1、 Overview

In precision measurement systems such as thermocouple temperature measurement, electronic scales, and medical ECG, the amplification of μ V level signals is often constrained by problems such as offset voltage drift and power supply noise interference. This article analyzes the principle of Zero Drift Op Amp technology and combines it with the key parameter performance of Hua Xuan Yang Electronics OPA333AIDBVR-HXY to analyze its error suppression mechanism in weak signal chains.

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2、 Main text

1. Technical pain points and zero drift operational amplifier principle

The input offset voltage (Vos) refers to the inherent voltage deviation of the input stage of the operational amplifier, and its temperature drift (TCVos) amplifies the error with temperature changes. The traditional operational amplifier has a Vos of over 100 μ V and a TCVos of about 2 μ V/℃, with an output error of up to 10mV at 100 times the gain - far exceeding the signal level of thermocouples at 10 μ V/℃.   

The zero drift architecture periodically eliminates Vos through automatic calibration techniques such as chopper modulation, reducing typical Vos to 3 μ V (Huaxuanyang OPA333AIDBVR-HXY) and TCVos as low as 0.01 μ V/℃, which is equivalent to introducing only 0.1 μ V error for every 10 ℃ temperature change.

>Engineering Calculation Example (Thermocouple Application):

>Assuming a measurement range of 0-100 ℃, gain G=100, signal change Δ V_sig=100 ℃ × 40 μ V/℃=4mV

>- Huaxuanyang OPA333 error:

>Vos error=G × Vos=100 × 3 μ V=0.3mV

>TCVos error=G × TCVos × Δ T=100 × 0.01 μ V/℃ × 100 ℃=0.1mV

>Total DC error=0.4mV (10% of signal quantity)

>   

>Brand A (typical parameters: Vos=25 μ V, TCVos=0.5 μ V/℃):

>Vos error=100 × 25 μ V=2.5mV

>TCVos error=100 × 0.5 μ V/℃ × 100 ℃=5mV

>Total error=7.5mV (187.5% of signal quantity)

>Formula basis: ADI MT-037 offset voltage model, boundary condition: 25 ℃ reference temperature

2. Comparison of anti-interference performance: CMRR and PSRR

Common mode rejection ratio (CMRR) measures the ability of operational amplifiers to suppress common mode noise, while power supply rejection ratio (PSRR) reflects the impact of power supply ripple on output. At the front end of a 24 bit ADC, 1mV power supply noise can cause>4LSB error.   

>Noise suppression calculation (5V power supply, ripple 50mV):

>- Huaxuanyang PSRR=126dB → Output noise=50mV × 10 ^ (-126/20)=0.025 μ V

>Brand A PSRR=100dB → Output noise=50mV × 10 ^ (-100/20)=0.5 μ V

3. Bandwidth and power balance design

The gain bandwidth product (GBW=350kHz) determines the signal response speed. In the electronic scale scenario (10Hz effective signal), the Huaxuanyang OPA333 can support a gain of 1000 times (theoretical bandwidth 350Hz), while similar devices from brand A (GBW=200kHz) can only achieve a gain of 200 times, requiring cascaded amplification to increase noise risk.   

Meanwhile, OPA333 static current of 1.7 μ A (SOT-23-5L package), in a portable device powered by CR2032 battery (200mAh):

>Range calculation:

>System total current=operational amplifier current+MCU standby current (2 μ A)=3.7 μ A

>Theoretical endurance=200mAh/3.7 μ A ≈ 6.2 years

>Brand A‘s same energy devices typically have a static current greater than 10 μ A, reducing the battery life to 1.9 years

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3、 Conclusion

The Huaxuanyang OPA333AIDBVR-HXY, with 3 μ V ultra-low Vos, 0.01 μ V/℃ near zero temperature drift, and 126dB PSRR, can reduce system errors by 50% -80% in μ V level signal amplification scenarios, especially suitable for:

1. Industrial sensors: thermocouple/RTD front-end, with a full temperature range error of<0.05% between -40 ℃ and 125 ℃

2. Medical equipment: ECG/EEG signal chain, 50Hz power frequency suppression ratio increased by 40dB

3. Battery meter: Static power consumption<2 μ A, CR2032 battery life extended to 5 years

Note: The data in this article is based on the testing conditions of Huaxuanyang Laboratory (TA=25 ℃, VCC=5V). Please refer to the specific system testing for actual application.