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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to
input / output of devices or systems among information communication devices, electro-acoustic
devices, measuring devices and systems, and transfer of acoustic signals of digitized devices or
systems. It is used for
2. Description of the Related Art Conventionally, the connection between an audio signal, which
is an analog signal, and a digital device / system is performed by using an analog microphone
and an analog-digital converter at the input side and a digital-analog converter at the output side
with an analog It was common to use a combination of loudspeakers or earphones. This method
not only requires special electronic devices such as analog-digital and digital-analog converters,
but also electronic circuits, devices and parts for both analog and digital, so that the price
increases and the reliability Not only there are drawbacks such as decrease and increase of
power consumption, but there are technically difficult problems such as generation of noise due
to mixture of analog signal and digital signal. One example of a device designed to compensate
for these drawbacks, which is described in Document 1, is a piezoelectric loudspeaker driven
directly by a digital signal. As schematically shown in FIG. 1, the electrodes of the piezoelectric
loudspeaker are radially divided, and the areas (angles) of the electrodes are made to correspond
to the respective digit positions of the digital signal. In FIG. 1, a is a sectional view of the circular
loudspeaker, b is an electrode structure on the piezoelectric diaphragm, 10 is a piezoelectric
diaphragm, 11 is a stainless sheet, 12 is an aluminum sheet, and 13 is an aluminum sheet. The
ring 14 is a drive electrode divided and isolated by a straight radial boundary. In this method, the
boundary to be divided and insulated is straight radial, and matches the nodes and antinodes of
the vibration member, that is, the natural divided vibration mode of the circular diaphragm, so
that sharp unevenness is generated on the frequency characteristics. In this example, a device
such as attaching a high rigidity stainless steel sheet or aluminum ring on the circumference is
used to suppress it, but the structure becomes complicated and the weight of the vibrator
increases and the efficiency is improved. There is a drawback such as deterioration. Also, under
such conditions, it is possible to convert a digital electrical signal to an analog acoustic signal, but
it is not possible to convert an analog acoustic signal to a digital electrical signal. Therefore, even
if an apparatus or system is configured using a device such as this example, there are drawbacks
such as the problem of noise caused by the mixing of analog and digital as described above
because the analog signal is handled at the input. The
SUMMARY OF THE INVENTION The present invention is intended to solve such problems not
solved by the prior art, and is excellent in efficiency and frequency characteristics, is simple in
structure, easy in construction, and is a digital electric The present invention provides a
converter for converting a signal into an analog audio signal and an apparatus for converting the
analog audio signal directly into a digital electrical signal.
SUMMARY OF THE INVENTION The present invention consists of two major elements, which are
inseparable from one another.
One of them is an electroacoustic transducer main body. 2 and 3 show an example of the
structure. The electro-acoustic transducer main body is generally short cylindrical, and FIG. 2 is a
cross-sectional view on the diameter thereof. In FIG. 2, 20 is a diaphragm, 21 is a vibration
detection electrode, 22 is a drive electrode, 23 is a sound hole, 24 is an insulating housing, and
25 and 26 are electret films. FIG. 3 is a plan view of the drive electrode in FIG. 2 as viewed from
the side of the vibrating film, and the fan-shaped electrode is divided into distorted electrodes,
which are respectively insulated by insulating bands of curves. In FIG. 3, reference numerals 30
to 37 denote drive electrodes which are divided and isolated into a plurality of pieces, and in this
example, they are divided into eight pieces to correspond to 8-bit digital signals. 38 is an
insulation band. In this example, in order to equalize the driving force to the vibrating membrane,
the whole is equally divided into three, and in order to correspond to the binary digital signal of
8 bits, the respective areas are 1: 2: 4: 8: 16: Three sets divided at a ratio of 32: 64: 128 are
arranged at positions of 120 degrees each. As a result, when a binarized digital signal is applied
to the drive electrode, an excitation force is generated on the vibrating film. The size is
proportional to the product of the surface potential (fixed) of the electret film on the drive
electrode, the voltage (fixed) of the electrode drive power supply and the area of the drive
electrode, and the distance between the vibrating film and the drive electrode at rest The area of
each of the drive electrodes divided among these is in inverse proportion to (constant) as
described above corresponding to each bit digit position of the signal. When a bit) is present, a
driving force having a magnitude corresponding to the position of the digit is simultaneously
generated and added on the vibrating membrane to become an excitation force. Thus, the
vibrating membrane vibrates as an analog quantity of a magnitude corresponding to a given
digital signal to emit an acoustic signal, and as a result, in the process of electro-mechanicalacoustic conversion, electro-mechanical conversion is simultaneously digital. -Also perform
analog conversion. Here, since each electrode and the portion which insulates this is a curve of
the end shown in the figure and intersects the node and antinode lines in the vibration mode
specific to the vibrating membrane, the influence of the natural vibration is small and it is flat as
it is An electroacoustic transducing characteristic of various frequency characteristics is
obtained. Next, the second element will be described. FIG. 4 is a block diagram of a digital
electro-acoustic transducer configured including the electro-acoustic transducer body described
above. In FIG. 4, 40 is an electro-acoustic transducer main body, 41 is an electrode drive power
source, 42 is an electrode drive circuit, and the connection / disconnection between the electrode
drive power source and the electrodes is supplied to a supplied digital drive signal. It is
something to do according to.
43 is a drive signal supply circuit, 44 is an arithmetic circuit, 45 is a digital microphone output
terminal, 46 is a polarity verification circuit, 47 is a differentiation circuit, 48 is a preamplifier,
49 is a digital input terminal.
The operation of the digital electroacoustic transducer according to the present invention will be
described. The electroacoustic transducer main body is one in which a condenser microphone
and a condenser speaker are integrated by sharing a diaphragm. Condenser microphones and
condenser speakers are well known, and it is known that the output voltage of the microphone is
proportional to the displacement of the diaphragm due to the external sound pressure and the
electret surface potential (or polarization voltage). The output sound pressure of the capacitor
speaker (or earphone) is proportional to the driving force electrostatically applied to the
vibrating membrane, and the magnitude thereof is the electret surface potential (or polarization
voltage) and an externally applied signal voltage, and the vibrating membrane It is well known
that this is determined by the size of the area of the driving electrode facing the. Therefore, the
electrode area is determined at a ratio of 1: 2: 4: 8: 16:... According to the digit position of each
bit of the digital signal, and as described above, when the bit is present, constant voltage The
connection between the electrode drive power supply and the divided electrodes is a "contact" to
provide a driving force. Thereby, a driving force having a magnitude according to the numerical
value of the digital signal is applied to the diaphragm. That is, electro-mechanical-acoustic
conversion via a diaphragm and digital-analog conversion are simultaneously performed. At this
time, assuming that the applied digital electric signal has a constant voltage for all digit positions
and has a sufficiently high clock frequency, the frequency characteristic of the driving force can
be regarded as flat. On the other hand, since the vibrating film has an inherent free vibration
mode determined by its shape and material, if the distribution of the driving force on the
vibrating film surface overlaps with the free vibration mode, resonance occurs to cause
unevenness in frequency characteristics. It is known that free vibration modes of a circular
vibrating membrane include modes with nodes and antinodes on the radius and those with nodes
and antinodes on concentric circles. In the present invention, the divided electrodes are shaped
like a deformation fan so that the driving force distribution does not overlap with these modes.
Although the electroacoustic conversion by the digital signal has been described above, the
vibrating film thus driven generates a vibrating force in proportion to the driving force, that is,
the digital electric signal and vibrates, and the vibration displacement is detected by the
detection electrode . The detected vibration displacement signal is adjusted in level by the
preamplifier, then sampled by a high speed clock signal, differentiated on the time axis, and
tested for increase and decrease in the vibration amplitude of the diaphragm. As a result, a test
value is generated that is -1 for increase (differential value is +), +1 for decrease (differential
value is-), and 0 for less than a threshold value with respect to the previous sample value. To the
arithmetic circuit.
The arithmetic circuit adds or subtracts the drive signal based on this value to create a new drive
signal. Here, when there is no digital electric signal supplied from the outside, what is detected
and given to the arithmetic circuit is due to the excitation force of the acoustic signal that
reaches the surface of the diaphragm via the sound hole. In the arithmetic circuit, addition and
subtraction are always performed so that the vibration displacement of the vibrating membrane
is small, so the vibrating membrane stands still against the acoustic signal with the accuracy
within the range of the least significant bit of the digital signal. . In other words, the pressure on
the vibrating membrane surface given by the incident acoustic signal and the driving force given
to the vibrating membrane from the arithmetic circuit via the drive signal supply circuit, the
electrode drive circuit, and the drive electrode are balanced within the error range. ing. That is,
since the balance of the excitation force from the front and back surfaces of the diaphragm is
balanced, the output of the arithmetic circuit, that is, the driving force has a reverse sign and has
a size proportional to the acoustic signal delayed by one sample and is digitized It is. That is, a
digital microphone is realized, and is shown as a digital microphone output terminal at 45 in FIG.
In this case, since the vibration displacement signal and its preamplifier only observe increase
and decrease, the requirement for linearity is such that monotonous increase and decrease within
a fairly narrow range are necessary. FIG. 5 schematically shows this. In FIG. 5, 50 is a pressure
waveform of an acoustic signal arriving at the vibrating membrane, 51 is a displacement of the
vibrating membrane and its vibration displacement signal (shown as one for simplicity because
both are proportional), 52 is a test circuit The threshold indicates the width of the limit increase /
decrease amount to test as +1 or -1, 53 is the input of the operation circuit based on the test
result, 54 is the operation result, and this value is sent to the drive signal supply circuit. give.
This is one sample delayed and is inversely proportional to the input acoustic signal. Reference
numeral 55 represents the result of calculation as an analog signal, which is in proportion to the
driving force to the diaphragm. 56はサンプリングのタイミングである。 In FIG. 5, all
horizontal axes are time. FIG. 6 is used as a speaker and earphone as a digital type sounding
body, and 60 is obtained by removing the 41 vibration detection electrode and the electret film
25 attached thereto from the digital type electroacoustic transducer main body shown in FIG. As
for the other parts, the 45 digital microphone output terminal in FIG. 4, the 46 test circuit, the 47
differential circuit, the 48 preamplifier and the like are removed.
transducer according to the present invention can be applied to any voice communication
system, audio equipment and the like. FIG. 7 shows a voice transmission system having a digital
transmission line as a simple example thereof. FIG. 7A shows an example of a voice
communication system according to the prior art. Here, 70 is a microphone according to the
prior art, 71 is a linear amplifier, 72 is an analog-digital converter, 73 is a digital transmission
line, 74 is a waveform shaper, 75 is a digital-analog converter, 76 is a linear amplifier, 77 is a
conventional Technical loudspeaker 78, the power supply of the system. Fig. 7b is an
introduction of the digital electroacoustic transducer according to the present invention. It is a
system having the same function. In FIG. 7b, 80 is a digital microphone according to the present
invention, 81 is a digital signal level adjuster (two), 73 and 74 are a digital transmission path and
waveform shaper like a, and 82 is a digital type sounding according to the present invention It is
a body. In FIG. 7, dotted lines indicate analog signal paths, and solid lines indicate digital signal
As already described in the previous paragraph in contrast to the prior art in FIG. 7, the utility of
the present invention can be understood from FIG. 7b that all of the system is digitized. That is,
the main feature is that the analog-to-digital converter and the digital-to-analog converter
present in FIG. 7a are eliminated. This is because the digital electroacoustic transducer according
to the present invention has functions of analog-digital conversion and digital-analog conversion.
This brings about various conveniences. Technically, it is free from noise, induced interference,
etc. due to the mixture of analog circuits and digital circuits. From the aspect of price, cost
reduction by standardization of parts and non-adjustment, etc., and from the aspect of operation
of equipment system, improvement of reliability by reduction of the number of parts is
immeasurable. The social and technical advantages of digitizing equipment and systems may be
Reference 1: Takesaburo Yanagisawa, "Current Status of Digital Direct Drive Speakers" Journal of
the Institute of Electronics, Information and Communication Engineers Vol. 78, No. 5 pp 565-569
June 1995
Brief description of the drawings
Fig. 1 Structure of digital direct drive type speaker already existing on reference 1 (reference
Fig. 2 Cross-sectional view of an electro-acoustic transducer main body of the digital electroacoustic transducer according to the present invention
Fig. 3 Structure diagram of driving electrode of electro-acoustic transducer main body in digital
electro-acoustic transducer of the present invention
Fig. 4 A block diagram in which all the components constituting the digital electroacoustic
transducer of the present invention are connected
Fig. 5 Operation explanation of each part of the digital electroacoustic transducer of the present
Fig. 6 A block diagram of a digital direct drive type sounding body constructed by extracting a
part of the digital electroacoustic transducer of the present invention
Fig. 7 Comparison of the embodiment of the present invention with the prior art
Explanation of sign
DESCRIPTION OF SYMBOLS 10 ... Piezoelectric diaphragm, 11 ... Stainless sheet 12 ... Aluminum
sheet 13 ... Aluminum ring 14 ... Drive electrode 20 divided by the boundary line of linear
radiation form ... Vibrating film, 21 ... Vibration detection electrode, 22 ... Drive For the electrodes
23: sound holes 24: insulating housings 30 to 37: divided driving electrodes 38: insulating band
40: electroacoustic transducer main body 41: power source for electrode driving 42: electrode
driving circuit 43: driving Signal supply circuit 44: Arithmetic circuit 45: Digital microphone
output terminal 46: Test circuit 47: Differential circuit 48: Preamplifier 49: Digital input terminal
50: Pressure waveform of acoustic signal coming from the outside to the diaphragm 51 ...
vibration displacement of the vibrating membrane and its vibration displacement signal (both are
proportional and are shown as one for simplicity) 52 ... Threshold width for testing with +1 or -1,
53 ... Test result, ie operation circuit input, 54 ... Operation result, ie electrode drive signal, 55 ...
Display of operation result of operation circuit as analog signal 56 ... Timing of sampling 60:
digital electroacoustic transducer body from which vibration detection electrode and electret film
attached thereto are removed, 70: microphone according to the prior art, 71: linear amplifier, 72:
analog-digital converter, 73: digital transmission Path 74: waveform shaper 75: digital-analog
converter 76: linear amplifier 77: prior art loudspeaker 78: system power supply 80: digital
microphone according to the invention 81: digital signal level adjustment 82, the digitizer
according to the present invention Pronunciation of the formula (in this case, earphone)
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