Zenith Electronics Corporation

Zenith Radio Corporation

Jouke N Rypkema

Gopalan Krishnamurthy

Victor G Mycynek

Michael D Flasza

Gordon E Kelly

Lester F Benjamin

A restrictive access control system includes a 3-state switch for controlling the operating mode of the system and limiting tuning access to only designated channels. Tuning information is provided to a microprocessor via a control panel keyboard for storage in a nonvolatile memory and for subsequent recall therefrom when desired channel information is entered in the control panel by a viewer. In one embodiment, a 3-position key actuated switch has a first OFF position, a second PROGRAM position, and a third ON position. In the ON and OFF positions, the key may be removed from the switch while in the second PROGRAM position the key may not be removed from the switch. Programming of the nonvolatile memory may only be accomplished with the key in second PROGRAM position for storing either desired channels or locking out undesired channels. From the second PROGRAM position, the key may be turned to either the first OFF position for viewing all available channels or to the third ON position whereupon only authorized channels can be viewed. Turning the switch between the various positions, or modes of operation, is not possible without the key so as to provide a high level of viewing security, while affording the key bearer not only channel programming access, but also the capability of limiting tuning access to only designated channels. Other embodiments include (1) a two position key switch with key detector and limited access control selector and (2) program and limited access control selectors in combination with an optical card reader.

Restrictive access control system

A tilt correction circuit for a color television signal processor includes a differential amplifier having a first tuned circuit tuned near the color carrier frequency and a second tuned circuit tuned near the picture carrier frequency. An IF video input signal is applied to the differential amplifier, the output of which reflects the relative effect of the two tuned circuits. A correction voltage is derived by peak detecting the color burst and comparing it with a reference voltage related to a nominal color burst level in a color television signal. The correction voltage is supplied to the other input of the differential amplifier to change the relative effects of the tuned circuits to adjust the frequency response over the IF band. A tilt defeat circuit is included for disabling the correction voltage where the magnitude of the correction voltage indicates the presence of a monochrome signal.

Automatic frequency response correction using color burst

An intercarrier signal detection circuit for a television receiver sound system comprises a SAW (Surface Acoustic Wave) filter coupled to the output of a tuner, the SAW filter having a response characteristic including two symmetrical lobes centered about 41.25 MHz and 45.75 MHz respectively. The signal developed at the output of the SAW filter is applied to an AGC-controlled IF amplifier and then separated into a 41.25 MHz sound IF component and a 45.75 MHz picture IF component. The 41.25 MHz sound IF component is applied to one input of a synchronous detector whose other input is injected with a carrier signal developed by a phase lock loop operated in response to the 45.75 MHz picture IF component. The synchronous cetector thereby produces a relatively clean 4.5 MHz intercarrier sound signal which is preferably enhanced by causing the injected carrier signal to exhibit a quadrature phase relationship with any 45.75 MHz picture IF remnants characterizing the separated 41.25 MHz sound IF component. The 45.75 MHz picture IF component and an amplitude limited representation thereof developed by the phase lock loop, are coupled to respective inputs of an additional detector for developing a baseband video signal which is used by an AGC circuit for controlling the gain of the IF amplifier.

Intercarrier signal detection circuit for a television receiver

A non-reactive limiter for limiting the amplitude of a carrier signal amplitude modulated by a modulating signal comprises a voltage divider including a fixed resistance and a variable resistance, the latter preferably comprising a PIN diode. The amplitude modulated carrier signal is applied across the voltage divider while a current is established through the PIN diode in response to the modulating signal for linearly varying its resistance in inverse relation to the instantaneous level of the amplitude modulated carrier signal so as to develop an amplitude limited carrier signal across the PIN diode.

Non-reactive limiter

An AGC system is described for setting a plurality of different AGC delay points for various channels or bands of channels in a television receiver. In one embodiment, the system includes an AGC control which develops a gain control signal for the UHF and VHF tuners, and an AGC delay circuit which determines the point at which the gain control signal becomes effective to initiate gain reduction in the tuners. Preferably, the delay circuit causes the AGC control to establish a first AGC delay point, corresponding to a given level of incoming signal strength, at which the gain control signal causes the VHF tuner to begin gain reduction, and establishes a different delay point corresponding to a relatively higher level of incoming signal strength at which the gain control signal causes the UHF tuner to begin gain reduction. In another embodiment, a separate AGC delay point is set for channel 6 to provide a more desirable delay point for other channels in the VHF band. The latter embodiment can also provide a customized AGC delay for each channel in the UHF and VHF bands.

AGC System for television receivers

A television signal processing apparatus is responsive to a received television signal for translating the frequency spectrum thereof to a frequency band characterized by a fixed frequency carrier signal frequency modulated in accordance with a baseband audio signal. The frequency modulated carrier signal is combined with an unmodulated CW muting signal having a frequency approximately equal to the frequency of the carrier signal to facilitate remotely controlled muting of the baseband audio signal in accordance with the FM capture effect.

Remote muting for CATV/STV converters

A frequency and phase lock loop is disclosed in which AFC and phase locking functions are completely separated thus permitting signal acquisition range and closed loop bandwidth parameters to be independently established. Interference between phase lock loop (PLL) and automatic frequency control (AFC) signals resulting in the loss of a beat frequency signal for matching VCO and reference signal frequencies is eliminated thus affording enhanced PLL frequency pull-in range.

Frequency and phase lock loop with separated AFC and phase locking

A television tuning system has a voltage controlled oscillator and frequency converter, cooperating to convert a receiver broadcast signal to an intermediate frequency signal and an intermediate frequency filter having a predetermined frequency response. Automatic frequency control means operative upon the voltage controlled oscillator to maintain correct frequency conversion include a limiter coupled to the intermediate frequency filter producing a constant amplitude output signal which is coupled directly to one input of a multiplier and to a surface acoustic wave filter having a predetermined frequency-dependent phase shift characteristic. The filter characteristic defines quadrature phase points at the picture carrier frequency and a selected frequency substantially midway between the picture and sound carriers. The filter output is coupled to the remaining multiplier input. A low pass filter couples the output signal of the multiplier to the voltage controlled oscillator thereby providing automatic frequency control. The output voltage characteristic of the multiplier includes zero crossings at the intermediate frequency picture carrier frequency and at a frequency between the intermediate frequency picture and sound carriers.

Growing community of inventors

Lombard, IL, United States of America

Jouke N Rypkema