Sawtooth scan circuit with hold feature

Claim 2

A sawtooth scan circuit with memory hold feature comprising: a storage capacitor (5) having one terminal connected to ground; a high input impedance voltage follower circuit (1,2,4) having a low impedance output (16), the other terminal of the capacitor (15) being connected to the control terminal of the voltage follower circuit; scanning pulse means (11) continuously providing repetitively occurring pulses connected to said capacitor (5) for gradually charging said storage capacitor (5) by repeated small increments of a predetermined minimum magnitude; a voltage threshold breakdown device (6) connected in series between said storage capacitor (5) and said scanning pulse means for discriminatively supplying output pulses of said scanning Means to said storage capacitor (5); a first electronic switch (13) for discharging said storage capacitor (5) when the output of said voltage follower circuit reaches a predetermined maximum value, and holding means including a second electronic switch (15) connected to attenuate said scanning pulses to a value insufficient to activate said voltage threshold breakdown device (6) and thereby to stop incrementally charging said capacitor (5) and thus to stop said scanning cycle in response to a hold signal supplied by an apparatus whose function is controlled or modified by the output of said voltage follower circuit.

Claim 3

A sawtooth scan circuit as defined in claim 1 in which: said voltage follower circuit comprises a field effect transistor (1); a voltage discriminator bistable switch means (22) is provided, adapted to turn on said first electronic switch (13) when a predetermined maximum output voltage is attained by said voltage follower circuit and also to turn off said first electronic switch (13) when the output of said voltage follower circuit reaches a predetermined minimum value; said second electronic switch (15) is a transistor and a bypass adapted to ground said scanning pulses in response to a hold signal.

Claim 4

A sawtooth scan circuit as defined in claim 2 in which the discharge path (6,8,12,20,13) of said storage capacitor (5) includes a series diode (12) in series between said first electronic switch (13) and said voltage threshold breakdown device. (6)

Claim 5

A sawtooth scan circuit as defined in claim 3 in which said voltage threshold breakdown device (6) is a gas discharge tube and in which said voltage discriminator bistable switch means (22) is a semiconductor controlled switch (SCS) having its anode gate electrode connected to a voltage divider fed by the power supply of the circuit.

Claim 6

A sawtooth scan circuit as defined in claim 3 in which a resistance-capacitance network, (7,8,9,10,14,20) is provided coupling the scanning pulse means (11) to the voltage threshold device (6), and includes a resistor (7) between ground and the pulse input side of said voltage threshold breakdown device (6).

Claim 7

A sawtooth scan circuit as defined in claim 5 in which said resistance-capacitance network (7,8,9,10,14,20) includes a series resistor (8) between said voltage threshold breakdown device and said coupling capacitor (9) and said series resistor (8) over other elements (12,20,19) of said discharge path to ground.

Claim 8

A sawtooth scan circuit as defined in claim 1 in which said scanning pulses are provided by flyback pulses of the line scanning circuit of a television receiver.

Claim 9

A sawtooth scan circuit as defined in claim 2 in which means are provided responsive to an output of said voltage discriminator bistable switch means (22) for preventing the operation of said holding means during discharge of the capacitor (5) by operation of said first electronic switch (13).

Claim 10

A sawtooth scan circuit as defined in claim 4 in which means are provided which are activated by a pulse formed either on the cathode of said semiconductor switch (22) or on the anode gate electrode thereof for disabling the application of a hold signal to said second electronic switch (15) during the period said first electronic switch (13) is closed.

Claim 11

A sawtooth scan circuit as defined in claim 1 in which said first and second electronic switches (13,15) are grounded emitter transistors (19,17).

Claim 12

Circuit as defined in claim 1 further comprising a resistance-capacitance network (7,8,9,10,14,20) to controllably couple the source of scanning pulses (11) to said voltage threshold breakdown device (6).

Claim 13

A sawtooth scan circuit as defined in claim 11 in which said second electronic switch (15) is adapted, when activated, to ground a shunt resistance (14) of said resistance-capacitance network (7,8,9,10,14,20) to form with a resistor (10) thereof, a voltage divider so designed that the scanning pulses suPplied to the voltage threshold breakdown device (6) are of a peak voltage less than the breakdown voltage of said voltage threshold breakdown device (6).

Claim 14

Circuit as defined in claim 11 wherein said resistance-capacitance network has a series input resistor (10) connected between said source of scanning pulses (11) and the junction of a branch (14) connected to said second electronic switch (15) and further comprises a coupling capacitor (9), of greater capacitance than said storage capacitor (5), in the series path (10,9,8,6) of said network.

Claim 15

In a television receiver having a line scanning circuit, said line scanning circuit having fly back pulses appearing therein, an electronically controlled tuning circuit requiring a sawtooth wave voltage, and a memory hold feature to hold, in response to a command signal, the value of the sawtooth wave voltage at selected levels below the maximum level of the sawtooth wave voltage; a sawtooth scan circuit with memory hold feature comprising a storage capacitor (5) having one terminal connected to ground; a high impedance input voltage follower circuit (1,2,4) having a low impedance output (16) connected to the electronically controlled tuning circuit, the other terminal of the capacitor (15) being connected to the control terminal of the voltage follower circuit; means (11) connecting the fly back pulses from the line scanning circuit to said capacitor (5) for gradually charging said storage capacitor by repeated small increments of a predetermined minimum magnitude, and including a voltage threshold breakdown device (6) connected in series between said storage capacitor (5) and said line scanning circuit for discriminatively supplying the flyback pulses to said storage capacitor (5); a first electronic switch (13) for discharging said storage capacitor (5) when the output of said voltage follower circuit reaches a predetermined maximum value corresponding to the maximum value of the sawtooth ray voltage; and holding means including a second electronic switch (15) connected to attenuate said fly back pulses to a value insufficient to activate said voltage threshold breakdown device (6) and thereby to stop incrementally charging said capacitor (5) and thus to stop said scanning cycle in response to the hold command signal supplied by the tuning circuit.

Claim 16

In a television receiver having a line scanning circuit, said line scanning circuit having fly back pulses appearing therein, an electronically controlled tuning circuit requiring a sawtooth wave voltage, and a memory hold feature to hold, in response to a command signal, the value of the sawtooth wave voltage at selected levels below the maximum level of the sawtooth wave voltage; a sawtooth scan circuit with memory hold feature comprising a storage capacitor (5) having one terminal connected to ground; a high impedance input voltage follower circuit (1,2,4) having a low impedance output (16) connected to the electronically controlled tuning circuit, the other terminal of the capacitor (15) being connected to the control terminal of the voltage follower circuit; means (11) connecting the fly back pulses from the line scanning circuit to said capacitor (5) for gradually charging said storage capacitor by repeated small increments of a predetermined minimum magnitude, and including a voltage threshold breakdown device (6) connected in series between said storage capacitor (5) and said line scanning circuit for discriminatively supplying the flyback pulses to said storage capacitor (5); a first electronic switch (13) for discharging said storage capacitor (5) when the output of said voltage follower circuit reaches a predetermined maximum value corresponding to the maximum value of the sawtooth ray voltage; and holding means including a second electronic switch (15) connected to attenuate said fly back pulses to a value insufficient to activate said voltage threshold breakdown device (6) and thereby to stop incrementally charging said capacitor (5) and thus to stop said scanning cycle in response to the hold command signal supplied by the tuning circuit.

Claim 17

In the television receiver of claim 14, wherein said voltage follower circuit comprises a field effect transistor (1); a voltage discriminator bistable switch means (22) is provided, adapted to turn on said first electronic switch (13) when a predetermined maximum output voltage is attained by said voltage follower circuit and also to turn off said first electronic switch (13) when the output of said voltage follower circuit reaches a predetermined minimum value; said second electronic switch (15) is a transistor and a bypass adapted to ground said scanning pulses in response to a hold signal.

Claim 18

In the television receiver of claim 15, means responsive to an output of said voltage discriminator bystable switch means (22) to prevent operation of said holding means during discharge of the capacitor (5) by operation of said first electronic switch (13).