This paper presents an ultra-low power, high sensitivity configurable CMOS fluorescence sensing front-end for implantable biosensors at single-cell level measurements. The front-end is configurable by a set of switches and consists of three integrated photodiodes (PD), three transimpedance amplifiers (TIA) for detecting a current range between 1 pA up to 10 mA. Also, an ambient light canceling technique is proposed to make the sensor operate under different environmental conditions. The proposed front-end could be configured for ultra-low light detection or ultra-low power consumption. The circuit is designed and fabricated in a 0.35 mu m standard CMOS technology, and the measurement results are presented. The minimum integrated input-referred current noise is measured as 1.07 pA with the total average power consumption of 61.8 mu W at an excitation frequency of 80 Hz. For ultra-low-power configuration, the front-end has an average power consumption of 119 nW and input integrated current noise of 210 pA at an excitation frequency of 20 kHz.

This paper proposes a dynamic range (DR) extension technique based on a two-step conversion for high-sensitivity multi-element pseudo-resistive (MEPR) transimpedance amplifiers (TIA). In optical biomedical sensors targeted for fluorescence measurement applications, the front-ends high sensitivity and wide DR are critical for accurately recording cellular variations. In this work, the most significant bits (MSB) are extracted by a 2-bit current digital-to-analog converter (DAC) then the least significant bits (LSB) are extracted by a 10-bit successive approximation register (SAR) analog-to-digital converter (ADC). The current DACs are composed of identical pseudo-resistor (PR) elements used in the TIA feedback to make the MSB extraction robust against the process and mismatch variations. This technique preserves the linearity of the conversion while using the current DACs to improve the DR. The proposed front-end implemented in 65 nm CMOS technology achieves a DR of 72.3 dB with current detection of 1 pA up to 4.13 nA at a sampling rate of 1 kS/s. The total front-end consumes a power of 45 mu w from a 2.5 V supply.

This paper presents a CMOS optical analog frontend for an implantable fluorescence biosensor for single-cell measurements. The front-end is configurable by a set of switches and consists of three integrated photodiodes (PD), three transimpedance amplifiers (TIA) for detecting a current range between 1 pA up to 10 mA. Also, ambient light and dark current canceling technique is proposed to make the sensor operate at different environmental conditions. The proposed front-end could be configured for ultra-low light detection or ultra-low power consumption. The circuit is simulated at the post-layout level. The minimum integrated input-referred current noise is obtained as 546 fA at the average power consumption of 1 μW for bandwidth (BW) of 1.4 kHz. For ultra-low-power configuration, the front-end has an average power consumption of 24 nW and input integrated current noise of 210 pA with 50 kHz BW.