JPH0619394B2 - Spectrum analyzer - Google Patents

Description

The present invention relates to an improvement of a superheterodyne spectrum analyzer.

[Conventional technology]

Since the present invention is an improvement of the patent application “Spectrum Analyzer” (hereinafter referred to as “prior application”) filed by the applicant on August 27, 1986, FIG. 4 shows a circuit diagram of this prior application as a conventional example. . Note that, in FIG. 4, a part of the circuit configuration of the prior application which is not directly related to the present invention is not shown.

In the figure, a ramp waveform is output from an amplifier U having an integrating capacitor C ₁ and the ramp waveform is output to a VCO (voltage controlled oscillator).
llator) Add to 5. Since the ramp waveform is applied to the VCO 5, the VCO 5 outputs the frequency _V that changes according to the applied voltage and applies the frequency _V to the mixer 3.

On the other hand, an input signal of frequency _i (generally, _i contains a large number of frequency components) is added to the low pass filter 1.
The low-pass filter 1 is for passing frequencies in the range that the spectrum analyzer is going to measure and for cutting other frequency components. The frequency of the output signal of the low-pass filter 1 is _L.

In the mixer 3, mixing (mixin
g) and output the output signal (frequency _M ) to the BP of the next stage.
It is added to the F amplifier (band pass filter amplifier) 9. _{The M} = _V − _L (1) BPE amplifier 9 selects and amplifies only the frequency around this certain frequency ₁ with a certain frequency ₁ .

FIG. 4 shows a so-called double superheterodyne system in which amplification is performed by the mixer 11, the oscillator 13 and the BPF amplifier 15 in order to further increase the frequency selectivity and gain. The apparatus of FIG. 4 operates even without the mixer 11, the oscillator 13 and the BPF amplifier 15.

The output of the BPF amplifier 15 has its amplitude detected by the detector 17, the noise component is removed by the video filter 19, and AD
Captured by the processor 34 via the converter 41.

Reference numeral 31 is a reference frequency oscillator, which outputs a highly stable frequency using a crystal oscillator controlled to a constant temperature, for example.

Reference numeral 32 denotes a variable frequency divider, which divides the output of the reference frequency oscillator 31 by the frequency division ratio N designated by the processor 34, adds the gate signal s2 for the frequency coefficient to the AND gate 35, and This signal s2 is added.

A counter 37 is a VCO that has passed through the AND gate 35.
The signal s1 from 5 is counted, and the coefficient value C is output to the comparator 38. A clear signal s1 is added to the counter 37 and the variable frequency divider 32 from the processor 34.

The comparator 38 compares the set signal M from the processor 34 with the signal C from the counter 37, and as a result, the signal
Add s4 to processor 34. When the signal s4 becomes active, the processor 34 reads the output s5 of the AD converter 41. The output s5 of the AD converter 41 is the video filter 19
The output signal (level signal) of is converted to digital.

The signal relating to the spectrum waveform is CR from the processor 34.
The signal sent to the T interface 40 and converted by the CRT interface 40 is added to the horizontal and vertical axes of the CRT 20.

Further, the setting signal D is sent from the processor 34 to the DA converter 46, where it is converted into an analog signal. This analog signal is applied to an integrator consisting of an amplifier U. As a result, a ramp waveform is generated, which is added to VCO5.

The operation of the spectrum analyzer of FIG. 4 configured as above will be described with reference to FIG. FIG. 3 shows the spectrum waveform displayed on the CRT 20 of FIG. However, circles and characters in the figure are for explanation and are not displayed.

The characteristic operation is to measure the oscillation frequency _V of the VCO 5, read the level signal at the frequency _V through the AD converter 41, set the frequency signal and the level signal, and grasp the spectrum signal with high frequency accuracy. It is designed to obtain a waveform.

That is, the signal s2 having a certain pulse width T _K designated by the processor 34 is applied from the variable frequency divider 32 to the AND gate 35. The AND gate 35 opens the gate during this pulse width T _K , and V
The signal from CO5 is applied to the counter 35. And Gade
The number of signals passing through 35 corresponds to the oscillation frequency of VCO 5.

Processor 34 for a period of a predetermined target frequency _a signal of the counter 37 T _K, the value can be pre-calculated pressure to when the counted sets this setting signal M to the comparator 38.

When the signal C from the counter 37 coincides with or exceeds the setting signal M, if the value Va of the AD converter 41 is immediately taken in, the frequency _a and the level signal Va can be grasped as a set (first). (See _a : Va in FIG. 3).

After that, the processor 34 sets the setting signal M at the next target frequency _b in the comparator 38 and repeats the above-mentioned operation to obtain the waveform data as shown in FIG.

[Problems to be solved by the invention]

However, when the frequency span to be swept is narrow in the spectrum analyzer as shown in FIG. 4, the frequency measuring means,
For example, it is necessary to increase the resolution of the counter 37. However, in this case, it takes a long time to measure the frequency for sampling the data of one point. As a result, there is a problem that the time required for one sweep becomes long.

An object of the present invention is to provide a spectrum analyzer having a high sweep speed and accurate frequency accuracy.

[Means for solving problems]

In order to solve the above problems, the present invention relates to a VCO (5) to which a ramp waveform voltage is applied, a mixer (3) for mixing an input signal passed through a low pass filter and an output signal of the VCO (5), and this mixer. A BPF amplifier (9) equipped with a bandpass filter by introducing the output of (3), a processor for setting a signal (M) corresponding to a target frequency ( ₁ , ₂ , ...) And an output frequency of a VCO (5). A comparator (38) for comparing the signal (M) with the signal (M) and outputting the result to the processor, and a pulse for outputting to the processor a signal for capturing the level signal of the spectrum waveform at a certain frequency interval. Generating means (31, 50), and in the processor, when the output signal of the comparator (38) becomes active, a flag is set and a level signal is taken in and the next target frequency is set. The corresponding signal (M) is updated, and the frequency value of the level signal without the flag is displayed by performing interpolation calculation using the frequency value of the level signal with the flag. .

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of a spectrum analyzer according to the present invention. 1 is different from the configuration of FIG. 4 only in that a variable frequency divider 50 is newly provided and the operation of the processor 34 is changed as described later. Variable frequency divider
The frequency dividing ratio of the processor 50 is suppressed by the signal A from the processor 34, the signal from the reference frequency oscillator 31 is divided, and a signal of a certain frequency is output to the processor 34. That is, the reference frequency oscillator 31 and the variable frequency divider 50 form a pulse generator controlled by the processor 34. On the other hand, with respect to the other circuits in FIG. 1, since the configuration of FIG. 4 is not changed, in FIG. 1, the same component element numbers as in FIG. Omit it.

FIG. 2 is a diagram depicting a spectrum waveform displayed on the CRT 20 in the apparatus of FIG. 1 and corresponds to FIG.

The operation of the spectrum analyzer of FIG. 1 will be described below. In FIG. 1, the variable frequency divider 50 outputs a signal s6 having a frequency designated by the signal A from the processor 34 to the processor 34.
Add to. The processor 34 takes in the level signal output of the AD converter 41 every time the signal s6 is applied. That is, the second
The data of the points indicated by black circles in the figure are captured.

Further, the processor 34 takes in the level signal s5 of the AD converter 41 even when the signal s4 of the comparator 38 becomes active. However, at this time, a flag is set in the level signal s5 to be taken in.
The level signal with this flag is the data of the points indicated by white circles in FIG.

The cycle in which the output signal s4 of the comparator 38 becomes active is set to be longer than the cycle of the signal s6 of the variable frequency divider 50. That is, as shown in FIG. 2, one of the plurality of pieces of captured data is frequency measured data.

In other words, according to the present invention, as shown in FIG. 2, the target frequency ( ₁ , _2, ...) Is set in the comparator 38 by the processor 34 at a certain frequency step, and the frequency of the spectrum waveform is measured. The level signal is flagged and captured. This operation is the same as that of the prior application, but the prior application measures the frequencies of all the data to be acquired (see _a , _b ... In FIG. 3), while the present invention provides Frequency measurement by the frequency step according to the other data (black circle in Fig. 2)
In accordance with the timing of the signal s6 from the variable frequency divider 50, the level signal is taken in without measuring the frequency.

The frequency of the signal s6 that is rotated by the variable frequency divider 50 is not measured. That is, the level signal S5 from the AD converter 41 fetched at the timing of the signal s6
Has not been measured at what frequency the data is.

Therefore, at the timing of the signal s6, which frequency level signal is obtained can be obtained by the microprocessor 34 by software interpolation calculation.

For this interpolation calculation, the frequency value at the timing of the gate signal s2 output from the variable calculator 32, the signal A for frequency division output to the variable frequency divider 50, or the comparator 38
Is performed using the update signal M output to.

In this way, the spectrum waveform as shown in FIG. 3 is displayed on the CRT 20.

In FIG. 2, the frequency intervals of the level signals to be sampled are drawn at constant intervals, but as described above, the data without a flag (black circles) is a variable frequency divider.
The data is taken in according to the cycle of 50, and the flagged data (white circles) is taken in at the cycle in which the signal s4 of the comparator 38 becomes active, so that the intervals are not actually constant.

It should be noted that if a numerical value indicating how many times the sample is to be accurately measured once is P (in FIG. 2, one of the four samples is accurately measuring the frequency, P = 4),
P is a constant set externally to the spectrum analyzer {frequency span D, sweep time T, number of sampling points N}
Can be determined by. If the sweep time T is determined, the time per measurement is T / (N / P) and the resolution is N /
(PT). Since this should be equal to or smaller than the frequency D / N per point, Therefore, Becomes However, this is a calculation that does not consider the circuit waste time and error. Therefore, in consideration of this, P becomes larger.

In this way, the processor 34 can automatically calculate the value of P,
As a result, the set value M can be given to the comparator 38.

[Effect of the present invention]

As described above, according to the present invention, the frequency is not measured at all sample points (see FIG. 2), but the frequency is measured once (second white circle) for P samples. There is.
Since the other samples (black circles) are interpolated using the frequency values of the frequency measurement points (white circles) to estimate the frequencies, a spectrum analyzer with high frequency accuracy can be realized. Moreover, since not all the sampled values are frequency-measured, high-speed sweeping can be performed.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a spectrum analyzer according to the present invention, FIG. 2 is a diagram showing an example of spectrum waveforms displayed on the CRT of FIG. 1, and FIG. 3 is a CRT of FIG.
FIG. 4 is a diagram showing an example of a spectrum waveform displayed in FIG. 4, and FIG. 4 is a diagram showing a configuration example of a conventional spectrum analyzer. 1 ... Low-pass filter, 3 ... Mixer, 5 ... VC
O, 9 ... BPF amplifier, 20 ... CRT, 31 ... Reference frequency oscillator, 50 ... Variable frequency divider, 34 ... Processor, 37
…… Counter, 38 …… comparator.

Claims (1)

[Claims] 1. A VCO (5) to which a ramp waveform voltage is applied
And the input signal and VCO (5) which passed the low pass filter
A mixer (3) for mixing the output signal of, a BPF amplifier (9) equipped with a bandpass filter by introducing the output of the mixer (3), and corresponding to target frequencies (f ₁ , f ₂ , ...). A processor for setting a signal (M), a comparator (38) for comparing a signal corresponding to the output frequency of the VCO (5) with the signal (M) and outputting the result to the processor, the BPF amplifier (9) Pulse output means for outputting to the processor a signal for capturing the level signal of the spectrum waveform related to the output signal from the processor) at a certain frequency interval.
1, 50), and in the processor, when the output signal of the comparator (38) becomes active, a flag is set and a level signal is taken in, and a signal (M ) Is updated, the spectrum analyzer displays the spectrum waveform by interpolating the frequency value of the level signal where the flag is not present using the frequency value of the level signal where the flag is present.