Pulse or digital communications – Systems using alternating or pulsating current
Reexamination Certificate
1999-10-25
2003-09-02
Pham, Chi (Department: 2631)
Pulse or digital communications
Systems using alternating or pulsating current
C375S260000
Reexamination Certificate
active
06614849
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is generally related to electronic circuits and systems that transmit and receive digitally sampled analog signals. More particularly, this invention relates to electronic circuits and systems that transmit and receive digital audio signals.
2. Description of the Related Art
The transmission of analog signals between a source of the analog signals and a reproduction of the analog signals at an output transducer is well known in the art. U.S. Pat. No. 5,596,648 (Fast) describes a wireless infrared audio transmission system where infrared LED emitters are activated by a frequency modulated pulse wave transmitted as light to a receiver. The audio analog signal modulates the frequency modulated pulse wave.
U.S. Pat. No. 5,596,603 (Haupt, et al.) illustrates another device for wireless transmission of audio signals. Refer now to
FIG. 1
for an overview of this structure. The analog source
5
provides a left channel L and a right channel R. The analog source
5
would be microphones, a FM tuner/receiver, or an analog recording media. The left channel L and the right channel R are inputs to analog-to-digital converters
15
and
20
. It is well known in the art that the analog sources can provide any number of channels. The left channel L and right channel R are chosen for illustration purposes.
Additionally, the analog signals from the analog source
5
can have been previously converted to digitized samples and then provided by the digital source
10
. The digitized samples of the analog signals are retained in a data buffer
25
. The digitized samples are then formatted in data frames in the data formatting unit
30
. In Haupt, et al. a data frame is 128 bits in length for each channel (left channel L or right channel R). The data frames are then transferred to the date modulator
35
. A carrier signal is then modulated with the data frames.
In the case of Haupt, et al., the data frames are changed from a 4 bit audio data to a 5 bit transmission data, which is used to activate and deactivate an infrared light emitting diode. The modulated carrier signal is transferred to a transmitter and then conveyed to the communication medium
45
. The infrared light is then radiated through the open atmosphere to a receiving light sensitive diode. In this case, the communication medium
45
is the open atmosphere.
It is well known that the transmitter
40
can produce radio frequency waves in addition to light. Further, the communication medium
45
can be either wire such as coaxial cable, twisted-pair cable or other forms of metallic (copper) inter-connection. Additionally, the communication medium
45
may be a fiber optic cable.
The receiver
50
will recover the modulated carrier signal from the communication medium
45
. Typically, a clocking or timing signal is included in the data frame and the modulated carrier signal. A clock extraction circuit
55
will develop the embedded clocking or timing signal and synchronize the receiving subsystem
100
with transmitting subsystem
95
. Classically, the clock extraction circuit
55
incorporates a phase locked oscillator, which can malfunction if there are errors in the transmitted modulated carrier signal.
The recovered modulated carrier signal is transferred to the demodulator
60
to extract the data frames. The data frames are then reformatted in the receive data formatter
65
to recreate the digitized samples of the analog signals. The recreated digitized samples are then transferred to the digital-to-analog converters
70
and
75
to reproduce the analog signals
80
and
85
. Alternately, the digitized samples of the analog data can be transferred
95
to external circuitry for further processing.
The wireless transmission as shown in
FIG. 1
is subject to corruption of the digitized samples during transmission. For instance, noise from an electronically ballasted halogen lamp would completely breakdown recovery of the transmission of the modulated carrier signal.
A solution to the corruption of the modulated carrier signal is to provide a level of redundancy for the digitized samples. U.S. Pat. No. 5,832,024 (Schotz, et al.) shows the use of forward error correction codes using the well known Reed-Solomon Coding. This will eliminate errors of relatively short duration, but will not prevent disruption of the output analog signals
80
and
85
due to long term digitized sample corruption.
To eliminate longer corruption of the digitized samples Schotz, et al. employs a convolutional interleaving circuit to separate the digitized samples of the analog signal that would normally be transmitted together. This allows the greater probability that a longer term error can be to be corrected.
If the error correction coding and the convolutional interleaving of the digitized samples cannot insure corrected digitized samples of the analog signals, the analog signal will be reproduced (especially in audio signals) as annoying cracks and pops in a speaker. To eliminate the cracks and pops, Schotz, et al. suggests that the digitized samples can be brought to a null level or muted. However, if the muting is activated suddenly, it is distracting and is annoying to the listener in an audio application.
U.S. Pat. No. 5,602,669 (Chaki) provides a digital transmitter-receiver that transmits a digital audio signal within a specified frequency band, and receives the specified frequency band. Chaki modulates a fundamental frequency using Quadrature Phase Shift Keying (QPSK). The QPSK modulated signal is transferred to an infrared emitter for transmission.
U.S. Pat. No. 5,420,640 (Munich, et al.) describes a memory efficient method and apparatus for synchronization detection within a digital data stream over a communication path. The digital data is arranged as a sequence of frames, each frame including a plurality of lines of data. The beginning of each frame is indicated by a frame synchronization word. The beginning of each line is indicated by a horizontal synchronization byte. An encoder, before transmission, interleaves the data. The decoder contains circuitry for locating the horizontal and frame synchronization data and contains circuitry for deinterleaving the digital data. Both the synchronization locating circuitry and the deinterleaving circuitry require access to a memory, but not at the same time. Therefore, a single memory is used with the synchronization recovery circuitry and deinterleaving circuitry alternately addressing the memory. The digital data stream of Munich, et al. pertains to video, audio and other related services of subscriber based television systems.
U.S. Pat. No. 5,745,582 (Shimpuku, et al.) teaches an audio signal transmitting and receiving system which can perform optical transmission of a digital format audio signal with small deterioration of the sound quality over the transmission path. The audio signal transmitting system has circuits to add an error correction signal to a digital audio signal. The digital audio signal with the error correction signal is then encoded and interleaved to generate an audio transmission signal. Repeating a digital control signal, which is to be used for the reproduction of the digital audio transmission signal, generates a continuous signal. A multiplexer combines the audio transmission signal and the continuous signal to generate a multiplexed signal. A modulation circuit then modulates a carrier signal similar to that described above with the multiplexed signal by a predetermined digital modulation method to generate a modulated signal within a predetermined frequency band. The modulated signal is transmitted by an optical transmission signal. A differential type QPSK modulation method creates the modulated signal preferably. Shimpuku, et al. further describes an audio signal receiving circuit for reproducing a digital audio signal and a digital control signal from the optical transmission signal. The audio signal receiving circuit has an optical receiver to convert the optical transmission signal to an electric
Chan Chee Oei
Chua Beng Huat
Lee Kah Yong
Siew Chee Kong
Ackerman Stephen B.
Free Systems Pte. Ltd.
Knowles Billy
Pham Chi
Saile George O.
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