| 摘要 |
PURPOSE:To improve greatly the image disturbance ratio without giving a big change to a high frequency amplifying circuit, by inserting a filter circuit which shows the image trap characteristics and the LPF characteristics into the input side of the high frequency amplifying circuit. CONSTITUTION:A tuner device contains a high frequency amplifying circuit 1, a local oscillating circuit 2 and a mixing circuit 3. A filter circuit 4 consisting of a capacitor and an inductance with a high frequency input/output terminals and an earth terminal has <=1dB loss of insertion of the receiving band and a large attenuation factor in a range of at least 250-320MHz. Thus the circuit 4 has both of the image trap characteristics and the LPF characteristics. Such filter circuit 4 is inserted into the front stage of the circuit 1. |
