| Operational amplifier as a circuit of the necessary basic unit, is widely used in power management chip, media player, handheld devices and vehicle navigation system, etc. Along with the power supply voltage is reduced, the operational amplifier need a wide range of input common-mode voltage in some applications. Therefore, the rail-to-rail operational amplifier as a special kind of operational amplifier become research hot spot in the field of op-amp. The rail-to-rail operational amplifier as a independent product is very scarce in domestic, most of which are integrated in the SoC, however, ADI, TI and MAXIM lead the trend in rail to rail operation amplifier field in the foreign. So to strengthen the study of this kind op-amp is very necessary in domestic. This op-amp project comes from industrial control chip as a single op-amp module, is used for the whole system.After analyzing the requirements of industrial control chip system, the author formulates the op-amp design index, designs a rail-to-rail operational amplifier. In order to solve rail-to-rail input range and high efficiency problem, the author chooses the CMOS complementary differential input structure and class AB output structure. After contrasts the three times the current mirror method, zener diode control, electronic zener diode control and three constant transconductance control. Three times the current mirror method is chosen to be the constant transconductance control circuit and a appropriate capacitance is choosen in the op-amp to undertake frequency compensation. After the circuit structure design and basic transistor size was determined, the author used cadence company SPECTRE circuit simulation software for circuit simulation, the results show that in the whole circuit input common-mode range transconductance can basic constant, range is less than15%, dc gain85db, the unit gain bandwidth18.9MHz, phase margin78deg, static power873uW in a typical process corner. The chip using tower jazz0.18umBCD technology for layout design and the design data has delivered to the foundry. |
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