Patent GB-1495553-A (GB)
Title: Sweep output generator including a local oscillator for the station selector of a television receiver
IPC: H03J5/02
Filed: 1974-11-28
Abstract: 1495553 Receiver channel selector, sweep generators MATSUSHITA ELECTRIC INDUSTRIAL CO Ltd 28 Nov 1974 [30 Nov 1973] 51616/74 Headings H3Q, H3P and H3H In a sweep output generator including a local oscillator 2, Fig. 1, for a station selector of a T.V. receiver, an A.C. signal from an oscillator 10 is superimposed on a sweep signal from 1 for application to a variable reactance element of the local oscillator, the sweep output signal from the local oscillator 2 is mixed at 5 with an output from an oscillator 4 so as to obtain a difference signal, this is demodulated at 7 and integrated at 9 to obtain a sweep output voltage and when the sweep output voltage coincides with a reference voltage from 15 corresponding to a selected station a comparator 12 provides an output for terminating the sweeping of the sweep signal to the local oscillator. The integral output (Vo, Fig. 3, not shown) from 9 can provide a linear display of the reception frequency by a voltmeter. When a channel number is selected by a keyboard 13 a reset generator 16 resets first and second voltage sweep circuits 1 and 3 which then start to sweep. When the sweep output voltage Vo from 9 coincides with the output voltage of a D-A converter as determined by a shift register 14 a voltage comparator 12 produces a stop signal to gate 17 which stops the sweep circuit 1. By holding the sweep voltage and applying it to a variable capacitance diode tuning element of a tuner the selected channel is tuned in. The channel number may be digitally displayed by a figure discharge tube coupled through a decoder to the channel memorizing circuit 14. AFC may be provided by connecting the output of amplifier 6 through a frequency discriminator to a LPF the output of which is coupled through a gate for superimposition on the output voltage of the sweep circuit 1. In Fig. 1 to ensure perfect tracking between the output frequencies of voltage controlled oscillators 2 and 4 AFC may be similarly provided via a gate circuit to the sweep circuit 3. In a modification (Fig 4, not shown) the frequency discriminator is replaced by a phase detector (18) which is connected in a phase locked loop also including the LPF 19 and a third voltage controlled oscillator (20). In a further modification the frequency discriminator 7 is replaced by a phase detector (21, Fig. 5, not shown) fed by a reference oscillator 24 and included in a phase locked loop including a LPF (22), a gate (23), the voltage sweep circuit 3, the voltage controlled oscillator 4, the mixer 5, the amplifier 6 and the phase detector (21). In the modifications the D-A converter 15 and circuit 14 may be replaced by a circuit (Fig. 6, not shown) in which a staircase sweep voltage for application to the voltage comparator 12 is produced by coupling a rectangular voltage (25) to an integrator (26). The output of a comparator 28, comparing the content of a counter (27) and the content of the channel number memorizing circuit (29), stops the rectangular wave generator 25 when the sweep voltage from integrator (26) corresponds to the selected channel.