High Performance OTA-R-C Continuous-Time Filters with Full CMOS Low Distortion Floating Resistors

Several techniques for the design of high performance fully-differential Continuous-Time Filters are introduced. The filter is based on OTA-Resistor-Capacitor (OTA-R-C) building blocks. A novel Common Mode FeedBack (CMFB) system for fully-differential amplifiers is proposed. The CMFB uses only 5 transistors and consumes in the order of 21% of the OTA power consumption. Alsof a low distortion floating resistor with low sensitivity to transistor mismatches is presented. This technique allows to control the ripple of the filter without sacrificing the filter dynamic range. Evenmore, both power consumption and silicon area are lower than OTA based resistors. The techniques are validated by the experimental results of a fourth order 100 kHz Low-Pass filter. The dynamic range of the filter is in the order of 66 dB for Total Harmonic Distortion (THD) ≪ -60 dB. The power consumption is only 1.9 mWattsf with supply voltages of ± 2.5 Volts. The chip has been fabricated in a 1.2 ¿m single poly N-well process. The experimental and expected results are in very good agreement.