A low offset current readout circuit for current mode image sensor
Current mode image sensors convert light signals into current signals,and during the readout phase the pixel cell needs to be biased to a clamping voltage to ensure that it is in the triode region.Aiming at the clamping voltage error in the current mode image sensor readout circuit,a low offset readout circuit based on the switched-capacitor has been proposed,which contains a clamping module,an offset correction module and a current readout module.The clamping module consists of an operational amplifier and a feedback transistor for biasing the pixel cell to a clamping voltage.The offset correction module consists of the capacitor and switch for storing and correcting the offset voltage of the clamping module.The current readout module consists of a current mirror for reading out the pixel cell current to the next level of circuitry.The operating phase of the offset correction module consists of an offset storage phase and an offset correction phase,which utilize the corresponding switching timing to store and correct the offset voltage of the clamping module,reduce the error of the required clamping voltage of the current mode image sensor,and improve the accuracy of the current readout.The circuit is designed in a 55 nm CMOS process.The results show that the 3σ error value of the clamping voltage is reduced from 5.01 mV to 0.45 mV,and the effective number of bits of the current readout circuit is 11.62 bits.At a 1.2 V supply voltage,the maximum power consumption is 240 μW.The layout area of the column current readout circuit is 2 400 μm2.
current mode image sensorreadout circuitclamping voltageswitched-capacitorlow offset
万方数据
维普
