| 摘要 |
PURPOSE:To perform normal demodulation during a low-level input period, by arranging a VCO and a VIF amplifier at symmetrical positions. CONSTITUTION:In the constitution of a one-chip PLL video audio demodulating semiconductor integrated circuit, the input of a VIF amplifying circuit and a VCO9 are balanced completely (while pins of the integrated circuit are even for balancing), the input pins of the VIF amplifying circuit 3 are made symmetric with the pins of the filter 6 of the VCO9 on an integrated chip circuit, and the VCO9 and the input of the VIF amplifying circuit 3 are put as far away as possible on an IC package. The filter 6 for VCO has a pin for an oscillation signal with a hundreds of mVpp. During RF input in a weak electric field (10- 15dBmu), the input level of the VIF amplifying circuit 3 is about 50-60dBmu (60dBmu=1m Vrms). Thus, the balanced type is employed and the pins are put as far away as possible to perform normal demodulation. |
