| 摘要 |
PROBLEM TO BE SOLVED: To obtain a spectrum analyzer, in which switching is made automatically and selectively from an internal reference signal to an external reference signal by providing a one-shot circuit having an RC time constant set longer than the period of the external reference signal. SOLUTION: When an external reference signal EXT has been inputted, the rectangular waveform thereof is outputted from a digital IC 16 and the Q output of a one-shot IC 18 goes to H. The control signal of a reference oscillator 11 goes to H and an internal reference signal INT goes to L by stopping oscillation of reference frequency. The L level internal reference signal INT is applied to one input terminal of a NAND gate 12. The Q output of the one- shot IC 18 is inverted from H to L by an inverter 17 and the other end of the NAND gate 12 goes to L, while the output thereof goes to H. The external reference signal inputted to a NAND gate 13 is outputted therefrom and delivered via a digital IC 15.
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