JPS5947263B2 - Frequency characteristics direct viewing device - Google Patents

Description

[Detailed Description of the Invention] For frequency sweeping in a spectrum analyzer, a tracking generator is driven with a lamp voltage, its output is applied to an arbitrary circuit under test, and the output of the circuit under test is used as an observation input signal of the spectrum analyzer. By doing so, the frequency characteristic curve of the circuit under test can be directly observed.

That is, the tracking generator always sends out an output with a frequency equal to the sweep frequency in the spectrum analyzer, and the attenuation or gain that this output undergoes due to the circuit under test is observed using the spectrum analyzer. However, especially when the output frequency of the tracking generator reaches a high frequency of several gigahertz, it is extremely difficult to always accurately match the sweep frequency of the spectrum analyzer and the output frequency of the generator.
This has resulted in the drawback that accurate frequency characteristics of the circuit under test cannot be observed. The present invention eliminates this drawback and provides a device that can accurately observe frequency characteristics even at high frequencies. FIG. 1 is a block diagram of an embodiment of the present invention, in which the spectrum analyzer s is equipped with a spectrum display section B and a lamp voltage generation section R for sweeping the frequency in the display section. The output of section R and the output of frequency modulation oscillator o are added to a drive circuit D of tracking generator T.

The output of this tracking generator T is input to an arbitrary circuit under test X, and the output of this circuit is applied to the spectrum analyzer S as an observation input. As is well known, the display section B of the spectrum analyzer s is an intermediate signal that mixes the output of a frequency sweep local oscillator driven by the output of the ramp voltage generator R with the input signal, and extracts it via a narrow band P wave generator. The frequency output is detected and input to the vertical axis of the display cathode ray tube, and the lamp voltage is applied to the horizontal axis of the cathode ray tube.

Therefore, the frequency of the input signal applied to the vertical axis of the cathode ray tube through the narrow band P wave generator described above is swept by the lamp voltage, and the spectrum of the input signal appears on the screen of the cathode ray tube. Furthermore, the output of the ramp voltage generator R and the output of the oscillator o in the spectrum analyzer s are added to the drive circuit D of the tracking generator T.
The output of the oscillator o is, for example, a sine wave with a period much smaller than the repetition period of the lamp voltage and with an amplitude significantly smaller than the amplitude of the lamp voltage.

Therefore, the output frequency of the generator is approximately determined by the lamp voltage applied from the spectrum analyzer S, but is further frequency modulated in a narrow range by the output of the oscillator 0. Therefore, in the drive circuit D, by appropriately adjusting the amplitude of the control voltage mentioned above and adding an appropriate bias voltage, the frequency is always almost equal to the sweep frequency from the tracking generator T to the spectrum analyzer S, and the sweep frequency is narrow. A constant amplitude output frequency modulated over a range is delivered. Since the output of the tracking generator T as described above is applied to the circuit under test X, the output has an amplitude corresponding to the attenuation or gain of the circuit under test at each frequency. This output signal is applied to the spectrum analyzer S as an observation input signal, and the frequency of the output signal is always frequency modulated in a range approximately equal to the sweep frequency in the spectrum analyzer S. Therefore, even if there is some deviation between the output frequency of the tracking generator T and the frequency observed by the spectrum analyzer when the frequency is not modulated as described above, they will always match in the process of frequency modulation. There are moments. In addition, if the output frequency of the tracking generator T and the frequency observed by the spectrum analyzer S after passing through the narrowband f-wave device as described above match, the output frequency from the circuit under test X is displayed on the vertical axis of the display cathode ray tube. A signal corresponding to the amplitude of the output is added. However, if there is a deviation between the above frequencies, the signal applied to the vertical axis of the cathode ray tube is significantly reduced depending on the frequency characteristics of the wave wave device. Therefore, as shown in Fig. 2, on the screen of the display cathode ray tube in the spectrum analyzer S, a large number of straight lines approximately in the vertical axis direction appear due to the frequency modulation of the tracking generator T, and the upper end of the line, that is, the output frequency of the above-mentioned generator, appears. The level at the point where the sweep frequency of the analyzer exactly matches corresponds to the amplitude of the output signal of the circuit under test X.

Therefore, the envelope curve obtained by connecting the upper ends of the group of straight lines represents the frequency characteristics of the circuit under test can. Further, as shown by the broken line in FIG. 1, the signal to be added to the vertical axis of the cathode ray tube in the display section B of the spectrum analyzer S is applied to a maximum value detection circuit M equipped with a digital storage device, and the output is sent to the cathode ray tube. By inputting the vertical axis, only the above-mentioned envelope curve can be expressed as shown in FIG. That is, the detector M detects the maximum value of the vertical axis output signal, that is, the level at the upper end of each straight line in the vertical axis direction in FIG. The detected value is stored in a digital storage device, converted again into an analog voltage, and applied to the cathode ray tube of the display section B as a vertical axis input. As described above with respect to the embodiments, the present invention generates a frequency sweep signal that is frequency-modulated in a minute range using a tracking generator, applies this to a circuit under test, and observes its output using a spectrum analyzer.

Therefore, even if there is some deviation between the output frequency of the tracking generator and the sweep frequency of the spectrum analyzer when no frequency modulation is applied,
In the process of frequency modulation described above, there is always a moment when the two frequencies exactly match. The output level of the circuit under test at that moment is displayed by the spectrum analyzer. Therefore, even in the high frequency region where it is difficult to obtain a signal with a frequency that exactly matches the sweep frequency of the spectrum analyzer, it is possible to directly observe the accurate frequency characteristics of the circuit under test.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a block diagram according to an embodiment of the present invention, and FIGS. 2 and 3 are examples of figures displayed by the apparatus shown in FIG.

Claims (1)

[Claims] 1. A spectrum analyzer to which the output of the circuit under test is applied as an observation input signal, a lamp voltage for frequency sweeping in the spectrum analyzer, and a lamp voltage having a sufficiently smaller amplitude than the lamp voltage. a tracking generator that is driven by an oscillation output with a cycle sufficiently smaller than the repetition cycle of the spectrum analyzer, always has a frequency substantially equal to the sweep frequency of the spectrum analyzer, and applies an output of constant amplitude that is frequency-modulated in a narrow range to the circuit under test; A frequency characteristic direct viewing device characterized by the following. 2. The frequency characteristic direct viewing device according to claim 1, which is provided with a circuit that detects the maximum value of the vertical axis output signal of the spectrum analyzer and inputs it as the vertical axis input of the spectrum display cathode ray tube.