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.

Keywords

• receiver
• cascade
• noise figure
• mixer
• image rejection