大幅度CCD输出信号降噪的相关双取样电路

电荷耦合器件(CCD)的输出信号构成复杂,包含有典型的KTC、1/f等类型的噪声,需要进行专门处理后才能获得与入射光信号相对应的高信噪比信号。文章针对具有较大幅度的CCD输出信号,采用宽电压工作的独立运放满足幅度较大的信号处理要求;通过在同一个运算放大器上实现噪声保持及信号采样的形式,消除了不同通道增益差异对信号的影响,获得了较高线性度的信号处理效果;同时结合CCD驱动器的设计,获取相关双取样技术所需的采样及保持脉冲信号,增强了采样与CCD输出信号间的关联程度,从而进一步提高了相关双取样技术消除CCD噪声的效果。采用这种信号处理电路后,将原来噪声处理的水平从约22 mV提高到了约1 mV,并且在一种精密的位移测量系统中得到应用,最后就具体电路设计的难点及注意事项进行了阐述。

Correlated double sampling circuit for noise reduction of CCD output signal with large amplitude

As an image sensor, Charge Coupled Device（CCD） features good linearity, high dynamic range and very low readout noise. The output signal from CCD contains much noise such as KTC and 1/f noise and so on. In order to obtain the high S/N signal, some methods must be taken to reduce noise greatly. The single operational amplifiers with large working voltage range are adopted to meet the need of large amplitude signal process. The influence of the gain difference between the signal path and noise path can be eliminated greatly by executing noise hold and signal sampling in the same operational amplifier. Higher linearity signal can then be obtained. Because the signal sampling pulse and noise hold pulse for the correlated double sampling technology are obtained from the CCD driver at the same time, the correlative degree between CCD output signal and signal sampling is enhanced greatly, and the ability of eliminating CCD noise is improved for the correlated double sampling technology. The noise has been reduced from about 22 mV to 1 mV with the correlated double sampling technology which has been applied to a precise displacement measurement system. Some difficulties and attentions in virtual circuit design are also pointed out.