WAVEFORM DISPLAY APPARATUS FOR EASILY REALIZING HIGH-DEFINITION WAVEFORM OBSERVATION

Abstract: A measurement part U100 measures the imput signal, sweeping the frequency in the measuring range of a predetermined frequency band, to obtain waveshape data which are developed on a frequency axis, like spectral data obtained by a spectral analyzer. The waveshape data measured by the measurement part U100 are displayed on a display device U500, being developed on the frequency axis, i.e., being in correspondence with the measurement frequency, via a displayed data processing part U20 included in a control part U200. The control part U200 has a measurement control part U30 for controlling the measurement part U100 and an enlargement/stability display processing part U40 for controlling the displayed data processing part U20. These parts U30 and U40 are provided so that data on waveshape which is enlarged or reduced, taking a predetermined point on the frequency axis as the center of the enlargement or reduction, by an enlargement or reduction factory under the changed condition of the measurement frequency set by a condition setting part U900 may he displayed. This enlargement/stability display processing part U40 plays the role of a highly fine waveshape observation being the essence of this invention and has the function of controlling substantially the display device U500 as the control part U200.

Description: The present invention relates to a waveform display apparatus of a frequency sweep type including a spectrum analyzer for analyzing the spectrum of a signal, a network analyzer for analyzing the characteristic of a circuit element, and the like and, more particularly, to a waveform display apparatus which can easily perform high-definition observation of a desired peak/dip portion in a displayed waveform. As is well known, a waveform display apparatus such as a spectrum analyzer, a network analyzer, or the like displays the spectrum of a signal to be measured, the transfer characteristic of a circuit element to be measured, or the like while developing it on the frequency axis. When a waveform is observed using a waveform display apparatus of such a frequency sweep type, it is required to be able to easily provide high-definition waveform observation for a user. However, a conventional spectrum analyzer, network analyzer, or the like cannot satisfy the above-mentioned requirement in the present state. These problems of conventional techniques will be described below taking spectrum analyzer as an example. In general, in a spectrum analyzer, when the spectrum of an unknown signal is to be analyzed and evaluated, the level and frequency of the spectrum displayed to be developed on the frequency axis must be observed. However, an actually displayed spectrum resolution suffers from a limitation due to, e.g. characteristics of elements constituting the spectrum analyzer. More specifically, each spectrum pattern to be observed is not always displayed by a single line segment, but has a mountain-like pattern in which a spectrum upper portion forms a moderate curve, and its lower portion is spread, although it depends on a measurement condition. The level and frequency of a maximum level point (peak) of a spectrum display having a mountain-like pattern correspond to those of a spectrum to be observed. For this reason, the maximum point of the spectrum must be searched. When some spectra are present in a narrow frequency range, and their levels and frequencies are to be measured, each spectrum must be selected, and the maximum level on a display must be detected. Furthermore, in some cases, a spectrum may be displayed to have a valley-like pattern in a direction opposite to the above-mentioned case. In this case, the level and frequency of a minimum level point (dip) correspond to those of a spectrum to be observed. In the spectrum analyzer for analyzing the spectrum in this manner, many functions allowing convenient analysis have already been added. Since the present invention provides some of these functions, various functions of the conventional spectrum analyzer will be individually explained in different items below for the sake of easy understanding of the characteristic features of the present invention. 1 ○ Zone Marker This function is disclosed in Japanese Patent Application, "Spectrum Analyzer" (Published Unexamined Japanese Patent Application No. 63-218869) by the same applicant (some common inventors) as the present invention. This reference corresponds to EP-A-0 283 804, which is used in forming the preamble of claim 1. More specifically, in the zone marker function, in order to facilitate observation of a peak (dip) of a spectrum within a desired frequency range displayed on a display device, a desired frequency range in a measurement frequency region is set as a zone, the zone can be horizontally moved in the measurement frequency region, the zone width is also variable, and a peak (the top of a mountain) or a dip (the deepest bottom of a valley) is indicated by a marker. (See Fig. 11) Thereafter, the same technique was disclosed as a U.S. Patent (USP 4,901,873). 2 ○ Zone Sweep (Partial Sweep) This function is disclosed in Japanese Patent Application, "Spectrum Analyzer" (Published Unexamined Japanese Patent Application No. 64-9371) by the same applicant (some common inventors) as the present invention. More specifically, in order to allow high-speed observation while maintaining original performance and functions of a spectrum analyzer, a signal is analyzed by analog sweep, so that variation states of a carrier wave and a signal adjacent to the carrier wave are displayed on a single screen to be easy to see, and components to be seen can be quickly observed. That is, in the zone sweep function, a narrow range adjacent to a signal of interest within a measurement frequency region is set as a zone (see Fig. 12), and only this zone range is repetitively swept. Spectrum data obtained by sweeping the narrow range is updated. However, data outside the zone (on the right and left sides of the zone shown in Fig. 12) are stored in a memory without being updated after they are obtained by a single sweep operation, and are displayed together. In this zone sweep function, the sweep range is narrowed to provide partial, high-speed performance. Thereafter, the same technique was disclosed as a U.S. Patent (USP 4,839,583). 3 ○ Signal (Center) Tracking This function is used in spectrum analyzers commercially available from U.S. companies (Type 8568 available from Hewlet-Packard Corp., Type 2410 available from Tektronix Corp., and the like). These spectrum analyzers shift the frequency as the abscissa for each sweep, so that a peak point of a spectrum displayed on a screen of a CRT as a display is always located at the center of the screen. More specifically, every time a sweep operation is performed, a peak point is searched by signal (center) tracking, so that the frequency of the peak point corresponds to the center frequency (center) on the screen. (See Fig. 13) 4 ○ Foreground (so-called FG) & Background (so-called BG) Two-frame Display This function is disclosed in Japanese Patent Application, "Spectrum Analyzer" (Japanese Patent Application No. 2-15432; filing date 1990-1-25) by the same applicant (some common inventors) as the present invention. A BG display indicates a wide-band sweep result (see a lower graph of Fig. 14), and when a desired signal within the sweep frequency range is selected by designating a zone (see the lower graph of Fig. 14), a bandwidth corresponding to the zone can be displayed as an FG display. The FG display is enlarged, as shown in an upper graph in Fig. 14. In addition, the zone designated on the BG display can be shifted, and the frequency which can be observed on the FG display can be changed in correspondence with a zone shift on the BG display. Thereafter, the same technique was filed in U.S.A (US. Serial No. 644,220; filing date 1991-1-22). 5 ○ Data Point Designation & Enlargement Function As an early technique associated with a digital storage oscilloscope, "Digital Measurement Apparatus" (Published Unexamined Japanese Patent Application No. 50-6380) is known. With techniques before this technique, all the several thousands of coordinate points on a display device do not have sufficient resolution for observation. The data point designation and enlargement function is developed in consideration of this situation, and includes an "apparatus for controlling addresses and display positions of data points to be displayed on a display device in response to selected data points and a selected enlargement coefficient" so as to display data at a limited number of coordinate points at a time (in other words, to enlarge and display the data). Thus, in the above-mentioned techniques added to a conventional spectrum analyzer, some problems remain unsolved. First, in the conventional technique 5 ○, a function of enlarging an image to be observed is realized by selecting desired data points and designating an enlargement coefficient. However, in order to compensate for insufficient functions of this technique upon actual high-definition observation of a spectrum, techniques described in items 1 ○ to 4 ○ have been added according to requirements of users. Of these techniques, the zone marker function 1 ○ and the zone sweep function 2 ○ will be examined below. When an observed spectrum drifts due to any cause, and falls outside the zone, the zone position must be set again. When a portion adjacent to an observed spectrum is to be enlarged, a user must instruct to change the center frequency (CENTER FREQ) by a panel operation so as to display the corresponding signal at the center of a screen of a CRT. (For example, an instruction for causing the frequency of the marker point to coincide with the center frequency must be issued.) The signal (center) tracking function 3 ○ will be examined below. In this function, only a portion inside a display range of a CRT screen is searched. For this reason, when a spectrum of a portion adjacent to a given signal is observed by sweeping a narrow band, the signal may abruptly drift, and may fall outside the CRT screen. In this manner, in order to search a signal in an observation disable state, a user must set a wider span (sweep frequency width) again to detect a signal to be observed, and thereafter, must narrow the span to restore an original state. The foreground FG & background BG two-frame display function 4 ○ will be examined below. In this function, in order to display two frame data, the display area on a panel surface of a device must be inevitably increased. That is, when the entire display area is suppressed to be reduced in scale, displayed data is not easy to see for a user. In addition, a user must set the zone position in the BG display again when a signal to be observed drifts. Furthermore, with this technique, spectrum data extends over two traces, and when data is saved or recalled, a large memory capacity is required. On the other hand, in order to visually display spectrum components included in a measurement signal, a spectrum analyzer as shown in Fig. 15 is conventionally used. In Fig. 15, a measurement unit P1 having a heterodyne receiver arrangement capable of sweeping a local frequency continuously sweeps and detects a predetermined frequency range of an input measurement signal, and outputs detection signals. A waveform memory P2 updates and stores the detection signals output during one sweep operation as a series of waveform data for each sweep operation. A display controller P3 displays waveform data stored in the waveform memory P2 on a display device P4 as a spectrum waveform to have the frequency axis as the abscissa. A start frequency setting unit P5 sets a sweep detection start frequency of the measurement unit P1. A center frequency setting unit P6 sets a sweep detection center frequency. A frequency span setting unit P7 sets a width (span) of a sweep detection frequency. A start·center frequency calculation unit P8 updates and sets a start or center frequency using a changed/set condition frequency with priority, so that the following relation can be established for condition frequencies from the frequency setting units P5, P6, and P7 for determining a range of the sweep detection frequency: Center frequency F(c) = Start frequency F(st) + Frequency span F(sp)/2 For example, when the start frequency is changed/set while the frequency span is fixed, the start·center frequency calculation unit P8 calculates and updates/sets a center frequency which can satisfy equation (1) for the new start frequency and the frequency span. Therefore, a spectrum waveform is shifted by a difference in start frequency, and the same applies to a case wherein the center frequency is changed/set. When the frequency span is changed/set while the start frequency is fixed, the spectrum waveform is displayed in an enlarged or reduced scale to have the start frequency as the center. When the frequency span is changed/set while the center frequency is fixed, the spectrum waveform is displayed in an enlarged or reduced scale to have the center frequency as the center. Therefore, when a spectrum waveform as shown in Fig. 16A is displayed on a screen of the display device P4, if a spectrum near the center frequency (F(c)) is to be observed in an enlarged scale, the frequency span can be decreased while the center frequency is fixed. Thus, the spectrum waveform is displayed in an enlarged scale to have the center frequency as the center, as shown in Fig. 16B. As shown in Fig. 17A, when a spectrum near a point a is to be observed in an enlarged scale, the spectrum waveform is shifted (by changing the start or center frequency) so that the point a is located at almost the center frequency, and thereafter, the frequency span is decreased while the center frequency is fixed. Thus, as shown in Fig. 17B, the spectrum near the point a is displayed in an enlarged scale to have the center frequency as the center, and further detailed spectrum observation is allowed. However, as an observation mode of a spectrum analyzer, adjustment of equipment or the like is frequently performed while alternately observing the overall spectrum and an enlarged spectrum of a portion of the overall spectrum. In this case, in the conventional spectrum analyzer shown in Fig. 15, as described above, if a portion to be observed in an enlarged scale is not moved to near the center frequency, when the frequency span is changed, a target waveform may fall outside a display range. In this technique, in order to restore the enlarged waveform to an original spectrum waveform, operations must be performed in a reverse order, resulting in inconvenience. For this reason, a marker point which is arbitrarily movable on a waveform may be provided, as has been realized in an oscilloscope, and a function (zoom function) of locating the marker point at a display center upon operation of a special-purpose enlargement key, and performing an enlarged-scale display to have the display center as the center may be utilized. However, with this technique, an enlarged waveform is fixed at the display center, resulting in inconvenience In the spectrum analyzer shown in Fig. 15, every time a waveform is enlarged, the frequency span and the start frequency are updated/set. Therefore, in order to display an original waveform, complicated operations are required. As a conventional apparatus which utilizes the above-mentioned signal (center) tracking function so as to visually display a spectrum component included in a measurement signal, a spectrum analyzer as shown in Fig. 18 is known. In Fig. 18, the same reference numerals denote the same parts as in the spectrum analyzer shown in Fig. 15, and a detailed description thereof will be omitted. More specifically, in Fig. 18, reference numeral P10 denotes a tracking unit for preventing movement of a spectrum waveform on a screen for a measurement signal suffering from a frequency drift. The tracking unit P10 detects an address corresponding to a maximum value of waveform data stored in a waveform memory P2 from a peak position detection unit 11, causes a frequency difference detection unit P12 to obtain the difference between a frequency corresponding to this address and the center frequency, and shifts a sweep detection frequency range by the difference. Therefore, when a spectrum waveform as shown in, e.g., Fig. 19A is displayed on a screen of a display device P4, and the tracking unit P10 is operated, the overall spectrum waveform is shifted, so that the position of a maximum-level spectrum A is located at the center of the screen (at the position of the center frequency), as shown in Fig. 19B. Thereafter, even when this measurement signal suffers from a frequency drift, since the sweep detection frequency range is shifted to follow this drift, the spectrum waveform can be observed while the maximum-level spectrum A is fixed at the center of the screen. However, in the conventional spectrum analyzer as shown in Fig. 18, when a spectrum ranging from a fundamental wave having a large level to high-order harmonics having small levels is observed on a single screen like in harmonic measurement, if the above-mentioned tracking function is operated for the measurement signal, the fundamental wave is fixed at the center of the screen, and a display range of harmonics is limited to a region half the entire screen, resulting in inconvenience. In the conventional spectrum analyzer, when the level of a spectrum to be subjected to tracking is smaller than the level of other spectra, condition frequencies (the start frequency, the frequency span, and the like) must be adjusted in advance to cause a spectrum having a large level to fall outside the sweep detection frequency range. As a result, observation on a single screen is undesirably disturbed. A conventional spectrum analyzer having an arrangement as shown in Fig. 20 is also known. Fig. 21A shows a display example measured by the arrangement shown in Fig. 20. A case will be explained below wherein measurement of up to 5th-order (5f₁) harmonic components of a signal to be measured whose fundamental wave f₁ is at 100 MHz, as shown in Fig. 21A, is performed using the arrangement shown in Fig. 20. A local oscillator 1a in a measurement unit 1 outputs a frequency-swept signal to a mixer 1b according to instructions from a control unit 10a and a sweep signal generation unit 11a, and causes the mixer to convert up to 5th-order harmonic components of an input signal to be measured into intermediate-frequency (IF) signals. Therefore, the local oscillator 1a continuously frequency-sweeps the input signal to be measured over a band of almost 500 MHz. The IF signals passing through a band-pass filter (to be referred to as a BPF hereinafter) 1c are detected by a detector 1d, are converted into digital data by an A/D converter 2, and are stored in a storage unit 3 in correspondence with the swept frequencies. Data stored in the storage unit (waveform memory) 3 are displayed on a display screen of a display device 4. The data display on the display screen is made on a coordinate system defined by the abscissa as a frequency axis and the ordinate as a level axis by a predetermined total number of dots, e.g. 500 points for each of the abscissa and the ordinate. An analysis resolution, a display resolution, and a comprehensive measurement resolution will be described below. 1 ○ Analysis resolution The analysis resolution is an index representing performance capable of analyzing adjacent signals, and is expressed by the band itself of the BPF 1c. When a measurement is performed while improving the analysis resolution, i.e. narrowing the band of the BPF 1c, the measurement S/N is also increased. In order to perform an optimal measurement by sweeping frequencies, a transient response with respect to the velocity of an IF signal passing through the band of the BPF 1c must be taken into consideration, and this relationship is given by the following inequality: (RBW) 2 ≥ K × BW/T where T: sweep time K: constant BW: frequency sweep bandwidth RBW: analysis resolution (bandwidth of the BPF 1c) Note that BW/T represents the sweep velocity. 2 ○ Display resolution of frequency axis (abscissa) The display resolution is determined by the total number of dots on the abscissa, and the frequency sweep bandwidth. More specifically, the display resolution = BW/(the total number of dots). 3 ○ Example of numeric values: If T = 2 sec, BW = 500 MHz, K = 2, and the total number of dots = 500, analysis resolution = 22.54 KHz display resolution = 1 MHz/dot The numeric values in this case reveal that the comprehensive measurement resolution visually observed from the display screen is determined by the display resolution, and is 1 MHz. The analysis resolution = 22.4 KHz is not effective. In general, the comprehensive measurement resolution tends to be determined by the display resolution as the frequency sweep bandwidth BW is larger, and tends to be determined by the analysis resolution as the bandwidth BW is smaller although it depends on the sweep time. In the conventional spectrum analyzer shown in Fig. 20, when only a portion near up to 5th-order harmonic components of a signal to be measured having a fundamental wave of, e.g., 100 MHz is to be measured, the following problems are posed. 1 ○ Conventionally, since measurement is performed by continuously sweeping frequencies up to almost 500 MHz corresponding to the 5th-order harmonic component, the measurement resolution (or display resolution) near respective harmonic components of interest is low, thus often causing a measurement error. For example, if a component other than a harmonic is present within the display resolution = 1 MHz per dot in the above-mentioned numeric value example, the harmonic and other components are undesirably measured at the same time. 2 ○ Since a band as wide as 500 MHz is measured, if there are many components other than harmonic components, an operation for specifying the harmonic components is necessary, resulting in inconvenience. In order to solve the above-mentioned problems, a measurement device for making a display as shown in Fig. 21B is known. This measurement device designates frequencies of respective harmonic components to measure the levels at the designated frequency points, and processes the data to display the data as a bar graph. In this measurement device, the above-mentioned problem 2 can be solved. However, when a signal to be measured which may include components other than harmonic components is to be measured, whether or not harmonic components are measured in practice cannot be confirmed. As described above, in the conventional spectrum analyzers and their associated measurement techniques, high-definition waveform observation cannot be easily provided to a user, and it is an urgent subject to realize this in this field. The present invention has been made in consideration of the above situation, and has as its first object to provide a waveform display apparatus of frequency sweep type, which can easily provide, to a user, high-definition waveform observation of a waveform displayed to be developed on the frequency axis. It is the second object of the present invention to eliminate some problems of, particularly, a conventional spectrum analyzer shown in Fig. 15, i.e. to realize a waveform display apparatus of frequency sweep type, which can easily allow alternate observation of the overall (spectrum) waveform, and an enlarged (spectrum) waveform of the overall waveform by only an operation for changing condition frequencies, can arbitrarily set a reference position of the waveform, and hence, can easily provide high-definition waveform observation to a user. According to the present invention, there is provided a waveform display apparatus of frequency sweep type as defined in claim 1. Fig. 1 is a block diagram showing a basic arrangement of a waveform display apparatus according to an embodiment of the present invention; Fig. 2 is a schematic view of a spectrum analyzer to which the waveform display apparatus according to the embodiment is applied; Figs. 3A and 3B are block diagrams showing an arrangement according to the first embodiment of the present invention; Figs. 4A, 4B, and 4C show display screen data for explaining operations of Figs. 3A and 3B; Fig. 5 is a principal part block diagram for explaining a modification of the first embodiment of the present invention; Figs. 6 and 7 are block diagrams showing arrangements of other modifications of the first embodiment of the present invention; Fig. 8 is a block diagram showing an arrangement according to the second embodiment of the present invention; Fig. 9A is a block diagram showing a modification of the second embodiment of the present invention; Fig. 9B is a chart showing an operation flow of the modification of the second embodiment; Fig. 10 is a diagram showing in detail a waveform memory according to the second embodiment of the present invention; Figs. 11 to 14 show display examples of the prior art; Fig. 15 is a block diagram showing an arrangement of a conventional apparatus; Figs. 16A and 16B and Figs. 17A and 17B show display screen data for explaining operations of the conventional apparatus; Fig. 18 is a block diagram showing an arrangement of a conventional apparatus which utilizes a center tracking function; Figs. 19A and 19B show display examples by the apparatus shown in Fig. 18; Fig. 20 is a diagram showing an arrangement of a conventional spectrum analyzer; Figs. 21A and 21B show conventional display examples; and Figs. 22 to Figs. 24A and 24B are views showing display examples according to the second embodiment of the present invention. Fig. 1 shows a basic arrangement of a waveform display apparatus. More specifically, a measurement unit U100 measures an input signal to be measured by sweeping frequencies within a measurement range of a predetermined frequency band so as to obtain waveform data developed on a frequency axis such as spectrum data in, e.g., a spectrum analyzer. Waveform data obtained by measurement in the measurement unit U100 is displayed by a display device U500 via a display data processor U20 included in a control unit U200 (to be described later) so as to be developed on the frequency axis of the display device, i.e., in correspondence with the measurement frequencies. The control unit U200 comprises a measurement controller U30 for controlling the measurement unit U100 to display waveform data obtained by enlarging or reducing waveform data before conditions are changed at a predetermined magnification to have a predetermined point on the frequency axis as the center on the basis of changes in conditions of the measurement frequencies set by a condition setting unit U900, and an enlargement display/stable display processor U40 for controlling the above-mentioned display data processor U20. Note that the enlargement display/stable display processor U40 controls high-definition waveform observation as the gist of the present invention, and has a function of substantially controlling the display device U500 as the control unit U200. The condition setting unit U900 comprises first and second parameter setting units U600 and U700 for selectively setting conditions consisting of the start frequency, the stop frequency, the center frequency, the frequency span, and the like associated with a measurement (sweep) range, and conditions associated with a display scale factor on the frequency axis of the display device U500 to desired values so as to set and change the measurement frequency conditions, and also comprises a reference parameter setting unit U800 for selectively setting conditions associated with a zone and a predetermined point (position) to be set on the frequency axis of the display device U500 to desired values. The detailed arrangements and embodiments of the above-mentioned units will be described in the first to second embodiments to be described later. As shown in this basic arrangement, the common basic concept of displaying waveform data is obtained by enlarging or reducing original display waveform data at a predetermined magnification to have a predetermined point on the frequency axis of the display device U500 as the center, thereby easily providing high-definition waveform observation to a user. Note that the predetermined magnification includes not only an enlargement magnification but also a reduction magnification, and of course, includes a magnification 1 as an intermediate magnification of the above magnifications since the present invention is achieved under the condition that waveform data to be displayed is suitable for observation with high definition. Fig. 2 is a view showing an outer appearance of a spectrum analyzer realized by the basic arrangement, and illustrates the display device U500 for displaying a spectrum waveform at the predetermined magnification, and various operation members U900 for executing respective measurement·display functions of the first to fifth embodiments to be described later. (First Embodiment: Zoom Function) A zoom (ZOOM) function according to the first embodiment of the present invention will be described below with reference to the accompanying drawings. Fig. 3A is a block diagram showing a schematic arrangement of a spectrum analyzer according to the first embodiment. Fig. 3B is a block diagram showing Fig. 3A in more detail in correspondence with the basic arrangement shown in Fig. 1. The same reference numerals denote the same parts as in Fig. 1 and Fig. 3A, and a detailed description thereof will be omitted. In Fig. 3A, reference numeral 10 denotes a measurement unit of this spectrum analyzer. The measurement unit 10 causes a mixer 12 to mix a measurement signal with a local oscillation signal from a local oscillator 11 capable of performing a sweep operation, causes a detector 14 to detect a signal passing through a band-pass filter 13 having a predetermined frequency, and causes an A/D converter 15 to output the detection signal as spectrum values (data) in units of frequencies. Note that the sweep frequency range of the local oscillator 11 is determined by the amplitude of a sweep signal from a sweep controller 16, and an offset voltage. A data converter 17 performs correction processing of data from the A/D converter 15, and stores the corrected data in a waveform memory 18. The waveform memory 18 has, e.g., 500 addresses, and the A/D converter 15 is assumed to output 500 spectrum data for each sweep operation. A display controller 19 causes a display device 20 to display the data stored in the waveform memory 18 together with another display information to be described later as a series of spectrum waveforms. A zone marker setting unit 21 displays and sets a zone having an arbitrary width at an arbitrary position on the frequency axis, and displays a marker at a peak point of a waveform within the zone. A zone center setting unit 22 is a portion for setting zone center information serving as a reference position in a zone center memory 23. A zone width setting unit 24 is a portion for setting zone width information in a zone width memory 25. An intra-zone peak detector 26 detects maximum data present within a set zone range of data stored in the waveform memory 18, and outputs its level and position data (address value) as a marker level and marker position data. A marker position memory 27 stores the marker position data, and a zone display position calculation unit 28 calculates the display position of the zone. A start frequency setting unit 30 is a portion for setting a sweep detection start frequency in the measurement unit 10 in a start frequency memory 31. A center frequency setting unit 32 is a portion for similarly setting a sweep detection center frequency in a center frequency memory 33. A frequency span setting unit 34 is a portion for setting a frequency span in a frequency span memory 35. A first start·center frequency calculation unit 36 calculates a start frequency or a center frequency of a sweep detection frequency of the measurement unit 10 on the basis of condition frequencies set in these memories 31, 33, and 35. More specifically, when the start frequency is changed/set while the frequency span is fixed, the first start·center frequency calculation unit 36 updates/sets the content of the center frequency memory 33 to satisfy the above-mentioned equation (1). Contrary to this, when the center frequency is changed/set, the unit 36 updates/sets the content of the start frequency memory 31. A marker frequency calculation unit 37 calculates a marker frequency on the basis of the start frequency, the frequency span, and the marker position. In a calculation of the marker frequency calculation unit 37, a value obtained by dividing the frequency span with the number of display points (500 in this case) is multiplied with the marker position data, and the product is added to the start frequency, thus obtaining the marker frequency. An intra-zone frequency deviation calculation unit 38 calculates the difference between the zone center frequency as a frequency at the reference position, and the marker frequency, and calculates a frequency deviation in such a manner that a zone center frequency obtained by adding, to the start frequency, a value obtained by dividing the frequency span with the number of display points, and multiplying zone center position data with the quotient is subtracted from the marker frequency. An old frequency span memory 39 stores a frequency span previously set in the frequency span setting unit 34 when a new frequency span is set in the frequency span setting unit 34. A second start·center frequency calculation unit 40 outputs a new start frequency and center frequency on the basis of the start frequency, the center frequency, the frequency span, and the old frequency span stored in the memories 31, 33, 35, and 39 when the frequency span setting unit 34 changes/sets the frequency span. The second start·center frequency calculation unit 40 calculates a new start frequency F(st) N with reference to a zone center frequency F(zc) on the basis of an old start frequency F(st) O , an old frequency span F(sp)O, and a new frequency span F(sp) N by the following equation: F(st) N = F(zc) - (F(zc) - F(st) O ) × (F(sp) N /F(sp) O ) In addition, a new center frequency F(c) N with reference to the zone center frequency F(zc) is calculated on the basis of an old center frequency F(c) O by the following equation: F(c) N = F(zc) - (F(zc) - F(c) O ) × (F(sp) N /F(sp)O) A frequency correction unit 41 corrects the new start frequency and the new center frequency calculated by the second start·center frequency calculation unit 40 by the frequency deviation from the intra-zone frequency deviation calculation unit 38. The new start frequency and the new center frequency corrected by the frequency correction unit 41 are respectively set in the start frequency memory 31 and the center frequency memory 33. An operation of this spectrum analyzer will be described below. For example, when a measurement signal is observed in a state wherein the start frequency = 100 MHz, the frequency span = 400 MHz, and the zone center position corresponds to a display point = 345, a spectrum waveform as shown in Fig. 4A is displayed on the display device 20, and a marker point m indicating the peak point within the zone is displayed at the position of a display point = 340. A marker frequency F(m) at this time is given by: F(m) = 100 + (400/500) × 340 = 372 (MHz) A zone center frequency F(zc) is given by: F(zc) = 100 + (400/500) × 345 = 376 (MHz) A frequency deviation ΔF between these frequencies is 4 MHz. When the frequency span is changed/set to 100 MHz, the second start·center frequency calculation unit 40 calculates a new start frequency and a new center frequency as follows according to the above-mentioned equations (2) and (3): New Start Frequency F(st) N = 375 - (376-100) × 100/400 = 307 (MHz) New Center Frequency (F(c) N = 376 - (376-300) × 100/400 = 357 (MHz) These calculated frequencies are respectively corrected by the frequency deviation ΔF (= -4MHz), and are respectively set in the start frequency memory 31 and the center frequency memory 33. For this reason, the local oscillation frequency of the local oscillator 11 is controlled, so that the sweep reception range of the measurement unit 10 is changed from 303 MHz to 403 MHz, and a spectrum displayed on the display device 20 is displayed in an enlarged scale at a ×4 magnification to have the zone center as the reference position as the center, as shown in Fig. 4B. In this case, since the marker frequency and the zone center frequency are corrected by the frequency correction units 41 and 42, they are expected to coincide with each other on the screen, but may not always coincide with each other due to a variation of a measurement signal or the linearity of the local oscillator 11. However, since this frequency correction is performed every time the frequency span is changed, a portion to be enlarged will not fall outside a display range. Upon this change of the frequency span, the zone center frequency becomes 372 (MHz) by calculating: 303 + (100/500) × 345 When the frequency span is reset to 400 MHz from this state (to have the frequency deviation ΔF = 0), the start frequency = 96 MHz, and the center frequency = 296 MHz are set, as shown in Fig. 4C, and are shifted by 4 MHz from the original waveform. However, this shift is negligible in relation to the frequency span, and does not pose a problem in actual observation. This zone can be set at an arbitrary position on the display screen. When the zone center is set to surround the peak point of a waveform to be enlarged, and the frequency span is switched, the waveform which is enlarged to have the zone center as the center can be observed. When the frequency span is reset to an original value, the original entire waveform can be observed. In this embodiment, when the frequency span is changed/set, the start frequency and the center frequency are automatically updated to have the zone center as the reference position as the center, and when the start frequency and the center frequency as other condition frequencies are changed, the sweep detection frequency range is merely shifted like in the conventional apparatus. However, as shown in Fig. 5, an old start frequency memory 50, an old center frequency memory 51, a start·span frequency calculation unit 52, a center·span frequency calculation unit 53, and respective frequency correction units 53 to 57 may be arranged, so that even when the start frequency or the center frequency is changed, enlargement or reduction can be reversibly performed to have the zone center as the center. In this case, the start·span frequency calculation unit 52 calculates a new start frequency and a new frequency span as follows: F(st) N = F(st) O + (F(zc)-F(st) O ) × A F(sp) N = F(sp) O × A (for A = (F(zc)-F(c) N )/(F(zc)-F(st) O )) These calculated values are corrected by a frequency deviation (ΔF) by the frequency correction units 54 and 55, and are set in the corresponding memories. The center·span frequency calculation unit 53 calculates a new center frequency and a new frequency span as follows: F(c) N = F(c) O + (F(zc)-F(c) O ) x B F(sp) N = F(sp) O x B (For B = (F(zc)-F(st) N )/(F(zc)-F(st) O )) These calculated values are corrected by a frequency deviation (ΔF) by the frequency correction units 56 and 57, and are set in the corresponding memories. Therefore, even when any one of condition frequencies, i.e., the start frequency, the center frequency, or the frequency span is changed, enlargement or reduction having the zone center as the reference position as the center can be performed. In the above embodiment, the frequency axis is changed to have the zone center as the reference position. However, the present invention is not particularly limited to the zone center. There is no essential difference even when the frequency axis is changed to have the left or right end of the zone as the reference position. In addition, in a spectrum analyzer which does not have a zone marker function, and manually sets a marker point, the frequency axis may be changed to have the marker point as the reference position. In this case, as shown in Fig. 6, a marker position setting unit 60 for variably setting a marker position is arranged, a frequency at the marker is input to the second start·center frequency calculation unit 40 in place of a zone center frequency, and the calculated new start frequency and center frequency can be respectively set in the corresponding memories, thus allowing enlargement/reduction of a spectrum waveform to have the marker point as the reference. As shown in Fig. 7, a value set from a reference position setting unit 61 in a reference position memory 62 may be input to a frequency deviation calculation unit 38' in place of a zone center, so that the position of a manually moved marker point can be largely moved to the preset reference position of the display screen upon changing of the frequency span. In the spectrum analyzer according to the first embodiment of the present invention, as described above, since enlargement/reduction on the frequency axis can be performed while the frequency at the reference position set on the screen is fixed, the entire spectrum waveform, and a spectrum waveform obtained by enlarging a portion of the entire waveform (by the ZOOM function) can be easily alternately observed by only changing the condition frequencies, and the reference position can be set at an arbitrary position, resulting in a very easy-to-use apparatus. Since a marker position can be close to the reference position by a change operation of the condition frequencies, operability can be greatly improved. Note that portions in Fig. 3B which do not correspond to Fig. 3A will be described later in the second and subsequent embodiments by denoting them by the same reference numerals as in Fig. 3A. (Second Embodiment: Magnifying Glass Display Function) A magnifying glass display function according to the second embodiment of the present invention will be described below. Fig. 8 is a block diagram showing an arrangement of a spectrum analyzer according to the second embodiment in correspondence with the basic arrangement shown in Fig. 1. A measurement unit U100 of this spectrum analyzer is arranged, as shown in Fig. 8. More specifically, the measurement unit U100 causes a mixer 101 to mix an input signal to be measured from an input terminal 8 with a signal from a local oscillator 105 so as to convert the input signal into an intermediate frequency signal IF, and causes a detector 103 to perform level detection via an IF processor 102 as an intermediate frequency circuit. In addition, the unit U100 sends digital (spectrum waveform) data obtained by converting the level-detected signal into a digital signal by an analog·digital (A/D) converter 104 to a waveform memory 5 included in a display data processor U20 of the next stage. On the other hand, a measurement controller U30 sweeps the frequency of the local oscillator 105 via a sweep signal generator 106 by a desired band so as to sweep a signal within a frequency region to be measured, and as a result, an input signal to be measured is measured by the measurement unit U100. The waveform memory 5 which received the digital (spectrum waveform) data corresponding to the input signal to be measured from the measurement unit U100 of the spectrum analyzer stores the digital data as the levels of the input signal to be measured in correspondence with the measurement frequencies, and outputs the stored data to display them on a display device U500 (for example, on a CRT screen). Upon reception of the output signal from the waveform memory 5, the display device U500 displays a spectrum on the display screen. This control is performed by a display controller 6 and a trace memory 7 included in the display data processor U20. Control for the measurement unit U100 and the waveform memory 5 is performed by the measurement controller U30. The arrangement and operation described so far are the same as the known technique. According to the present invention, a first parameter setting unit U600 for setting parameters for operating the spectrum analyzer is arranged. The first parameter setting unit U600 is used by a user to set parameters, e.g., a total frequency range (a center frequency and a frequency span), units of the scale (scale factor) of the display screen, a resolution bandwidth (RBW), a video bandwidth (VBW), and the like. Parameters set by the first parameter setting unit U600 are stored in a first parameter memory T12 included in an enlargement display/stable display processor U40 as needed. In order to determine a magnifying glass display range, a zone setting unit T9 for setting a zone is arranged in a reference parameter setting unit U800, and sets the center position and width of the zone. These data are stored in a zone setting memory T11. The zone center position serves as an enlargement central position in the magnifying glass display. Furthermore, a second parameter setting unit U700 is arranged, and sets a scale factor (or magnification) to be displayed in an enlarged scale. The position on the frequency axis as the center of enlargement is as one characteristic feature of the present invention, and represents coinciding points between an enlarged waveform and a non-enlarged waveform (foreground and background waveforms). Based on these three parameters or the data set by the zone setting unit T9, a frequency parameter for sweep-displaying a waveform with the [scale factor set by the second parameter setting unit U700] without changing the position on the frequency axis is calculated by a frequency calculation unit T15, and the calculation result is stored in a second parameter memory T13. Data from the first and second parameter memories T12 and T13, and the zone setting memory T11 are consequently used in control by the measurement controller U30 or the display controller 6, as shown in Fig. 8. As described above, in the arrangement of the second embodiment, a portion for setting an arbitrary one frequency within a measurement frequency region of a waveform displayed at the first scale factor corresponds to the second parameter setting unit U700 in the embodiment shown in Fig. 8, and a portion for setting the second scale factor also corresponds to the second parameter setting unit U700, but may be realized by the zone setting unit T9. A control unit for enlarging a waveform at the intra-zone scale factor as compared to a waveform outside the zone is constituted by the frequency calculation unit T15, the second parameter memory T13, and the display controller 6 shown in Fig. 8 in addition to the measurement controller U30. As has been described above with reference to Fig. 23 and Figs. 24A and 24B, a sweep operation of the magnifying glass display function includes three different sweep methods. These methods will be described below in correspondence with the above arrangement. Parameters set by the first parameter setting unit U600 are those for sweeping portions corresponding to A ○ and C ○ in Fig. 23, i.e., for sweeping the overall signal. Parameters set by the second parameter setting unit U700 are those for sweeping a signal inside the zone set as a portion B ○ in Fig. 23. A sweep width information generator T14 controls sweep operations of the portions A ○, B ○, and C ○ in Fig. 23. Based on zone information set by the zone setting unit 9, the generator controls sweep start frequencies of the portions A ○, B ○, and C ○ in Fig. 23. The display controller 6 can have its principal function of arranging the portions A ○, B ○, and C ○ in Fig. 23 as one trace, and controlling to display a zone, and can also have a function of performing scroll processing of a waveform inside the zone. Fig. 10 shows an example wherein the waveform memory 5 is split into two memories. When the waveform memory is split into two memories, sweep operations for A ○ and C ○ are continuously performed (therefore, a sweep operation of a background portion of B ○ is also performed), and data are stored in a waveform memory 51. A waveform memory 52 stores data obtained by only a sweep operation of B ○. Fig. 9A shows a modification of the second embodiment. In Fig. 9A, in addition to the arrangement shown in Fig. 8 for realizing the magnifying glass display function, an intra-zone feature point detector T16 for receiving a feature point designation signal in a set zone, and detecting a feature point from information stored in the waveform memory 5 is arranged so as to execute zone tracking. A peak is normally designated as a feature point in the zone. However, a dip is sometimes designated. Based on the position of the feature point within the zone, and the frequency at that point, parameters such as a frequency for determining the zone so as to locate the designated point at the predetermined position (e.g., the center) of the zone are calculated by the frequency calculation unit T15, and data in the second setting parameter memory T13 are rewritten with these parameters. Based on the rewritten information, the display controller 6 is consequently operated, and a desired display is made on the display device U500. Fig. 9B is a flow chart showing in detail an operation shown in Fig. 9A. The intra-zone feature point detector T16 determines whether or not a detected feature point is located at the center of the zone (step S1). If the feature point is located at the center, a display is made without changing the zone position (step S7); if the feature point is shifted from the center, a position shift amount A from the center is calculated (step S3). Thereafter, the sweep start frequency of the zone is increased by an amount (A·ΔF Z ) corresponding to the position shift amount (step S4). At the same time, a calculation for changing the position of the zone with respect to the entire screen by an amount (A·SP Z /SP O ) corresponding to the shift amount A is performed (step S5). In the above description, ΔF Z , SP O , and SP Z respectively represent ΔF Z : a frequency deviation per unit shift amount, SP O : a frequency span set by the first parameter setting unit, and SP Z : a frequency span in the zone. In Fig. 22, this value corresponds to a₃ in the figure. Note that a change in position is stored in the zone setting memory T11 (step S6). These functions are performed by a zone changing unit T18. Sweep and display operations of the zone are performed according to the stored (updated) content (value) of the zone setting memory T11, i.e., the new start frequency and new zone position (step S9). With this function, since the feature point can always be displayed at the center of the zone, an easy-to-see intra-zone display can be made. The frequency calculation unit 15 shown in Fig. 9A calculates frequency parameter values to be set as first and second parameters according to the difference between a frequency at the reference position and a frequency at the feature point, and the measurement controller controls the measurement unit according to these pieces of information, thereby realizing a so-called intra-zone signal tracking function with which a peak of a waveform is always present within a zone. The second embodiment of the present invention can provide the following effects. First, since a spectrum near a desired signal can be simultaneously measured while observing a wide-band spectrum, an enlarged image at a desired position can be displayed without changing one point on the frequency axis (without movement in position) while observing the overall image. Since a trace within the zone can be displayed as a trace continuous with the overall trace, data can be displayed as one frame by one trace unlike in the FG & BG two-frame display function. In this manner, since a one-trace display can be attained, a memory capacity necessary for saving or recalling trace data can be decreased, and for example, maximum value holding processing (MAXHOLD) and average processing (AVERAGE) can be easily realized. Since the one-trace display is made, a substantially two-channel display for simultaneously displaying traces of different detection modes can be easily realized. In the signal tracking function of the prior art, since a waveform is always displayed at the center of the CRT screen, it is not easy to intuitively grasp the frequency drift width of a signal. However, in the zone tracking function of the present invention, since the one-trace display is made, the drift width can be read from movement of the displayed zone. In addition, the drift width can be directly read by observing a moving amount of the zone along the scale of the overall abscissa. The difference between the zone tracking function of the present invention and the signal tracking function of the prior art will be examined below. In the conventional signal tracking function, when a signal falls outside a screen, a wide frequency span must be set again to capture a signal again. However, in the "zone tracking" function of the present invention, since a wide-band spectrum is originally displayed on the entire screen, a signal can be easily captured again by only turning on/off the magnifying glass function. In this manner, according to the second embodiment, a spectrum analyzer which can improve the conventional zone marker, zone sweep, signal tracking, and FG & BG two-frame display functions, and can eliminate inconvenience in operations can be provided.

Claims: A waveform display apparatus of frequency sweep type, comprising: a measurement unit (U100) for measuring a signal by sweeping a frequency range under a predetermined measurement frequency condition so as to obtain waveform data corresponding to the frequency range; and a display device (U500) for displaying the waveform data obtained by said measurement unit (U100) by developing the waveform data on the frequency axis, characterized in that said apparatus further comprises: first parameter setting means (U600) adapted to change one of four frequency parameters when two out of said four frequency parameters are set to determine a measurement frequency range, said four parameters including a start frequency, a stop frequency, a center frequency, and a frequency span, said parameters defining the predetermined measurement frequency condition; reference parameter setting means (U800) for setting an arbitrary position on the frequency axis on said display device (U500) as a reference position; and control means (U200) adapted to change when said first parameter setting means (U600) changes the one of the four frequency parameters, the measurement frequency range in said measurement unit (U100) according to the changed parameter while maintaining the frequency at the reference position on said display device (U500) set by said reference parameter setting means (U800) to be equal to the reference frequency position before the one frequency parameter is changed. A waveform display apparatus according to claim 1, wherein said control means (U200) includes a feature point detection unit (T16) for detecting a frequency at a feature point of the waveform data obtained by said measurement unit (U100), and a frequency deviation calculation unit (T15) for detecting a difference between the frequency at the feature point detected by said feature point detection unit (T16) and the frequency corresponding to the reference position set by said reference parameter setting means (U800), and controls the measurement frequency range in said measurement unit (U100) in accordance with the difference information from said frequency deviation calculation unit (T15), so that the frequency at the reference position coincides with the frequency at the feature point. A waveform display apparatus according to claim 1 or 2, wherein said reference parameter setting means (U800) includes means for setting a condition representing a zone on the frequency axis on said display device (U500), a predetermined position in the zone being set as the reference position. A waveform display apparatus according to claim 2 or 3, wherein said feature point detection unit (T16) includes means for detecting a frequency at the feature point corresponding to the waveform data in the zone.

Inventors: IIYOSHI KATSUHISA, IMAZU YOSHIFUMI, KAMIYAMA KATSUHIKO, KATAYAMA AIICHI, KAWAUCHI TAKEHIKO ANRITSU FAMI, TAKANO MITSUYOSHI, WADA TAKAHIRO, IIYOSHI, KATSUHISA, IMAZU, YOSHIFUMI, KAMIYAMA, KATSUHIKO, KATAYAMA, AIICHI, KAWAUCHI, TAKEHIKO, ANRITSU FAMIRIE NURUMIZU 306, TAKANO, MITSUYOSHI, WADA, TAKAHIRO
Applicants: ANRITSU CORP, ANRITSU CORPORATION
Application year: 1991
Main classification: G01R23
IPC codes: G01R13, G01R23