A FAST AND LOW SETTLING ERROR CONTINUOUS-TIME COMMON-MODE FEEDBACK CIRCUIT BASED ON DIFFERENTIAL DIFFERENCE AMPLIFIER ¤ TOHID MORADI KHANESHAN †,§ , SAEED NAGHAVI ‡,¶ , MOJDE NEMATZADE † , KHAYROLLAH HADIDI † , ADIB ABRISHAMIFAR ‡ and ABDOLLAH KHOEI † † Microelectronics Research Laboratory, Urmia University, Urmia, Iran ‡ Microelectronics Research Laboratory, Iran University of Science and Technology, Tehran, Iran § t.moradi@urmia.ac.ir ¶ saeed _ naghavi@elec.iust.ac.ir Received 12 September 2013 Accepted 21 December 2013 Published 10 February 2014 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. Keywords: Folded; cascode ampli¯er; common-mode feedback block (CMFB); fully di®erential op-amp; continuous-time; high-speed; high-accuracy. 1. Introduction By scaling down of CMOS technology, supply voltages and transistors channel length are shrunk. 1 This improves e±ciency of digital circuits; however, in analog *This paper was recommended by Regional Editor Piero Malcovati. ¶ Corresponding author. Journal of Circuits, Systems, and Computers Vol. 23, No. 5 (2014) 1450065 (15 pages) # . c World Scienti¯c Publishing Company DOI: 10.1142/S0218126614500650 1450065-1