The Design of a Low Noise and Low Power Current Readout Circuit for Sub-pA Current Detection Based on Charge Distribution Model

In this article, we proposed an analytical model based on charge distribution for switched- capacitor trans-impedance amplifiers (SCTIAs). The changes in the load state of the amplifier under different operating conditions and the influence of the gain of the operational amplifier (Opamp) on the trans-impedance gain are analyzed to improve the design theory of switched-capacitor trans-impedance amplifiers. According to the conclusion drawn from the analysis, the trans-impedance amplifier (TIA) has been designed by adopting "correlated double sampling technology" and "cross-connection technology" to optimize input-referred noise current, power consumption, and trans-impedance gain. As a result, the trans-impedance gain reaches up to 206 dB, while the bandwidth is 3 kHz. The current readout system achieves an input-referred noise current floor of 2.96 f A / root Hz at 1 kHz, and the power consumption of the system is 0.643 mW. The circuit has been simulated with the technology of 0.18 mu m, and the layout area is 1000 mu m x 500 mu m.