Pulse or digital communications – Transmitters
Reexamination Certificate
2000-01-14
2001-02-20
Booure, Tesfaldet (Department: 2734)
Pulse or digital communications
Transmitters
C375S376000, C381S001000, C348S481000
Reexamination Certificate
active
06192086
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to communications systems and, more specifically, to communications systems employing the BTSC standard.
2. Description of the Prior Art
BTSC-compatible encoders are used to encode stereo audio signals into television signals. Existing systems typically use an analog approach. The analog approach is environmentally sensitive and requires extra circuitry to be compatible with digital television systems.
Existing digital BTSC-compatible encoders are embodied on existing digital signal processing (DSP) chips. Such DSP chips are costly relative to application specific integrated circuits when mass produced.
Therefore, there is a need for a digital BTSC-compatible encoder circuit embodied in an application specific integrated circuit.
SUMMARY OF THE INVENTION
The disadvantages of the prior art are overcome by the present invention, which in one aspect is a BTSC encoder that is integrated onto an application specific integrated circuit. The encoder includes a low pass filter that is responsive to a digital representation of an audio signal that has a sample rate of F
S
. The low pass filter generates a corresponding second digital signal having an pseudo-interpolated sampling rate of 4F
S
. A digital infinite impulse response pre-emphasis filter generates a pre-emphasized output signal corresponding to the second digital signal. A digital signal compressor that is responsive to the pre-emphasized output signal, generates a compressed digital signal corresponding to the pre-emphasized output signal. A digital phase locked loop that is responsive to a video sync pulse having a sync pulse frequency, generates a third digital signal corresponding to a sinusoid having a frequency equal to twice the sync pulse frequency and a having a sampling frequency equal to 4F
S
. A first digital multiplier multiplies the compressed digital signal by the third digital signal, thereby generating a BTSC digital signal.
These and other aspects of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the following drawings. As would be obvious to one skilled in the art, many variations and modifications of the invention may be effected without departing from the spirit and scope of the novel concepts of the disclosure.
REFERENCES:
patent: 4561012 (1985-12-01), Acampora
patent: 5796842 (1998-08-01), Hanna
patent: 6037993 (2000-03-01), Easley
Roger Darr, “Designing Low-Cost Digital BTSC Stereo Encoders for Consumer Video Source Equipment,” IEEE Eectronic System Product, 2000, pp3 40-341.
Antec Corporation
Booure Tesfaldet
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