Alternate sweeping system for use in oscilloscope

In an alternating sweeping system for use in an oscilloscope of the type wherein a sweeping signal and a delayed sweeping signal are alternately supplied to a horizontal deflection circuit of the oscilloscope, and wherein a unblanking signal and a delayed unblanking signal are alternately supplied to a brightness modulation circuit, widths of the delayed sweeping signal and the delayed unblanking signal made to be less than one half of width of the sweeping signal and the unblanking signal so that the delayed blanking signal and the delayed unblanking signal are used a plurality of times during an interval in which the sweeping signal and the unblanking signal are used once.

BACKGROUND OF THE INVENTION 
This invention relates to an improvement of an alternate sweeping system 
for use in an oscilloscope. 
An alternate sweeping system has been used for a high grade oscilloscope 
for the purpose of displaying a waveform along an enlarged or expanded 
time axis. According to the alternate sweeping system a sweeping signal 
having a large signal width and a delayed sweeping signal having a small 
signal width are alternately applied to the horizontal deflection circuit 
of a cathode ray tube so as to alternately display a waveform with a not 
enlarged time axis and a waveform with an enlarged time axis. 
FIG. 1 diagrammatically shows such manner of display of a pulse signal, for 
example, in which A shows a waveform caused by a not delayed sweeping 
signal and B a waveform caused by a delayed sweeping signal. A thick line 
portion of A is enlarged as shown in B. 
However, the waveform caused by the delayed sweeping signal has a time axis 
enlarged more than several ten times of that of the waveform caused by the 
not delayed sweeping signal so that when sweeping with the delayed 
sweeping signal, the time required for an electron beam to impinge upon 
the fluorescent screen of the cathode ray tube is shortened with the 
result that the quantity of light emitted at bright lines decreases, thus 
making it difficult to observe the waveform caused by the delayed sweeping 
signal. 
This phenomenon results in the following disadvantage. More particularly, 
where an image signal waveform is to be observed, a waveform of one frame 
is displyed by a not delayed sweeping signal, while a waveform for an 
interval of 1H (an interval between the beginning of one horizontal 
scanning line and the beginning of the next horizontal scanning line) is 
displayed with a delayed scanning signal. In this case, as the ratio of 
enlargement of the time axes becomes large, the quantity of light emitted 
by bright lines of the waveform displayed for 1H decreases greatly, 
thereby not only making difficult to observe visually the displayed 
waveform but also making it impossible to photograph the displayed 
waveform. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of this invention to provide an improved 
alternate sweeping system for use in an oscilloscope capable of increasing 
the brightness of a waveform displayed by a delayed sweeping signal. 
According to this invention, there is provided an alternate scanning system 
for use in an oscilloscope of the type wherein a sweeping signal and a 
delayed sweeping signal synchronous therewith and having a narrower signal 
width than the sweeping signal are alternately applied to the 
oscilloscope, and wherein an unblanking signal corresponding to the 
sweeping signal and a delayed unblanking signal corresponding to the 
delayed sweeping signal are alternately applied to said oscilloscope, 
characterized by means for using the unblanking signal and the delayed 
unblanking signal a plurality of times during an interval in which the 
sweeping signal and the unblanking signal are used once.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In one embodiment of this invention shown in FIG. 2, a sweeping circuit 10 
generates a sweeping signal Ss and an unblanking signal Su synchronous 
with the sweeping signal and having the same width t1 as the sweeping 
signal Su. The sweeping circuit 10 comprises a gated multivibrator 12 such 
as a flip-flop circuit with an output of rectangular pulse wave form, an 
integrating circuit 13 integrating the output of the gated multivibrator 
12 to generate the sweeping signal Ss, and a hold-off multivibrator 14 
resetting the gated multivibrator 12 when the output of the integrating 
circuit 13 exceeds a predetermined level. When a trigger pulse is applied 
to the gated multivibrator 12 as an input thereof, a gate signal of the 
rectangular pulse wave form as shown in FIG. 3a is outputted from the 
gated multivibrator 12. The gate signal also serves as a unblanking 
signal. The gate signal is sent to the integrating circuit 13 for 
converting it to a saw tooth signal Ss as shown in FIG. 3c. The saw tooth 
signal is inputted into the hold-off multivibrator 14 so that, when the 
saw tooth signal reaches the predetermined threshold level, the 
multivibrator 14 may reset the gated multivibrator 12 to complete a 
sweeping cycle. A delay sweeping circuit 20 generates a delayed sweeping 
signal Sds synchronous with the sweeping signal Ss but having shorter 
width t2 than Ss, and a delayed unblanking signal Sdu synchronous with the 
delayed sweeping signal Sds and having Sds width as the same. 
The delay sweeping circuit 20 comprises a comparator 22 which compares the 
output of the integrating circuit 13, that is the instantaneous value of 
the sweeping signal Ss, with a reference signal S.sub.R, the comparator 22 
producing a set signal when the sweeping signal Ss exceeds the reference 
signal S.sub.R, a gated multivibrator 23 for producing a delayed gate 
signal as a delayed unblanking signal Sdu in response to an output of the 
comparator 22, an integrating circuit 24 for receiving the delayed gate 
signal to produce a delayed sweeping signal Sds, and a reset multivibrator 
25 for resetting the gated multivibrator 23 when the output of the 
integrating circuit 24 exceeds a predetermined level. 
It is to be noted that signals Ss and Sds have a saw tooth waveform, but 
signals Su and Sdu have a rectangular waveform. It is also to be noted 
that the ramp duration of the delayed sweeping signal is shorter than that 
of the sweeping signal for the purpose of being used for enlarged sweeping 
operation. 
These sweeping signals Ss and Sds are supplied to stationary contacts of a 
transfer switch SW1, an analogue switch for example. The transfer switch 
SW1 applies either one of the signals Ss and Sds to a horizontal 
deflection circuit 30 of a cathode ray tube, not shown. The unblanking 
signals Su and Sdu are also applied to a transfer switch SW2 similar to 
transfer switch SW1 and operated synchronously therewith. The transfer 
switch SW2 sends either one of the unblanking signals to the brightness 
modulation circuit 40 of the cathode ray tube. 
A counter 50 is provided to count the number of the leading edges of the 
unblanking signals Su (shown by FIG. 3a) for producing a control pulse 
(shown by FIG. 3b), which is used to control the transfer switches SW1 and 
SW2. While the control pulse is at a high level the movable contacts of 
the transfer switches SW1 and SW2 are thrown to the side of the delay 
sweeping circuit 20, whereat while the control pulse is at a low level, 
the transfer switches SW1 and SW2 are thrown to the side of the sweeping 
circuit 10. Now suppose that the counter 50 is constituted by a three 
stage counter such as J-K type flip-flops with two stage, for example. In 
FIG. 3a with a first building up portion of the unblanking signal Su, the 
level of the control pulse from the counter 50 becomes low and the 
transfer switches SW1 and SW2 are thrown to the side of the sweeping 
circuit 10 as shown in FIG. 2. Next at a second building up portion a2 of 
the unblanking signal Su, the control pulse becomes high and the transfer 
switches SW1 and SW2 are switched to the side of the delay sweeping 
circuit 20. Further, the control pulse having been kept in high level at a 
third building up portion a3 of the unblanking signal Su, the transfer 
switches SW1 and SW2 do not perform the switching operation. Again at a 
building up portion a4 of the unblanking portion Su the counter 50 
produces a low level output signal as the control pulse and then the above 
operation is repeated. In this example, while the sweeping signal Ss and 
the unblanking signal Su are selected once, the delayed sweeping signal 
Sds and the delayed unblanking signal Sdu are selected twice or more, so 
that sweeping signal (FIG. 3c) and unblanking signal (FIG. 3d) are sent 
out alternately from the transfer switches SW1 and SW2 in the sequence 
shown. 
Accordingly, during the width t1 of the sweeping signal (FIG. 3c) a 
preparatory sweeping is made with not enlarged time axis, but during the 
width t2 of the signal shown in FIG. 3c, delayed sweepings with their time 
axes enlarged are repeatedly and continuously performed. At the same time 
a brightness modulation is effected by the blanking signal shown in FIG. 
3d corresponding thereto so that the fluorescent screen of the cathode ray 
tube is luminescence each time a sweeping is made. When the delayed 
sweeping is made twice consequently, the quantity of light during this 
period t2.times.2 becomes substantially equal to that emitted during 
period t1 thus enabling easy observation and photographing of the waveform 
during the delayed sweeping. 
In this example a three stage counter is used. However, it is advantageous 
to use a programmable counter so as to control the number of counts 
according to the ratio of time axis enlargements of the preparatory 
sweeping and the delayed sweeping. The ratio of the number of uses of the 
sweeping signal Ss and the unblanking signal Sds to that of the delayed 
sweeping signal Sds and the delayed unblanking signal Sdu can be selected 
as desired. A signal obtained by inverting a signal shown in FIG. 3c may 
be used as the control signal for reversing the order of operations of the 
transfer switches SW1 and SW2. 
As above described according to the sweeping system of this invention the 
brightness of the displayed waveform can be increased at the time of the 
delayed sweeping thus making easy observation and photographing.