Design Of CTIA Readout Circuit For Fluorescence Detection Biochip

Along with the increasing application of fluorescence detection technology in the field of life science,the demand for detecting weak light signals is becoming more and more large.There are many advantages in the Capacitive Trans-impedance Amplifier(CTIA)readout circuit based on CMOS image sensor,such as on chip integration,high gain,low noise and large flux.Point.But within the traditional read-out circuit,the weak light signal is influenced by the dark current and nonlinear effect caused by the bias voltage of the photodiode,which would directly restrict the accuracy and signal to noise ratio of the fluorescence detection readout circuit,so the traditional read-out circuit have not been to meet the fundamental demand of the fluorescence detection.In order to improve the system performance of fluorescence detection,the architecture of CTIA readout circuit system are presented,the working principle of the CTIA readout circuit system and the theoretical analysis of the noise performance are elaborated.In the CTIA circuit,a new dual gain structure is proposed,in which the low gain(LG)and high gain(HG)modes are controlled by a gain switch.Meanwhile,the Ttype switch designed in the deep well technology was applied to reduce the charge injection and leakage.In the sampling circuit system,the Correlated Double Sampling(CDS)is followed by a single end output integral circuit to form a noise reduction circuit,which achieves high precision and low noise by reducing system maladjustment and low frequency noise.At the same time,the CDS circuit also acts as the Sample and Hold circuit.There are characteristics of low power consumption and simple structure in the designed circuit.In the column amplifying circuit,programmable multi gain signal transmission is realized to meet the needs of different applications of the system.Based on the TSMC 65 nm CMOS technology,the designed circuit are simulated and verified with the Cadence platform.Measurement results showed that the nonlinear error is 0.96% in LG mode and 1.34% in HG mode.The designed circuit can detect the optical current of 244 pA and detect the dark current of 21.7fA at the same time.The signal to noise ratio(SNR)reaches 15 dB,which can basically meet the application requirement of the fluorescence detection.