21世纪的SAR ADC

chuxp

只有E文了，这应该是SC DAC例子中较容易理解的了。

For these reasons, switched capacitor (or charge-redistribution) DACs have become popular in newer SAR ADCs. The advantage of the switched capacitor DAC is that the accuracy and linearity is primarily determined by high-accuracy photolithography, which in turn controls the capacitor plate area and the capacitance as well as matching. In addition, small capacitors can be placed in parallel with the main capacitors which can be switched in and out under control of autocalibration routines to achieve high accuracy and linearity without the need for thin-film laser trimming. Temperature tracking between the switched capacitors can be better than 1 ppm/°C, thereby offering a high degree of temperature stability. Modern fine-line CMOS processes are ideal for the switched capacitor SAR ADC, and the cost is therefore low.

A simple 3-bit capacitor DAC is shown in Figure 3. The switches are shown in the track, or sample mode where the analog input voltage, A_IN, is constantly charging and discharging the parallel combination of all the capacitors. The hold mode is initiated by opening S_IN, leaving the sampled analog input voltage on the capacitor array. Switch S_C is then opened allowing the voltage at node A to move as the bit switches are manipulated. If S1, S2, S3, and S4 are all connected to ground, a voltage equal to –A_IN appears at node A. Connecting S1 to V_REF adds a voltage equal to V_REF/2 to –A_IN. The comparator then makes the MSB bit decision, and the SAR either leaves S1 connected to V_REF or connects it to ground depending on the comparator output (which is high or low depending on whether the voltage at node A is negative or positive, respectively). A similar process is followed for the remaining two bits. At the end of the conversion interval, S1, S2, S3, S4, and S_IN are connected to A_IN, S_C is connected to ground, and the converter is ready for another cycle.

Figure 3: 3-Bit Switched Capacitor DAC

原文链接：http://www.analog.com/en/analog-to-digital-converters/ad-converters/products/tutorials/CU_tutorials_MT-021/resources/fca.html