| Recently, with the increasing application of portable electronic products and rapid development of the high performance VLSI System Integration, the design technique of Low-Voltage Analog Integrated Circuit attracts people increasingly. However, for the limit of noise and voltage offset limitation, the Analog IC cannot utilize the minimum size of the components. As a result, there are little benefits from regarding the characteristic size reduction. In addition, the reduction of supply voltage forces great decrease of analog circuit unit on dynamic range and speed, which lead to more complicated of circuit design. In order to increase the operational performance and the dynamic range of input/output signal, preferably the dynamic range cover the entire supply voltage scope (i.e. Rail-to-Rail), it is necessary to develop the design of operational differential input/output stage. Among them, the design of Rail-to-Rail operational amplifier with stable transconductance becomes a hot spot.This paper has made widespread investigation of the low-voltage Rail-to-Rail input/output stable transconductance technology, and has analyzed the principles of these techniques as well as their pros and cons. Based on these technical achievement, this paper designs a CMOS operational amplifier with±1.5V Rail-to-Rail input/output stable transconductance.This paper has involved the following subjects:1. It has made the widespread investigation of the related domestic and foreign research, carefully compared the advantages and disadvantages of each kind of realization electric circuit, and studied the structure and the principles of each kind of electric circuit. On the basis of the related technical achievement, it set forth its own design proposal and has confirmed feasible implementation.2. According to process properties and requirement of CMOS, the paper has designed the circuit forms used in each stage, such as bias circuit, Rail-to-Rail stable transconductance input stage, cascode stage, Rail-to-Rail output stage, and miller compensation capacitors, and the like. Especially, for design of Rail-to-Rail stable transconductance input stage, a variety of stable transconductance methods were compared, and finally the level-shifts circuit was employed, the total transconductance change of input stage is fixed about 8%. For design of Rail-to-Rail output stage, AB-type feed-forward output stages is used to enhance the dynamic range of output voltage, without circuit power increase, and having a good high-frequency characteristic.3. In the domain design, making the domain to be symmetrical as far as possible, and reducing the parasitic capacity and the parasitic resistance caused by dismatch components. And for tubes with wide channel, interdigital transistors are used to replace the simple folding MOS transistor structure, which reduces the S/D junction area and gate resistance. 4. The Hspice simulation indicated that the operational amplifier can work on -1.5V—+1.5V, achieves the Rail-to-Rail input/output, with the rate of change of transconductance is stably about 8%, the DC gain 90dB, the phase allowance 70 degrees. It has realized the design of a operational amplifier of Rail-to-Rail input/output stable transconductance. |
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