The Design Of Chopped Instrumentation Amplifier In TMR Magnetometer

With the continuous development of space exploration technology,the flight path and posture control of aircraft and satellites are increasingly demanding.While the magnetometer used to measure the space magnetic field determines the accuracy of the flight trajectory.Because of its excellent performance,the TMR sensor is often used for measuring the vector parameters of the space magnetic field in the magnetometer.The TMR sensor converts the magnetic field signals to analog signals,and instrumentation amplifier is used to detect weakly output signal of magnetic resistance sensor which seriously limits the extractive accuracy of weak signal and restricts the performance of the circuit.In addition,the feature size of the integrated circuit is getting smaller and smaller.Although it helps to improve the integration of the chip,the circuit itself is becoming more and more dysfunctional.Overall,designing instrumentation amplifiers of high performance and specialisation is critical.This paper designs instrumentation amplifiers according to the characteristics of the TMR magnetometer header's output signal which is small.The common instrumentation amplifiers are the structures of three operational amplifiers,capacitive coupling and current feedback.And the common dynamic offset compensation techniques are chopping and auto-zeroing technology.Each structure or technique has its own advantages and disadvantages.Based on the analysis of all kinds of circuits and the dynamic offset compensation technologies,we determine the system structure of the instrumentation amplifier and quantitatively analyze noise and offset voltages in the circuits.The first stage opamp of instrumentation amplifier is the main source of noise and offset voltage,while the output ripple is mainly from the chopper.In this paper,chopping technology is used to modulate the noise and offset voltage of the first stage opamp to high frequency,and then the high frequency ripple is cancelled by autocorrection feedback loop;The multi-path structure eliminates the notch generated by the autocorrection feedback loop and increases the phase margin of the whole circuits.The characteristics and stability of the instrumentation amplifier are analysed and the current attenuator is used in order to reduce the equivalent input noise while not increasing the chip power consumption and area.This design uses Huahong 0.35?m CMOS process to design instrumentation amplifier circuits,draw the layout,and make the post simulation.The chip power supply voltage is 5V and chopping frequency is 200 kHz.The equivalent input noise of chip is 18.5nV/ sqrt(Hz).Flicker noise corner is 19.92 mHz,The equivalent input noise is 26.2nV/sqrt(Hz)at 19.92 mHz.The unity gain bandwidth is 1.663 MHz with load capacitance of 30 pF and the closed-loop gain is 40 dB.The current consumption of instrumentation amplifier is 1.3mA.The maximum offset voltage that can be suppressed is 24 mV.