Development of a High-performance Amplifier for Johnson Noise Thermometer
HAN Qi-na1,ZHOU Kun-li1,QU Ji-feng1,DONG Xian-ying2,ZHANG Jian-qiang3,LI Jing-hui1,WANG Miao-er1
1. National Institute of Metrology, Beijing 100029, China
2. Chengdu Aircraft Industrial (Group) Co. Ltd, Chengdu,Sichuan 610091, China
3. Shandong Computer Science Center, Jinan, Shandong 250353, China
Abstract：A amplifier with low-noise, low-distortion, and high common-mode rejection ratio (CMRR) is critical for the noise thermometer. A high-performance amplifier for noise thermometers composed of three stages of preamplification, instrumentation amplification and buffer amplification is designed. An ultra-low noise junction-field-effect-transistor (JFET) pair IF9030 is used as the input of the pre-differential amplifier stage. An instrument is developed to automatically measure the transfer characteristics of the JFET pair, so as to achieve a better matching of the characteristics. Cross-correlation technologies are performed to suppress the uncorrelated noise in the circuit, thus the nonlinear distortions under the background noise could be accurately measured. The results show that the background noise of the amplifier is about 1.2nV/Hz1/2. The CMRR within 100kHz is higher than 90dB, and in the 100kHz to 1MHz, the CMRR decreases to lower values with the frequency increasing. fortunately, it is still larger than 70dB even at frequencies close to 1MHz. When the amplifier is excited by a two-tone signal with a frequency of 400kHz, 401kHz and an effective amplitude of 8μV, the second-order intermodulation distortion and the second-order harmonic distortion are 79dB and 85dB lower than the fundamental, respectively.
韩琪娜,周琨荔,屈继峰,董先莹,张建强,李京慧,王淼儿. 噪声温度计用放大器设计与性能评估[J]. 计量学报, 2020, 41(10): 1234-1239.
HAN Qi-na,ZHOU Kun-li,QU Ji-feng,DONG Xian-ying,ZHANG Jian-qiang,LI Jing-hui,WANG Miao-er. Development of a High-performance Amplifier for Johnson Noise Thermometer. Acta Metrologica Sinica, 2020, 41(10): 1234-1239.
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2020, Vol. 41 
