Study of 1 MHz /spl sim/ 30 MHz voltage-controlled LC oscillator
The required 1 MHz/spl sim/30 MHz 100 Hz step frequency sine signal is obtained by frequency mixing between 2 kHz and 100 Hz step sine signals generated by a voltage-controlled oscillator, MC1648, that is controlled by a PLL, MC145146. The MC145146 is a PLL large-scale IC using a double mode frequency synthesizer, and the frequency setting is realizing by programming a 4 bit data bit, 3 bit address code and 1 bit signal selection bit. The MC145146 includes a 12 bit programmable reference counter (frequency dividing range: 3/spl sim/ 095), a 10 bit main counter (counting range: A=0/spl sim/127), a two phase discriminator, double mode control logic and flip-latch which is used to receive input data and address code. Matched with a double mode frequency demultiplier, a 4 Hz frequency resolution can be obtained.