Abstract: A manual AFT switch and a manual FINE TUNE switch are configured so that whenever the FINE TUNE switch is engaged the AFT detector output is automatically disconnected from the AFT input of a tuning voltage control circuit. Furthermore a loading circuit coupled to the AFT input and driven by either the AFT switch or FINE TUNE switch assures the desired impedance at the AFT input whenever the output of the AFT detector is so disconnected.Automatically defeating the AFT circuit during manual fine tuning tends to optimize fine tuning by eliminating a component of correction voltage contributed by the AFT system, a face of which the lay viewer is likely to be unaware.

Abstract: A detector with independent TURNON and TURNOFF time constants. The TURNOFF time constant is connected between the output of an input transistor and the input of an output transistor. The TURNON time constant is coupled by a diode to the output of the output transistor and is connected to a Schmitt Trigger, ultimately driving an ON/OFF relay in a television receiver. Although the time constants are independently selectable, in a specific application of the invention the TURNON time constant may be chosen to be approximately twice the period of the detector input signal and about five times the TURNOFF time constant. Various configurations of series and parallel RC time constants are shown.

Abstract: A multivibrator constructed from cross-coupled, dual-input (NAND) gates. Each gate has a clamping network connected between its output and one input. The clamping circuit assures that the gate whose output is at a logic ZERO level changes output state in response to a trigger signal that is applied to trigger steering networks associated with both gates. As a result, the gate whose output is at a logic ONE level subsequently changes state thereby assuring predictable triggering and the desired bistable multivibrator action.

Abstract: A circuit for generating an accurately-timed noise-free signal for gating the chrominance burst portion of the composite video signal. The horizontal sync pulses are differentiated and clamped to the horizontal blanking pulses. The output pulses are then applied to a gating diode that is conductive only when those pulses have an amplitude above a predetermined bias level. The resultant pulses are coupled to the input of a burst gate so that the gate is open only for a period of time substantially coterminous with the burst period.The burst gate is thereby rendered immune to noise signals occurring during the active line period and the accuracy of the gating signal is independent of the television receiver's horizontal time base.

Abstract: In a VIR-responsive Tint Control system a dematrixing circuit for synthesizing, from the individual chrominance demodulator outputs, a ZERO-COLOR reference signal. The VIR chrominance interval signal and the ZERO-COLOR reference signals are used as input to a feedback loop that also includes the receiver's chrominance subcarrier oscillator. By comparing the VIR chrominance interval signal to the synthesized ZERO-COLOR reference subcarrier oscillator phase errors are corrected by virtue of a single sampling of the VIR signal.

Abstract: A variable gain amplifier controlled by alternate sources of gain-control signal. A first, substantially, constant, source has an amplitude corresponding to the amplifier's maximum gain condition. A second, variable, source allows the amplifier gain to be continuously varied. In a chrominance amplifier for a television receiver, the continuously variable source is normally selected so as to develop the desired chrominance level. During the reception of a VIR signal, the constant source is selected so as to effect the maximum amount of VIR correction. The gain-control sources are switched, via analog gates, through substantially identical filter-decoupling networks.

Abstract: A circuit for selectively supplying current to the horizontal oscillator from one of two voltage sources. The first voltage source is primarily used to supply current to the horizontal output stage and supplies the oscillator only during startup of the horizontal deflection system. The second source is derived from a winding on the flyback transformer and supplies current to the oscillator after the startup period, that is, after its voltage or another or other voltages developed by sources derived from flyback windings have reached values sufficient to assure sustained operation of the horizontal deflection system. A startup detector responsive to a flyback-derived voltage determines which of the two voltage sources provides current at the output of the starting network, that is, at the power supply terminal of the horizontal oscillator.

Abstract: In a television receiver containing both circuitry returned to the AC line and circuitry returned to an isolated chassis ground, a voltage supply isolated from the AC line for a horizontal oscillator returned to the chassis ground. The supply is developed by a winding magnetically coupled to an inductor in a switching regulator that is coupled to the AC line and operates at a frequency substantially equivalent to the horizontal oscillator frequency. With the horizontal oscillator operative, supply voltages for the remainder of the receiver's line-isolated circuitry can then be derived from windings on the flyback transformer.

Abstract: A vertical amplifier provides a deflection or yoke current independent of the yoke impedance or other impedances in the yoke current path. The amplifier comprises a general-purpose operatonal amplifier that develops an output voltage in a manner that maintains identical voltages at its inverting and non-inverting inputs. A feedback resistance is connected in the yoke current path, thereby developing a voltage indicative of the yoke current. As a result, the yoke current waveform can be made identical to or a desired variation of a current commanding voltage waveform applied to the non-inverting input. A particular variation of the feedback resistance transforms an S-shaped current waveform into a sawtooth voltage waveform, thereby providing the desired deflection linearity.

Abstract: A shutdown circuit both electrically and magnetically isolated from the horizontal deflection circuit and the flyback transformer. The voltage across a winding magnetically coupled to an inductive element carrying the current required by the deflection circuit and the flyback transformer is detected. The horizontal deflection circuit is disabled in response to voltages above a predetermined value. In an Iso-Hot type receiver having an oscillator coupled to the deflection circuit by an optically operating drive circuit, the drive circuit is rendered optically non-transmitting.

Abstract: A circuit utilizing a single clamp, and therefore requiring only a single bias supply, to DC clamp the inputs of the three chrominance amplifiers is shown. The clamp employs a switch that is connected to the bias supply and coupled by separate diodes to the inputs of the chrominance amplifiers. The switch and diodes are conductive only during the horizontal retrace period. As a result, during the retrace period, the amplifier inputs are clamped to a DC value determined by the bias supply; during the trace, or information-bearing period the inputs are isolated from the supply, as well as from each other.

Abstract: A horizontal output stage including a switching device for coupling the input of the horizontal output transistor to a feedback network and bias means during startup and to the secondary of an interstage coupling transformer during steady-state operation. During startup the output transistor operates in an oscillatory mode thereby developing an alternating current in the flyback transformer. The supply voltage for the horizontal oscillator is derived from a winding on the flyback transformer. Once this supply voltage reaches the value required for sustained operation of the oscillator, the switching device disconnects the output transistor from the feedback network and couples it to the interstage transformer so that the output transistor is driven by the signal developed by the horizontal oscillator.

Abstract: A circuit for enhancing the operation of a first voltage supply magnetically coupled to and derived from a second voltage supply. A signal source indicative of the voltage developed by the first supply is coupled to a detector. The detector operates to selectively couple a switchable momentary load across the second supply in response to outputs of the first supply below a desired value. The momentary load causes an additional incremental current to flow through an inductive element in the second supply and results in greater voltage induced in a winding of the first supply that is magnetically coupled to the inductive element.

Abstract: A vertical deflection amplifier includes a preamplifier having an input at which is applied a DC feedback signal for the stabilization of the amplifier's DC output. In order to assure an undistorted or unattenuated vertical deflection upon initial turn-on of the receiver, a fast-start circuit superimposes a transient voltage on the DC feedback signal. The fast-start circuit allows the amplifier's output to reach its quiescent DC output level in a period of time that is substantially shorter than the time constant of a sampling network from which the DC feedback signal is derived.

Abstract: A receiver incorporating a phase-locked loop to demodulate a signal comprising a plurality of distinct baseband components is disclosed. The loop filter circuit includes an adjustable resistive element for varying the loop damping factor, thereby providing optimum separation of the baseband components. In addition, the loop filter circuit provides a bandpass high-frequency noise output to a noise-activated muting circuit.

Abstract: A network for combining a switchable and variable tuning voltage with an AFC voltage so as to effect a change in the tuning control voltage at a tuner's tuning control terminal is disclosed. The network compensates for time delays associated with the AFC time-constant in a manner such that the tuning control voltage responds in proportion to and substantially instantaneously with changes in the tuning voltage. The compensation reduces the probability of AFC false-locking phenomena when, for example, switching from one channel of a television receiver to another.

Abstract: A digital gain control system is disclosed. A clock oscillator drives a counter which in turn provides an output to a D/A converter. The analog output of the converter is used to develop a signal for controlling the gain of a gain-controlled amplifier. In order to compensate for the nonlinear gain versus control current characteristic of the amplifier, additional circuitry is employed so that the initial increment in control current, that is, the increment that occurs as the counter goes from the 0000 to the 0001 state, is significantly greater than the remaining increments. In conjunction with volume control circuitry for audio amplifiers, this circuitry assures a muted condition in the 0000 state, and an audio output corresponding to at least the minimum discernible level in the 0001 state.

Abstract: A method and circuit for detecting and removing chrominance signal components from the luminance channel of a television receiver is shown. The luminance channel is separated into distinct subchannels, one of which has a filter providing attenuation at the chrominance subcarrier frequency. A detection circuit operates to select the output of the filtered subchannel whenever a chrominance subcarrier signal appears in the luminance channel. The detection circuit is sensitive to the phase relationship between the chrominance signal and a portion of the luminance signal and is therefore substantially immune to signals other than chrominance subcarriers, including high frequency components of the luminance signal.

Abstract: Disclosed herein are a circuit and a method for providing an appropriately-timed signal to the input of a chrominance burst gate. Horizontal synchronizing pulses are differentiated and clipped so that positive-going, exponentially decaying pulses are developed substantially coincidentally with the chrominance burst signal. The resultant pulses are then applied to one terminal of a switch. Horizontal flyback pulses are phase-delayed so that their peak amplitude occurs during the burst period. The phase-delayed pulses are applied to another terminal of the switch so that resultant pulses are shorted to ground except during a predetermined portion of the horizontal flyback period. As a result, a burst gating signal having a pulse width effectively equal to and coincident with the burst signal period is generated and applied to the input of the burst gate.

Abstract: Cathode ray tube adjusting apparatus in a color television receiver includes a matrix and amplifier circuit coupled to a chrominance signal source, selectively coupled by a "service-normal" switch to a luminance or reference signal source. The matrixing and amplifying circuit includes a control grid DC bias potential development circuit and a cathode DC bias potential adjusting circuit, and is coupled to a cathode ray tube. In the "service" switching position, the DC bias potential adjusting circuit is varied to provide the proper cut-off potential conditions for the cathode ray tube. In the "normal" switchingposition, chrominance and luminance signals are matrixed and luminance signal drive is adjusted to provide the proper color temperature appearing on a viewing screen of the cathode ray tube.