Amplifiers – Sum and difference amplifiers
Patent
1995-06-07
1997-12-02
Mottola, Steven
Amplifiers
Sum and difference amplifiers
330126, H03F 345
Patent
active
056940815
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to circuits that use signal conditioning circuitry to eliminate interferences caused by magnetic fields, electric fields, and electro-magnetic or radio frequency fields on conductors that provide electrical connection between devices in a system. The present invention also relates to various electronic circuit that drive conductors, the electronic circuits including signal conditioning circuit to overcome the adverse effects of their loading on the signal source. More specifically, the present invention relates to audio amplifiers, power amplifiers, video amplifiers, etc. that use signal conditioning circuitry for achieving the above-noted benefit.
2. Description of Related Art
Conductors that provide electrical connection between devices in a system are often the source of many types of electrical interference. Magnetic fields, electric fields and electro-magnetic or radio frequency fields are known to interfere with the fidelity of signals conveyed over conductors which are subjected to those fields. Furthermore, the ground or reference conductor of a typical signal carrying pair of conductors are often connected to different local ground potentials between one end of the conductor as compared to the other, and currents are known to flow in such conductors which then produce voltage drops on that conductor which also interfere with the fidelity of the signals being conveyed. In addition, these conductors, especially when very long, present loads to the signal source that may adversely effect the fidelity of the signal.
The problems of conveying signals over conductor pairs in various types of electronic circuits including amplifier systems such as audio amplifier systems, power amplifier systems, video amplifier systems, etc. is well known. The conveyance of signals, especially between powered devices, is often plagued by electro-magnetic interference.
One method employed to reduce these interferences modulates the signal so that it can be easily separated from the interference, and then demodulates the signal at the destination. For example, an analog-to-digital converter can be utilized to convey digital impulses over the connecting conductors instead of analog voltage potentials. The destination device in such instances must then convert the signal back to an analog signal potential. Such approaches, while effective, can be very costly, and require extensive circuitry at both the sending and receiving ends of the conductors. Such methods are exemplified by U.S. Pat. No. 4,922,536 to Hogue.
Another common method to reduce these interferences is to convey such signals in a differential manner. A common approach utilizes a three conductor shielded cable where two of the conductors deliver the signal and its arithmetic inverse, and a third conductor, usually a shield, conveys the ground reference potential voltage. The conditioning circuit, usually placed at the destination end of the conductors, forms the difference between the potential of the first signal carrying conductor and the second signal carrying conductor. In theory, both conductors are subject to the same interferences, and the subtraction of the signals as conveyed will eliminate the common mode noises. This approach, while effective in eliminating most interference is nevertheless expensive and difficult to implement. To adapt this approach in the general case of processing signals between subsystems requires active circuitry at the sending end to form the inverse signal, and a separate active circuit at the receiving end to subtract the signals. Multiple conductors are also required to be contained within a single shield, which is more costly than conductors having only one conductor surrounded by a shield. Such methods do not, however, address any interference or other affects of the cables that connect the transmitter and receiver to source and destination respectively. Such methods are exemplified by U.S. Pat. No. 4,979,218 to Strahm, and is described a
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"Grounding and Shielding Techniques", Ralph Morrison, 3rd Edition, 1986, pp. 69-71 no month.
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