A signal conditioning system that receives inputs from at least one pair of conductors connected to its input. Each such input is processed by an input filter and presented to a buffer amplifier. Each such input filter and buffer amplifier refers to and is powered by independent power sources whose power return reference potentials are independently determined by the potential of the corresponding input signal potential reference conductor for the signal frequencies of interest. The outputs of all such buffer amplifiers, the power return reference potentials, and the power return reference potential of the conditioning circuit output are all appropriately added or subtracted in the next circuit stage. This circuit stage consists of an amplifier buffer having low output impedance which is powered by another independent power source whose power return reference potential is independently determined by the potential of the output signal reference conductor. The output of this circuit stage is connected to an output inductor circuit which in turn drives the output signal conductor. The output includes a filter, and is designed to decouple unstable loading conditions while rejecting external influences on the output signal. The invention also includes means that connect the reference potential of the destination of the output conductors to the system power ground potential. The present invention provides a relatively inexpensive and efficient way of reducing or eliminating interference caused by coax cabling in audio, power and video amplifiers, for example.
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27. A circuit for conditioning video signals in a video system, the circuit comprising:
a) a first stage for generating at least one intermediate video signal which is proportional to a potential difference between at least one applied video signal and at least one return reference signal corresponding to the at least one applied video signal; said first stage further generating at least one inverted applied video signal corresponding to the at least one applied video signal; and b) a second stage, operatively coupled to the first stage, for generating an output video signal which is a sum of said at least one intermediate video signal generated in the first stage plus an output return reference signal minus a potential of the inverted applied video signal.
38. A circuit for conditioning signals in a system, comprising:
a first stage having an amplifier circuit for receiving, from an input source, an input signal and an input source reference potential and generating an intermediate signal which represents the sum of the input source reference potential and a proportion of the input signal; a first power supply circuit coupled to said first stage, said first power supply circuit comprising voltage regulation means for drawing a constant current from the power supply with respect to changes in the input source reference potential to isolate the power supply from said first stage; and a second stage coupled to said first stage, and responsive to said intermediate signal, for generating an output signal which is proportional to the input signal.
28. A circuit for conditioning signals in a system, comprising:
a first stage having a buffer amplifier for receiving at least one input signal and generating therefrom at least one intermediate signal which is proportional to a potential difference between the at least one input signal and at least one return reference signal corresponding to the at least one input signal; a power supply circuit coupled to said first stage for providing a constant current with a high impedance to increase electrical isolation between the first stage and the at least one return reference signal; and a second stage, operatively coupled to the first stage, for generating an output signal which is a sum of the at least one intermediate signal generated in the first stage minus a potential of the at least one return reference signal plus an output return reference signal.
26. A circuit for amplifying and conditioning audio signals in an audio system, the circuit comprising:
a) a first stage for generating at least one intermediate audio signal which is proportional to a potential difference between at least one applied audio signal and at least one return reference signal corresponding to the at least one audio signal, said first stage further generating at least one inverted applied audio signal corresponding to the at least one applied audio signal; b) a second stage, operatively coupled to the first stage, for generating an output audio signal which is a sum of the at least one intermediate audio signal generated in the first stage plus an output return reference signal minus a potential of the inverted applied audio signal; and c) a power amplifier for current amplifying the output audio signal generated in the second stage.
14. A system for amplifying and conditioning signals, the system comprising:
a first circuit comprising: a) an input for receiving at least one input signal; b) a first stage for generating at least one intermediate signal which is proportional to a potential difference between the at least one input signal and at least one return reference signal corresponding to the at least one input signal, said first stage further generating at least one inverted signal corresponding to the at least one input signal; and c) a second stage, operatively coupled to the first stage, for generating an output signal which is a sum of the at least one intermediate signal generated in the first stage plus an output return reference minus a potential of the inverted signal; and a second circuit comprising an amplifier for current amplifying the output signal from the second stage of the first circuit.
36. A circuit for conditioning signals in a system having a power supply and a power supply reference potential, said circuit comprising:
a first stage having an amplifier circuit for receiving, from an input source, an input signal and an input source reference potential different from the power supply reference potential, said first stage generating an intermediate signal which represents the sum of the input source reference potential and a proportion of the input signal; a first power supply circuit coupled to said first stage, said first power supply circuit isolating the power supply from said first stage by drawing a constant current from the power supply with respect to changes in the input source reference potential; and a second stage coupled to said first stage, and responsive to said intermediate signal, for generating an output signal which is proportional to the input signal.
1. An amplifier circuit comprising:
a first stage for amplifying at least one applied signal and for generating at least one intermediate signal proportional to a potential difference between the at least one applied signal and at least one return reference signal corresponding to the at least one applied signal; a second stage, operatively coupled to the first stage, for frequency filtering the intermediate signal, the second stage generating at least one filtered intermediate signal and an inverted filtered intermediate signal which is proportional to a potential difference between the filtered intermediate signal and the at least one return reference signal corresponding to the at least one applied signal; and a third stage for generating an output signal which is a sum of the filtered intermediate signal generated in the second stage minus a potential of the inverted filtered intermediate signal generated in the second stage.
44. A signal conditioning circuit in a system having at least one input source, a power supply and an output device, said signal conditioning circuit being interposed between the at least one input source and the output device and being coupled to the power supply, the at least one input source and the output device having a first reference potential and the power supply having a second reference potential different from the first reference potential, said signal conditioning circuit comprising:
an amplifier stage having an amplifier circuit for receiving an input signal and the first reference potential from the at least one input source and generating an intermediate signal that represents the sum of the first reference potential and a proportion of the input signal; and a power supply circuit coupled to the power supply and to said amplifier stage for isolating the power supply from said amplifier stage by drawing a constant current from the power supply with respect to changes in the first reference potential.
40. A signal conditioning circuit in a system having at least one input source, a power supply and an output device, said signal conditioning circuit being interposed between the at least one input source and the output device and being coupled to the power supply, the at least one input source having a first reference potential, the output device and the power supply having a second reference potential different from the first reference potential, said signal conditioning circuit comprising:
a first stage coupled to a second stage; a power supply circuit coupled to the power supply and to said first stage for isolating the power supply from said first stage by drawing a constant current from the power supply with respect to changes in the first reference potential; said first stage having an amplifier circuit for receiving an input signal and the first reference potential from the at least one input source and generating an intermediate signal that represents the sum of the first reference potential and a proportion of the input signal; and said second stage responsive to said intermediate signal for generating an output signal which is proportional to the input signal.
43. A signal conditioning circuit in a system having at least one input source, a power supply and an output device, said signal conditioning circuit being interposed between the at least one input source and the output device and being coupled to the power supply, the at least one input source and the power supply having a first reference potential and the output device having a second reference potential different from the first reference potential, said signal conditioning circuit comprising:
a first stage coupled to a second stage; a power supply circuit coupled to the power supply and to said second stage for isolating the power supply from said second stage by drawing a constant current from the power supply with respect to changes in the second reference potential; said first stage having an amplifier circuit for receiving an input signal and the first reference potential from the at least one input source and generating an intermediate signal that represents the sum of the first reference potential and a proportion of the input signal; and said second stage responsive to said intermediate signal for generating an output signal which is proportional to the input signal.
41. A signal conditioning circuit in a system having at least one input source, a power supply and an output device, said signal conditioning circuit being interposed between the at least one input source and the output device and being coupled to the power supply, the at least one input source having a first reference potential, the output device having a second reference potential different from the first reference potential and the power supply having a third reference potential different from the first and second reference potential, said signal conditioning circuit comprising:
a first stage coupled to a second stage; a first power supply circuit coupled to the power supply and to said first stage for isolating the power supply from said first stage by drawing a constant current from the power supply with respect to changes in the first reference potential; a second power supply circuit coupled to the power supply and to said second stage for isolating the power supply from said second stage by drawing a constant current from the power supply with respect to changes in the second reference potential; said first stage having an amplifier circuit for receiving an input signal and the first reference potential from the at least one input source and generating an intermediate signal that represents the sum of the first reference potential and a proportion of the input signal; and said second stage responsive to said intermediate signal for generating an output signal which is proportional to the input signal.
32. Apparatus for conditioning signals, comprising:
a) a first circuit part having a first buffer amplifier for receiving a first applied signal and generating therefrom a first intermediate signal proportional to a potential difference between said first applied signal and a first return reference signal corresponding to said first applied signal, and having a first power supply circuit for providing a constant current to said first buffer amplifier with a high impedance, said first power supply circuit having a first power return reference potential independently determined by a potential of said first return reference signal; b) a second circuit part having a second buffer amplifier for receiving a second applied signal and generating therefrom a second intermediate signal proportional to a potential difference between said second applied signal and a second return reference signal corresponding to said second applied signal, and having a second power supply circuit for providing a constant current to said second buffer amplifier with a high impedance, said second power supply circuit having a second power return reference potential independently determined by a potential of said second return reference signal; c) a third circuit part, operatively coupled to said first circuit part, for generating a first output signal which is a sum of said first intermediate signal plus an output return reference signal minus a potential of said first return reference signal; d) a fourth circuit part, operatively coupled to said first circuit part, for generating a second output signal which is a sum of a potential of said second return reference potential plus said output return reference signal minus said second intermediate signal; and e) an output circuit for bridging said first and second output signals.
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This application is a 371 of PCT/US95/05293 filed Apr. 28, 1995 and a continuation-in-part of application Ser. No. 08/234,343 filed Apr. 28, 1994, now U.S. Pat. No. 5,436,593, which is a continuation-in-part of application Ser. No. 07/879,941, filed May 8, 1992, now U.S. Pat. No. 5,386,148.
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 at pages 69-71 of "GROUNDING AND SHIELDING TECHNIQUES IN INSTRUMENTATION", by Ralph Morrison, 3rd Edition, 1986, Wiley-Interscience.
One source of interference in the conveyance of these differential signals between electronic subsystems is referred to as the ground loop. Because it is common for there to be multiple electronic paths between the reference potentials of each subsystem, and since such paths commonly include sources of interference, these alternative paths are often responsible for the interference present in those systems. Such ground loops are generally overcome by eliminating any electrical connection by conductors between the subsystems. "GROUNDING AND SHIELDING TECHNIQUES IN INSTRUMENTATION" by Morrison describes the elimination of the effects of the electrical connections between subsystems that convey their signals by differential means through the use of tandem differential amplifiers powered by electrically isolated power supplies.
The first differential amplifier in the Morrison reference calculates the difference between the signals being conveyed, and the second differential amplifier adds the reference potential of the destination to the result of the first differential amplifier. The result is that the reference potentials of the source of the differential signal may differ from the reference potential of the destination without effecting the expression of the signal at the destination. However, such an approach is not easily adapted to electronic systems consisting of single ended two wire signal conductors. Consequently, this approach suffers from the same limitations as devices that convey signals by differential means. For example, there are no means suggested in Morrison for the elimination or suppression of the magnetic field interference that may be picked up between the two conductors enclosed in the shield, due to differences in the magnetic field voltages induced in those conductors. Moreover, Morrison does not address the pickup of electric field interference or any other cable affects due to the output cable.
The circuits shown in the Morrison reference are also particularly subject to the variation of op-amp characteristics. In particular the output impedance of the opamps used to determine A1 will negatively impact the interference rejection of any common mode voltage differences between source and destination reference potentials as that impedance relates to the difference resistors of gain stage A2. As this circuit characteristic is extremely gain and temperature dependent, such inaccuracies are not easily controlled without increased expense in the design of the output stages of those circuits or without compromises inherent in the utilization of higher impedances than would be appropriate in achieving other performance objectives such as thermal noise and bandwidth which are adversely affected by higher resistor values in this case.
It is an objective of the present invention to provide various types of electronic circuits including amplifier systems, such as audio, power and video amplifier systems, with circuitry to suppress or eliminate the expression of all types of interference in the wiring conveying analog voltage potential signals from a source to a destination. This is accomplished in the present invention by the unique combination of novel interference rejection circuits that address the sources of interference in these systems in a less costly and more efficient manner than other approaches.
It is another objective of the present invention to remove any effect that the loading of such wiring or the effects of the loading of the destination in these devices may have upon the accuracy of the signal as conveyed by the source of the signal.
It is a further objective of the present invention to accomplish the preceding objectives with a minimum number of precision resistors producing greater effective rejection than the prior art for a given cost.
An additional objective of the present invention is the reduction in sensitivity of the circuit action to the characteristics of the gain circuits and/or operational amplifier circuits employed by the circuit to achieve the various aims herein described.
Another objective of the present invention is to provide an economical means of adjusting gain in these systems without affecting the resulting interference rejection in practical applications.
Yet another objective of the present invention is to afford greater rejection of electric field interference and any electric field affects, such as dielectric absorption, due to output cable physics.
A further objective of the present invention is to effect these objectives without altering the accuracy or fidelity of the signal(s) being conveyed between subsystems.
Another objective of the present invention is to provide a device which accomplishes every objective of the present invention as described forthwith by means of an independent circuit which can easily be inserted into the existing wiring between popular electronic devices such as the above-described amplifier systems, for example, and which can accomplish every objective of the present invention as described forthwith with a minimum amount of time required to install the device in these systems.
It is a further objective of the present invention to provide all of the functions associated with state of the art amplification systems while achieving the above-noted benefits with a minimum amount of additional circuitry and without adding any additional active circuitry in the signal path.
A further objective of the present invention is to provide for the conditioning of single ended or differential signals with the same circuit organization and interconnecting wire cable(s).
A further objective of the present invention is to provide for the conditioning of differential signals, or any number of signals, where each signal is produced with reference to independent potential references which make higher levels of interference rejection possible.
It is also an objective of the present invention to accomplish every objective of the invention as described forthwith while utilizing signal wiring between devices which consists of two conductors arranged concentrically. This type of cabling is known as "COAX" which is a shortening of the term "CO-AXIAL", and which refers to a cable whose circular conductors share the same major axis.
Referring to the drawing:
FIG. 1FIG. 1 FIGS. 1A and 1B (or the "front end" depicted in broken line box 600 in FIG. 3 FIGS. 3A and 3B) is shown in block diagram form as block 403.
As shown in FIG. 4, the fight and left outputs of signal source 400 can be fed through coax cables 401 and 402, respectively, to the input of preamp 403. As noted above, preamp 403 can consist of the signal conditioning circuitry depicted in FIG. 1 FIGS. 1A and 1B, or can consist of the "front end" circuitry 400 as depicted in FIG. 3 FIGS. 3A and 3B. Preamp 403 provides voltage amplification and eliminates noise in the signals being processed, without compromising signal quality. The output of preamp 403 can then be provided to the input of power amplifier 410. Power amplifier 410 provides current amplification of the signals on lines 411 and 412 for driving right and left speakers 420 via lines 413 and 414 when operating in stereo, for example. When operating in mono, lines 413 and 414 can be bridged to drive a single speaker.
According to this embodiment of the present invention, preamp 403 can be provided as a separate unit from power amplifier 410, or can be provided as an integral unit with power amp 410. If preamp 403 is provided as a separate unit, instead of providing individual power supplies for power amp 403 and power amp 410, power can be supplied to preamp 403 from power amp 410 via cable 430.
FIG. 5 is similar to FIG. 4, but includes an additional electronic component 500. Component 500 can consist of an equalizer, crossover, noise reduction or effects processor circuitry, etc. or any combination thereof. The present invention can be used in any state of the art amplification system to eliminate noise without altering the effect of any other type of processing and without compromising sound quality in any way.
It is preferable that the majority of the voltage amplification of the amplifier system of the present invention take place in preamp 403 and that any circuitry that reduces gain be provided after preamp 403. The majority of the current amplification of the amplifier system of the present invention occurs in power amp 410. However, it may also be preferable that speakers 420 include their own current amplification circuits, particularly if speakers 420 consist of bass speakers. In addition, the present invention makes it possible to provide such current amplification without the necessity of isolated power supplies which are costly and lower in performance. In order to achieve the best results, it is preferable that if intermediate processing units are provided between the voltage amplification circuitry and the current amplification circuitry, that the power supplies for driving each of these units be isolated power supplies.
The signal conditioning circuitry of the present invention can also be used for conditioning other types of signals besides audio signals. For example, as shown in FIG. 6, the video signals from camera 600 can be fed through coaxial cable 610 to the input of signal conditioning circuit 620. Signal conditioning circuit 620, consisting of the signal conditioning circuitry depicted in FIG. 1 FIGS. 1A and 1B, suppresses or eliminates noise or interference introduced by the coaxial cables and provides a relatively clean output signal. The output signal can then be fed via coax 630 to video display 635 for immediate display and/or to remote video recorder 640 for recording. Signal conditioning circuit 620 can be provided as a unit separate from camera 600, display 635 and recorder 640, or can be incorporated into an input or output stage of display 635 and/or recorder 640.
The foregoing has set forth exemplary and preferred embodiments of the present invention. It will be understood, however, that various alternatives will occur to those of ordinary skill in the art without departure from the spirit and scope of the present invention.
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