Design Of An 8-channel Serial 12bits Analog-to-Digital Converter

Design and implement of an 8-channel serial 12-bit ADC were described. Successive Approximation Register (SAR) is the configuration adopted. And multi-switch circuit and data register are integrated in the circuit to realize multi-channel and serial interface. The output of Band gap reference is 4.096V, the temperature coefficient is 15ppm/℃by optimizing the circuit. Moreover, the comparator is applied of a three-stage latch configuration. It not only realizes the high gain, but also decreases the system delay. An unique configuration of equal-valued poly-silicon resistors and rationed capacitors assembled is adopted in D/A converter implementation, which avoid the mismatch of big capacitors and minish the linear error because of the application of resistors.The circuit was fabricated on the 0.5μm process (N-well, double poly and double metal) of CSMC. Introducing the customize layout manually, the die chip is 2.5×2.2mm2. Finally, its performance has been tested. The result shows that the design satisfied the request. The converter time is 7.5μs, the converter bit is 12 bits, the operation current is 2.8 mA, and INL and DNL are within the 1LSB.Small size, low power and serial interface to connecting easily are the advantages of this kind of converter. So it is the best choice for the application, such as consumer electronic, medical instruments and portable products and so on.