regarded as a way for solving the problems of synchronous circuit design such as clock skew, worst case delay and heavy global clock loading. Conventional asynchronous circuits consist of a stage controller (Ctrl), completion detection circuit (CD), functional logic block, and latch. The completion detection circuit is the key element for high performance asynchronous circuits since it provides the timing information for the stage controller to control the operation of the asynchronous pipeline. In this paper, a new completion detection circuit has been proposed using partial voltage swing. The proposed circuit can achieve higher performance and lower power than the previous CD design for detecting a large number of outputs. Experimental results show that the proposed completion detection circuit has 5%-18% better performance and can save up to 90% of the dynamic power compared with previous designs.