Method and apparatus for synchronizing internal and external video signals
First Claim
1. A method of synchronizing a programmable sync generator output with an external video signal where the sync generator frequency is controlled by a voltage controlled oscillator comprising the steps of:
- detecting the beginning of a frame in the video signal by digitizing the video signal,monitoring the digitized signal for determining the beginning of a frame,producing a start pulse for starting the sync generator at the beginning of a frame, andafter one start pulse is produced, inhibiting any additional start pulses so long as the video signal is present;
starting the sync generator when the frame begins so that initially the sync generator output signal is synchronized with the video signal;
comparing the phases of the output signal and the video signal and generating a voltage according to phase differential; and
adjusting the voltage controlled oscillator with the generated voltage to null the phase differential, whereby the output signal is synchronized with the external video signal.
2 Assignments
0 Petitions
Accused Products
Abstract
An automotive video display of a scene from a camera has a graphics window to display vehicle information. A video graphics controller has a programmable synchronous generator for the graphics window which is synchronized or gen-locked with the camera or external video signal. A digital sync separator provides digital external sync signals. A start circuit monitors the external sync signals to detect the start of a video frame and starts the sync generator which is initially in synchronism with the external signal. A phase locked loop maintains the synchronism. A crystal oscillator circuit includes an inductor and a varactor which is tuned to vary the oscillator frequency enough to track the external video signal.
19 Citations
9 Claims
-
1. A method of synchronizing a programmable sync generator output with an external video signal where the sync generator frequency is controlled by a voltage controlled oscillator comprising the steps of:
-
detecting the beginning of a frame in the video signal by digitizing the video signal, monitoring the digitized signal for determining the beginning of a frame, producing a start pulse for starting the sync generator at the beginning of a frame, and after one start pulse is produced, inhibiting any additional start pulses so long as the video signal is present; starting the sync generator when the frame begins so that initially the sync generator output signal is synchronized with the video signal; comparing the phases of the output signal and the video signal and generating a voltage according to phase differential; and adjusting the voltage controlled oscillator with the generated voltage to null the phase differential, whereby the output signal is synchronized with the external video signal.
-
-
2. A method of synchronizing a programmable sync generator output with an external video signal wherein the beginning of a frame is indicated by the beginning of an odd field and where the sync generator frequency is controlled by a voltage controlled oscillator comprising the steps of:
-
detecting the beginning of a frame in the video signal by digitizing the video signal, and monitoring the digitized signals for determining the beginning of an odd field; starting the sync generator when the frame begins so that initially the sync generator output signal is synchronized with the video signal; comparing the phases of the output signal and the video signal and generating a voltage according to phase differential; and adjusting the voltage controlled oscillator with the generated voltage to null the phase differential, whereby the output signal is synchronized with the external video signal.
-
-
3. A method of synchronizing a programmable sync generator output with an external video signal where the sync generator frequency is controlled by a voltage controlled oscillator comprising the steps of:
-
detecting the beginning of a frame in the video signal by digitizing the video signal to obtain composite and vertical sync signals and an odd/even field signal, and monitoring the pulse width of the composite sync signal and the states of the vertical sync signal and the field signal for the start of a frame; starting the sync generator when the frame begins so that initially the sync generator output signal is synchronized with the video signal; comparing the phases of the output signal and the video signal and generating a voltage according to phase differential; and adjusting the voltage controlled oscillator with the generated voltage to null the phase differential, whereby the output signal is synchronized with the external video signal. - View Dependent Claims (4, 5)
-
-
6. Apparatus for synchronizing a programmable sync generator with an external video signal comprising:
-
a start circuit coupled to the video signal for furnishing a start pulse to the sync generator at the beginning of a frame to initially synchronize the sync generator output signal with the video signal, the start circuit comprising a sync separator for digitizing the video signal to obtain a composite sync signal, and a circuit for monitoring the width of the composite sync signal pulses to detect the start of a frame; a phase locked loop for maintaining synchronism including the sync generator, a voltage controlled oscillator coupled to the sync generator clock input, and a phase comparator; and the phase comparator being responsive to the video signal and the generator output and includes means for producing a voltage for controlling the oscillator frequency.
-
-
7. Apparatus for synchronizing a programmable sync generator with an external video signal comprising:
-
a start circuit coupled to the video signal for furnishing a start pulse to the sync generator at the beginning of a frame to initially synchronize the sync generator output signal with the video signal, the start circuit comprising a sync separator for digitizing the video signal to obtain composite and vertical sync signals and an odd/even field signal, and a circuit for monitoring the width of the composite sync signal pulses and the states of the vertical sync signal and the field signal for the start of a frame; a phase locked loop for maintaining synchronism including the sync generator, a voltage controlled oscillator coupled to the sync generator clock input, and a phase comparator; and the phase comparator being responsive to the video signal and the generator output and includes means for producing a voltage for controlling the oscillator frequency.
-
-
8. Apparatus for synchronizing a programmable sync generator with an external video signal comprising:
-
a start circuit coupled to the video signal for furnishing a start pulse to the sync generator at the beginning of a frame to initially synchronize the sync generator output signal with the video signal, the start circuit comprising a sync separator for digitizing the video signal to obtain composite and vertical sync signals and an odd/even field signal; and a circuit for detecting the start of a frame including a timer for generating a reference pulse width for each composite sync pulse, a circuit for comparing each composite sync pulse to a reference pulse to detect short pulses, the short pulses occurring at the beginning of each field, and a circuit for validating a short pulse as the start of a frame when it is coincident with vertical sync and field signals consistent with the start of a frame; a phase locked loop for maintaining synchronism including the sync generator, a voltage controlled oscillator coupled to the sync generator clock input, and a phase comparator; and the phase comparator being responsive to the video signal and the generator output and includes means for producing a voltage for controlling the oscillator frequency. - View Dependent Claims (9)
-
Specification