International Journal of Innovations in Engineering and Technology 58 High Swing Ultra-Wide Bandwidth with Very High CMMR Fully Differential Operational Amplifier in 0.18μm CMOS Priyanka Sharma , Rajesh Khatri Department of Electronics and Instrumentation Engineering priyanka_gs84@rediffmail.com Abstract- This p a p e r presents a low power, h i g h gain and high CMRR fully differential ultra-wide bandwidth operational amplifier with wide dynamic range . The design uses two-stage gain, high swing common-mode feedback, ‘doublet-free’ pole-zero cancelation and g m –boosting techniques to increases the unity gain frequency. Design and implementation results for a 1.2GHz, 1.8V supply, fully differential op-amp with 3 V differential output swing and 85 dB low frequency gain, 145 dB CMRR in 0.18μm digital CMOS technology are presented. Keywords – CMRR, Gain, Common mode feedback. I. INTRODUCTION Constraints imposed by advanced IC process technologies, modern electronic system requirements, and the economics of circuit integration have created new challenges in analog circuit design. With the advancement of CMOS process technologies and the increasing popularity of battery-powered mobile electronic systems comes the demand for lower-voltage analog circuit designs. In addition, the drive to reduce system costs is forcing the integration of both analog and digital circuitry onto a single die. Both of these changes have a detrimental impact on analog circuit performance. With a reduction in power supply voltage comes a decrease in both the peak SNR and the dynamic range of an analog circuit. Integrating analog circuitry and noisy digital circuitry on the same die further degrades analog performance due to noise injection through a common power supply and/or power distribution network, the die substrate, and/or capacitive coupling between conductors. Many analog design techniques and methodologies have been devised to enable high performance analog signal processing in today’s environment. Fully differential analog signal processing is one technique that has become widespread because it reduces the problems associated with both reduced signal swings and noise coupling. Using a differential design technique effectively doubles the maximum signal swing in the circuit. Also, all external noise sources that influence both signal paths of a balanced differential system in the same way, to a first order approximation, will be rejected. This is due to the fact that, in a differential system, the signal of interest is the difference between the signals in the two signal paths. Thus any noise common to both signal paths will be subtracted away. For the same reason, the total harmonic distortion of the circuit due to non-linear elements can be reduced. Each distortion component at a frequency that is an even harmonics of the fundamental signal frequency will be subtracted away from the differential signal because it is a common in both signal paths [3].Operational amplifiers are the backbone for many analog circuit designs. It is a fundamental building block for many circuit designs that utilize its high gain, high input impedance, low output impedance, high bandwidth and fast settling time. Operational amplifier (Op-Amp) is one of the basic and important circuits which have a wide application in several analog circuits such as switched-capacitor filters, algorithmic, pipelined and sigma-delta A/D converters, sample- and hold amplifiers etc. The speed and accuracy of these circuits depend on the bandwidth and DC gain of the Op-amp. Larger the bandwidth and gain, higher the speed and accuracy of the amplifier [2]. Operational amplifiers are a critical element in analog sampled-data circuits, such as SC filters, modulators. Higher and higher clock frequency requirement for these circuits translates directly to higher frequency requirement for the Op-amp. A