In this paper, an electrocardiographic (ECG) signal processing IC, which is used for portable biomedical application, was designed using continuous-time technique. The circuit consists of an instrumentation amplifier (INA) with driven-right-leg circuit (DRL), a 5th order G/sub m/-C low pass filter (G/sub m/-C LPF) operating in sub-threshold mode, and amplifiers. DRL circuit is used to detect small amplitude signal in the presence of large common-mode voltage from the human body. The CMRR of the INA is 78 dB and the G/sub m/-C LPF has a cutoff frequency of 18 Hz. As a result of using the DRL, a small signal can be detected in the presence of large common-mode differential. The circuit consumes 1.23 mW when operating from with a supply voltage of /spl plusmn/1.5-V and occupies a core area of 0.94 mm/sup 2/. The circuit was designed in a 0.35/spl mu/m CMOS process and simulation results have successfully demonstrated the functionalities.