Proposed Prediction Adc Algorithm : Prediction, Judgement, And Final Conversion
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The proposed prediction ADC algorithm contains three key procedures: prediction, judgement, and final conversion. At the beginning, the prediction circuit generates common MSBs from a data memory that stores the digital results of the pixels in the previous row. Then the judgement circuit creates two analog boundary voltages based on the predicted MSB values and check whether the current pixel’s analog value is between the two boundary voltages based on Eq. (1). Finally, if the predicted MSB values are correct, the ADC only performs the LSB conversions. Otherwise, the ADC performs a full A/D conversion. This algorithm can be implemented with various ADC structures, e.g., single-slope ADC, SAR ADC, or cyclic ADC. Also different data…show more content… This can be achieved by using a voltage scaling DAC or a switched-capacitor DAC.
Examples of implementation options with different ADC types are shown in Fig. 5. In these examples, a 5-bit conversion is applied with the same input signal and the same scenario: (1) In Row1, since there are no previous rows, the prediction is not available, the conversion starts with the second step, which is a complete A/D conversion, (2) In Row2, the first step prediction is successful. So in the second step, only a partial A/D conversion needs to be performed. (3) In Row3, the first step prediction is failed and thus a complete A/D conversion is performed.
In the first example of Fig. 5 (a), a local DAC is applied to a judgement circuit for step 1 and an SAR ADC is used for step 2. In the conversion of Row1, a full SAR A/D conversion is performed. A simplified schematic of the SAR ADC is shown in Fig. 6. At the beginning of the conversion, switch SR is turned ON and switches S0, S1, S2, S3, and S4 are connected to GND to reset the capacitor array. Then SR is turned OFF, and S0-S4 are sequentially switched to VREF. During this process, if VCOMP is 0 then the switch remains at VREF, otherwise, it turns back to GND. The final position of S0-S4 is the conversion result. Next, in the conversion of Row2, assume the prediction circuit pick up the first three MSB values from Row1 as a prediction (in this case