| 摘要 |
PURPOSE:To prevent a decrease in stereophonic separation with an antenna input by adding an automatic level control circuit to the PM system of a conventional stereophonic demodulating circuit. CONSTITUTION:An ALC (automatic level control) circuit 13 is added between the PM detector 10 and matrix circuit 6 of a general stereophonic demodulating circuit, and the DC control voltage of an AM detector 7 to be applied to an AGC (automatic gain control) circuit 12 is added to the control voltage for the circuit 13 while the both are put out of phase with each other. Further, when the control voltage is so set that the circuit 13 operates with a lower input than the circuit 12, an output P varies in level similarly to an output A, and therefore the outputs P and A have no level difference, so that their ratio is made constant. Further, S=(A+P)/(A-P), where S is stereophonic separation, and when A=P, the separation has a maximum value. Therefore, this circuit sets the separation S large invariably without reference to variation in antenna input, and is effectively used for a carmounted stereo, etc., having frequent variation in input. |
