| 摘要 |
PURPOSE:To make a multiplication circuit high accurate by using an R-2R resistance ladder D/A converter as a multiplication circuit, in an FM stereo demodulating circuit multiplying a pseudo sinusoidal wave to a composite signal. CONSTITUTION:The D/A converter 37 consists of the R-2R resistance ladder and performs multiplication to a composite signal c(t) being a reference input voltage. The composite signal c(t) is applied to the D/A converter 37 and also to a pilot signal extracting circuit 38, which extracts a pilot signal 19kHz and supplies it to a phase comparator PD40 of a PLL circuit 39. A VCO41 is locked to 608kHz with the PLL operation of the PLL circuit 39, a binary counter 42 counts 608kHz and inputs outputs Q0-Q3 to an address of an ROM45. Data D0-D7 representing each instantaneous value dividing equally one period of the sinusoidal wave into 16 are stored in 16 continuous addresses of the ROM45 and applied to a code input terminal of the D/A converter 37. |
