Network-on-chip (NoC) has been used as the new on-chip communication paradigm. Asynchronous NoCs are power efficient and robust to process variation but they are slow. One reason for the low speed is the way that asynchronous routers use to build wide channels. To meet the bandwidth requirement, current routers broaden their channels by synchronizing multiple sub-channels. The C-gate and buffer trees introduced by the synchronization increase the cycle period. A new flow control method is proposed to use multiple independent sub-channels to transmit data. Since the synchronization is removed, the cycle period of all sub-channels are reduced speeding up the network. Two routers, one using multiple independent sub-channels and one using the synchronized wide channel, are implemented at the layout level. The simulation results show that the new router using multiple independent sub-channels reduces the router latency and the cycle period without any area overhead. The new flow control method may introduce an extra cycle to the average frame latency but this is compensated by the reduced cycle period provided that the frames are long enough.