Patent GB-1526100-A (GB)
Title: Electronic channel selecting apparatus for selecting tuning voltages
IPC: H04N5/44
Filed: 1976-04-02
Abstract: 1526100 Receiver channel selection SANYO ELECTRIC CO Ltd 2 April 1976 [3 April 1975] 13471/76 Heading H3Q In a channel selector having any one of stores 5, Fig. 1, of tuning voltage generators CHA-CHD, Fig. 1A, an individual channel selecting signal SA received by one CHA of the generators CHA-CHD causes gating and disabling signals to gates 2 and stores 5 respectively of the generators CHA-CHD so that the one store assumes an inactive state and the store 5A of the selected generator CHA receives the selecting signal via an associated gate 2A and assumes an active state whereby a preset tuning voltage PA corresponding to the selected broadcasting channel is switched via a switch 6A to a voltage controlled variable reactance of a tuner TU. The tuning voltage generators CHA-CHD and control circuit CTL can be transistor circuits (Figs. 2A, 2B and 3, not shown) which have outputs OA-OD) from drive circuit 8A transistors (Q4A-Q4D) connected via LED's (DA-DD, Fig. 4, not shown) for channel indication and resistors (RA-RD) to a common resistor (Ro). When a touch switch TC is selected the store 5A transistors (Q7A-Q9A) cause increased current through resistor (Ro) which is detected by comparator transistors (Q11, Q12) of detector 9 and this decreases the voltage at (N Vc) supplied to the store transistors (Q7-Q9) and gate transistors (Q5, Q6) to render them inactive. This renders any store previously active inactive so that only the selected store remains in the active state. A delay circuit 10 ensures that the generators CHA-CHD only change state if a channel selecting signal is applied to SA-SD for a sufficient time. The preset tuning voltage from a potentiometer 17A is then applied via switch 6A to the tuner TU. The effect of the base emitter voltages of transistors Q10, Q11, Q15 and Q<SP>1</SP>27) forming the switches 6 are eliminated by constant current source transistors (Q<SP>1</SP>20-Q<SP>1</SP>26, Q16, Q17). Variations caused by temperature are also compensated by this circuit. The generators CHA-CHD can be capacitively coupled in the form of a ring counter (Fig. 6, not shown) so that the active generators can be stepped by remote control pulses applied to a circuit 15. A band switch 16 for VHF selects a VHF tuner and switches between lower and higher VHF bands by means of switching diode and for UHF selects both the UHF tuner and VHF tuner in cascade and disables the local oscillator of the VHF tuner. Switches SWA-SWD (Figs. 5 and 7, not shown) enable the band associated with each generator CHA-CHD to be individually selected. AFT is disabled on turn on of the power supply and during channel switching by a circuit 13 in which a transistor (Q30) grounds the AFT signal supplied at (F) to the tuner in response to an initial set circuit 11 and the detector 9 respectively. Initial set circuit 11 also provides an output from a transistor (Q26) to select the tuning voltage generator CHA on turn on of the power supply. The circuits may employ MOSFET's instead of the integrated bipolar transistor circuits disclosed.