| 摘要 |
PURPOSE:To obtain a stable and highly accurate carrier frequency with no control by providing pulse generating circuits different in oscillation frequency and a circuit which selects the oscillation outputs of said pulse generating circuits by a digital input. CONSTITUTION:Pulse generating circuits 10 and 11 of an FSK modulator deliver output pulses different in output frequency. These pulses are supplied to one of NAND circuits 16 and 17 of a frequency selection circuit 12. While the voltages at both ends of a pull-up resistance 7 are applied to an inverter 14 of the circuit 12 with the operation of a switch 8. A pulse inverted by the inverter 14 and the digital values of ''0'' and ''1'' obtained by inverting said pulse by an inverter 15 are supplied to the other one of circuits 16 and 17. The outputs of both circuits 16 and 17 are supplied to an NAND circuit 18, and the circuit 12 selects the outputs of circuits 10 and 11. Then the output of the circuit 12 is divided by dividers 13 and 6. In such a way, eliminates the circuit control is eliminated and the output of a stable and highly accurate carrier frequency is secured. |
