U.S. patent application number 13/092957 was filed with the patent office on 2011-09-29 for procedure and device for linearizing the characteristic curve of a vibration signal transducer such as a microphone.
Invention is credited to Samad F. Pakzad.
Application Number | 20110235826 13/092957 |
Document ID | / |
Family ID | 37910030 |
Filed Date | 2011-09-29 |
United States Patent
Application |
20110235826 |
Kind Code |
A1 |
Pakzad; Samad F. |
September 29, 2011 |
Procedure and device for linearizing the characteristic curve of a
vibration signal transducer such as a microphone
Abstract
A procedure and device for linearizing the characteristic curve
of a vibration signal transducer such as a microphone that includes
collecting signals, transmitting the signals, extracting
information from the signals, dephasing such information by 180
degrees compared to the initial signals and taking the algebraic
sum of the initial signals and dephased information.
Inventors: |
Pakzad; Samad F.; (Mery Sur
Oise, FR) |
Family ID: |
37910030 |
Appl. No.: |
13/092957 |
Filed: |
April 24, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11364646 |
Feb 27, 2006 |
7945057 |
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13092957 |
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60656685 |
Feb 25, 2005 |
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Current U.S.
Class: |
381/119 ;
381/120 |
Current CPC
Class: |
H04R 3/04 20130101; H04R
27/00 20130101 |
Class at
Publication: |
381/119 ;
381/120 |
International
Class: |
H04B 1/00 20060101
H04B001/00; H03F 99/00 20090101 H03F099/00 |
Claims
1. A system for linearizing characteristic curve of a vibrating
signal transducer, said system comprising: an amplifier; a first
adapter, wherein an input signal is transmitted to a first input of
said amplifier through said first adapter, after being captured by
an input transducer; wherein said first adapter adjusts a level of
said input signal reaching said amplifier; and a second adapter,
wherein an output of said amplifier is connected to a dynamic input
of said amplifier, through said second adapter.
2. The system for linearizing characteristic curve of a vibrating
signal transducer as recited in claim 1, wherein said system
comprises one variable resistor.
3. The system for linearizing characteristic curve of a vibrating
signal transducer as recited in claim 1, wherein said system
comprises one operational amplifier or audio amplifier.
4. The system for linearizing characteristic curve of a vibrating
signal transducer as recited in claim 1, wherein said system
comprises a signal equalizer.
5. The system for linearizing characteristic curve of a vibrating
signal transducer as recited in claim 1, wherein said input
transducer is a microphone.
6. The system for linearizing characteristic curve of a vibrating
signal transducer as recited in claim 1, wherein said input
transducer is a static microphone or dynamic microphone.
7. The system for linearizing characteristic curve of a vibrating
signal transducer as recited in claim 1, wherein said system is
used or implemented in a hearing aid, microphone, telephone, cell
phone, wireless phone, cordless phone, magnetic pick-up, telephone
telecommunication channels, public address system, television,
video camera, radio broadcast or transmission, or recording.
8. The system for linearizing characteristic curve of a vibrating
signal transducer as recited in claim 1, wherein said system is
implemented in an integrated circuit.
9. The system for linearizing characteristic curve of a vibrating
signal transducer as recited in claim 1, wherein said second
adapter equalizes signals.
10. The system for linearizing characteristic curve of a vibrating
signal transducer as recited in claim 1, wherein said amplifier is
an operational amplifier or audio amplifier.
11. The system for linearizing characteristic curve of a vibrating
signal transducer as recited in claim 1, wherein said first adapter
or said second adapter comprises a variable or adjustable
resistor.
12. The system for linearizing characteristic curve of a vibrating
signal transducer as recited in claim 1, wherein said first adapter
or said second adapter comprises a resistor and a capacitor.
13. The system for linearizing characteristic curve of a vibrating
signal transducer as recited in claim 1, wherein said system
comprises a phase inverter.
14. The system for linearizing characteristic curve of a vibrating
signal transducer as recited in claim 1, wherein said system
comprises a signal mixer.
15. The system for linearizing characteristic curve of a vibrating
signal transducer as recited in claim 1, wherein output of said
system is transmitted to one or more output transducers or
speakers.
16. The system for linearizing characteristic curve of a vibrating
signal transducer as recited in claim 1, wherein said amplifier
comprises a mixer.
17. The system for linearizing characteristic curve of a vibrating
signal transducer as recited in claim 1, wherein said amplifier
mixes signals.
18. The system for linearizing characteristic curve of a vibrating
signal transducer as recited in claim 1, wherein said amplifier
comprises a dephaser.
19. The system for linearizing characteristic curve of a vibrating
signal transducer as recited in claim 1, wherein said amplifier
dephases a signal.
20. The system for linearizing characteristic curve of a vibrating
signal transducer as recited in claim 1, wherein said input signal
is dephased.
21. The system for linearizing characteristic curve of a vibrating
signal transducer as recited in claim 1, wherein said first input
of said amplifier is a negative input or negative terminal of said
amplifier.
22. The system for linearizing characteristic curve of a vibrating
signal transducer as recited in claim 1, wherein said amplifier is
configured in a single-ended input configuration, wherein an input
of said amplifier is not connected to a signal external to said
amplifier.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of a co-pending US
application by the same assignee, same inventor, and same title,
with Ser. No. 11/364,646, now allowed as a US patent, to be issued
in or about May 2011, which is based on a provisional U.S.
application 60/656,685, filed Feb. 25, 2005.
BACKGROUND OF THE INVENTION
[0002] Vibration signals, such as sound signals, are transmitted
between different points under many circumstances. Many of these
require transcoding and/or amplification. For example, orchestras
and musical groups play in public, and their sounds must be
amplified for a group of listeners; telephones and radios transmit
voices and music over long distances, the first via wires, the
second via radio waves; hearing aids amplify sounds collected from
the user's environment and deliver them to the eardrum or to said
user's ear bone structures; television takes images collected using
a video camera, transforms them into electronic signals and then
recreates them on viewers' screens after decoding.
[0003] In all instances, the signals are collected at the
transmitting point, transformed into electronic signals, generally
amplified, and then reconstituted at the reception point.
[0004] The transducers that transform the mechanical vibrations
into electronic signals (as is the case for microphones), those
that transform the electronic signals into mechanical vibrations
(as is the case for speakers), and the devices and components that
connect these transducers in a complete system are made from a wide
range of materials and active and passive circuits.
[0005] The lack of homogeneity that results from these multiple
elements has a direct influence on the transmission of signals
between the "input" transducer and the "output" transducer, such
that the signals are not transferred in a linear manner, making
their transfer efficiency variable depending on the frequency
used.
[0006] For a transducer of any kind, the level of reproduction of
the signal based on its frequency must be established, yielding a
curve called the "characteristic curve." A device that integrates
such a transducer must include methods that allow this curve to be
monitored in order to correct, to the extent possible, problems
that may occur in signal reproduction.
[0007] In addition, during the signal transfer there is a
phenomenon that occurs wherein a fraction of the signal transmitted
and received by the output transducer returns to the input
transducer and is added to the main signal. This phenomenon
generates instability in the system and tends to cause signal
fluctuations, especially at higher yield frequencies; the more that
energy increases, the greater the level of feedback.
[0008] The most well-known manifestation of this phenomenon is
called the "Larsen effect" or "Larsen." It occurs when input
signals, such as voice signals, picked up by, for example, a
microphone, are amplified, transmitted to a speaker, and then
returned to the microphone which captures them along with the new
signals. The new and returned signals are then reamplified, which,
due to the non-linear nature of the elements making up the transfer
chain, results in a fluctuation of the whole signal, which in turn
results in a very loud screech that is characteristic of the Larsen
effect.
[0009] The microphone thus "hears" not only the voice, but also the
speaker, and this effect increases with greater microphone
sensitivity, greater speaker volume and shorter distance between
the microphone and the speaker.
[0010] This phenomenon may be created at will and observed by
bringing the microphone of a telephone handset close to a speaker
plugged into an amplifier.
[0011] There are several known methods for addressing the problems
created by this feedback: [0012] limiting the microphone
sensitivity, the theory being that by reducing the input signal,
the sounds coming from the speaker will not be picked up; [0013]
limiting the speaker power, the theory being that by reducing the
output level, the sounds from the speaker will not reach the
microphone; and [0014] increasing the distance between the
microphone and the speaker, or facing them in specific directions,
the theory being that reducing the physical proximity between the
microphone (input transducer) and the speaker (output transducer)
may prevent the sounds from the speaker from being picked up by the
microphone.
[0015] All of these methods help reduce feedback, but the
limitations that they impose often limit the system capabilities
and reduce the expected quality. Items such as portable wireless
telephones (cell phones) or, to an even greater extent, hearing
aids must be contained in the most compact structure possible,
which is completely incompatible with the concept of keeping a
large distance between the microphone and the speaker (or earpiece
in this case). As a result, in such devices, sound levels must
automatically be kept low, which is not satisfactory since it
limits the possible design options for the device.
[0016] Another method for addressing the Larsen effect consists of
filtering the signals at one or multiple points in the transfer
chain, in order to "trap" the fluctuations. This method is not very
effective and it contributes significantly to the non-linear nature
of the entire device since the filters themselves are some of the
most non-linear devices made. Another disadvantage of this method
is that it results in a significant distortion of the output
signals, which changes the transmission and seriously affects the
qualitative characteristics of the input signals, such as the
elimination of treble, muffling, etc.
[0017] In the field of telecommunications, feedback has such
negative consequences, such as muffling of sound, that duplex links
are simply prohibited for critical applications, such as
communication of military information. For these applications,
duplex links are replaced by "alternative bilateral" links in which
only one of two speakers is permitted to talk at a time, or
alternatively, the other can listen, but must wait to speak until
there is a pause or the speaker will be abruptly interrupted. This
is extremely inconvenient and even unusable in certain
situations.
SUMMARY OF THE INVENTION
[0018] The present invention overcomes these disadvantages by
changing each characteristic curve into nearly a straight line,
which in turn has the effect of eliminating the instability caused
by feedback and fluctuations.
[0019] Briefly, one aspect of the invention is a method of
processing vibration signals by (1) collecting signals, called
"input signals", (2) transmitting and amplifying them, creating
"initial signals", (3) extracting "duplicate signals" from the
initial signals and dephasing the duplicate signals by 180 degrees
from the initial signals, and (4) taking the algebraic sum of the
input signals and the signals duplicated by mixing the two, wherein
the duplicate signals are extracted, transferred, dephased and
mixed at the same level as that of the initial signals, and
amplifying the level of the input signals to the level of the
initial signals.
[0020] Other characteristics of this process may include: [0021]
adjusting the level of the duplicate signals to match that of the
input signals; and [0022] dephasing the duplicate signals and
obtaining "image signals", then mixing the input signals and the
image signals, then linearly amplifying the signals resulting from
this mixing, or [0023] dephasing the input signals, then mixing the
input signals and the duplicate signals, then linearly amplifying
the signals resulting from this mixing; or [0024] conducting a
single operation to increase the level of the input signal, invert
the phase of the duplicate signals and mix these two types of
signals, plus linearly amplify the signals resulting from this
mixing.
[0025] An additional aspect of the invention is a device for the
treatment of vibration signals comprising an input
pickup-transducer for these signals, electronic transfer circuits,
a phase inverter, at least one amplifier, and at least one output
transducer-transmitter for processed signals, wherein the
electronic circuits include one branch circuit connected to both
the output of a linear amplifier and the input of the same linear
amplifier, with methods implemented to ensure that the input signal
level and output signal level for the linear amplifier are
equal.
[0026] Other characteristics of this device may include: [0027] an
equalizer used to ensure that the input signal level and output
signal level for the linear amplifier are equal; [0028] the
equalizer being part of the circuits creating the linear amplifier;
[0029] the equalizer being adjustable; [0030] the equalizer being
placed on the branch circuit; [0031] the equalizer being placed at
the input of the linear amplifier; [0032] the phase inverter being
placed on the branch circuit; the phase inverter being placed
between the input pickup transducer and the linear amplifier,
[0033] the phase inverter being part of the linear amplifier
itself, such as in an "operational amplifier"; [0034] a circuit
consisting of two transistors placed in a emitter-emitter
formation, and a variable resistor linked to the whole.
[0035] The invention will be better understood after reading the
detailed description below with reference to the figures. Of
course, the description and the figures are given only for
informational purposes and are not restrictive in nature.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] FIG. 1 is a general diagram of a well-known type of device,
illustrating the Larsen effect.
[0037] FIG. 2 is a graphic depicting a characteristic curve that
could be that of the device in FIG. 1.
[0038] FIG. 3 is a theoretic graphic showing the basic operation of
the invention, which consists of creating not only the device's
characteristic curve, but also its symmetric curve, shifted 180
degrees, with the curve derived from the algebraic sum of the two
theoretically being equal to a straight line lying directly over
the x-axis.
[0039] FIG. 4 is the same type as FIG. 3, but corresponds to an
actual device in accordance with the present invention.
[0040] FIG. 5 is a general diagram of a device in accordance with
the invention.
[0041] FIG. 6 is a more detailed diagram than the one in FIG. 5 and
is more specifically focused on an embodiment of the invention's
characteristic branch circuit.
[0042] FIG. 7 is a more detailed diagram than FIG. 5 that is
specifically focused on an embodiment of the linear mixer.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] FIG. 1 illustrates a well-known configuration consisting of
an input transducer, microphone A, amplification-transmission
circuit B, and an output transducer, in this case speaker C. An
"input" impedance adapter is typically installed at the input of
circuit B and an "output" impedance adapter is installed at the
output of circuit B. The sound produced by musical instrument D is
picked up by microphone A, transformed into electrical signals to
be sent to circuit B, amplified to a greater or lesser extent, and
then sent to speaker C, which transforms the received electrical
signals into sounds.
[0044] As shown, part of the sound transmitted by speaker C bounces
off objects and surfaces in the surroundings and is picked up by
microphone A, which is depicted by a simple arrow and dotted line
F1. This sound is treated exactly like the main sound: i.e., it is
transformed into electric signals, amplified and transmitted. If
the feedback level is significant, this creates significant
disturbances, such as the characteristic screech of the Larsen
effect, as described above.
[0045] The characteristic curve of this familiar device may be that
which is depicted in FIG. 2. As shown, the device has a
transmission pattern for instantaneous sounds expressed in decibels
or volts (y-axis) that is highly variable depending on the
frequency expressed in Hertz (the x-axis). A sound added at, for
example, a frequency of approximately 1,000 Hertz will result in a
particularly violent sound being transmitted because at this
frequency, the device has a very high transmission capacity. The
same would be true for each spike in the curve, which here is at
approximately 2,000 and 9,000 Hz. By contrast, a sound added at a
frequency of approximately 100 Hz, or, at the other extreme, over
100,000 Hz is practically imperceptible.
[0046] The invention enables the undesirable consequences of the
Larsen effect to be eliminated. The invention does not operate
using the same methods as previous attempts, namely via methods
that have immediate and detrimental effects on transmission
quality.
[0047] The primary cause of disturbances related to feedback or the
Larsen effect is the non-linear nature of the device's
characteristic curve. Starting from the basic principle that one
cannot prevent sound from spreading freely, and thus, from bouncing
back to the microphone from its point of transmission, the
invention is based on a principle called "pre-stabilization", which
involves making the characteristic curve as linear as possible
until it practically becomes a straight line. In this way, the
sensitivity of the input transducer (microphone), the power of the
output transducer (speaker), and the relative proximity of these
two transducers are of little importance--the sounds received after
rebounding by the input transducer no longer have any material
effect.
[0048] FIG. 3 depicts the results of the signal treatment
comprising part of this invention. Each sound transformed into an
electronic signal corresponds to a point on upper curve 1 to create
that particular device's characteristic curve. Using the invention,
the signals referred to herein as "initial signals" are extracted
to obtain signals referred to herein as "duplicate signals".
[0049] The duplicate signals derived from the initial signals are
dephased by 180 degrees, creating curve 2, which is exactly
symmetrical to curve 1. In other words, curve 2 is the mirror image
of curve 1. From here on, the term "image signals" will be used to
describe signals shifted by 180 degrees.
[0050] These series of signals are then combined to obtain the
algebraic sum of the two.
[0051] If the amplitudes (for example, expressed in decibels or
volts) of curves 1 and 2 were completely equal, the result of this
algebraic sum would be equal to zero. It would consist of a
straight line superimposed on the x-axis.
[0052] In other words, the signals provided to the output
transducer (speaker) would be nonexistent. The sounds transmitted
by the output transducer would then equal complete silence.
[0053] As this scenario is obviously not going to be reproduced in
reality, it is necessary that the algebraic sum have a positive
result (i.e., one that is greater than zero).
[0054] FIG. 3 shows that this is indeed the case, since line 3
representing the result of the algebraic sum of curves 1 and 2 lies
above the x-axis.
[0055] Thus, during the operation of the device, regardless of the
random fluctuations possible in the characteristic curve 1, the
signal is combined with its negative mirror "image" and the device
continues to produce a characteristic curve that is practically a
straight line.
[0056] FIG. 4 shows a more realistic scenario in which the
algebraic sum of curves 1a and 2a gives rise to curve 3a, which is
very close to a straight line, but is nonetheless slightly curved.
The consequences of feedback on the sounds transmitted are
nonetheless imperceptible since the resulting curve 3a no longer
has even a single spike.
[0057] FIG. 5 depicts a device, such as a public address system, in
accordance with the present invention. It includes an input
transducer represented by a microphone 10, a connector 11, an input
impedance adapter 12, a connector 13, a linear mixer 14 having two
inputs 15 and 16, a connector 17, a linear amplifier 18, a
connector 19, an output impedance adaptor 20, and a branch circuit
21 leading to the second input 16 on the linear mixer 14, Branch
circuit 21 includes an adapter 22 and a phase inverter 23 connected
in series.
[0058] The signals exit from the output impedance adapter 20 on
connector 24 and then to power amplifier 25. The signals then pass
through connector 26 to an output transducer consisting of a
speaker 27.
[0059] This device operates as follows:
[0060] The sound emitted by the musical instrument D is collected
by the microphone 10, which in turn converts the mechanical
vibrations of the air into corresponding electronic signals (input
signals) that are then handled by the electronic circuits.
[0061] The signals transmitted by connector 11, or "input signals,"
are brought to an acceptable impedance level by adapter 12, the
operation of which is well known by people in the industry.
[0062] At the output of the linear amplifier 18, the signals
("initial signals") are sent to the output impedance adapter 20,
and a duplicate of these signals is sent to circuit branch 21.
These duplicate signals ("duplicate signals") are sent to the phase
inverter 23 via adapter 22.
[0063] This inverter 23 creates a phase shift of 180 degrees, which
graphically results in the creation of the points of curve 2, at
the same time that the initial signals create the points of curve
1.
[0064] As is well known, the effect of electronic circuits on AC
signals is based on the frequency of these signals. Thus the
dephasing is typically not uniformly 180 degrees for all signal
frequencies received by the phase inverter 23 because components of
different values are needed for each frequency. However, in certain
embodiments of the invention, well-known operational amplifiers may
be used, making the dephasing uniform across the entire audio
frequency bandwidth. As a result, an average dephasing is
accomplished in which the phase change is as close as possible to
180 degrees.
[0065] The resulting signals ("image signals") are carried to input
16 of the linear mixer 14, which in turn provides signals that are
the result of the algebraic sum of input signals received by input
15 and the image signals received by input 16.
[0066] The characteristic curve of the combined signals (i.e., the
input signals plus the image signals) resulting from the linear
mixer 14 is similar to curve 3a--i.e., the characteristic curve is
almost a straight line, as each frequency was amplified the same
way by the power amplifier 25.
[0067] When operating in accordance with known techniques, the
duplicated signals are calibrated so as to be only a fraction of
the original signals.
[0068] This "calibration" can be obtained by a resistor, which,
significantly, reduces the level to make it compatible with that of
the input signals, which is very low.
[0069] The result of this process is the introduction of a time
factor, which creates a slight delay between the input signal and
the image signals. As a result, it is never possible to take the
algebraic sum of the two types of signals since there is a shift
between curves 1 and 2.
[0070] It is possible that, by chance, a positive value will
correspond with the same negative value, but it is impossible to
ensure that everything operates normally. Even worse, if a strong
positive value or spike happens to correspond with a weak negative
value, the result is abrupt amplification with violent Larsen
effect.
[0071] Although it is possible to obtain an acceptable mix on a
narrow bandwidth of frequencies, the opposite effect is obtained on
the harmonic values of this bandwidth. In other words, even if the
feedback can be avoided at certain frequencies, it is only
strengthened at others.
[0072] As a result of these circumstances, previous attempts to use
phase return were unsuccessful, even to the extent that
manufacturers highlighted as an advantage in their technical
specifications the fact that their products did not use phase
return.
[0073] Using the present invention however, there is no delay
between the input signals leading to input 15 and the image signals
leading to input 16 since there is no time factor to create a
delay. If there was a discrepancy resulting from the resistor in
adapter 22, it would be completely insignificant and have no effect
because the resistance of the resistor is extremely small and only
equalizes (rather than changing) the output level of operational
amplifier 18 at connector 19 and its input level at connector
17.
[0074] In addition, as shown below, this resistor may simply be
eliminated.
[0075] The eventual discrepancy is measured in microseconds and is
imperceptible to the human ear.
[0076] FIG. 6 provides an example of a circuit in accordance with
the invention that is simple and economical. The elements have the
same reference numbers as the elements that are depicted in FIG.
5.
[0077] Instead of linear amplifier 18, an operational amplifier 30
(or audio amplifier) is used, a type that is well known by people
in the industry and is currently available in various forms with
different features.
[0078] It exists in the form of an integrated circuit, which
considerably reduces the number of components needed outside of the
operational amplifier 30.
[0079] Operational amplifier 30 has an input 31 for the power
supply, and inputs 32 and 33 marked "+" and "-" respectively, as
well as multiple other inputs (not shown) that are separate from
those mentioned previously.
[0080] Input 33 is marked "-" to signify that the signals that will
enter here will be dephased 180 degrees.
[0081] The input signals coming from the microphone 10 enter
operational amplifier 30 at input 33 "-", whereas circuit branch 21
is connected to dynamic input 34, allowing the mixing of image
signals and input signals and resulting in their linear
distribution, which is the desired effect.
[0082] The purpose of adapter 22 is not to calibrate the duplicate
signals so that they have a different level than those of the
initial signals, but rather to equalize the signals at the input
and output of amplifier 30 as described above.
[0083] Adapter 22 includes a capacitor 35, 15 to 20 .mu.F (micro
Farad) for example, connected to a very low resistance variable
resistor 36, 10.OMEGA. (Ohm) for example. Because of the relative
values of these components, adapter 22 does not cause any
perceivable delay in the transfer of the duplicate signals.
[0084] This feature of the invention is important as it guarantees
that the input signals and the image signals are sufficiently
simultaneous, such that there is practically no discrepancy between
curves 1a and 2a (FIG. 4). The resulting curve, 3a, is thus
straight, or almost straight with no spikes.
[0085] The operational amplifier 30 carries out the dephasing and
mixing of both types of signals, as well as their
amplification.
[0086] However, the level of output at 19 remains equal to the
level of output at 17 after the eventual adjustment of the variable
resistor 39.
[0087] At the (13-17) connections (the linear mixer is removed) is
adapter 37, which includes a capacitor 38 connected to a variable
resistor 39. Adapter 37 allows the level of the input signal to be
adjusted before it reaches the operational amplifier 30.
[0088] This highly simple and compact circuit can be integrated
into a single component, which is small and consisting of synthetic
materials (or "resin") with contacts 40, 41, 42 and 43 (exposed
conductive parts) that are accessible from the outside to attach
it.
[0089] It can also be combined with other circuits and/or
components in a single resin structure so that it is very
difficult, even impossible to isolate it to identify its
uniqueness.
[0090] This uniqueness, however, may be identified by isolating the
circuit, or even by removing it and reattaching the connections,
cutting one or more of its external connections, or using a shunt
to neutralize it.
[0091] Before doing this, the Larsen effect is not observable,
whereas afterward it is present.
[0092] Naturally, when the circuit that is the object of the
invention is combined with other components and/or circuits, the
demonstration is more difficult because in isolating the circuit,
the other components and/or circuits are also isolated in such a
way that the entire structure being examined is no longer
operational.
[0093] After having carried out this excessive "subtraction" of
components, it is necessary to compensate for it with an
"addition", by adding the missing components.
[0094] In this way, the structure being examined is recreated
without the inventive circuit and is functional. However, before
these operations the Larsen effect is not observable, whereas after
them it is present.
[0095] However, all of this is useless if it is possible to
directly observe the presence of the circuit that is the object of
the invention, specifically on printed circuits (or "cards") or on
diagrams.
[0096] In view of the considerable number and diversity of
operational amplifiers and low frequency amplifiers available on
the market that can be used to implement the invention, the
components associated with amplifier 30 itself are not represented
in FIG. 6, since these components are already well known to people
in the industry.
[0097] The compactness and low cost of the circuit that is the
object of the invention allow it to be used for multiple
applications that cannot be listed in an exhaustive fashion. These
applications include, but are not limited to, the following:
telephone telecommunication channels, wireless telephones,
telephones, cordless phones, microphones, magnetic pick-ups,
hearing aids, etc.
[0098] FIG. 7 shows a more detailed, high performance operating
mode designed for professional installations with high level
technical requirements. Applications for this embodiment include,
but are not limited to, the following: public address systems,
television and radio broadcasters, recording studios, etc.
[0099] The invention offers sound reproduction quality that far
surpasses the current requirements of major industry players in
terms of both the purity and fidelity of the reproduced sounds when
compared with the original sounds.
[0100] The elements in FIG. 7 bear the same reference numbers as
the corresponding elements in FIGS. 5 and 6.
[0101] In this embodiment, the input 32 "+" to operational
amplifier 30 is used rather than the input 33 "-" used previously.
The initial signals at connection 19 are accordingly not shifted
180 degrees.
[0102] Phase inverter 23 in this embodiment comprises two
transistors 51 and 52 mounted head-to-tail and a low resistance
adjustable resistor 53.
[0103] The input signals from microphone 10 are passed through
connector 13 to the base of transistor 51, while the duplicate
signals from branch circuit 21 are applied to its emitter.
[0104] The adjustable resistor 53 is used to adjust the level of
the inverter 23 to that of the microphone 10, which can be either
static or dynamic.
[0105] The purpose of this assembly is to make the signals
collected at the emitter of transistor 51 linear, exactly as if the
characteristic curve of the microphone 10 was itself linear, which
in reality is not the case.
[0106] In other words, the impedance of microphone 10, which is
more reactive for frequencies higher than 1,000 Hz (Hertz) is
changed by a very low resistor by adjusting resistor 53 without
losing its sensitivity.
[0107] Because the value of a resistor is independent from the
frequency of the signals transmitted, the signals collected from
the emitter of transistor 51 are smooth and linear without spikes
and cannot create even the slightest Larsen effect. It is
understood that this feature is of the highest importance because
it eliminates the major fault of all microphones, i.e., the degree
to which they are non-linear.
[0108] Because the purpose of a transistor is to provide signals
with much higher levels than those received, the input signals
received from the emitter of transistor 51 are both linear and
amplified.
[0109] The features of transistor 51 can be freely chosen so that
it provides input signals that are compatible with the duplicate
signals, which is why the variable resistor 36 of adapter 22 cannot
only be very small, but even completely eliminated.
[0110] In summary, the input signals are adjusted to the duplicate
signals, whereas in the previous examples, the duplicate signals
have been adapted to the input signals.
[0111] The phase inverter 23 carries out the dephasing of a delay
of a half phase between the initial signals and the input signals
because of the combination of the resistor 53 and the capacitor
54.
[0112] The transistor 52 collects the mixed signals, which are
essentially linear and inputs them into the "+" input 32 of the
operational amplifier 30, since they only need to be amplified and
not re-dephased.
[0113] The transistor 51 dynamically mixes the two types of
signals, regardless of their frequencies.
[0114] In an audio assembly, the most defective and non-linear
element is the microphone. As it is placed at the entry to the
assembly, its non-linearity is multiplied by the amplification and
ends up in the total gain.
[0115] For example, when a microphone produces several millivolts
and the output power consists of several dozen watts, the following
is obtained:
g = ( 10 / 1000 ) 2 600 .times. G = 100 Watts 4 ##EQU00001##
in which:
[0116] G=power gain
[0117] g=voltage gain
[0118] The result is:
[0119] G=1,500,000,000
[0120] g=12,250
[0121] The defects due to the non-linear nature of the microphone
are thus amplified in this example 12,250 times.
[0122] Professionals do not take into account jumps in amplitude of
the characteristic curve of microphones that are less than or equal
to twice the base value.
[0123] As a result, deformities in this curve affect the output
power and are amplified 12,250 times. The resulting sound is
transmitted and then bounces off objects, obstacles and walls
before returning to the microphone. It is thus easy to understand
that these defects in linearity result in a deafening and
intolerable screech when an attempt is made to increase the
power.
[0124] With the invention, the microphone also picks up the
feedback sounds, deforms them and transcodes them into input
signals at connection 13.
[0125] The duplicate signals enter at point 16, which corresponds
to the output of the phase inverter 23, and are dephased with
respect to the input signals.
[0126] When the system begins to get unstable, the level of the
input signals taken in at connection 13 increases, as do those of
the opposite signals taken in at point 16.
[0127] The signals taken in at connection 13 introduce a weak
current into the base of transistor 51, which, due to
amplification, is more significant in the emitter at point 16.
[0128] As the duplicate signals enter at the same point 16, they
generate an opposite current in variable resistor 53.
[0129] However, the difference between the two types of signals
remains unchanged and the system does not have a tendency to
fluctuate, which is what gives rise to the Larsen effect.
[0130] By reducing the resistance of resistor 53, the current in
the emitter caused by the input signals increases, but by also
reducing the resistance of resistor 36 of adapter 22, the opposite
current of the mirror image increases and the difference between
the two currents does not change.
[0131] The low resistance (up to only a few dozen Ohms) of resistor
53 opens the base-emitter junction of transistor 51, meaning that
the microphone is dynamically parallel with variable resistance
53.
[0132] In conclusion, the microphone with a resistance of hundreds
of Ohms, which is reactive and non-linear, becomes an assembly of
only a few dozen Ohms that is purely resistive (and not reactive)
and naturally linear with the same sensitivity.
[0133] It is necessary to note that a non-reactive, linear
microphone does not exist in reality.
[0134] The invention was described in terms of its use in devices
that include a microphone, an amplification chain and a speaker.
However, as previously indicated, it can be used in conjunction
with many other electronic devices for which the linearization of
input signals is important. It can also be used for the treatment
of mechanical vibrations, where it is useful to linearize a
transducer that transforms mechanical vibrations into electronic
signals.
* * * * *