EP1063866B1 - Digitaler Lautsprecher - Google Patents

Digitaler Lautsprecher Download PDF

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Publication number
EP1063866B1
EP1063866B1 EP19990401288 EP99401288A EP1063866B1 EP 1063866 B1 EP1063866 B1 EP 1063866B1 EP 19990401288 EP19990401288 EP 19990401288 EP 99401288 A EP99401288 A EP 99401288A EP 1063866 B1 EP1063866 B1 EP 1063866B1
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EP
European Patent Office
Prior art keywords
transducers
drive
digital
module according
drive circuit
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EP19990401288
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English (en)
French (fr)
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EP1063866A1 (de
Inventor
David R. Thomas
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Texas Instruments France SAS
Texas Instruments Inc
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Texas Instruments France SAS
Texas Instruments Inc
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Priority to EP19990401288 priority Critical patent/EP1063866B1/de
Priority to DE69939976T priority patent/DE69939976D1/de
Priority to JP2000156862A priority patent/JP2001016675A/ja
Priority to CN 00117967 priority patent/CN1310575A/zh
Publication of EP1063866A1 publication Critical patent/EP1063866A1/de
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/005—Details of transducers, loudspeakers or microphones using digitally weighted transducing elements
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R19/00—Electrostatic transducers
    • H04R19/005—Electrostatic transducers using semiconductor materials
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H04R1/32—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only
    • H04R1/40—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by combining a number of identical transducers
    • H04R1/403—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by combining a number of identical transducers loud-speakers

Definitions

  • the invention relates to digital loudspeakers, more especially but not exclusively to a digital loudspeaker suitable for generating sound output in response to a unary digital drive signal.
  • the unary loudspeaker proposed by Hooley is designed to operate with a conventional binary digital input signal which is converted into unary digital form prior to supply to the transducers by a binary-to-unary encoder.
  • the output transducers are then driven by a unary drive signal based on the output of the encoder.
  • a unary digital loudspeaker for reproducing sound from a 10-binary digit (i.e. bit) digital audio signal.
  • the unary loudspeaker proposed by Hooley comprises a plurality of substantially identical output transducers each operative to convert one of a plurality of unary digital signals into a sound pulse so that the cumulative effect of the output transducers is to produce an output sound representative of the input signal.
  • all the transducers need to be the same.
  • differences between the transducers will average out, so that errors caused by transducer non-uniformity will not be cumulative, but will rather tend to cancel out statistically. This is another advantage over binary digital coding in which transducers driven by the different order bits must be precisely matched.
  • suitable acoustic output transducers could be based on conventional electrostatic transducers, piezo-electric transducers or electromagnetic transducers, since these are capable of being integrated and could be arranged in an array.
  • piezo-electric output transducers it is stated that one piece of piezo-electric material could be divided up into a large number of equal area regions each with its own electrode for separate connection to distinct unary digital signals, again resulting in a transducer array.
  • PCT/GB96/00736 contains no further detail on how a suitable acoustic output transducer might be constructed in the numbers required.
  • US patent no. 4,515,997 describes a digital loudspeaker according to the preamble of claim 1. More specifically, it describes a method of and apparatus for converting a digital signal to sound, the digital signal being encoded in a sequence of code words at a signal encoding frequency, the code words representing the analogue sound pressure of an original audio signal, with de-coding of the digital signal occurring after electro-accoustic transduction through mechanical rectification and characteristics of a listener's ear, including utilising a plurality of substantially identical sound pressure generating elements each having an individual driver associated therewith, and selectively energising the drivers in a pulsed manner at the signal encoding frequency in the combination in response to a respective order of the bits of each code word of a digital signal from a most significant bit to a least significant bit.
  • the sum of the air pressures produced by the sound pressure generating elements in response to each of the successive code words of the digital signal has a magnitude corresponding to the analogue value of the respective code word, and the auditory system of the listener has the characteristics of a low passed filter whereby the listener receives the sum of the air pressures as the analogue sound pressure of the original audio system.
  • European patent application publication no. EP 0561 566 describes a solid state miniature condenser and condenser microphone. It comprises a fixed perforated backplate that constitutes a fixed electrode in a parallel plate condenser, a diaphragm sensitive to incident sound pressure waves that constitutes a moveable plate in the parallel plate condenser, means to position the diaphragm in relationship to the backplate without applying appreciable tension to the diaphragm, and FET circuitry which provides an output proportional to the change in capacitance of the condenser when the diaphragm moves in relationship to the backplate.
  • a single module can be provided which has 2 10 -1 or 2 12 -1 acoustic output transducers, sufficient for the reproduction of speech or music to a reasonable quality with the output transducers being driven by unary digital drive signals.
  • unary digital loudspeakers can be employed in applications such as hand-held telephones, especially hand-held video telephones which are held at arms' length by the user in order to view the video image. It is generally problematic to use acoustic output transducers based on conventional binary digital drive signals for such applications owing to the distance between the apparatus and the user's ears. Conventional hand-held telephones rely on the proximity and alignment of the acoustic output transducers to the ear, neither condition being met with a hand-held video telephone.
  • a digital loudspeaker comprising a plurality of acoustic output transducers and a drive circuit.
  • the drive circuit has an input for receiving a digital audio signal and a plurality of outputs connected to respective ones of the acoustic output transducers.
  • the acoustic output transducers are constructed from a lower panel and an upper panel spaced apart by electrically insulating material.
  • Each transducer includes a first conductive layer in or on the lower panel and a second conductive layer in or on the upper panel, the first and second conductive layers of each transducer being arranged to form respective first and second plates of a capacitor.
  • At least one of the outputs of the drive circuit is connected across the first and second conductive layers of each transducer for supplying a drive signal thereto.
  • the second conductive layer of each transducer extends over a diaphragm portion of the upper panel which is suspended above the lower panel by a resilient support portion of the upper panel.
  • the diaphragm portion of each transducer is movable responsive to electrostatic forces induced by application of a drive signal across the first and second conductive layers by one of the outputs of the drive circuit connected thereto, thereby to generate a pressure pulse.
  • a digital loudspeaker comprising a semiconductor substrate, or a substrate on which is formed a semiconductor layer (for example silicon-on-sapphire).
  • An array of acoustic output transducers and a drive circuit are then formed in the semiconductor material.
  • Each of the transducers includes a first conductive layer adjacent the substrate and a second conductive layer suspended above the first conductive layer across a gap, the conductive layers being epitaxial layers formed on the semiconductor substrate or underlying semiconductor layer.
  • the conductive layers are connected as for the above-described embodiment and the drive circuit is preferably an integrated circuit formed in the semiconductor material.
  • the drive circuit is configured to receive a conventional binary digital audio signal and convert it into unary form for driving the acoustic output transducers. In other embodiments, the drive circuit is configured to receive a digital audio signal that is already in unary form.
  • an integrated digital loudspeaker module comprising an array of between 2 n and 2 n+1 acoustic output transducers, where n is not less than 4 or 5, and drive circuitry including an input for receiving a digital audio signal and output lines arranged to provide an independent drive capability to a number of groups of the transducers, where said number is less than 2 n-1 but more than twice n.
  • the movable diaphragms may be connected by resilient supports to respective laterally adjacent parts of the module, the resilient supports providing restoring forces for the diaphragms in respect of the electrostatic forces generated by the drive signals.
  • the resilient supports and the diaphragms are formed integrally with each other in some embodiments, i.e. from a common piece of material, the resilient supports being thinned regions of that material.
  • Figure 1 shows in section an acoustic output transducer used in one embodiment of the invention.
  • each transducer comprises a lower panel 1 and a upper panel 2.
  • the panels 1 and 2 are arranged parallel to each other and spaced apart by insulating material 3 with a separating gap 4 being formed between a lower side 5 of the upper panel and an upper side 6 of the lower panel.
  • the panels 1 and 2 are based on silicon wafers and the insulating material is a polymer insulator arranged in pillars extending between the panels. In other embodiments, the insulating material 3 could be formed from the material of the upper or lower panels.
  • the lower panel 1 has a conductive layer 7 in the form of a metal layer, for example metal or highly-doped semiconductor, arranged on an lower side 8 thereof.
  • the upper panel 2 has a conductive layer 9 in the form of a metal layer or a layer of highly-doped semiconductor, arranged on an upper side 10 thereof.
  • the conductive layers 7 and 9 are positioned a distance 'd' apart and, for the loudspeaker drive circuit described further below, form first and second plates of a parallel plate capacitor.
  • the conductive layers 7 and 9 are provided with respective tracks (not shown) via which a drive signal is applied to the transducer in use.
  • the tracks may for example be of standard silicides or metal such as gold, aluminium or copper.
  • the upper panel 2 at each transducer has a waisted bridge portion 18 interconnecting a thicker peripheral portion 19 and a thicker central diaphragm portion 20.
  • the waisted bridge portion 18 is sufficiently thin that the diaphragm portion 20 is resiliently supported relative to the peripheral portion 19.
  • the diaphragm portions 20 of the module are circular, the resilient support portions 18 are ring-shaped and the peripheral portions occupy a square area.
  • the shape of the diaphragm portions may be varied and is not fundamental to performance of the transducer elements. For example, oval, square or rectangular diaphragms could be used instead of circular ones.
  • the parameter ⁇ is the dielectric permittivity, which will be a compound value taking account of the fact that the gap 'd' will generally be part air or vacuum, and part silicon or other wafer material.
  • the parameter V is the applied voltage of the drive signal which will be a function of time V(t), typically in the form of drive pulses.
  • the parameter A is the effective area of the parallel plate capacitor formed by the conductive films.
  • the relevant area for the equation of motion for the diaphragm will be the movable area of the transducer, i.e. the area of the diaphragm portion 20.
  • the transducer can be viewed as a forced harmonic oscillator in which the applied drive force is that induced electrostatically by the drive signal V(t).
  • the resilient support portion 18 provides a restoring force with a spring constant 'k', the value of which will depend on its dimensions and mechanical properties.
  • a damping term (b dx/dt) can be added to the left-hand side of the above equation if appropriate, for example to take account of air viscoscity.
  • Conventional diaphragm modelling techniques can then be applied to calculate what shape of drive pulse will produce a linear, or more approximately linear, response of the diaphragm portion 20.
  • a pulse shaping circuit may be included, as is described further below.
  • the silicon wafers may, for example, be 5 inch diameter wafers (5 inches amounts to approximately 12.5 cm) having a thickness of 625 micrometers. Any other industry-standard diameter could conveniently be used.
  • a wafer is etched from the upper side 10 to thin over a circular area which will form the upper side of the resilient support and diaphragm portions 18 and 20 of each transducer.
  • the wafer is then etched from the lower side 5 over a ring area to form a thinned bridge for the resilient support portion 18.
  • the thickness in section of the resilient support portion 18 may be chosen to provide any desired characteristic spring constant. For example, the thickness may be in the range 5 to 100 micrometers, or beyond. One specific value is 20 micrometers.
  • the thickness chosen will depend on the mass, and thus inertia, of the diaphragm portion 20.
  • the thickness chosen will also depend on the radial dimension of the resilient support portion 20.
  • the diaphragm portion 20 will generally be thicker than the resilient support portion 18, but this is not necessarily the case.
  • the thickness of the diaphragm portion 18 will be relevant for the definition of the mass 'm' of the moving part of the transducer in the above equation of motion.
  • One specific value for the thickness of the diaphragm portion is 300 micrometers.
  • conductive layer 7 is applied to one side of a wafer by metallisation and a PECVD nitride layer (not shown) is added.
  • Polymer insulator posts 3 are then applied by deposition and patterning to the other side of the wafer.
  • the deposition and patterning can use photo-imageable polyimide.
  • the posts may be from 10 micrometers to 50 micrometers in height, or higher, for example between 50 and 500 micrometers in height.
  • the height of the posts is preferably chosen so that, in the finished device, the lower side 5 of the diaphragm portion of the upper panel can physically contact the upper side 6 of the lower panel 1 without fracture or permanent damage to the resilient support portion 18 which deforms responsive to the drive signal. In this way, the transducer has some inherent protection against being overdriven.
  • the lower panel 1 and upper panel 2 are then joined together using standard alignment and bonding procedures.
  • the first and second conductive layers 7 and 9 in the present embodiment remain spaced apart even if the diaphragm portion of a transducer is brought into physical contact with the lower panel by overdriving. This ensures that no electrical short can occur across the plates of the capacitor as a result of such contact.
  • This function can be achieved with a number of arrangements of the conductive layers, not just that of the present embodiment. For example, it is achieved if the first conductive layer 7 is formed in or under the lower panel 1 remote from the upper side 6 of the lower panel facing the upper panel 2. It is also achieved if the second conductive layer 9 is formed in or on the upper panel 2 remote from the underside 5 of the diaphragm portion 20 facing the lower panel 1.
  • the above-described transducer is part of a transducer array formed as an integrated module.
  • Each transducer has a square footprint with a centrally-arranged circular diaphragm, the array being formed as a square grid.
  • the pulse shaping circuit 22 Adjacent the diaphragm 20 of each transducer, there is provided drive circuitry in the form of a pulse shaping circuit 22.
  • the pulse shaping circuit 22 is designed, having regard to a non-linear response function for the diaphragm computed from the above equation of motion, so that a standard square-shaped input pulse received by the pulse shaping circuit is transformed into a non-square pulse shape that at least partially compensates for the non-linear diaphragm response, thereby to produce an acceptably uniform acoustic pulse output pressure.
  • the pulse shaping circuit 22 can be designed to provide a ramp at the start of each drive pulse.
  • the diaphragm response may be further varied by provision of a viscous medium, such as a liquid or gas, in the space between the diaphragm and lower panels 1 and 2, thereby providing a further design parameter.
  • a viscous medium such as a liquid or gas
  • the module's pulse shaping circuits 22 are formed in the peripheral portions 19 of the silicon upper panel 2 of each transducer as integrated circuits, using standard photolithographic patterning techniques. Alternatively, the pulse shaping circuits and other drive circuitry could be formed in the lower panel 1 in another embodiment.
  • one pulse shaping circuit for each row or pairs of rows of transducers, with the drive pulses for each row all being routed through the associated pulse shaping circuit.
  • the pulse shaping circuit output could be connected to all of the transducers of its row or pair of rows.
  • a column selector circuit would then be arranged to selectively connect the output of each pulse shaping circuit to any one of the associated transducers, responsive to an input to the selector circuit supplied by the encoder circuit.
  • a binary-to-unary encoder circuit 24 is provided to one side of the transducer array.
  • the encoder circuit 24 is formed as an integrated circuit in a lateral extension of the silicon upper panel 2 using standard photolithographic patterning techniques.
  • the encoder circuit 24 has an input 26 for receiving a 6-bit binary digital audio signal.
  • the encoder circuit is made up of a unipolar logic gate array. Alternatively, offset or two's-complement types of logic may be used, as described in PCT/GB96/00736 .
  • Figure 4 shows the structure of the encoder circuit 24 in more detail.
  • the six tracks of the 6-bit binary digital input 26 are connected to a binary-to-binary converter 30 which converts the 6-bit binary digital input into nine 3-bit binary digital outputs 32.
  • the three least significant bits form one of the 3-bit outputs.
  • the 4th least significant bit forms another of the 3-bit outputs, the 5th least significant bit forms a further two of the 3-bit outputs and the 6th least significant bit forms the remaining four 3-bit outputs.
  • the nine 3-bit outputs are connected to respective encoder sub-modules in the form of unipolar 3-bit binary-to-unary converters 34, each for providing seven unary digits of output which are supplied to respective rows of the transducers in the track groups 28 already mentioned with reference to Figures 2 and 3 .
  • the converters 34 are clocked by a clock signal CLK to ensure synchronisation of their outputs.
  • the clock signal may be generated internally by the transducer module or may be received as part of, or derived from, the input signal 26.
  • the encoder circuit 24 is configured so that in use the currently active transducers, i.e. those connected to outputs of the encoder circuit that are carrying drive signals, are clustered generally in a cohesive active area, preferably an area in a mid-region of the array. As the sound level is increased, the encoder circuit is configured to select for driving previously inactive transducers lying adjacent the previously active area, so as to maintain the generally cohesive nature of the active area. Similarly, as the sound level is decreased, transducers are removed from the edge of the previously active area. It will however be understood that a proportion of the active transducers, preferably a small proportion, may be physically remote from the active transducers that collectively form a generally cohesive area.
  • Figure 5 shows the logic gate structure of one of the unipolar 3-bit binary-to-unary converters 34.
  • the other converters 34 are the same.
  • the upper one of the illustrated three input lines is for the most significant bit of the 3-bit input.
  • the lower one of the three illustrated input lines is for the least significant of the three bits.
  • the seven unary output lines 36 collectively form one of the groups 28 illustrated in Figure 4 , and also Figure 2 and Figure 3 .
  • each module will have 2 n , 2 n-1 or 2 n -1 transducers to be compatible with the unary reproduction of a conventional n-bit binary digital audio signal.
  • different numbers of transducers may be provided through the use of power control as described in PCT/GB96/00736 .
  • each transducer By using conventional silicon micromachining and other conventional silicon processing techniques, it is possible to vary the area of each transducer through several orders of magnitude without changing the basic design.
  • the individual length dimension of each transducer could be 10 millimeters or 0.1 millimeters.
  • a transducer array of 2 16 -1 output transducers With an individual transducer area of 0.1-by-0.1 millimeter, a transducer array of 2 16 -1 output transducers would occupy a total area of 2.2cm-by-3cm for example.
  • This scalability, together with the highly reproducible nature of silicon technology, means that almost any practically desirable number of output transducers can be integrated into a single module of a pre-defined total area.
  • insulator materials such as sapphire could also be used for the panels.
  • a sapphire lower panel could be used in combination with a silicon upper panel with the drive circuitry primarily incorporated in the upper panel.
  • the loudspeaker module could be manufactured from a single wafer with the space between the upper and lower panels being formed by selective etching.
  • FIG. 6A to Figure 6F show in sequence fabrication steps of an acoustic output transducer used in another embodiment of the invention, by schematic illustration of cross-sections through a wafer during various stages of processing. The formation of only one transducer element is illustrated, but it will be understood that a large two-dimensional array of similar transducers will typically be fabricated.
  • Figure 6A shows a conducting n++ Silicon substrate on which has been deposited a sacrificial layer of silicon dioxide.
  • Figure 6B shows the structure of Figure 6A on which has been patterned a layer of resist after etching to remove portions of the sacrificial oxide layer that are distributed around an area which is ultimately to form the diaphragm of a single transducer element.
  • Figure 6C shows the structure of Figure 6B after deposition of intrinsic silicon, which is an insulating material, and subsequent removal of the resist shown in Figure 6B .
  • the intrinsic silicon is deposited to form a ring of insulating pillars (when viewed from above) around an area which will form the diaphragm in the finished device.
  • Figure 6D shows the structure of Figure 6C after patterning with a further layer of resist, the resist leaving an open area somewhat smaller than and concentric with the enclosed area defined by the intrinsic silicon pillars, and subsequent etching to remove an upper part of the area of silicon dioxide that remains exposed, thereby to thin the silicon dioxide layer over this area.
  • Figure 6E shows the structure of Figure 6D after removal of the resist and deposition of a thick layer of metal covering the thinned area of silicon dioxide and extending laterally to cover the intrinsic silicon pillars.
  • Figure 6F shows the structure of Figure 6E after removal of the remaining parts of the sacrificial silicon dioxide layer to form the final structure of the transducer element (except for structure associated with subsequent metallisation, passivation etc. which is not shown).
  • Figure 6F is additionally provided with reference numerals corresponding to those used in Figure 1 and showing elements of the transducer.
  • the n++ substrate forms a lower panel 1 which is conductive so that provision of a separate conductive layer is not necessary.
  • the metal layer forms the upper panel 2.
  • the intrinsic silicon pillars form the insulating material 3.
  • a gap 4 is formed by the space left after etching away the remainder of the sacrificial silicon dioxide layer and is bounded on its upper side by the metal layer and on its lower side by the substrate.
  • the metal layer has a thicker central area forming the diaphragm portion 20, regions laterally coextensive with the pillars 3 which form the peripheral portion 19 and a ring-shaped region lying radially adjacent and within the pillars 3 which form the resilient support portion 18 of the transducer.
  • Transducer drive circuits may be integrated circuits formed in the semiconductor material of the transducer array using conventional processing techniques. This is possible with an array made of transducers as described with reference to Figure 1 or Figure 6F . Moreover, the transducer drive circuits may be distributed among the transducer elements, laterally adjacent the array, or partly among the transducer elements and partly laterally adjacent the array.
  • the substrate 1 may include an intrinsic layer on its upper side to prevent physical contact by the metal layer causing an electrical short of the capacitor.
  • the substrate may also be insulating rather than conductive and have a conductive layer, such as a metal layer on its underside for forming one plate of the parallel plate capacitor.
  • the upper layer 2 may include silicon, silicon dioxide or silicon nitride as well as, or instead of, metal. Many other variations will be apparent.
  • GaAs technology could be used.
  • the lower side 5 of the upper panel 2 and the upper side 6 of the lower panel could be the lower and upper surfaces of respective GaAlAs epitaxial layers, with the gap 4 being formed by selective lateral dry etching of an intervening GaAs layer using CCl 2 F 2 . Details of this etch process are given in an article by Martin Walther et al in Journal of Applied Physics, volume 72, 2069 (1992 ). In this case, it will be understood that references to upper and lower panels will be references to upper and lower portions of semiconductor material originating in the same wafer, with the lower portion being lower epitaxial layers, or the substrate itself, and the upper portion being etched upper parts formed from epitaxial layers.
  • the integrated loudspeaker module of many embodiments will be the total area permitted for the transducer array, the number of bits of resolution (from which follows the number of transducers required) and the output power capability.
  • the shape of the integrated module may also vary depending on the application. For example, for a hand-held video telephone, the transducer modules may be rectangular strips for arrangement on adjacent sides of a display panel.
  • a loudspeaker will be made from one integrated module or a relatively small plural number of modules, for example between 2 and 10 modules.
  • Figure 7 shows schematically a digital signal processor 40 used in an alternative embodiment arranged to one side of the transducer array.
  • the digital signal processor forms a part of the drive circuit including binary-to-unary encoding circuitry 24 arranged to receive a binary digital input 26 and pulse shaping circuitry 22 arranged to modify the shape of each drive pulse prior to routing of that pulse to one of the drive signal outputs 28.
  • the digital signal processor 40 is loaded with a binary-to-unary conversion routine for determining which drive circuit outputs receive drive pulses responsive to the binary digital audio signal.
  • the conversion routine can be based on a look-up table or may incorporate an algorithm. In this regard, it is noted that no addressing in a conventional sense is required for the unary outputs, because each output has equal significance.
  • the digital signal processor 40 is loaded with a pre-determined non-linear response function or characteristic of the transducers, and is operable to compute the output pulse shapes of the drive pulses based on this response.
  • Figure 8A and Figure 8B show an integrated module according to another embodiment of the invention which uses alternative drive circuitry. Illustrated is an 8-by-8 array of 64 acoustic output transducers.
  • Figure 8A shows an upper part of the module with circular diaphragms and associated upper conductive layers 9, whereas Figure 8B shows a lower part of the module with lower conductive layers 7.
  • the arrangement of digital audio signal input 26, encoder 24, and the general layout of the transducers, will be understood by reference to the above-described embodiments.
  • the present embodiment may be based on transducers according to Figure 1 or Figure 6F .
  • the drive circuitry includes an additional component in the form of a column select circuit 25 connected to receive address data from the encoder circuit 24 which may be a microprocessor, more especially a digital signal processor.
  • Selection lines 38 connect the column select circuit 25 with the upper conductive layers 9 of the transducers. Illustrated are eight separate selection lines 38 to the upper conductive layer 9 of each individual transducer of columns 1 and 8, four separate selection lines 38 to the upper conductive layers 9 of adjacent pairs of transducers in columns 2 and 7, two selection lines 38 to the upper conductive layers 9 of two groups of four transducers in columns 3 and 6, and a single selection line 38 to the upper conductive layers 9 of all the transducers in each of columns 4 and 5.
  • the module of this embodiment includes one pulse shaping circuit 22 for each row of transducers.
  • the pulse shaping circuits 22 are each individually connected to an output of the encoder circuit 24 by a connection line 39.
  • the lower conductive layers 7 of the transducers of each row are electrically connected to each other, as illustrated by an elongate rectangular area in Figure 8B , and to the output of the pulse shaping circuit 22 for the row concerned.
  • a given individual transducer element is driven by an electrostatic driving force to output sound only when there is an appropriate combination of a drive signal to its row through the relevant one of the pulse shaping circuits 22 and a select signal to its upper conductive layer 7.
  • the grouping needs to be such that in use incremental changes in the number of transducers to be driven can be effected across a broad range of total number of active transducers without having to switch on and off a significant proportion of the active transducers.
  • the encoder 24 is implemented as a digital signal processor so that the module can be driven having regard to which individual transducers are active to minimise transients between sampling intervals.
  • the present embodiment will have a number of individually drivable transducers less than the total number of transducers of the array, but substantially more than the number of an equivalent binary driven transducer array.
  • This provides an interim subbinary design of drive circuitry which requires less connection lines than pure unary drive circuitry in which each transducer has its own connection lines so that it is fully independently drivable, but has significantly more connection lines than a binary drive circuit and is thus drivable without the major drive transients that occur with a binary drive in which an array of 2 n transducers is subdivided into only n independently drivable transducer blocks of 1, 2, 4, 8 and 2 n-1 transducers.
  • the largest block of collectively driven transducers will comprise no more than 2 n-3 , more preferably 2 n-4 , transducers.
  • This compares with a binary driven transducer array of 2 n transducers which the largest block would have 2 n-1 collectively driven transducers.

Claims (18)

  1. Digitales Lautsprechermodul mit einem Substrat, auf dem ein Feld von akustischen Ausgangswandlern gebildet ist, und mit einer Ansteuerschaltung (24), die einen Eingang (26) zum Empfangen eines digitalen Audiosignals aufweist und mehrere Ansteuersignalausgänge (28) bereitstellt, wobei jeder Ansteuersignalausgang (28) mit einem entsprechenden der akustischen Ausgangswandler elektrisch verbunden ist, um Ansteuerimpulse an diesen zu leiten, wobei jeder der Wandler eine an das Substrat angrenzende erste leitende Schicht (7) und eine zweite leitende Schicht (9) aufweist, die mit einem Spalt (4) über der ersten leitenden Schicht (7) aufgehängt ist, wobei zumindest ein Teil der zweiten leitenden Schicht (9) eine bewegliche Membran (20) bildet, wobei die ersten und zweiten leitenden Schichten (7, 9) mit entsprechenden der Ausgänge (28) der Ansteuerschaltung elektrisch verbunden sind, so dass jeder Wandler in der Ansteuerschaltung einen Kondensator bildet, wobei im Betrieb in Reaktion auf die von einem entsprechenden Ansteuersignalausgang (28) gelieferten Ansteuerimpulse elektrostatische Kräfte zwischen den ersten und zweiten leitenden Schichten (7, 9) erzeugt werden, die eine Bewegung der Membran bewirken, um ausgehenden Schall zu erzeugen, dadurch gekennzeichnet, dass die Ansteuerschaltung so ausgebildet ist, dass sie ein unäres Ansteuersignal liefert, das die den Wandlern über die Ansteuersignalausgänge (28) zugeführten Ansteuerimpulse bildet.
  2. Digitales Lautsprechermodul nach Anspruch 1, bei dem die beweglichen Membranen durch federnde Halterungen (3) mit entsprechenden seitlich angrenzenden Teilen des Moduls verbunden sind, wobei die federnden Halterungen in Bezug auf die von den Ansteuersignalen erzeugten elektrostatischen Kräfte Rückstellkräfte für die Membranen bereitstellen.
  3. Digitales Lautsprechermodul nach Anspruch 2, bei dem die federnden Halterungen (3) und die Membranen aus einem gemeinsamen Materialstück einstückig miteinander ausgebildet sind, wobei die federnden Halterungen verdünnte Bereiche dieses Materials sind.
  4. Digitales Lautsprechermodul nach Anspruch 1, 2 oder 3, bei dem das Substrat und die ersten leitenden Schichten (7) einen Teil einer unteren Platte (1) und die zweiten leitenden Schichten (9) und die Membranen einen Teil einer oberen Platte (2) bilden.
  5. Digitales Lautsprechermodul nach Anspruch 4, bei dem die obere Platte (2) aus einem Halbleitermaterial besteht und die Ansteuerschaltung (24) eine in der oberen Platte ausgebildete integrierte Schaltung ist.
  6. Digitales Lautsprechermodul nach Anspruch 4, bei dem die untere Platte (1) aus einem Halbleitermaterial besteht und die Ansteuerschaltung (24) eine in der unteren Platte (1) ausgebildete integrierte Schaltung ist.
  7. Digitales Lautsprechermodul nach Anspruch 4, bei dem die obere und die untere Platte (1, 2) aus einem Halbleitermaterial bestehen und die Ansteuerschaltung (24) eine in der oberen und in der unteren Platte (1, 2) ausgebildete integrierte Schaltung ist.
  8. Digitales Lautsprechermodul nach Anspruch 1, 2 oder 3, bei dem das Substrat aus einem Halbleitermaterial besteht oder eine Schicht Halbleitermaterial aufweist und die ersten und zweiten leitenden Schichten (7, 9) epitaktische Schichten sind, die auf dem Halbleitermaterial gebildet sind.
  9. Digitales Lautsprechermodul nach einem der vorhergehenden Ansprüche, bei dem die Ansteuerschaltung (24) eine integrierte Schaltung ist, die in einem Halbleitermaterial des Substrats oder auf dem Substrat gebildet ist.
  10. Digitales Lautsprechermodul nach einem der vorhergehenden Ansprüche, bei dem die Ansteuerschaltung (24) eine Impulsformungsschaltungsanordnung (22) aufweist, die so ausgebildet ist, dass sie die Ansteuerimpulse dahingehend ändert, in Reaktion auf vorbestimmte nichtlineare Merkmale des Ansprechverhaltens der Wandler den Impulsausgangsdruck der Wandler während der Ansteuerimpulse gleich zu halten.
  11. Digitales Lautsprechermodul nach Anspruch 10, bei dem die Impulsformungsschaltungsanordnung (22) Teil eines digitalen Signalprozessors (40) ist, der mit den vorbestimmten nichtlinearen Merkmalen des Ansprechverhaltens der Wandler geladen und so betreibbar ist, dass er auf dieser Grundlage Ausgangsimpulsformen für die Ansteuerimpulse berechnet.
  12. Digitales Lautsprechermodul nach einem der vorhergehenden Ansprüche, bei dem die Ansteuerschaltung (24) eine Codierschaltung aufweist, die so eingerichtet ist, dass sie ein binäres digitales Audiosignal am Ansteuerschaltungseingang empfängt.
  13. Digitales Lautsprechermodul nach Anspruch 12, bei dem die Codierschaltung so eingerichtet ist, dass sie das binäre digitale Audiosignal, das am Ansteuerschaltungseingang (26) empfangen wird, in das unäre digitale Audiosignal umwandelt, das an die Ansteuerschaltungsausgänge (28) geliefert wird.
  14. Digitales Lautsprechermodul nach einem der Ansprüche 1 bis 11, bei dem die Ansteuerschaltung (24) eine Codierschaltung aufweist, die so eingerichtet ist, dass sie ein unäres digitales Audiosignal am Ansteuerschaltungseingang (26) empfängt.
  15. Digitales Lautsprechermodul nach Anspruch 14, bei dem die Codierschaltung so eingerichtet ist, dass sie jedes unäre Zeichen des unären digitalen Audiosignals, das am Ansteuerschaltungseingang (26) empfangen wird, an einen der Ansteuerschaltungsausgänge (28) liefert.
  16. Digitales Lautsprechermodul nach einem der Ansprüche 12 bis 15, bei dem die Codierschaltung Teil eines digitalen Signalprozessors (40) ist, der mit einer Umsetzroutine geladen ist, um zu bestimmen, welche Ansteuerschaltungsausgänge (28) in Reaktion auf das am Ansteuerschaltungseingang (26) empfangene digitale Audiosignal Ansteuerimpulse erhalten.
  17. Digitales Lautsprechermodul nach einem der vorhergehenden Ansprüche, bei dem die ersten und zweiten leitenden Schichten (7, 9) so angeordnet sind, dass sie durch Isoliermaterial beabstandet bleiben, wenn eine der Membranen durch Übersteuerung in physikalischen Kontakt mit darunterliegendem Material gebracht wird, wodurch ein elektrischer Kurzschluss an den Platten des Kondensators verhindert wird.
  18. Digitales Lautsprechermodul nach einem der vorhergehenden Ansprüche, bei dem das Feld von Ausgangswandlern zwischen 2n und 2n+1 akustische Ausgangswandler enthält und bei dem die Ansteuersignalausgänge (28) mit entsprechenden der akustischen Ausgangswandler elektrisch verbunden sind, so dass einer Anzahl von Gruppen von Wandlern eine unabhängige Ansteuerfähigkeit verliehen wird, wobei die Anzahl der Gruppen geringer als die Hälfte von 2n aber größer als zweimal n ist.
EP19990401288 1999-05-28 1999-05-28 Digitaler Lautsprecher Expired - Lifetime EP1063866B1 (de)

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EP19990401288 EP1063866B1 (de) 1999-05-28 1999-05-28 Digitaler Lautsprecher
DE69939976T DE69939976D1 (de) 1999-05-28 1999-05-28 Digitaler Lautsprecher
JP2000156862A JP2001016675A (ja) 1999-05-28 2000-05-26 スピーカ
CN 00117967 CN1310575A (zh) 1999-05-28 2000-05-29 扬声器

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DE69939976D1 (de) 2009-01-08

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