用于触摸屏控制电路的低功耗模数转换器设计

为了降低触摸屏控制电路的功耗,本文提出了一种低功耗逐次逼近型模数转换器(SAR ADC)。对该SAR ADC所采用的电容阵列数模转换器(DAC)、比较器和逐次逼近寄存器等进行了研究与设计。首先,基于两级并串耦合电容设计电容阵列DAC结构,并设计配套的参考电平转换方案。接着,设计两级全动态比较器,并分析比较器的工作原理。然后,基于动态逻辑设计低功耗低误码逐次逼近寄存器。最后,基于180nm CMOS工艺,在1V电源电压,200kHz采样频率和96.243kHz输入频率条件下对SAR ADC进行了仿真。仿真结果表明:积分非线性误差(INL)和微分非线性误差(DNL)分别为0.222/-0.203LSB和0.231/-0.184LSB,无杂散动态范围(SFDR)为76.56dB,信噪失真比(SNDR)为61.50dB,有效位(ENOB)为9.92位,功耗为0.464μW,品质因素(FOM)值为2.4fJ/Conv.-step。本文设计的低功耗SAR ADC满足触摸屏控制电路应用要求。

Design of low power analog-to-digital converter for the control circuit of touch screen

In order to reduce the power consumption of the touch screen control circuit, a low power successive approximation analog-to-digital converter (SAR ADC) was proposed. The capacitor array digital-to-analog converter (DAC), comparator and successive approximation register were studied and designed. Firstly, based on two-stage parallel-series capacitor, the capacitor array DAC and reference voltage switching scheme is designed. Next, two-stage fully dynamic comparator is designed and the principle is analyzed. Then, based on the dynamic logic, successive approximation register with low power and low error code is designed. Finally, the ADC was implemented in 180 nm CMOS technology 1 V power supply and simulated at the input frequency F_in=96.243 kHz and sampling frequency F_s=200 kHz. The Simulation result indicates that values of Integral Non-Linearity(INL) and Differential Non-Linearity(DNL) are 0.222/-0.203 LSB and 0.231/-0.184 LSB respectively. Spurious Free Dynamic Range(SFDR) is 76.56 dB, Signal to Noise and Distortion Ratio is 61.50 dB, Effective Number of Bits(ENOB) is 9.92 bits. The power dissipation is only about 0.464 μW, figure of merit (FOM) is equal to 2.4 fJ/Conv.-step. In conclusion, the low power SAR ADC proposed in this paper meets the application requirement of touch screen control circuit.