High-linearity switched-capacitor circuits in digital CMOS technologies

Graduation date: 1998In this thesis, novel design techniques have been proposed for implementing high-linearity SC circuits in a standard digital CMOS process. They use nonlinear MOSFET capacitors instead of linear double-poly capacitors. To reduce their nonlinearities, a bias voltage is applied to keep MOSFET capacitors in their accumulation regions. For further reduction of distortion, two capacitors can be connected in series or in parallel so that a first-order cancellation of the nonlinearity can be achieved. Experimental results demonstrated that the among these techniques series compensation is the most effective for reducing the nonlinearity of MOSFET capacitors.\ud A novel predictive SC amplifier has been proposed for its insensitivity to op-amp imperfections. Experimental results show that the S/THD of the predictive SC amplifier was 10 dB larger than that of the non-predictive one. It was also shown that a predictive circuit was effective for reducing the nonlinearity caused by the op-amp and/or the MOSFET capacitors.\ud It has been demonstrated that a two-stage op-amp with a large output swing can be fabricated in a standard digital CMOS process. The frequency compensation was accomplished using a source follower and a MOSFET capacitor. An SC amplifier using this two-stage op-amp and double-poly capacitors was fabricated, and it exhibited a large linear output range.\ud A MOSFET-only digitally controlled gain/loss circuit was designed and fabricated in a 1.2μ CMOS process. It demonstrated that the series compensation is effective not only for a large output swing in an amplifier, but also for a large input swing in an attenuator.\ud A pipeline D/A converter utilizing MOSFET capacitors was designed as another application of charge processing technique. It consisted of three parts: a V-Q conversion stage, a charge transfer stage, and a Q-V converter.\ud A new switch configuration which enables the series compensation to have a large bias voltage has also been proposed. It was shown that it works well, and it will be helpful for low-voltage operation, too