Fast scan cyclic voltammetry (FSCV) is a technique that measures the concentrations of neurotransmitters in vivo or in vitro. Conventional FSCV uses a triangle waveform, which starts from -0.4V, sweeps to +1.3V and returns to -0.4V. It makes not only a large background signal, but also a small signal from oxidation and reduction of a neurotransmitter. These large background signals can be removed by a background subtraction technique which extracts only the oxidation and reduction signals. After that, analyze the subtracted signal to estimate the concentration of the neurotransmitter. It has a limit in detecting low-level concentration of neurotransmitter because a large quantization error comes from the wide range of analog-to-digital convertor (ADC). To measure low-level concentrations of a neurotransmitter, the range of the ADC was decreased to lower the quantization error. Even though using a narrow range of ADC has a low quantization error, it cannot measure the whole voltammagram. For this reason, the waveform is changed for the background signal to become flat, where the oxidation signal arises, and move these flat sections to ADC-range using hardware subtraction. Eventually, we can measure the oxidation signal in a narrow range with low quantization error.