HETERODYNE RECEIVING DEVICE OF LOW NOISE AND IMAGE SUPPRESSION

摘要

PURPOSE: A heterodyne receiving device of low noise and image suppression is provided to add a filter to an output end of a driver in a frequency converter, in order to increase a conversion gain with an IF output in an RF signal frequency band and to lower the conversion gain in an image frequency band, thereby improving noise index performance. CONSTITUTION: A local oscillating circuit outputs a local oscillating signal having a low high frequency content. Mixing circuits convert a different frequency between an input signal outputted from an amplifier and the local oscillating signal into a certain IF. The mixing circuits comprise as follows. A driver(110) inputs the input signal and the local oscillating signal, and performs a filtering function for image suppression and low noise. A switch(120) switches the outputted signal of the driver(110), and transmits the switched signal to an IF output unit(130). The IF output unit(130) conversely outputs the input signal and an IF in accordance with the local oscillating signal. The driver(110) includes a filter(115) consisting of an inductor(L1) and a capacitor(C1) on a drain output end of a field effect transistor(M1).