Abstract: In a tuning control system for a television receiver, an analog AFT signal is sampled during blanking intervals when the amplitude of the video carrier is relative constant and therefore cannot affect the amplitude of the AFT signal significantly. This reduces the AFT filtering requirements.

Abstract: A television receiver includes apparatus for stabilizing an on-screen character display by which the deflection signal source is controlled for operating in a free-running mode, substantially unaffected by signal variations on the sync input line, rather than in a synchronized mode when sync is unreliable or otherwise undesirable. As another feature, the deflection signal source is caused to operate at substantially the same frequency in either mode.

Abstract: A blanking signal is generated in a television receiver when a channel change selection is made. The blanking signal is low-pass filtered and thereafter controls the muting of the audio channel. Muting and un-muting are thus accomplished gradually, without audio disturbance. The tuning voltage is allowed to change to the new value required only after a delay period following the start of the blanking signal. Muting is therefore substantially complete before tuning transients can occur.

Abstract: A character generator in a receiver provides a character signal in raster scan form for display with a received video signal. An oscillator, not synchronized with the horizontal synchronizing component of the video signal, supplies a clock signal to the generator for controlling timing of character elements. A control unit provides a control signal representative of a time difference between the clock signal and the horizontal synchronizing component. A delay unit, interposed in the clock signal path, selectively imparts delay to the clock signal in response to the control signal for reducing line-to-line variations in the timing of displayed character elements.

Abstract: A double conversion tuner stabilized against drift includes a first local oscillator included in a phase locked loop (PLL) and a second local oscillator included in an automatic fine tuning (AFT) loop. A switching arrangement selectively allows the AFT signal to control the second local oscillator only when the operation of the PLL has been completed and if the picture carrier of the IF signal produced at the output of the tuner is within the AFT control range to prevent the second local oscillator from being tuned incorrectly.

Abstract: A digital fine tuning system for a television receiver includes a counter arrangement for measuring the frequency of the IF picture carrier by counting cycles of the IF picture carrier during a measurement interval and comparing the count at the end of the measurement interval to a predetermined count related to the nominal frequency of the IF picture carrier. To prevent counting, and thereby frequency measurement errors, due to the overmodulation of the picture carrier during image intervals, the frequency measurement operation is enabled during a predetermined portion of the vertical retrace interval when the picture carrier is not overmodulated.

Abstract: In a tuning system of a television receiver, the local oscillator (LO) signal and IF picture carrier are selectively coupled to the clock input of the same down counter. The down counter is selectively enabled to count cycles of the LO signal on IF picture carrier during respective LO and IF measurement intervals. A predetermined initial count related to a desired frequency of the LO signal or a predetermined initial count related to a desired frequency of the IF picture carrier are loaded into the down counter during LO and IF presetting intervals which occur just prior to corresponding LO and IF measurement intervals. The counts of the counter at the ends of each of the LO and IF measurement intervals are compared to zero to generate LO and IF error signals representing the frequency deviations, if any, of the LO signal and the IF picture carrier from the respective desired frequencies. The LO and If error signals are utilized to control a tuning voltage for the receiver's tuner.

Abstract: A counter arrangement for measuring the frequency of a local oscillator signal produced in a television tuning system includes a main down counter and an auxiliary down counter. Prior to a measurement interval, the channel number of the selected channel is loaded into the main down counter and a number which is related to the frequency separation, S, in mHz, between the channels by the relationship:PS+Pwhere P is an integer greater than zero, is loaded into the auxiliary down counter. During the measurement interval, the main counter is enabled to count down from the channel number in response to the local oscillator signal. Each time the count of the main counter equals zero, the count in the auxiliary counter is reduced by one and the channel number is again loaded into the main counter. When the count in the auxiliary counter equals P, a band dependent number is loaded into the main counter.

Abstract: In a phase locked loop tuning system including a phase comparator for producing a pulse type error signal representing the phase and frequency deviation between a frequency divided version of the local oscillator signal and a reference frequency signal and a mode switch for coupling the error signal to an integrator for developing a tuning voltage when a channel is initially selected and thereafter for coupling an AFT voltage to the integrator to modity the tuning voltage to correct for a frequency deviation of the IF signal, switching duty cycle control apparatus is provided for controlling the duty cycle at which the AFT voltage is coupled to the integrator in accordance with the selected channel and more particularly with its band to make the AFT response more consistent throughout the tuning range.

Abstract: A signal seeking tuning control system of a television receiver is first caused to operate in a first mode to search a frequency range surrounding a selected channel in accordance with predetermined conditions of a picture synchronization signal, and thereafter caused to operate in a second mode to search essentially the same frequency range but this time in response to predetermined conditions of an automatic fine tuning signal.

Abstract: The channel selection apparatus of a tuning system includes a present channel number register, a temporary register, a saved channel number register and a control unit for selectively controlling the three registers to (a) interchange the contents of the present and saved channel number registers when a swap key is activated, (b) enter the contents of the present channel number register in the saved channel number register without disturbing the contents of the present channel register when a favorite channel store key is activated, and (c) enter the contents of the saved channel number register in the present channel number register without disturbing the contents of the saved channel number register when a favorite channel recall key is activated.

Abstract: A detector for determining the validity of a composite synchronization signal to indicate the presence of a picture carrier includes two threshold comparators set just below and just above the maximum and minimum amplitude excursions, respectively, of the synchronization pulses. The output pulses of the threshold comparators are counted during a reference interval to determine if the frequency of the synchronization pulses is correct. Due to the threshold comparators, noise transients are detected and counted so as to cause an incorrect frequency indication. In addition, reference pulses are counted during the duration of the output pulses generated by one of the threshold comparators to determine if the width of the synchronization pulses is correct. The number of incorrect counts of the frequency or width is counted during a measurement interval. If the number of incorrect counts exceeds a predetermined limit, the composite synchronization signal is not a valid one.

Abstract: In a television receiver, a keyboard encoding arrangement which makes use of an existing register for storing binary signals representing control information and existing connections coupled to respective stages of the register includes transmission gates for selectively coupling the connections to respective switches of a keyboard. The switches of the keyboard are also coupled to sense circuits for detecting the presence or absence of binary signals. A counter selectively counts in response to sense signals generated by the sense circuits and generates count-representative signals which control the selective coupling and decoupling of binary signals stored in the register to the sense circuits through operated switches of the keyboard. A decoder is responsive to the count signals to generate control signals related to operated switches.

Abstract: A phase locked loop tuning system includes a phase comparator for generating pulse error signals having pulses with durations corresponding to the magnitude of a phase and/or frequency deviation between a frequency reference signal and a frequency-divided signal derived from a local oscillator signal. A low pass filter is responsive to the pulse error signals for generating a tuning voltage for controlling a voltage controlled local oscillator to tune standard frequency RF carriers. So that a substantial portion of the tuning system may be incorporated in a single integrated circuit, a pulse converter is provided to convert an analog AFT signal to pulse error signals similar to those generated by the phase comparator but with durations representing the magnitude of a deviation between the frequency of the IF picture carrier and its nominal value. The AFT related pulse error signals are selectively applied to the low pass filter to accommodate the tuning of nonstandard frequency RF carriers.

Abstract: A television receiver includes a tuning system comprising a phase locked loop (PLL) configuration and an automatic fine tuning (AFT) configuration which are selectively enabled to operate in response to respective levels of a MODE signal to tune standard and nonstandard frequency RF carriers. In the absence of the RF carrier for a selected channel, the operations of PLL and AFT configurations are alternately enabled and the level of the MODE signal changes accordingly. The MODE signal is applied to a capacitor which develops a control voltage for turning the receiver "off" after the MODE signal has changed levels for a predetermined time because of the absence of a RF carrier.

Abstract: In a phase locked loop type of tuning system for a television receiver having provisions for tuning the receiver to non-standard frequency carriers having frequencies arbitrarily near respective frequencies of the standard broadcast carriers, a digital frequency deviation detector is provided to determine whether the frequency of at least one variable frequency signal developed by the tuning system is within a predetermined range of its nominal value. The frequency deviation detector includes a D type flip-flop to generate a signal whose frequency is equal to the difference between the frequency of the variable frequency signal and a fixed frequency signal. A counter is enabled during a predetermined portion of at least one cycle of the difference signal to count period (cycles) of the fixed frequency signal. The accumulation of at least a predetermined count indicates that the variable frequency signal is within a predetermined frequency difference with respect to the frequency of the fixed frequency signal.

Abstract: A tuning system for a television receiver includes a first phase locked loop configuration for controlling the frequency of the receiver's local oscillator signal in accordance with the number of the channel presently being tuned and a second phase locked loop configuration for controlling the frequency of the local oscillator signal to reduce any frequency deviation between the receiver's IF picture carrier and 45.75 MHz corresponding to a frequency offset between the associated RF carrier and the standard RF carrier frequency for the channel being presently tuned due to the frequency translation provided by a television distribution system. The tuning system includes control units for automatically changing the channel number and selectively enabling the operation of the first and second phase locked loop configuration in accordance with a tuning algorithm so that active channels may be automatically located and tuned while preventing the receiver from being erroneously tuned to undesirable signals.