| Image sensors play a very important role in the production, living and scientific research. The signal extraction circuit integrated with the pixel can greatly improve the performance and reduce the cost of sensors. Because of the rapid development of CMOS process, CMOS image sensors can achieve this goal. The AGC (Automatic Gain Control) amplifier is an important module in the signal extraction circuit of the CMOS image sensor, which can improve the dynamic range of the CMOS image sensor.In this paper, the theoretical of AGC amplifier was analyzed, which showed that KYGA and KDFT should take great value to make the error of the AGC loop small, and also made a conclusion that the loop settling time is independent of the magnitude of the input step signal characteristics. The module AGC amplifier of the CMOS image sensor’s signal extraction circuit was designed in standard CMOS process to meet the requirement of integrating the extraction circuit with the pixel. In the design, the variable gain amplifier (VGA) used a linear transconductance to increase the linearity larger, and used two stage VGA to increase the gain dynamic range; a peak detection was designed to monitor output signal size, and use a MOS in the threshold forming the micro current to discharge in the peak detector; a simple structure of voltage shifting was designed for corresponding to the peak signal with the VGA gain control signal; a bandgap reference not needing the start circuit was designed as the bias voltage reference source of the whole circuit.This AGC amplifier circuit was simulated, optimized and laid out by Cadence software. It used SMIC0.35um standard CMOS process and3.3V power supply voltage to verify each module, which all met the performance requirements. The layout areaed0.31um×0.22um. The AGC amplifier could compress100KHz signal from0.6m305mVto150m～350mV, realize54.12dB to7.36dB dynamic compression. The power consumption was3.63mW. The AGC amplifier could meet the requirements of most of CMOS sensors. |
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