A Fast and Low Settling Error Continuous-Time Common-Mode Feedback Circuit Based on Differential Difference Amplifier

Abstract

A high-speed and high-accuracy continuous-time common-mode feedback block (CMFB) is presented. To satisfy speed and accuracy requirements, some modi¯cations have been applied on di®erential di®erence ampli¯er (DDA) CMFB circuit. The proposed method is applied to a folded cascode op-amp with power supply of 3.3 V. In order to verify the proposed circuit, simulations are done in 0.35 m standard CMOS technology. In the worst condition when the output common-mode (CM) voltage is initialized to VCC or GND, only 1.1 ns is required to set the output CM voltage on the desired level. Also in a wide range of input CM voltage variations, the deviation of the output CM voltage from reference voltage is less than 6 mV, so simulation results con¯rm the expected accuracy and speed while simultaneously the proposed CMFB circuit preserves other characteristics of DDA CMFB circuit such as unity gain frequency, 3-dB bandwidth, phase margin and linearity. 1450065-3 J CIRCUIT SYST COMP 2014.23. Downloaded from www.worldscientific.com by FLINDERS UNIVERSITY LIBRARY on 02/03/15. For personal use only. A Fast and Low Settling Error Continuous-Time CM Feedback Circuit 1450065-13 J CIRCUIT SYST COMP 2014.23. Downloaded from www.worldscientific.com by FLINDERS UNIVERSITY LIBRARY on 02/03/15. For personal use only. A Fast and Low Settling Error Continuous-Time CM Feedback Circuit 1450065-15 J CIRCUIT SYST COMP 2014.23. Downloaded from www.worldscientific.com by FLINDERS UNIVERSITY LIBRARY on 02/03/15. For personal use only.

An Ultra High speed Low power Low settling time error and wide dynamic range voltage Continuous-time Common-Mode Feedback Circuit in 0.18µm CMOS

“…The diode-connected transistor produces a huge delay in the feedback signal's path. By removing this transistor, the speed of the CMFB circuit will be increase extremely [1]. Therefore, the main purpose of the proposed CMFB circuit is to enhance the speed and precision of the conventional differential difference amplifier (DDA) CMFB circuit while simultaneously conserving other characteristics of the DDA circuit such as unity gain frequency, 3-dB bandwidth, phase margin and linearity.…”

“…Using fully differential op-amps in a feedback application, applied feedback determines differential signal voltages, but doesn't affect common-mode output voltage. Therefore, it is necessary to add a common-mode feedback circuit to stabilize voltage at a proper common-mode voltage that maximizes the op-amp output swing [1].…”