中圖分類號： TN85
文獻標識碼： A
DOI：10.16157/j.issn.0258-7998.201068
中文引用格式： 張廣顯. 接收機下變頻器級聯(lián)噪聲系數(shù)研究[J].電子技術應用，2021，47(1)：7-10.
英文引用格式： Zhang Guangxian. Study on cascade noise figure of receivers with down converter[J]. Application of Electronic Technique，2021，47(1)：7-10.

Study on cascade noise figure of receivers with down converter

Abstract： According to the definition of noise figure，this paper deduces the cascade noise figure formula of receivers with mixers. By using this formula，it is easy to calculate and analysis the system noise figure affected by the device noise figure, gain and filter image rejection. The position of image rejection filter behind the low noise amplifier needs place as close as to the mixer. The gain before the filter and filter image rejection needs high enough, at least greater than 20 dB. Through the proper design and image rejection, the noise figure of the receiver which has two-stages, three-stages frequency conversion will decrease close to 6 dB and 9 dB, than when the image noise do not be rejected at all.

Key words : receiver；cascade；noise figure；mixer；image rejection