The thesis is composed of tow topics: a high performance current-balancing instrumentation amplifier (IA) for ECG (Electrocardiogram) monitoring systems and an IA with CMRR (Common-Mode Rejection Ratio) self-calibration. In the first topic, a high common mode rejection ratio (CMRR) and a low input referred noise instrumentation amplifier (IA) is presented for ECG applications. A high pass filter (HPF) with a small-Gm OTA using a current division technique is employed to attain small transconductance, which needs only a small capacitor in the HPF such that the integration on silicon is highly feasible. The proposed design is carried out by TSMC standard 0.18 £gm CMOS technology. CMRR is found to be 127 dB and the voltage gain is 45 dB according to the simulation results. The second topic discloses an instrumentation amplifier with CMRR self-calibration capability. The propose design is also carried out by TSMC standard 0.18 £gm CMOS technology. To achieve a CMRR of more than 80 dB, a calibration resistance string and a detection circuit have been utilized. The DC gain of the proposed design is 60 dB and the frequency bandwidth is bound in 10 KHz, which is adaptable for biomedical signal acquisition applications.