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设计了一种适用于OTA-C滤波器的高线性运算跨导放大器(OTA).该OTA采用新型的乘法器输入级,以获得大的线性跨导输入范围;采用一种新的共模负反馈(CMFB)策略,将主放大器输出电压线性压缩后再引入CMFB电路,以改善传统CMFB结构对OTA输出线性范围的限制.在SMIC.35μm标准CMOS工艺下仿真,结果显示:输入级的线性跨导差分输入电压范围达到了-2～2V,等效跨导在1μS时,直流(DC)开环增益达到了76dB,共模抑制比(CMRR)为140dB,电源抑制比(PSRR)为144dB.基于这种OTA设计了OTA-C二阶低通巴特沃斯滤波器.通过调节OTA的跨导,滤波器在1pf的负载电容下的截止频率从11kHz变化至419kHz;当截止频率为100kHz时输出为3Vp-p@100kHz时的总谐波失真(THD)为-47dB.
A high linearity operational transconductance amplifier (OTA) for OTA-C filters is designed. The OTA uses a new type of multiplier input stage to achieve a large linear transconductance input range. A new common-mode negative Feedback (CMFB) strategy to linearly compress the main amplifier output voltage before it is introduced into the CMFB circuit to improve the linearity of the OTA output limits of the conventional CMFB structure.The simulation results show that the linear span of the input stage Conducted differential input voltage range of -2 ~ 2V, equivalent transconductance at 1μS, DC open-loop gain of 76dB, CMRR of 140dB, power supply rejection ratio (PSRR) of 144dB. Based on this OTA, OTA-C second-order low-pass Butterworth filter was designed. By adjusting the transconductance of OTA, the cutoff frequency of the filter under 1pf load capacitance changed from 11kHz to 419kHz; when the cutoff frequency was 100kHz, The total harmonic distortion (THD) at 3Vp-p @ 100kHz is -47dB.