Design Of High Precision Continuous Time ?-? Modulator

In recent years,with the support of the country,the integrated circuit industry has developed rapidly.As a bridge between analog and digital,analog-to-digital converter is widely used in signal acquisition.When you need to acquire weak signals,you need to use a high-resolution Analog Digital Converter.The ?-?(sigma-delta)ADC is composed of analog modulator and digital filter.The modulator uses oversampling and noise shaping techniques to reduce in-band quantization noise and improve the signal-to-noise ratio(Signal Noise Ratio,SNR)and ADC accuracy.Compared with discrete-time modulators,continuous time is not constrained by the settling time,enabling lower power consumption.This paper designs a 15-bit high-precision continuous-time delta-sigma modulator embedded in a smart sensor chip.Based on the basic principle of the ?-? modulator,this paper analyzes the different structures of the ?-? modulator,and provides a theoretical basis for the subsequent circuit design.In order to make the designed circuit meet the system index,the Simulink library in MATLAB software is used to mathematically model and verify the sigma-delta modulator.Based on the established modulator model and modulator structure diagram,specific circuits such as the integrator,bandgap reference,quantizer,clock circuit,counter,DAC module in the analog modulator are designed and simulated.In order to solve the instability caused by component mismatch,In the transconductance amplifier,dynamic component matching technology is used to improve the error caused by component mismatch,thereby ensuring the stability of the circuit.In order to solve the problem that sequential logic circuits are prone to timing confusion,a new structure is proposed in the counter to keep the timing logic of the sequential logic circuits accurate.In order to solve the problem that the quantization is affected by non-linear factors and reduce the quantization error to improve the accuracy,a unit-time quantization and multi-bit feedback structure is used when designing a continuous time ?-? modulator.In order to reduce the temperature coefficient of the reference voltage and current and the power consumption of the circuit,when designing the bandgap reference source,a current proportional to the absolute temperature and a current weighted sum technique complementary to the absolute temperature are used.At the same time,the amplifier works in subthreshold technologyIn the Cadence Virtuoso simulation environment,Nuvoton 0.35um,2p3m8k CMOS process is used to design a continuous-time delta-sigma modulator with 1 order and 1 bit quantization and 6 bit feedback.The modulator works at a power supply voltage of 3 V and a clock frequency of 32k.Under a sinusoidal input signal of 60mV and 7.8125Hz,the SNR is greater than 92.06dB,and the accuracy meets the requirements of 15bit system design.