| 摘要 |
PURPOSE: A switch trap circuit of a tuner is provided to prevent 40.4MHz beat frequency by using a switch trap circuit to trap 40.4MHz frequency. CONSTITUTION: A tuner having a fixed trap includes a switch trap circuit(100). The switch trap circuit(100) is connected to a rear end of the fixed trap in order to trap 40.4MHz beat frequency. The switch trap circuit includes a switching circuit(110) and a trap(120). The switching circuit(110) is formed with the first transistor and the second transistor. The first transistor is switched according to an external input signal. The base of the second transistor is connected to a collector of the first transistor. The trap(120) is formed with a resistance connected to the rear end of the fixed trap, the first and the second capacitors connected to both ends of the resistance, and a coil connected to a connection node of the first and the second capacitors and a collector of the second transistor of the switching circuit(110).
|
