Abstract: In a television receiver having digital signal processing, an automatic chrominance gain control apparatus employs a combination of analog gain control and digital gain control stages. Specifically, the analog gain control stage provides a range of fine gain control by altering the frequency response characteristic of the intermediate frequency (IF) amplifier circuits. This is sometimes referred to as "IF tilt" control. The digital gain control stage provides coarse gain control in predetermined increments using a shifter in the digital signal processing circuits. The total gain required is calculated and is apportioned between the coarse and fine gain control stages by a microprocessor.

Abstract: A signal processing apparatus includes a scaling device for increasing the magnitude of a signal from a source to better use the dynamic range of processing apparatus, and to reduce the effects of noise and error sources. This is particularly useful in a television receiver where the maximum magnitude of the (B-Y) chrominance signal component of a composite video signal is smaller than that of the (R-Y) chrominance signal component. To provide improved resolution of the (B-Y) signal components, a gain scaling arrangement increases the magnitude of the (B-Y) signal component to more closely approximate that of the (R-Y) signal component. In a TV receiver having digital signal processing apparatus, a digital multiplier scales the digitized (B-Y) signal component thereby to reduce the errors inherent in processing digital data having a limited number of bits, especially where such processing includes rounding or truncating operations which can introduce additional errors or decrease resolution.

Abstract: A digital-to-analog converter includes a plurality of pairs of complementary conductivity field-effect transistors (FETs) coupled for applying reference potentials to a resistive ladder network in response to the bit values of an input digital word. A variable voltage generator develops gate biasing voltage for the FETs of one conductivity. The biasing voltage has a magnitude controlled in response to a bridge circuit including a further pair of complementary conductivity FETs also coupled to the reference potentials. As a result, the complementary conductivity FETs are automatically caused to exhibit matched conductivity characteristics.

Abstract: Digital representations of analog signals are limited in resolution accuracy by the number of bits in the digital output signal of an analog-to-digital converter which limits the number of analog output levels produceable by a digital-to-analog converter. The apparent resolution accuracy can be improved, however, by the addition of two "dithering" signals, one at a lower frequency and one at a higher frequency, to increase the number of transitions of the least significant bit (LSB) of the digital signals. In a television receiver employing digital signal processing apparatus, dither signals having magnitudes equivalent to 1/2 and 1/4 LSB and at frequencies related to the TV line frequency and the color subcarrier frequency are preferred.

Abstract: A digital signal peaking apparatus combines input digital signals with filtered and scaled representations thereof to produce controllably peaked digital signals. A digital filter produces the relatively higher frequency components of the input digital signals which are controllably scaled by a digital multiplier in accordance with a multiplier coefficient. A control arrangement develops the multiplier coefficient having a value determined in accordance with the peak magnitude of the higher frequency components of the input digital signals relative to the value of a peaking control level signal.

Abstract: A digital signal coring circuit removes from a stream of incoming digital data words low-valued variations lying between upper and lower threshold reference values. Upper and lower threshold values are adjusted in response to the value of the outgoing cored digital data words so that such low-valued variations are removed over the entire range of values of the digital data words, and not merely around a baseline value.

Abstract: A digital ratio detector for detecting digitized frequency-modulated (FM) signals develops sum and difference signals from input digital signals and from delayed representations thereof. The sum and difference signals are detected and further sum and difference signals are developed and are applied to respective lowpass digital filters having controllable gain. A gain control circuit develops a gain control signal which is applied to the digital lowpass filters to control the respective gains thereof so that the filtered digital signals produced by one of the digital filters includes digital representations of the deviations of the FM carrier.

Abstract: Apparatus providing a magnified picture display for a television receiver employs a reduced-size digital memory which stores only the digitized video signal components necessary to generate video signals to produce the magnified picture display. A simplified user-controlled picture positioning arrangement generates write and read addressing signals for the digital memory representative of both the picture area of the magnified picture display and of the normal picture display therein which is to be magnified. Writing of the digitized video signal components of the normal picture display into the digital memory is accomplished in "real time" whereas reading of the stored data from the memory and signal processing to develop interpolated digitized video signal components of the magnified picture is accomplished at a reduced processing rate on a line-by-line basis in between memory write cycles.

Abstract: The present invention provides for the generation of digitally dithered digital signals which can have an apparent quantizing resolution unaffected by truncation of the least significant bit. The truncated digital signal is dithered in an ordered fashion by adding thereto a bit developed in response to one condition of the truncated bit and is not dithered in response to another condition thereof. The original digital signal can be reconstructed by combining successive samples of the truncated digital signals. One feature of the present invention provides a truncation of digital signals.

Abstract: A digital television receiver includes an analog-to-digital converter having a controllable scaling factor and offset. To improve resolution of the digital samples, the scaling factor is increased and the offset is changed when the synchronizing and color reference burst portions of the composite video signal are being converted. In addition, the scaling can be greatly increased at selected times so that the phase of the color reference burst can be more accurately determined.

Abstract: An automatic color control (ACC) for a digital television receiver is compatible with and is unaffected by variation of the phase of the color subcarrier signal introduced in demodulating the color subcarrier to effect control of tint. ACC is effectuated by digital gain control for scaling the digital words representing the sampled magnitudes of the color subcarrier burst signal. Quadrature demodulation of the color subcarrier produces color signal digital words I and Q which are each sampled and latched during the color subcarrier burst. The sampled digital words are each squared and are then summed together. The summed digital word is compared to a chroma reference digital word and the difference digital word is employed to scale the color subcarrier digital words.

Abstract: A circuit for supplying first and second currents to a load comprises two current generators for providing those currents during first and second time intervals and a resistance through which those currents flow. Two control potentials developed by two semiconductor junctions are applied across the resistance. First and second control circuits control the two current generators so that the first and second currents are provided during the first and second time intervals, respectively. The current supply circuit is useful in a multivibrator wherein the timing capacitor thereof is the load to which the first and second currents are supplied.

Abstract: An automatic color burst magnitude control (ACC) for a digital television receiver is compatible with and is unaffected by variation of the phase of the color subcarrier signal introduced in demodulating the color subcarrier to effect control of tint. ACC is effectuated by digital gain control for scaling the digital words representing the sampled magnitudes of the color subcarrier burst signal. Quadrature demodulation of the color subcarrier signal produces color signal digital words I and Q which are each sampled and latched during the color subcarrier burst. The averages of the sampled I and Q digital words are applied as respective portions of the address of a read only memory (ROM). The ROM provides error words indicating whether the chroma burst amplitude is too large or too small. A control device responds to the error word to scale the color subcarrier digital words, and therefore scale the chroma burst amplitude to a predetermined magnitude.

Abstract: A class D power amplifier employing two N-channel field-effect power transistors includes an arrangement which develops a biasing voltage for the upper N-channel transistor. The biasing voltage exceeds the magnitude of the power source voltage so that the upper N-channel transistor can exhibit low channel ON resistance whereby substantially the entire supply voltage is applied to a load device. A transistor switch becomes conductive across a resistance which couples biasing voltage to the upper N-channel transistor when the biasing voltage exceeds the supply voltage.

Abstract: The gain of the chroma signal in a digital television receiver is controlled in accordance with the value of a composite gain factor which is an accumulation of gain control factors provided by a user color control, automatic chroma control, and chroma overload. Gain control according to the composite gain factor is realized by a coarse gain block, which increments or decrements the chroma signal gain in increments of six dB, and a fine gain control over a range of six dB or less, in finely controlled increments. In a preferred embodiment, the digital chroma gain system is operated under control of a microprocessor, which receives signals representative of chroma overload, user control settings, and chroma burst amplitude. The microprocessor then calculates the composite chroma signal gain and apportions the gain between the coarse and fine gain control blocks.

Abstract: A signal-seeking tuning system for a television receiver scans the VHF and UHF signal bands until a present TV channel signal is detected. Tuning voltage is developed by a digital-to-analog converter in response to a binary word stored in an up-down counter. The value of the binary word increases when a scan-up signal is applied and decreases when a scan-down signal is applied. Scanning is stopped by inhibiting changing of the binary word when a valid sequence of AFT signals is detected.Thereafter, the tuning voltage is compensated for drifts by incrementing or decrementing the binary word whenever the AFT signal departs from a predetermined condition. This correction is inhibited, however, when the RF carrier signal is lost so that the desired tuning is not also lost, whereby the selected channel is still tuned when the RF carrier signal reappears.

Abstract: First and second transistors of first and second types that can exhibit respective first and second potentials of first and second opposite polarities between their respective input and common electrodes when respective currents flow in conduction paths between their respective output and common electrodes. The transistors are connected in cascade with the input electrode of the first transistor connected to an input point, the common electrode of the first transistor connected to the input electrode of the second, and the conduction path of the second transistor coupled to a load. A circuit for operating the first transistor at the first potential to compensate, at least in part, for the second potential comprises a third transistor of the first type to which is applied a potential of the first polarity between its input and common electrodes to establish a current in its conduction path.

Abstract: A television tuning system includes UHF and VHF signal paths each tuned by a tuning voltage and coupled to a common signal path by a diplexer. So that UHF signals will be attenuated so to not cause interferences with a VHF channel signal which is selected to be viewed, the UHF filter is detuned when a VHF channel is selected. Detuning the UHF filter is accomplished by modifying the tuning voltage for the UHF filter responsive to the VHF band-switching voltage.

Abstract: A television tuning system includes UHF and VHF signal paths each tuned by a tuning voltage and coupled to a common signal path by a diplexer. So that UHF signals will be attenuated so to not cause interference with a VHF channel signal which is selected to be viewed, the UHF filter is detuned when a VHF channel is selected. Detuning the UHF filter is accomplished by modifying the tuning voltage for the UHF filter responsive to the VHF band-switching voltage.

Abstract: A digital filter arrangement is provided which both demodulates and filters the color mixture signals in a television receiver. Samples of a digital chrominance signal are clocked into first and second registers such that the first register is loaded with samples of a first color mixture signal and the second register contains samples of a second color mixture signal. Output taps are connected between various ones of the stages of the first and second registers and weighting function circuits. The weighting function circuits associated with each register are in turn coupled to respective ladder networks of adders, which combine the weighted signals samples so as to exhibit, at an output stage adder, a lowpass response characteristic which is appropriate for the respective color mixture signal. The two digital registers are aligned in time in accordance with their respective peak impulse response characteristic to product filtered color mixture signals in a proper timed relationship.