Design techniques for high-performance full-CMOS OTA-RC continuous-time filters
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In this paper, several techniques for the design of high-performance fully differential continuous-time filters are introduced. These techniques are used for the design of a fourth-order doubly terminated lowpass filter. The filter is based on operational transconductance amplifier (OTA) resistor-capacitor (RC) building blocks. For the voltage-to-current transducer a linearized OTA with a novel common-mode feedback (CMFB) system is employed. The CMFB takes advantage of the direct connection of the OTA's. For the control of the filter ripple, a low-distortion floating resistor with low sensitivity to transistor mismatches is used. This technique allows control of the ripple in a wider range without sacrificing the filter dynamic range. The techniques are validated by the experimental results of both an OTA and a fourth-order 100-kHz lowpass filter. The dynamic range of the filter is about 66 dB with total harmonic distortion (THD) < -60 dB. The power consumption is around 1.9 mW, with supply voltages of +2.5 V. The filter has been fabricated in a 1.2,-m single-poly n-well CMOS process. 1992 IEEE
