The Design Of An Operational Amplifier With Low Offset Based On GSMC 0.13um Process

The offset of amplifiers limits the amplification of high-precision signals and even saturates amplifiers when the amplification factor is large.So,it is necessary to study how to reduce the offset of amplifiers.At present,there are few domestic researches on offset suppression technology and low offset precision op amps.The offset of amplifiers in domestic researches still has a gap of 1-2 orders compared with foreign researches.Foreign manufacturers still occupy the market of low offset precision op amps.In recent years,the United States blocked the export of semiconductor technology and products to China.So,it is essential for the development of related industries to design a low-offset op amp which based on domestic semiconductor processes.The paper studies the source of the offset of amplifiers and the method of suppressing offset.The current mainstream offset suppression methods include trimming,chopping modulation and auto-zeroing.Trimming is not able to reduce the temperature drift of the offset.Auto-zeroing causes broadband noise aliasing.The chopping modulation also has defects but more advantages,the paper chooses to use chopping modulation to suppress the offset of the op amp.Chopping modulation can limit bandwidth and cause output ripple.In the paper,the following methods are used to solve the problems.Firstly,the multipath is used to remove the limitation of bandwidth.The op amp is divided into a main path which is a high-frequency low-gain path and the auxiliary path which is a low-frequency high-gain path.The chopping modulation is located at the auxiliary path which determines the offset of the op amp.While the main path determines the bandwidth of the op amp.Secondly,a combination of chopping modulation and auto zero is used to reduce the output ripple which is caused by chopping modulation.The op is based on GSMC 0.13 μm CMOS process.The core area of the layout of the op amp is 630μm x 630μm.The simulation of the op amp is based on Cadence Spectre.The supply voltage is 3.3V.The unity gain bandwidth is 3.53MHz.The input equivalent offset voltage is less than 14.9μV,and the input equivalent ripple is less than 175μV.The temperature drift of offset is 63nV/℃.A signal whose frequency is higher than the frequency of chopping modulation can be amplified by the op.The op amp is low offset,wide bandwidth and low ripple,which can meet the requirement of the amplification of low-frequency tiny signals.