Study And Design Of Sigma_Delta Modulator Applied In Capacitive Touch Controller IC

Since2007, Apple introduced the first touch smartphone, touch technology cameinto the consumer electronics market and quickly integrated into electronic products topeople’s daily life. A wide variety of touch technology, such as resistive, SAW, infrared,capacitive, and so on. Undoubtedly, the most popular one in current market is thecapacitive touch technology.ADC plays an important role in Data conversion which plays an important rolenaturally become the most important part in touch IC. Traditional nyquist ADCtechnology requirements are relatively high, because the mismatching in analog circuitcomponents will affect the conversion precision. Sigma_Delta ADC based onoversampling and noise shaping technology do not ask for too much of match. It is lessdemanded for match of its components, and this structure ADC analog circuitcomponents is relatively smaller, higher conversion accuracy, easier to implement,lower cost, and has been widely used in the analog-to-digital conversion members.This paper first introduces the basic principle of the capacitive touch control, thenintroduces the basic theories and basic characteristics of ADC, and Sigma_Delta ADCmodulator oversampling and noise shaping techniques. Based on all of these，the oneorder3bits quantified continuous-time type Sigma_Delta ADC is presented, through theestablishment of a model，the entire system is verified by simulation, signal-to-noiseratio can reach50dB, accuracy can achieve8bits.Focuses on the design of the various modules in this paper the one order3bitsquantitafied continuous-time Sigma_Delta ADC framework, main modules are below:the common-mode voltage module, bandgap reference voltage source and currentsource, integrator, comparator, clock generation circuit and the design of the DAC. ByEDA software simulation, the simulation results of the various modules, and modulatoroverall simulation results, to meet the design requirements. After this, the layout of thecircuit design focuses on three important modules: bandgap reference, operationalamplifier, comparator.