In a correlating device, two switched-capacitor-type analog signal integrators are connected in cascade. The analog signal integrator in the first stage samples an analog input voltage at a predetermined cycle, determines the sign of the sampled value according to a binary-code sequence, integrates the sampled value, and outputs the resultant value. The analog signal integrator in the next stage samples an input voltage at a reset cycle of the analog signal integrator in the first stage, integrates the sampled value, and outputs the resultant value. This structure can prevent saturation of the correlating device without decreasing the gain of each analog signal integrator to a greet degree even when the sequence length becomes longer. Therefore, even if a high operation speed is required and if the sequence length of the binary-code sequence becomes longer, it is possible to provide a correlating device capable of achieving both an improvement of the operation accuracy and a reduction in the power consumption at a time.
In the present invention of Correlated Modulation Imaging (CMI), the weak optical image signal (and therefore the signal current) is modulated, and the signal integration direction is correlated to the modulation. Therefore, the dark and/or background current, which are not modulated, are cancelled, while the signal current is integrated. As a result, the total integration time of the signal of each pixel is increased, and its signal to noise ratio and dynamic range are improved. Besides, the CMI noise spectrum peaks at the modulation frequency, and therefore, the detector's 1/f and other low frequency noises can be suppressed. In the present invention, the method and theory of CMI, as well as the means and steps for the realization of CMI, are explicitly developed. Two versions of CMOS devices (CMI unit pre-amplifier version 1 and 3), with their circuitry design and testing data are presented as the critical component for correlated modulation imaging. A prototype chip of the CMI circuitries has been fabricated by the MOSIS 0.5-micron foundry. SPICE circuitry simulation has demonstrated the functioning of CMI unit pre-amplifier version 1 and 3 as designed. Experimental work has demonstrated the functioning of CMI unit pre-amplifier version 1 as designed, as well as the key features of CMI--increase of integration time, and improvement of signal to noise ratio and dynamic range.
System and method for a multi-standard sigma-delta modulator. A preferred embodiment comprises an integrator coupled to a signal input, wherein the integrator is configured to sum a difference between an input signal and an output of the sigma-delta modulator. A dithering circuit, also coupled to the signal input, is used to produce a dithering sequence. A summing point combines an output of the integrator and the dithering circuit while a quantizer converts the combined outputs into one of several discrete levels. The sigma-delta modulator further comprises a reset circuit to reset the sigma-delta modulator if the integrator becomes saturated. The sigma-delta modulator, as described, is compatible with G.Lite, ADSL, and ADSL+ variants of the digital subscriber line technical standards.
