Resistorless BiCMOS voltage reference with isolated substrate potential for biomedical implants

This paper shows a resistorless BiCMOS voltage reference with isolated substrate potential for an inductively powered biomedical implant. The reference voltage source has been designed in a 350nm High Voltage BiCMOS process. The reference voltage is used as part of an biomedical implant system to generate the positive supply voltage V_DD and the substrate potential V_SS used as negative supply. Therefore the reference voltage has to be highly insensitive and independent on substrate variations. The proposed design shows 1.4% accuracy over process variations and mismatch. The line sensitivity was measured to be 4mV/V. Measurements have proven that the isolation of the output of the reference voltage from the substrate potential is working properly. The power supply rejection ratio without any filtering capacitor at 10Hz and 10MHz is lower than -60dB and -35 dB, respectively.