Design Of High Speed Operational Amplifier

In recent years, with the development of integrated IC chip manufacturing process and update of the circuit structure, higher demand was proposed for the operational amplifier. As the rise of information appliances, mobile phone, PDA, networking, active stage was provided to the operational amplifier. Because the high speed operational amplifier has much good performance and characteristics of high frequency bandwidth, fast settling time, small distortion and noise, large output current, good DC characteristics and low supply voltage, it has been widely used in analog video processing and transmission and communication systems, etc.In this paper, the high-speed operational amplifier was mainly used in base-band low pass filter and base-band AGC chip, in which high signal to noise ratio was required. As the base-band frequency ranges from 4 MHz to 33 MHz, high gain bandwidth product and large output swing are demanded. Taking into account the requirement of economic and low-noise, the operational amplifiers was implemented in CSMC 0.5μm CMOS Mixed-signal process. The structure of two stage and fully differential was used in the opamp, high gain provided by the first stage and large output swing provided by the second stage. Using a common mode feedback for each stage gives a more stable output voltage. A novel scheme of frequency compensation was adopted, in which the non-dominant pole was canceled by using a zero in left plane which is produced by adding a feed-forward amplify circuit. The measurement results indicate that under the condition of supplied voltage of 3.3V, op-amp gets a DC gain of 65.5 dB, unity gain bandwidth product of 350 MHz output swing of±2.7V, the common mode range of 0.4 V～2.2V, common mode rejection Ratio and power supply rejection ratio were 62.16 dB and 67.96 dB. The measurement results meet the basic requirement of the specification.The application background and some typical application situation as well as some typical structures of high-speed operational amplifier were introduced in chapter I. The design process, which including the structural analysis (input stage, output stage, the common mode feedback stage, frequency compensation stage, biasing circuit stage, current and voltage reference stage) and the design parameters (open-loop gain, slew rate, noise, gain bandwidth product, etc.). Particularly, the design of common mode feedback circuit and frequency compensation circuit were mainly introduced. The main performance parameters of high-speed operational amplifier were simulated in chapter III. The main performance parameters of high speed op-amp were tested in chapter IV.