| 摘要 |
PURPOSE:To secure the steady AFC output voltage which has no effect of the element dispersion and the temperature drift and thus to ensure the beautiful TV picture images by adding the slice circuit consisting of a pair of diodes to the AFC output circuit. CONSTITUTION:The differential amplifier circuit consists of resistance 2-5 plus transistor Tr6 and 7, and the AFC off-circuit comprises Tr8 12. Here the slice circuit is formed with diode 14 and 15 in the AFC output circuit, and AFC output voltage ES is set to be identical to reference voltage E0 even though voltage E4 may drift by the one diode-equivalent amount higher or lower than voltage E0. Resistance 16 and 17 divide VCC to obtain voltage E0 which is equal to the center value of the slice voltage. Thus, voltage EA and EB becomes equal to E0 in the form of ES when the AFC is on and with no signal given, ensuring the steady AFC output voltage. As a result, the frequency lead-in range becomes symmetrical at all times with no fear of reduction of the range. Thus, the change of the local frequency caused by the temperature drift and other factors can be absorbed. |
