High Input Impedance OTA-Less NS-ADC with Chopped VCO for Multi-channel, Non-invasive EMG Monitoring

Abstract

Power, area, and input impedance are important parameters for multi-channel, non-invasive EMG monitoring. In addition, 1/f noise and 3rd harmonic due to nonlinearity must be considered. Recently, while dealing with the above problems, a VCO-based ADC has been high-lighted. VCO based ADC improved the efficiency by making the circuit digital-intensively. However, it still has 1/f noise, input impedance, and area issues. This paper focuses on solving the above problems in the simplest way. Chopping is applied directly to the VCO to eliminate 1/f noise. However, as a disadvantage, noise is generated every certain period, which degrades the noise performance of the entire structure. Total input capacitance(only bulk of the VCO is seen) are reduced by using DC-coupled input. Therefore, the input impedance is obtained to 1Gohm. The ADC structure based on open circuit obviates to consider DAC complexity. The elimination of the analog block further lowers power consumptions. Thus, the area occupies 0.028mm2 and ADC consumes 2uW. Also, by using bulk-driven VCO, we achieved 72dB of SFDR performance without any additional technique.