Low Voltage, High-precision Op Amp Design Study

Operational amplifier is widely used in all kinds of analog and mixed-mode circuit. As the industry moves towards lower power supply voltages, more and more people put there effort on the study of low-voltage precision op-amp. The lower supply also makes the dynamic range of signal reduced. This requires the op-amp a rail-to-rail input and output stage. The new rail-to-rail low-voltage op-amp can be applied in DVD player, sound card, cellphone, GPS system and so on. Products of this kind of op-amp are available from many famous integrated circuits companies, such as TS185X series of STMicroelectronics, AD860X of Analog Device Inc. , LT180X of Linear Technology Corporation and so on. On the other hand , very little research work has been done in our country . In order to change this backward situation, the research work on the low-voltage op-amp is necessary.The main work has been finished in paper is below:1. All kinds of structure of low-voltage op-amp were compared and analyzed, such as the three-times current, redundant difference pair, DC level shifter input stage, large current output, very low-voltage output stage.2. a new circuit was designed On the base of the structure of other papers. A complementary input stage, which consists of a P-channel pair and a N-channel pair, was used in the circuit, so that the common mode input range can extend from rail to rail. A DCLS is used to shift the n-transistor curve leftward to overlap the p-transistor curve properly and keep constant transconductance in the whole common mode input range. A push-pull output stage was used in the circuit to extend output voltage from rail to rail and A class AB biasing is used to improve the power efficiency of the circuit.3. A good result is gotten under the Star-Hspice simulation. The dc gain is 90 dB, the offset voltage is 40 u V while driving 10kΩ, the unity-gain frequency is 10MHz with phase margin 67°, the slew rate is 10W us while driving 10pF.4. The layout of the circuit was finished according Shanghua 0.6 u double mental double poly process design rule. The question which should be noticed in layout is also introduced. The data of layout has been sent to Shanghai corporation for fabrication.