Patent GB-1312932-A (GB)
Title: Tuning system for selecting channels
IPC: H03J5/02
Filed: 1970-04-13
Abstract: 1312932 Selecting systems MATSUSHITA ELECTRIC INDUSTRIAL CO Ltd 13 April 1970 [14 April 1969 (3) 16 April 1969 (2) 23 May 1969 28 May 1969 (2) 23 June 1969 8 Aug 1969 (2)] 17489/70 Heading G4H [Also in Division H3] A channel selecting system, comprises a channel selection circuit 227 (Fig. 9) including a digitally controlled analogue voltage generator 66 (Fig. 3) and a plurality of gates 201 1 - 201 12  corresponding to respective channels each having a tapping of a load 205 1 -205 12  fed via a diode 204 1 -204 12  to a common output point 219 and a binary signal generator 200 feeding an input to the channel selection circuit such as to select a corresponding one of the gates so as to cause current to flow through only the load circuit of the selected gate to produce a voltage at the common output point 219 for applying to variable capacitance diodes 209- 212 of a tuner 217 to tune in a corresponding channel. Binary signals from generator 200 are fed to the D-A converter including diodes 66 and NAND gates 14-29, Fig. 3 corresponding to 201 1 -201 12 , Fig. 9, to turn on one of the NAND gates and diodes 47-62, 204 1 -204 12  and supply the tapped voltage from the associated load 205 1 -205 12  to tune the variable capacitance diodes 209-212 in a V.H.F. tuner of a TV set. Also the channel selected is indicated by a pilot lamp 203 1 -203 13  or figure indicator discharge tubes (Figs. 11a, 11b, not shown). An OR circuit 232 and switch circuit 233 control the on or off state of switching diodes 213-216 so as to tune the V.H.F. tuner to low or high V.H.F. channels in accordance with the channel selected. Electronic switch circuits 234 and 235 are arranged to turn on the power supply to only the V.H.F. tuner when channels 1 to 12 are selected and to only the U.H.F. tuner 221 when gate 202 13  is selected so that a voltage on resistor 230 is fed to variable capacity diodes 224-226. The diodes 66 (Fig. 3) may be formed as an integrated circuit. In a modification of, Fig. 3 (Fig. 4, not shown), the diodes 66 gate transistors and V.H.F. load resistors (within 98) may be formed as an integrated circuit and resistors (111-114) for the U.H.F. tuner may also be in integrated circuit form. In Fig. 9 the resistors 205 1  to 205 12  may be formed on the same semi-conductor chip as that containing the channel selection circuit 227 and counter circuit 200. Tiansistors (240 1 -240 16 , Fig. 10, not shown), may be used to form the part of Fig. 9 controlling the pilot lamps 203 1 -203 13  and transistor circuits (241, 242, 249 and 251) form the OR circuit 232 and switch circuits 233, 234 and 235 of Fig. 9. In a modification (Figs. 12 and 13, not shown) preset channels may also be selected in the U.H.F. tuner and lamps (237 and 239) indicate whether a V.H.F. or U.H.F. band is selected. The binary pulse generator 200 includes a clock pulse generator (117, Fig. 5, not shown), which drives a reversable counter (118- 120) so that channels may be selected in either direction. The clock pulse generator (148, Fig. 6, not shown) is rendered operative by closing one of switches (150, 151), which determines the direction, to trigger a transistor (149). The period of the clookpulse generator is determined by an RC network (178, 179). The clock pulse generator may be an astable transistor multivibrator (Fig. 7, not shown), including all components except the capacitors (156, 157) in an integrated circuit. In a further clock pulse generator (Fig. 8, not shown) including a Schmitt trigger transistor pair (160, 161) timing is provided by resistor (173) and a capacitor (174) and the cycle is repeated by means of a transistor (167) which conducts to discharge capacitor (174). This pulse generator circuit may be in integrated circuit form except for the capacitor (174). Skipping of unauthorized channels is obtained by a switching circuit (Fig. 14, not shown) which includes transistors (247 and 248) and a terminal (249) corresponding to transistors (149) and (191) and terminal (192) of (Fig. 6, not shown). The unauthorized or unrequired channel is selected by opening a switch (255 2 ) to its associated indicator lamp (254 2 ) such that when switches (246 and 251) are closed to start the clock pulse generator (148) and a monostable pulse generator (253) a control signal from a transistor (262) operates transistor 248 to allow skipping of the unauthorized channel to stop the pulse generator (148) at the next required channel. The switches (246, 251) may be electronic optical or magnetic switches. In modifications of this signal from the video IF and horizontal sync. signals are detected (Figs. 16 and 17, not shown) and are used to control a switch circuit terminating the pulses from the clock pulse generator (148) when the next authorized channel is received. The switch (150, Fig. 6, not shown),  controlling the clock pulse generator (280, Fig. 19, not shown), may correspond to the output of an AND gate (290) such that the clock pulse generator (280) ceases oscillation only when the binary signal appearing at the outputs (272- 275) of the J-K flip-flops (276-289) corresponds to the binary signal added to the terminals (286-289) so that the desired signal may be received by adding the corresponding binary signal to terminals (286-289). If a binary signal corresponding to the authorized channel is added to (286-289) the non-authorized channel will be skipped. A further circuit for selecting the authorized channel is disclosed (Fig. 20, not shown). Authorized channels are selected by switches (295) to provide outputs from selected ones of the NAND gates 201, Fig. 9, in a circuit 298 at terminals (291-294) for the comparison input terminals 286-289 in (Fig. 19, not shown). A channel indicator (Fig. 21a and 21b, not shown), having an indicator board and including a ratchet gear (299) may be operated by a ratchet relay from the output of the clock pulse generator (280). Remote control may be obtained by pushing a button to select the desired channel (Fig. 18, not shown), which includes a supersonic frequency oscillator (263).