Research And Design Of Differential Current Feedback Operational Amplifiers

In recent years, the current feedback operational amplifier (CFOA) has gained the attention of researchers in the field of analog and mixed-signal integrated circuit (IC) applications for their high potential bandwidth, high slew rate, and near gain-independent bandwidth. CFOAs are typically built by cascading a positive current conveyor with a voltage buffer.The Second Generation Current Conveyor (CCⅡ) has been used as the most important and versatile active building block in a variety of electronic circuit in instrumentation and communication systems. Today they replace the conventional OPAMP in so many applications such as active filters, analog signal processing, and A/D, D/A converters. The function of CCⅡis mainly decided by the accuracy of current and voltage transfer, so we must adopt the fit circuit structure to achieve an accurate voltage control and high current driving capability.In this paper, a novel CMOS differetial positive second generation current conveyor (CCⅡ+) with a±1.5 V power supply is presented which achieves an accurate voltage transfer and dissipates less power. We also design a high performance CFOA making use of the CCⅡ+. It is based on a two-stage CMOS differential operational amplifier and also provides accurate current and voltage control. It also adopts the linearl conductance structure to improve the output signal swing and input common mode range. Thanks to its simple circuit topology with a class AB output stage, the proposed CCⅡ+has a high current driving capability and low power consumption. The frequency response properties is effectively improved by using compensation circuit consisting of Miller capacitors and zeroing resistors. In addition, the impact of class AB transistors on the standby current is analyzed.Simulation results using LTPICE with CSMC 0.35μm technology are also presented, simulation results show that the CCⅡ+has achieved a voltage transfer error equal to a 0.0534 dB with-3 dB frequency of about 68 MHz and the current transfer error is 0.007 dB with-3 dB frequency of 272 MHz. Moreover, the resistance at terminal X is as low as 50Ω, current driving capability is from-0.62 mA to 1.07 mA with a power consumption of only 2mW; Simulation results also show that the CFOA has obtained near gain-independent bandwidth,263MHZ unity gain bandwidth,307.7 V/μs slew-rate and power consumption around 3 mW.