the filter and the noise figure of the first downconverter
(1) low noise amplifier
Match the best noise measure is closely related with the sensitivity of hair / common base circuit, in order to ensure a high-performance, low-power, usually this by choosing a high-performance, low-power transistors and input end of the antenna circuit and the output of image rejection filter conjugate matching. While the rear stage of the noise contribution to be as small as possible, i.e. the mirror as small as possible to suppress the insertion loss of the filter and the noise figure of the first downconverter.The pros and cons of the antenna performance and matching state is closely related to the sensitivity of the machine.
(2) The image reject filter
Major completed image rejection function, which is the key to ensure a high degree of image rejection. Vocabulary The batteries generally require a low insertion loss and high image frequency suppression degree, usually by the SAW filter, the LC element forming the filter or a combination of both the filter constitute, due to the size of the SAW filter and a larger loss, high cost, and this article elliptic function using the combination of the series and parallel resonant LC element constituting the multi-stage filter design when considering the tolerance of the component values in both the mass production.
(3) The first lower frequency converter and the first local oscillator and 21.4MHz, the first IF crystal filter and amplifier,Carrier signal to 21.4MHz first IF filtered amplified and fed to the second mixer, local oscillator and an IF amplifier and frequency discriminator ASIC. In this paper, the low local oscillator key level circuit is mixing and oscillation transistor selection of high-performance, low-power consumption, as well as the appropriate circuit topology, notebook battery inverter carrier signal and local oscillator signal from the base class input, IF-collector output circuit of hair.