General Instrument Corporation

Daniel J Marz

Clyde N Robbins

Louis Caporizzo

John D Schilling

A method and apparatus are provided for recovering a desired baseband signal from a signal represented by in-phase and quadrature-phase signal components, while automatically correcting phase error present between these signal components. In general, the method of the present invention involves providing to the input of a local signal generating circuit, a first signal representative of the in-phase signal component, and generating therefrom local in-phase and quadrature-phase signals. One of the local in-phase and quadrature-phase signals is phase shifted by a selected amount of phase correction. The local in-phase signal is multiplied by the first signal to produce a first resultant signal. The local quadrature-phase signal is multiplied by the second signal representative of the quadrature-phase signal, to produce a second resultant signal. The first resultant signal and the second resultant signal are then summed so as to produce an output signal representative of the desired baseband signal.

Method and apparatus for recovering baseband signals from in-phase and

The need for replacing the dedicated external output filter each time a different channel is selected is eliminated through the use of a switchable array of low and high pass filters which forms a filter circuit which may be varied for use with any channel. The band pass of the filter is selected in accordance with the selected channel number. The channel number is decoded to actuate RF relays which switch selected filters into the circuit.

Agile output band pass filter for agile up converter

The converter has two mixer stages each including a phase locked loop with an oscillator controlled by a phase comparator. The frequency reference to both stages is provided by a single master reference. The frequency of the oscillator in the first stage is offset to accommodate the three different broadcast frequency conventions. A high frequency reference permits the second stage to compensate for noise kilohertz away from the carrier. A local oscillator output which is also phase locked to the master reference is provided for an external video modulator.

Low phase noise agile up converter

An on channel frequency agile PLL demodulator is provided using a precise and stable oscillator, such as a VCXO having its output frequency variable over a limited range. The output of the oscillator is multiplied by a multiplication factor to produce a mixing frequency. The multiplication factor scales the limited range of the oscillator to produce a proportionate mixing frequency deviation. A frequency synthesizer is used to enable the demodulator to detect signals on different channels. In one embodiment, the output of the frequency synthesizer is mixed with the scaled oscillator output to provide a mixing frequency having a fixed deviation for all channels.

On channel agile FM demodulator

A carrier is received containing a plurality of signals within a first frequency band, for example television signals within the cable television band. The signals are upconverted to a second frequency band above the first band wherein a selected one of the upconverted signals will reside at an intermediate frequency within the second band. The selected upconverted signal is input to a homodyne detector operating at or near intermediate frequency. In-phase and quadrature signals output from the homodyne detector are digitally processed to recover a baseband signal.

Up-conversion homodyne receiver for cable television converter with

A method and apparatus are provided for descrambling a sinewave scrambled television signal. The television signal is applied to a dual loop circuit that detects AM sinewave modulation on the television signal sound carrier. The detected modulation is applied to the picture carrier of the television signal in a first loop of the circuit to cancel the AM sinewave modulation therefrom. The detected modulation is applied to the sound carrier of the television signal in a second loop of the circuit to increase the AM sinewave modulation on the sound carrier within the loop. The net loop gain of the first loop is then lowered to minimize the application of noise from the sound carrier to the picture carrier.

Dual loop sinewave descrambler and method of descrambling

Circuitry for producing an extremely linear frequency modulated audio carrier for use in the head end of a video signal distribution system, such as a cable television system. A reference oscillator operating at a relatively high frequency, such as the video carrier frequency, generates a signal which is divided down to a relatively low frequency. A voltage controlled oscillator operating at the relatively low frequency is used to frequency modulate the audio signal. After modulation, the audio carrier is upconverted utilizing a signal frequency which is also derived from the original reference frequency, thus providing a stable and linear frequency modulated audio carrier particularly suitable for transmission of stereo program audio.

FM modulator

An automatic frequency control tracks a television signal before and after a period of interruption. The automatic frequency control comprises a voltage controlled feedback loop including a voltage controlled local oscillator and a mixer for mixing the output of the oscillator with the TV signal. The output of the mixer is filtered to remove unwanted components of the mixed signal and to equalize sidebands of the television signal. The output of the filter is supplied to a detector which is tuned to a component of the television signal, and produces a voltage corresponding to the frequency of the component. The output of the detector is supplied to the voltage control input of the local oscillator to track the television signal component. Circuitry automatically senses the absence of the TV signal component from the mixer, and automatically applies a reference voltage to the voltage control input of the oscillator when the TV signal component is absent. The detector is operative to detect the television signal component following the application of reference voltage to the oscillator so that when the television signal returns, the detector is capable of tracking it.

Automatic frequency control

An apparatus and method are provided for receiving and reproducing stereo television sound. A transmitted television signal is received that contains a first component comprising the sum of first and second stereophonically related audio signals and a second component comprising the difference between the first and second stereophonically related audio signals. The first and second components are converted to produce a first sound carrier centered at a first intermediate frequency and a second sound carrier centered at a second intermediate frequency. The first component is detected from the first sound carrier at the first intermediate frequency. The second component is detected from the second sound carrier at the second intermediate frequency. The detected first and second components are combined to produce a left channel audio output and a right channel audio output. By using a standard intercarrier detector for the first (L+R) component and an independent FM detector for the second (L-R) component, distortion caused by interfering harmonics of the television horizontal line frequency with vertical scan frequency sidebands falling within the (L-R) subchannel is prevented. A second audio program ('SAP') signal can also be recovered using the independent FM detector to avoid such distortion.

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Holland, PA, United States of America

Daniel J Marz