US3571755A

US3571755A - Sweep oscillator

Info

Publication number: US3571755A
Application number: US816250A
Authority: US
Inventors: Mitsuhiro Ejiri
Original assignee: Iwatsu Electric Co Ltd
Current assignee: Iwatsu Electric Co Ltd; Iwasaki Tsushinki KK
Priority date: 1968-04-18
Filing date: 1969-04-15
Publication date: 1971-03-23
Anticipated expiration: 1988-03-23
Also published as: NL6906070A; GB1262671A; DE1919862A1; DE1919862B2

Abstract

A sweep oscillator used to generate a sawtooth wave that can be amplified to serve for deflecting the electron beam of a cathoderay tube in synchronism with any of input pulses, where the different slopes of the sawtooth wave are successively switched automatically until any of the input pulses is not received within a predetermined first interval starting in synchronism with the start of the sawtooth wave and, when the number of the input pulses received within a predetermined second interval included within the duration of the sawtooth wave and longer than the first interval is less than the predetermined number, a sawtooth wave having the gentlest slope is generated.

Description

United States Patent s41 swear OSCILLATOR 3Claims,l7l)rawingfigs. [52] Us. 331/143, 328/i85,33l/153 [5!] Int. H03k4/08 [50] FieldotSearch 331/143,

sweep GATE [56] References Cited UNITED STATES PATENTS 3,493,961 2/1970 Hansen Primary Examiner-John Kominski Attorneys-Robert E. Burns and Emmanuel .l. Lobato ABSTRACT: A sweep oscillator used to generate a sawtooth wave that can be amplified to serve for deflecting the electron beam of a cathode-ray tube in synchronism with any of input pulses, where thedifferent slopes of the sawtooth wave are successively switched automatically until any of the input pulses is not received within a predetermined first interval starting in synchronism with the start of the sawtooth wave and, when the number of the input pulses received within a predetermined second interval included within the duration of the sawtooth wave and longer than the first interval is less than the predetermined number, a sawtooth wave having the gentlest slope is generated.

MIENIEU mm M SHEET 01 0F 10 fl HOLD CIRCUIT H 1 V1! Y W Z CONTROL SAlX/XggTH CIRCUIT GENERATOR F 1-7 AUTOMATIC SELECT/0N CIRCUIT f RESET i CIRCUIT 21 HOLD F 2 CIRCUIT S It? SAW room f 1g wasp WAVE 0 w GATE w asumamn V0 ,1 I L Iat.GATE 2 #21313 COUNTER CIRCUIT I f L I ,2 IHV FRIFQM I; ira/v0 "MATE 51mm? I 22557 l9 COMPARATO we HOLD 2 CIRCUIT I r a 4 I SWEEP saw-room WAVE $0 GATE Lil/2 GENERATO ug 5 ,7 a 1st. GATE 9% sgmE CI IT {/8 {/2 21116415, j, FR21. l a5 DIV/DER CIRCUIT DIFEER ENTIATOR 3 CIRCUIT PATENTED mes 187i 3571'- 755 I SHEET 13 [1F 10 HOLD CIRCUIT SWEEP 15!. GATE W4 D/l-'!-'ER- ENTIATOR HOLD CIRCUIT {2 j 4 5 Fig. "f?

I I SWEEP sAw-roorH f GATE CEVAVZ'QXETORV L m B/$TABLE FRED. MONO CIRCUIT DIVIDR 73555 PATEN'TED HAR 2 3:97:

SHEET an 1 0 WAVE We GENERATOR SAW-TOOTH Isl. GATE cIRcu/f MONO STABLE DELAY 7 cmcu/r W10 '4 FREQ. DIV/DER CIRCUIT D/FFER EN TIA TOR B/STABLE GATE 1 sws Hllllllllll Fig; 9

iii f gggglllgllil PATENTEU mas I97! SHEET 05 0F 10 lllllllfllL PATENTED MAR23 1911 SHEE 07 0F 10 w mm PATENTEDHARNIQYI v 3.571; 155

- sum 09 or 10 PATENTED

HAR23 I97l SHEET

10 or 10 Fig. I6

swans oscutn'ron This invention relates to a sweep oscillator used to generate a sawtooth wave that can be amplified to serve for deflecting the electron beam of a cathode-ray tube in synchronism with any of input pulses.

in conventional sweep oscillators of this type, the number of cycles to be displayed on a cathode-ray tube in preset in case of observation of the waveform of an input signal, and the sweep period of the sawtooth wave generated is automatically switched in response to the start control by a manual switch so that the input signal of the preset number of cycles can be observed on the cathode-ray tube.

However, the conventional sweep oscillators have disadvantages such that the automatic switch operation of the sweep period of the sawtooth wave is not started without control of the manual switch, and thatif the frequency of the input signal alters from a high frequency to a lower frequency the sweep period of the sawtooth wave is not automatically switched without another control of the manual switch. in other words, the sweep period of the sawtooth wave is not switched automatically in accordance with the change of the frequency of the input signal.

An object of this invention is to provide an automatic sweep oscillator eliminatable of the above-mentioned defects of the conventional ones, switchable successively of the period of the sawtooth wave towards the shorter period if the frequency of the input signal alters from lower to higher, and resettable automatically of the longest period of the sawtooth wave if the frequency of the input signal alters from higher to-lower.

Accordingly, the automatic sweep oscillator of this invention has the following merits over the conventional ones:

1. Manual control is not necessary even if the frequency of the input signal alters.

2. Since the period of the sawtooth wave is automatically switched in accordance with the frequency of the input signal, steady synchronization of the sawtooth wave with the frequency of the input signal is always obtained.

The principle of this invention will be better understood from the following more detailed discussion taken in conjunction with the accompanying drawings, in which the same or equivalent parts are designated by the same reference numerals, characters and symbols, and in which:

Fit l is a block diagram for describing the principle of construction of this invention;

H68. 2, 3, 4, 5, 6 and 7 are block diagrams each for illustrating an embodiment of this invention;

FlGS. d, 9, it), ll, 12 and 13 are time charts explanatory of the operations of the embodiments shown in FIGS. 2, 3, 4i, 5, 6 and 7 respectively;

HG. l4 is a block diagram for illustrating in details an embodiment of this invention;

H08. l5, l6 and 17 are time charts explanatory of the operation of the embodiment shown in HQ 14; and

HG. 16 shows time charts explanatory of the principle of determining reference levels used in the embodiment shown in FIG. l4.

With reference to P16. 1, the principle of construction of this invention will first be described. This automatic sweep oscillator of this invention for generating a sawtooth wave synchronized with any of input pulses applied from an input terminal Vl comprises: (1) a sawtooth wave generator I for generating a sawtooth wave synchronized with one of a plurality of predetermined different slopes, (2) a hold circuit ll generating an output when the sawtooth wave reaches a predetermined level, (3) a control circuit ill for determining the duration of the sawtooth wave by starting the sawtooth wave in synchronism with one of the input pulses and by terminating the sawtooth wave in synchronism with the output of the hold circuit ll, (4) an auto selection circuit IV for switching successively the different slopes of the sawtooth wave from a gentle one to a sharp one and for stopping the switching when any of the input pulses is not received within a predetermined first interval starting in synchronism with the start of the sawtooth wave, and (5) a reset circuit V for controlling the automatic selection circuit lV so that the sawtooth wave generator l generates a sawtooth wave having the gentlest slope when the number of input pulses received within a predetermined second interval included within the duration of the sawtooth wave and longer than the first interval is less than the predetermined number. The sawtooth wave generated is obtained at an output terminal Vll. Actual embodiments of this invention will be described below.

in an embodiment of this invention shown in FIG. 2 a sweep gate 2 produces a sweep gate signal w in response to one of input pulses w. applied from an input terminal 1. A sawtooth wave generator 4 generating a sawtooth wave w in synchronism with the sweep gate signal W A hold circuit 21 for closing the sweep gate 2 when the sawtooth wave w reaches a voltage (determined so as to be sufficient to fullsweep the horizontal scanning of a cathode-ray tube in case of applying this invention to an oscilloscope using the cathoderay tube) and for holding the closed state of the gate 2 until restoration of the level of the sawtooth wave w;, to the original level. A first gate 6 produces a gate signal w, started in synchronism with the start of the sweep gate signal W and terminated when the sawtooth wave w reaches a first predetermined level. An AND gate 8 passes the input pulses w only when the gate signal w is applied from the first gate 6. A monostable circuit 9 is triggered by the output of the AND gate 8 and produces an output pulse having a width determined by the time constant of this circuit 9. A counter it) counts the number of output pulses from the monostable circuit 9. Predetermined different slopes of the sawtooth wave W3 are switched in accordance with the counting state of the counter 10. A second gate 12 is opened in synchronism with the termination of the gate signal w., and closed when the sawtooth wave w reaches a predetermined second level. An inhibit gate 13 is opened in case of no output of a l/N frequency divider 14 (described below) and passes the input pulses only in the opened period of the second gate 12. The l/N frequency divider 1d divides by l/N the repetition frequency of the pulses passed through the inhibit gate 13. This division ratio MN is determined in consideration of the number of cycles to be displayed on the cathode-ray tube. A comparator w generates an output pulse w when the level of the sawtooth wave reaches a predetermined threshold level. An inhibit gate 16 inhibits or passes the output pulse w of the comparator 19 in response to generation or nongeneration of the output pulse w from the l/N frequency divider respectively. A monostable circuit 17 is triggered by the output pulse W9 of the inhibit gate 16 and generates a reset pulse the duration of which is determined in accordance with the time constant of this monostable circuit 17. This reset pulse is applied to the counter 10 to reset the counting state of the counter 10 so as to make the sawtooth wave generator t generate the sawtooth wave w having the gentlest slope.

The operation of this embodiment will be described with reference to H6. 7.

At first, the operation of successive automatic selection of different sweep periods is described. It is assumed that the input signal is a pulse train (w in FIG. 8) timed with successive cycles of a signal to be synchronized with the sawtooth wave W3. The state of the gate signal W is revemd in response to one of pulses of the pulse train w,. The sawtooth wave generator 4 starts the generation of the sawtooth wave w,, in response to the reverse of the state of the gate signal W2. The first gate 6 is opened at the same time as shown by the gate signal W4 and closed at an instant when the level of the sawtooth wave W3 reaches a predetermined level at a point A. W pulses of the input pulse train w are received within the duration of this gate signal W4, these pulses pass through the AND gate 8 and trigger the monostable circuit 9. The number of the output pulses of the monostable circuit 9 is counted by the counter 10. Accordingly, the counting state of the counter ill) is counted up and the predetermined different slopes of the sawtooth wave W3 corresponding to the successive counting states of the counter 10 are successively switched at the sawtooth generator 4 in accordance with the successive counting up of the counting state of the counter 10. This switching operation of the slope of the sawtooth wave w continues until no pulse is received within the duration of the gate signal w.,.

The reset operation of this embodiment to an original state where the sawtooth wave generator 4 generates the sawtooth wave having the gentlest slope will be described below. The second gate 12 generates the gate signal W5 started in timed with the termination of the gate signal w and terminated when the level of the sawtooth wave w reaches a predetennined threshold level at a point B. The input pulses (w, applied within the duration of this gate signal w passes through the inhibit gate 13 unless this inhibit gate 13 is closed by the output of the 1/N frequency divider as mentioned below. If it is as sumed that the l/N frequency divider 14 is designed as a 1/3 frequency divider, the state of the output signal w of this frequency divider 14 is reversed by the third of pulses (w,) passed through the inhibit gate 13 as illustrated in FIG. 8. At the same time, the inhibit gate 13 is closed by this output signal w, so that any of the input pulses (w,) cannot pass through the inhibit gate 13. Moreover, the inhibit gate 16 is closed by the output signal w so that the output pulse w,, of the comparator 19 generated when the level of the sawtooth wave reaches a predetermined level at a point C cannot pass through the inhibit gate 16. However, if the state of the frequency divider 14 is not reversed within the duration of the gate signal w, the output pulse w, of the comparator 19 passes through the inhibit gate 16 opened and triggers the monostable circuit 17. This condition is obtained in the case where the number of pulses (w,) included within the duration of the gate signal W5 is less than the number (N) predeternrined. The output pulse of the monostable circuit 17 resets the counter to its original counting state corresponding to the gentlest slope of the sawtooth wave w As mentioned above, the successive selection of different sweep periods (i.e.; different slopes) of the sawtooth wave w and the resetting to the gentlest slope of the sawtooth wave W3 can be automatically performed by the embodiment of this invention shown in FIG. 2. In other words, if the sawtooth wave w if applied as the horizontal scanning wave (sweep signal) of an oscilloscope using a cathode-ray tube, the period of the sawtooth wave W is successively switched in an automatic manner from longer to shorter until the number of cycles of a signal displayed on the oscilloscope becomes equal to a predetermined number N determined by the frequency-division ratio 1/N of the frequency divider 14. Moreover, this synchronized condition will be satisfied by the same operation as mentioned above if the frequency of the displayed signal changes from lower to higher. However, the frequency of the displayed signal changes from higher to lower after the abovementioned synchronization, the succeeding synchronization will be obtained by perfonning the above-mentioned switching operation after the resetting of the period of the sawtooth wave w to the shortest period in accordance with the fore mentioned resetting operation.

With reference to FIGS. 3 and 9, another embodiment of this invention will be described. In this embodiment,

circuits

2, 4, 6, 8, 9, 10, 12, 13, l4, 16, 17 and 21 are the same as those of FIG. 2 respectively. A ditferentiator 19 generates a pulse w timed with the rise time (start) of the gate signal w applied from the sweep gate 2. A delay circuit 20 delays the output signal w, of the llN frequency divider by a time A T. In this embodiment, the operation in successively selecting the different slopes of the sawtooth wave W3 is the same as the operation in the embodiment shown in FIG. 2. However, the resetting operation to the shortest period of the sawtooth wave w, is different from the resetting operation of the embodiment shown in FIG. 2. The delay time A T of the delay circuit 20 is determined so as to be sufficiently longer than the duration of the output pulse w of the differentiator 19 so that the output pulse w cannot pass through the inhibit gate 16 unless the output w, of the 1/N frequency divider 14 is generated. As the result of this construction, the output pulse w, can be passed through the inhibit gate 16 only when the above mentioned synchronization condition is performed, so that the output pulse W9 triggers the monostable circuit 17 so as to reset the

circuits

4, 9, 10 and 14.

FIG. 4 shows another embodiment of this invention, in which all of circuits except the second gate 12 are the same as those shown in FIG. 2 respectively. While one of the inputs of the second gate 12 is connected to a line 7 of the output of the first gate 6 in FIG. 2, one of the inputs of the second gate 12 of this embodiment is connected to a line 3 of the output of the sweep gate 2. Operational waves W W w and W4 of this embodiment are, as shown in FIG. 10, the same as the waves w,, W W and w shown in FIG. 8 respectively. While the start of the second gate 12 is timed with the termination time of the gate signal W; in the embodiment shown in FIG. 1, the start of this second gate 12 in this embodiment is timed with the start of the gate signal W2. The termination of the gate signal W5 obtained from the second gate 12 is delayed by an appropriate time from the termination time of the gate signal w, obtained from the first gate 6. These termination times of the gate signals W4 and W5 are determined in the

gates

6 and 12 as shown by points A and B in FIG. 10 respectively. Threshold levels determining the points A and B are concerned in the number of pulses of the input pulse train w, included within the duration of the sawtooth wave W3.

FIG. 5 shows another embodiment of this invention which comprises the automatic selection function (i.e.;

circuits

2, 4, 21, 6, 8, 9 and 10) of the embodiment shown in FIG. 3 and the resetting function (i.e.;

circuits

12, 13,14, 16, 17, 19 and 20) of the embodiment shown in FIG. 4. Operative waves of respective parts of this embodiment are shown in FIG. 11. Details of the operation of this embodiment are omitted since this operations will be readily understood with reference to the operations of the forementioned embodiments.

FIG. 6 is another embodiment of this invention, in which a bistable circuit 12a is employed instead of the second gate 12. The state of this bistable circuit 12a is set in response to the termination of the gate signal W4 obtained from the first gate 6 and reset in response to the termination of the gate signal w obtained from the sweep gate 2. Other circuits are the same as those of the embodiment shown in FIG. 2. Operational waves of respective parts of this embodiment are shown in FIG. 12. Waves w,, w, w;, and w, are the same as those shown in FIG. 8 respectively. The wave w, of the output of the bistable circuit starts in response to the termination of the gate signal w. obtained from the first gate 6 and terminates in response to the termination of the gate signal w obtained from the sweep gate 2. Other waves w to W9 are the same as those shown in FIG. 8 respectively.

FIG. 7 shows a modification of the embodiment shown in FIG. 6, in which the differentiator 19 and the delay circuit 20 described in the embodiments of FIGS. 3 and 5 are employed instead of the comparator 19. Operational waves of respective parts of this embodiment are shown in FIG. 13. Waves w,, W W W4, w,,, w and w, are the same as those shown in H6. 12 respectively. The delay circuit 20 delays the output signal w, of the UN frequency divider 14 by a delay time T so that the output signal W8 of the differentiator 19 is inhibits in the inhibit gate 16 in case of synchronization condition. If the output signal W7 is not obtained in case of no synchronization condition, the output pulse w passes through the inhibit gate 16 opened and triggers the monostable circuit 17 so as to reset the

circuits

9, 10 and 14 through'a line 18.

More detailed discussion of an embodiment of this inven tion will be described below with reference to FIGS. M, 15, 16 and 17. MG. 14 shows a detailed block diagram of an embodiment of this invention corresponding the embodiment shown in FIG. s. In this block diagram, only different circuits or connections from the embodiment of FIG. 6 will be described. A shaper 22 generates a triangular wave W 4 synchronized with an input signal W13 by limiting the level of the input signal W3). A difierentiator 23 generates a pulse train each pulse of which is timed with the start of each pulse of the triangular wave. An unblanking amplifier 24 amplifies the output of the sweep gate 2 to apply the amplified signal to the grid or cathode of a cathode-ray tube through a terminal 25 to turn on the beam for the duration of the sawtooth wave w. The first gate 6 generates the gate signal w, started in response to the start of the gate signal w and terminated in response to the termination of the gate signal w, or when the level of the sawtooth wave reaches a predetermined threshold level. The monstable circuit 9 comprises an inhibit gate 9-1 and a rnonostable circuit 9-2. The counter comprises a ring counter 10-1 and a bistable circuit 10-2. This bistable circuit 10-2 is set by the trigger pulse generated from the counter 10-1 when the counting state of the counter 10-1 reaches a counting state corresponding to the sharpest slope of the sawtooth wave w and reset by the output of the inhibit gate 16. The 1/N frequency divider 14 comprises a scale-of-N counter 14-1, a pulse converter generating an output pulse when the counting state of the counter 14-1 becomes indicate the highest counting state thereof, and a bistable circuit 14-3 set by the output pulse of the pulse converter 14-2 and reset in response to the termination of the output (the wave W2) of the sweep gate 2). The rnonostable circuit 17 may be provided with a manual reset switch as shown.

With reference to FIG. 15, the automatic selection operation of different sweep periods of the sawtooth wave W3 from longer to shorter is at first described. An input signal W13 is applied through a line 1 to the shaper 22, in which this input signal W13 is converted to a triangular wave w,4. This triangular wave w,4 is converted to a pulse train w including pulses P P P P, which are applied to the sweep gate 2. The state of the output signal w of the sweep gate 2 is reversed to the state 1 in response to the first pulse P In response to this reverse operation, the sawtooth wave generator 4 starts to generate the sawtooth wave W3. The first gate 6 generates the output signal w. starting in response to the start of the signal W and terminating in response to the termination of the signal w or when the level of the sawtooth wave w reaches a threshold level (predetermined in this first gate 6 to set the number of cycles of the input signal W13 included within the duration of the sawtooth wave W3). Any of pulses P P P;,,.... included within the duration of the signal w are passed through the AND gate 8 and the inhibit gate 9-1 since this inhibit gate 9-1 is not inhibited from the output of the monostable circuit 17 at this time. Pulses (i.e.; P and P in this case) passed through the AND gate 8 and 9-1 trigger the monostable circuit 9-2, which generates a triangular wave w,2. Pulses timed with the start instants of cycles of the triangular wave W12 trigger the ring counter 10-1 and the hold circuit 21, so that the counting state of the counter 10-1 changes successively to control the sawtooth wave generator 4 generate the sawtooth wave W3 W having successively sharper slopes, and so that the state of the hold circuit 21 is reversed. In response to the reverse operation of the state of the hold circuit 21, the state of the output signal W2 of the sweep gate 2 is restored from the state 1 to the state 0. A time A l is a delay time in the hold circuit 21 from a time triggered by the start of the wave w,2 to a time resetting the sweep gate 2. The above mentioned operations are repeated until none of pulses P P P is included within the duration of gate pulse (W4). FIG. shows three cycles of the above-mentioned operations. When the counting state of the counter 10-1 reaches a counting state corresponding to the sharpest slope of the sawtooth wave W3, the state of the bistable circuit 10-2 is set and this set state of the bistable circuit 10-2 resets the state of the rnonostable circuit 4-2.

As mentioned above, synchronization between the input signal W13 and the sawtooth wave W3 is performed. Waves W13, W14, w W3, W2, W4, W W w 5 and w.6 show operational waveforms of respective parts designated in FIG. 14 in the case of this synchronization condition. In this case, the scale N of the counter 14-1 is three so that the repetition frequency of the pulse train W is counted down to one-third at the output of the pulse converter 14-2. Details of the operation of this condition are omitted since this operation will be understood with reference to the operation of the forementioned embodiments (particularly to the operation of theembodiment shown in FIG. 6).

The operation of the embodiment shown in FIG. 14 in the case of changing the frequency of the input signal w,3 from higher to lower will be described below as illustrated by signals W13 and w,3a in FIG. 16. This is the resetting operation to the gentlest slope of the sawtooth wave When the input signal" W 3 changes its frequency as show by the wave w 3a, the "waves W14 and W are also changes to waves 14a and w respectively as shown. However, the waves W W W4 and W5 are not changedQWhile the bistable circuit assumes the state 1, the AND gate 13 is opened so that pulses of the pulse train W passes through the opened AND gate 13. However since the frequency of the input signal w of this case is lower than the frequency of the former input signal W only two pulses can pass through the AND gate 13 at an interval where the AND gate is opened by the signal W5. Accordingly, the state of the counter 14-1 is not changed to the state 1 and the bistable circuit 14-3 assumes the state 0. Therefore, the inhibit gate 16 is not inhibited at this time. If the reference level of the comparator 19 is determined as shown by a point B on the wave W3, the comparator 19 generates a pulse w when the level of the s sawtooth wave reaches this reference level in the comparator 19. This pulse W is applied to the rnonostable circuit 17 and the bistable circuit 10-2 through the inhibit gate 16 opened. At this time, the state of the rnonostable circuit 17 changes to the state 1 lasting a duration T as shown by a wave w The wave w inhibits the inhibit gate 9-1 within an interval equal to the duration T and resets the counting state of the counter 10-1 to a state corresponding to the gentlest slope of the sawtooth wave W3. Moreover, the wave w resets the state of the hold circuit 21 to the original state. At the same time, the state of the bistable circuit 10-2 is reversed bythe output pulse of the counter 10-1 of this case and restored by the wave w passed through the opened inhibit gate 16 while the reset of the rnonostable circuit 9-2 is temporarily stopped by the reversed output of the bistable circuit 10-2.

The principle of the determination of the point A (the threshold level of the first gate 6) and of the point B (-the reference level of the comparator 19) will be described below with reference to FIG. 17. The duration I of the wave w obtained from the first gate 6 is concerned in determining the number of cycles of the input signal (W13) included in the duration of the sawtooth wave W3. This number of cycles is equal to the displayed cycles on the cathode-ray tube in case of applying this invention to a cathode ray oscilloscope. This number of cycles is inversely proportional to the time length of the duration t,. In case of the above-mentioned synchronization, a condition t t is essential, where 1 is the period of the input signal W13.

The set interval of the bistable circuit l2a(i.e.; the opened interval of the AND gate 13 is designated by a time t starting from the termination of the wave w (i.e.; the point A) and terminating in response to the termination of the wave W2. Therefore, a condition 2 NT (if N is three as assumed above, t 3 T) is satisfied. A time t shows an allowance of time for determining the point B and terminated in response to the termination of the wave w. This time i is essential to be smaller than the period t of the input signal W The reason for this is as follows. If four cycles (larger than the number N 3) of the input signal W is to be included in the duration of the sawtooth wave w it is unneccessary to switch the slope of the sawtooth wave to the gentlest one unless the input signal w less than three cycles is received within the duration of the sawtooth wave w If the'input signal w more than four cycles is received within the duration of the sawtooth wave W3, the output wave w (obtained at the point B) is not necessary since this wave w cannot pass the inhibit gate 16 inhibited by the output of the bistable circuit 14-3.

I claim:

' 1. An automatic sweep oscillator for generating a sawtooth wave synchronized with any of input pulses, comprising:

a sawtooth wave generator for generating a sawtooth wave synchronized with one of a plurality of predetermined different slopes",

a hold circuit generating an output when the sawtooth wave reaches a predetermined level;

a control circuit for determining the duration of the sawtooth wave by starting the sawtooth wave in synchronism with one of input pulses and by terminating the sawtooth wave in synchronism with the output of the hold circuit;

an automatic selection circuit for switching successively the diflerent slopes of the sawtooth wave from a gentle one to a sharp one and for stopping the above-mentioned switching when any of the input pulses is not received within a predetermined first interval starting in synchronism with the start of the sawtooth wave, and W a reset circuit for controlling the automatic selection circuit so that the sawtooth wave generator generates a sawtooth wave having the gentlest slope when the number of the input pulses received within a predetermined second interval included within the duration of the sawtooth wave and longer than the first interval is less than the predetermined number.

2. An automatic sweep oscillator, as in claim 1 in which the predetermined second interval starts from the termination of the first interval.

3. An automatic sweep oscillator, as in claim 1 in which the predetermined second interval starts from the start of the first interval.

Claims

1. An automatic sweep oscillator for generating a sawtooth wave synchronized with any of input pulses, comprising: a sawtooth wave generator for generating a sawtooth wave synchronized with one of a plurality of predetermined different slopes; a hold circuit generating an output when the sawtooth wave reaches a predetermined level; a control circuit for determining the duration of the sawtooth wave by starting the sawtooth wave in synchronism with one of input pulses and by terminating the sawtooth wave in synchronism with the output of the hold circuit; an automatic selection circuit for switching successively the different slopes of the sawtooth wave from a gentle one to a sharp one and for stopping the above-mentioned switching when any of the input pulses is not received within a predetermined first interval starting in synchronism with the start of the sawtooth wave, and a reset circuit for controlling the automatic selection circuit so that the sawtooth wave generator generates a sawtooth wave having the gentlest slope when the number of the input pulses received within a predetermined second interval included within the duration of the sawtooth wave and longer than the first interval is less than the predetermined number.