Abstract:
An optical microphone which comprises a source of light connectable to a power source for illuminating an acoustically sensitive membrane; a photo detector having an output for transforming light reflected by the membrane into electrical signals proportional to the intensity of the reflected light; and a circuit for measuring the level of signals at the output of the photodetector for controlling the current fed to the source of light by the power source so that the current is low when the output signals of the photodetector are lower than a defined value, and the current is high when the output signals of the photodetector are higher than the defined value.

Description:
[0001]    This Application claims the benefit of priority from IL Patent Application No. 144497, filed Jul. 23, 2001.  
         FIELD OF THE INVENTION  
         [0002]    The present invention relates to optical microphones, and more particularly, to optical microphone systems and a method for decreasing the power consumption of an optical microphone.  
         BACKGROUND OF THE INVENTION  
         [0003]    An optical microphone is a device that consists of a source of light, such as an LED or laser, for producing light energy, and an acoustically sensitive membrane that reflects the light energy in the direction of a photo detector. The output signal of the photodetector is the output of the optical microphone.  
           [0004]    The sensitivity of an optical microphone is a function of the current supplied to its light source. The higher this current, the higher the microphone&#39;s sensitivity At the same time, the higher current requires a greater supply of energy, which is not always available under different working conditions, and is especially problematic in the case of cellular telephones, wherein the entire energy of the device is supplied from a. small battery having a relatively small energy capacity  
         SUMMARY OF THE INVENTION  
         [0005]    It is therefore a broad object of the present invention to provide an optical microphone system having small power consumption, controlled sensitivity and background noise suppression capability.  
           [0006]    It is a further object of the present invention to provide a method for decreasing the power consumption of an optical microphone.  
           [0007]    The invention therefore provides an optical microphone, comprising a source of light connectable to a power source for illuminating an acoustically sensitive membrane; a photo detector having an output for transforming light reflected by the membrane into electrical signals proportional to the intensity of the reflected light, and a circuit for measuring the level of signals at the output of the photodetector for controlling the current fed to the source of light by the power source so that the current is low when the output signals of the photodetector are lower than a defined value, and the current is high when the output signals of the photodetector are higher than the defined value.  
           [0008]    The invention further provides a method for decreasing the power consumption of an optical microphone, the method comprising generating light by means of a power source feeding a source of light; illuminating a reflecting membrane responsive to acoustical signals; receiving light signals reflected by the membrane and transforming the light signals into electrical signals; measuring the electrical signals, and controlling the current applied to the source of light from the power source as a function of the level of the electrical signals.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures so that it may be more fully understood.  
         [0010]    With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.  
         [0011]    In the drawings:  
         [0012]    [0012]FIG. 1 is a schematic block diagram of the optical microphone of the present invention;  
         [0013]    [0013]FIG. 2 is a more detailed schematic block diagram of an optical microphone including a light source current controller;  
         [0014]    [0014]FIG. 3 is a detailed schematic block diagram of a further embodiment of an optical microphone including a controlled signal level; and  
         [0015]    [0015]FIG. 4 is a schematic block diagram of a still further embodiment of an optical microphone having a pulse generator.  
     
    
     DETAILED DESCRIPTION  
       [0016]    [0016]FIG. 1 illustrates a basic block diagram of an optical microphone system according to the present invention. A source of light  2 , e.g., a light-emitting diode (LED), a laser, or any other source of light, emits light towards an acoustically sensitive membrane  4 . The light reflected by the membrane is received by photodetector  6 , converted into corresponding electrical signals, and fed to the output  8  of the microphone system. The output  8  from photodetector  6  is also connected to a circuit  10  for measuring the levels of the output signals. Circuit  10  leads to a current controller  12 , which controls the light source current from an input  14  in accordance with the output signal levels.  
         [0017]    The levels of the output signals, corresponding to the levels of the incoming acoustical signals, are measured by circuit  10 , which measures the microphone&#39;s output signal level and accordingly produces its own output signals. The measurement results are fed to controller  12 , for controlling the current feeding the light source  2  in two ways: if the output signal level is low, the value of the current feeding the light source  2  is low; if the output signal level is high, the value of the light source feeding current is high. Hence, the controller  12  transforms the output signal from circuit  10  into current, to feed the source of right  2 , in two distinct states: a stand-by state, wherein a very small current feeds the source of light  2 , and a working state, wherein normal current is fed to the source of light  2 .  
         [0018]    The change of currents fed to the light source  2  results in a change in the microphone&#39;s sensitivity and a change in the microphone&#39;s power consumption resulting from the input acoustical, signal. In the stand-by state, the power consumption is very small, and the microphone&#39;s sensitivity is very low. In the working state, power consumption is nominal and the microphone&#39;s sensitivity is normal.  
         [0019]    When someone talks adjacent to the microphone, the acoustical signal on membrane  4 , the signal at output  8 , and the output signal from circuit  10  are all high, and controller  12  is in the working state, i.e., it feeds normal current to the source of light  2 ; thus, the sensitivity of the microphone is normal. When the speaker pauses or listens to what is said by the person to whom he is speaking, the acoustical signals on membrane  4 , the output signal  8 , and the output signal from circuit  10  are low, and controller  12  is in the stand-by state, i.e., it feeds low current to the source of light  2 , and the sensitivity of the microphone is low. Consequently, when the microphone&#39;s sensitivity is normal, the current consumption is normal, and upon a pause in speech, the microphone&#39;s sensitivity is very low and the current consumption is also low.  
         [0020]    Naturally, a low sensitivity microphone suppresses all background noises. Hence, if the speaker is not talking but only listening, the power consumption is decreased to a minimum value and the background noise is suppressed. When the speaker starts to talk, the microphone&#39;s power consumption is normal and its sensitivity returns to normal  
         [0021]    [0021]FIG. 2 is a more detailed block diagram of an optical microphone according to the present invention, showing that circuit  10  of FIG. 1 is composed of an alternating current (AC) amplifier  16 , a rectifier  18  and a direct current (DC) amplifier  20 .  
         [0022]    Amplifier  16  amplifies the output signal from photodetector  6  to increase the sensitivity of the regulation. Rectifier  18  transforms the alternating signals into a direct voltage proportional to the amplitude of the signals, and the DC voltage is amplified by DC amplifier  20 . The output signal from amplifier  20  corresponds to the microphone output signal level at output  8 . Controller  12  receives the signals and produces corresponding currents to feed the source of light  2 . The regulation of current is thus correlated with the output signal from amplifier  16 . If the level of this automatic control. Output signals from amplifier  16  are fed to both controller  12  and to attenuator  22  through line  24 . Attenuator  22  may alternatively be connected at other places in the circuit, e.g., between photodetector  6  and amplifier  16 , or between rectifier  18  and amplifier  20 . In all cases, the attenuator&#39;s function is to compensate for the changes in signal levels caused by changes in the sensitivity of the optical microphone  
         [0023]    Specifically, when the acoustical signal level at membrane  4  and at the output of amplifier  20  decreases due to the regulation of the current level from controller  12  to the source of light  2 , the signals at attenuator  22  win similarly be decreased, and there will not be a further attenuation of the signals to rectifier  18 .  
         [0024]    As mentioned above, at the stand-by state, the current of the light source  2  is very small and the sensitivity of the microphone is very low; tl 1us, the speaker&#39;s voice has to be sufficiently strong to enable the switching of the microphone from the standby state to the working state. In order to ameliorate this problem, as shown in FIG. 4, a pulse generator  26  may be connected ill circuit between the feedback lines  24  and controller  12 . In the stand-by state, pulse generator  26  produces pulse signals which ate fed through controller  12  to the source of light  2 . The current of a pulse from generator  26  may be sufficiently high to assist the switching of the microphone into the normal working state by means of the speaker&#39;s voice. Thus, the sensitivity of the microphone during the application of a pulse is not as high as at the normal state, but is sufficiently high to switch the microphone into the normal state.  
         [0025]    At the same time, because the feeding of the light source  2  is made by pulses, the common power consumption of the microphone is the same as, or even less than, that described above with regard to FIGS.  1  to  3 .  
         [0026]    It will he evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrated embodiments and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scone of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.