Patent GB-1262671-A (GB)
Title: Sweep oscillator
IPC: G01R13/24
Filed: 1969-04-16
Abstract: 1,262,671. Sweep generator; automatic frequency control. IWASAKI TSUSHINKI K.K. 16 April, 1969 [18 April, 1968; 14 Feb., 1969], No. 19378/69. Headings H3A and H3P. A generator 4, Fig. 2, whose output sawtooth w 3  duration is controlled by a gate 2 opened by an input signal pulse w 1  (Fig. 8) at 1 and closed by a hold circuit 21 responsive to a predetermined amplitude of the sawtooth, is capable of producing a plurality of predetermined slopes (having, therefore, correspondingly different frequencies), and successively increasing slopes are automatically selected by a circuit (e.g. 6, 7, 8, 9, 10) whenever an input pulse w 1  is detected during a predetermined interval w 4  from the start of the sawtooth, the selection being stopped at that slope for which no such input pulse is detected; and the generator is reset to give the lowest value of slope when less than a given number of input signal pulses w 2  is received during a second predetermined period w 5  longer than the first. The second period w 5  may begin at the start or the end of the first pulse w 4 . In the automatic selection circuit 6, 7, 8, 9, 10, a gate 6 generates the pulse w 4  by being first set by an input pulse w 1  and then reset by a predetermined level A of the sawtooth w 3 . An AND gate 8 is enabled by w 4  and passes an input pulse w 1 , if such occurs during w 4 , to a monostable 9 and counter 10. The count reached by the counter sets the slope of the generator 4 output, such that no input pulse w 1  occurs during w 4  (which is now narrower). The gate 12 is set to produce the leading edge of pulse w 5  by the end of pulse w 4  from gate 6, or alternatively (Figs. 4, 10, not shown) by the start of sweep gate 2 output pulse w 2 . The gate 12 then enables a a gate 13 to pass input signal pulses w 1  to a divider 14. When the given number of pulses N (say 3) has been counted (w 6 ) the divider output w 7  changes and inhibits a gate 16. The other input to gate 17 is from a comparator 19 sensing when the sawtooth w 3  has reached a selected level C and thereupon producing a pulse w 8 . This pulse w 8  is only passed by gate 16 when the number of pulses w 6  in the period w 5  is less than N (representing a drop in input signal frequency w 1 ) so that the divider 14 produces no inhibiting output w 7 . The output of gate 16 triggers a monostable 17 which acts on monostable 9 and counter 10 to cause the generator 4 to reset to its lowest slope. From this slope, the generator is then again switched up through successively increasing slopes until one appropriate to the new input signal frequency is reached. In modifications, the comparator 19 is replaced by a differentiator (19, Figs. 3, 5, 7, not shown) receiving the sweep gate output w 2 , and a delay (20) then has to be provided between divider (14) and gate (16) to ensure that w 8  is not accidentally passed if intended to be inhibited. The gate 12 may be replaced by a bi-stable (12). In a more detailed embodiment including the above features (Fig. 14, not shown), the divider 14 includes a counter (14-1), a pulse converter (14-2) and a bi-stable (14-3); and the counter 10 includes a ring counter (10-1) and a bistable (10-2). The input signal passes through a shaper and a differentiator to the sweep gate. The monostable 17 for initiating reset of the generator 4 to its lowest slope output is provided with a manual input.