An all electronic tuning system is described for establishing a frequency of a local oscillator in a television receiver. When a channel selection is made, a number representing the desired channel is entered in a memory circuit. A first plurality of frequencies is generated in response to a channel selection, and a VCO employed as a local oscillator is caused to increase in frequency. When the VCO frequency differs from the first plurality of frequencies by a predetermined amount, a second plurality of frequencies is generated. Each frequency generated in said second plurality of frequencies is compared with said VCO frequency. When a predetermined difference exists between said VCO frequency and said second plurality of frequencies, a count is recorded. When the recorded count is equivalent to the number obtained in the memory circuit, the VCO tuning is inhibited and the VCO frequency is stabilized until a subsequent channel selection is made.

Electronic system for automatically tuning to a selected television channel

Digital frequency measuring circuitry is disclosed which includes a first shift register, the content of which is increased by a fixed amount at the beginning of each cycle of the input signal to be measured. Thereafter the content of the first register is caused to exponentially decay until the next input cycle is detected where the process is repeated. At the beginning of each cycle of the input signal, the content of the first register is transferred to a second or memory register where the data is used to drive a gage or other output device. To improve gage performance during low frequency input the memory register is also updated whenever the content of the first register is less than the content of the memory register. Also, if the input signal is removed any significant residual in the first register is eliminated by decrementing the first register to insure that the gage accurately represents the input condition.

Digital frequency measuring circuitry

A varactor tuner frequency controller wherein a tuning voltage is developed for optimumly tuning a VHF tuner or a UHF tuner to any one of a plurality of channels. A capacitor utilized to store charge for developing the tuning voltage is discharged by means of a pulse developed by a monostable circuit which is gated by a bandswitch reset pulse. Charging of the capacitor is provided for by a positive current source which supplies a substantially constant current to the capacitor in the absence of a hold signal, the hold signal only being present when a selected channel has been reached. In the presence of a hold signal, the current supplied by the positive current source is modified in accordance with an automatic fine tuning signal, and a negative current source supplies a substantially constant current to the capacitor approximately equal to the current supplied by the positive current source in the absence of the hold signal to effect a stopping of the sweep. When irregular spaced channels are being tuned, the negative current source is momentarily disabled in the presence of a hold signal to provide for an incremental sweep of the tuning voltage to place the tuning voltage within a range which will provide for proper automatic fine tuning operation.

Varactor tuner frequency controller

A tuner bandswitching system for a television receiver tuning system wherein a reset pulse generated at the completion of the selection of a channel to be received is utilized to determine the initial stable state of a series of bistable circuits and to provide a bandswitch reset pulse for use in establishing an initial voltage output from a voltage sweep generator utilized to scan a varactor tuned VHF tuner or a varactor tuner through one or more bands of frequencies. The bistable circuits control switching voltages supplied to the VHF tuner and the UHF tuner to provide for sequencing of the tuning system serially through, for example, the low VHF band, the high VHF band, and the UHF band until the appropriate band has been selected wherein the selected channel can be tuned. When the selected channel is tuned, a hold signal is developed. Data identifying the channel being received during a sweep through a given band is accumulated in a counter. At a predetermined output of the counter (e.g., "06" or "13") in the absence of the hold signal, the state of the bistable circuits is changed. As the state of a bistable circuit is changed, a bandswitch reset pulse is provided to again reset the voltage sweep generator in preparation for the scanning of the next band in the aforementioned sequence of bands.

Tuner bandswitching system for a television tuning system

A novel technique and apparatus for stabilizing the frequency of a controllable oscillator is disclosed. The output frequency of the oscillator is periodically sampled and the sampled signal is counted during a first sampling period, the sampled count being stored. During a subsequent sampling period, the oscillator output pulses are counted once again, this subsequent sampled count being compared with the first sampled count. An error signal is generated representative of any difference noted between the first sampled count and the subsequent sampled count, this error signal being applied to the controllable oscillator so as to set the output frequency thereof. The frequency correction technique continues throughout the operation of the oscillator during successive sampling periods.

Digital counter frequency control system

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Digital counter frequency control system