This thesis consists of two subjects of research: eliminating, by avoidance or removal, the effects of different types of interference on small signal recording, and a body-sensor transmitter application utilizing piezo sensors. The first topic demonstrates ECG signal and noise signal recording in the presence of various types of interference. A low-pass filter is proposed to remove power-line interference of ECG signals, and a switch between high-pass filters before amplification is proposed to avoid motion artifacts in the ECG signal. Finally, a low-cost noise recording system for educational uses that can record and analyze the noise of resistors and amplifiers in the LabVIEW program is proposed. The second topic concerns the application of a body-sensor transmitter. The sensor uses piezo film and combines the characteristics of piezo film with the characteristics of the human body and can exchange information by capacitor coupling. The signal used in the body-sensor transmitter is designed for a fixed frequency using narrow band-pass filters and is received by receivers via four methods as confirmation. Finally, the charge amplifier designed to detect signals is fabricated using a 0.35£gm 2P4M CMOS process.