Three different topics associated with their respective applications are proposed in this thesis. The first topic is the implementation of a transimpedence preamplifier for 16 Mbps infrared transceiver modules. The design of the preamplifier is aimed at the VFIR (very fast infrared) which is supposed to provide a 16 Mbps data transmission rate. The second topic is focused on the implementation of a robust reference clock generator design for DDR synchronous devices. A pulse generator circuit to generate pulses corresponding to the rise edges and fall edges of a given clock is presented. The third topic is to carry out a cost-effective voice dialer. It focuses on the voice feature extraction and the recognition of Chinese numbers 0 to 9. We present a low-cost method to implement such an algorithm by using 8051-ICE.