Design of 8-bit low power SAR ADC in 45 nm for biomedical implants

The utilisation of low power SAR (Successive Approximation Register) Analog-to-Digital Converters holds significant importance in the domain of bio-medical signal acquisition. The present study showcases the utilisation of an 8-bit CMOS SAR-ADC for integration into the analog front end of bio-signal acquisition. The focus of this technology pertains to the monitoring of implanted bio-signal devices, with a specific emphasis on ECG/EEG signals. A capacitive digital-to-analog converter (DAC) is suggested as a means to attain power consumption in the microwatt range. This approach enables comparisons to be made without any energy consumption, leading to a substantial enhancement in energy efficiency. Furthermore, a comprehensive theoretical examination of comparator offset voltages has been conducted to enhance the offset performance of the comparator operating at low supply voltage. The analysis indicates that optimization of the comparator is achieved solely through the adjustment of transistor sizes, without the implementation of any specific offset cancellation techniques. Simulations indicate that the optimization of the offset voltage to approximately 5 mV occurs when there is variation in the common-mode input voltage at a 1 V supply. The proposed Analog-to-Digital Converter (ADC) layout has been successfully executed utilizing the 45 nm Complementary Metal-Oxide-Semiconductor (CMOS) technology. The Analog-to-Digital Converter (ADC) attains a Spurious-Free Dynamic Range (SFDR) of 64.02 dB and consumes 1.9 mu W of power at a sampling rate of 1.1 MHz and a supply voltage of 1 V.