Abstract:
An apparatus and method for making a microphone that is not susceptible to RF noise and that can be fabricated to be very thin. The microphone includes a light transmitter configured to generate light, a waveguide having optically aligned transmit, vibrating and receive sections, and a receiver. Light from the transmitter is configured to be transmitted through the transmit section, vibrating section and the receive section of the waveguide, and to the receiver. The vibrating section of the waveguide is configured to vibrate in response to received acoustic energy, so that the light received by the receive section is modulated in proportion to the acoustic energy. In response, the receiver converts the modulated light to an electrical signal that is indicative of the received acoustic energy. Since the microphone of the present invention uses a thin waveguide to modulate the acoustic energy, it is not susceptible to RF noise, and it can be made to have a very thin profile.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority of provisional application No. 60/917,607 which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a microphone, and more particularly, to a microphone that includes a polymer waveguide that modulates a light signal to be proportional to receive acoustic energy and a receiver that converts the modulated light signal into a corresponding electrical signal that is indicative of the received acoustic energy. 
         [0004]    2. Background of the Invention 
         [0005]    Microphones are commonly used in a wide variety of applications, for example in the transmitters of land-line telephones and cell phones, in the broadcast, recording and entertainment industries, in auditoriums or conference rooms, and other locations where persons make public appearances or speeches. A typical microphone includes a membrane that is mounted adjacent a cavity in an acoustic housing. A capacitor and an amplifier circuit are coupled to the membrane within the housing. When acoustic energy is received through the cavity, it causes the membrane to vibrate. As the membrane vibrates, the charge on the capacitor is proportionally altered. The amplifier amplifies the varying charge, generating a corresponding electrical signal that is indicative of the received acoustic energy. 
         [0006]    There are a number of problems associated with known microphones, such as that described above. They tend to be sensitive to radio frequency (RF) noise. This is particularly problematic with cell phones for example, where RF signals are being transmitted and received. There is also no way to filter or otherwise reduce the amplification of ambient noise. The thickness of the acoustic housing can also be a problem in certain applications. Again, using cell phones as an example, manufacturers are continually striving to provide consumers with smaller and thinner cell phones. The thickness of the acoustic housing used for the microphone may therefore be a limiting factor in how thin cell phones can be made. 
         [0007]    A microphone that is not susceptible to RF noise and that can be fabricated to be very thin is therefore needed. 
       SUMMARY OF THE INVENTION 
       [0008]    An apparatus and method for making a microphone that is not susceptible to RF noise and that can be fabricated to be very thin is disclosed. The microphone includes a light transmitter configured to generate light, a waveguide having optically aligned transmit, vibrating and receive sections, and a receiver. Light from the transmitter is configured to be transmitted through the transmit section, vibrating section and the receive section of the waveguide, and to the receiver. The vibrating section of the waveguide is configured to vibrate in response to received acoustic energy, so that the light received by the receive section is modulated in proportion to the acoustic energy. In response, the receiver converts the modulated light to an electrical signal that is indicative of the received acoustic energy. Since the microphone of the present invention uses a thin waveguide to modulate the acoustic energy, it is not susceptible to RF noise, and it can be made to have a very thin profile. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0009]      FIG. 1  is a perspective view of a polymer waveguide microphone according to the present invention. 
           [0010]      FIG. 2  is a diagram illustrating light distribution curves of the waveguide in response to received acoustic energy in accordance with the present invention. 
           [0011]      FIG. 3  is a polymer waveguide with lenses used in the microphone according to another embodiment of the present invention. 
           [0012]      FIG. 4  is a light transmitter used with the polymer waveguide microphone according to the present invention. 
           [0013]      FIG. 5  is a light receiver circuit used with the polymer waveguide microphone according to the present invention. 
           [0014]      FIG. 6  is a polymer waveguide used in a microphone having an extended dynamic range in accordance with one embodiment of the present invention. 
           [0015]      FIG. 7  is a multi-phase light receiver circuit used with the polymer waveguide microphone according to another embodiment of the present invention  FIG. 8  illustrates a method of making a polymer waveguide in accordance with the present invention. 
       
    
    
       [0016]    Like elements are designated by like reference numbers in the Figures. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]    Referring to  FIG. 1 , a perspective view of a polymer waveguide microphone according to the present invention is shown. The microphone  10  includes a light transmitter  12 , a receiver  14  and a waveguide  16  positioned between the transmitter  12  and the receiver  14 . The waveguide  16  includes three sections, including a transmit section  18 , a vibrating section  20  and a receive section  22 . A waveguide groove  24 , filled with an optically transparent material, traverses the three sections. The groove  24  on the three sections  18 ,  20  and  22 , the transmitter  12  and the receiver  14  are all optically aligned with one another. 
         [0018]    The transmit section  18  and the receive section  22  are each mounted on a substrate  26 . The vibrating section  20 , however, is positioned in the free space between the transmit section  18  and the receive section  22 . This arrangement allows the vibrating section  20  to freely vibrate in response to receive acoustic energy (as represented by the arrows. As evident in the figure, the waveguide groove  24  on the transit section  18  and the vibrating section  20  is continuous. A gap  28 , however, is provided between the groove  24  on the vibrating section  20  and the receive section  22 . 
         [0019]    During operation, the transmitter  12  generates light, which is conducted down the groove  24  of the transit section  18  and the vibrating section  20 . In response to the acoustic energy, the vibrating section  20  vibrates. The waveguide groove  24  on the receive section  22 , which is optically coupled with the groove  24  on the vibrating section, receives light which is in proportion to the acoustic energy received at the vibrating section  20 . 
         [0020]    Referring to  FIG. 2 , a diagram illustrating the spatial light distribution of the polymer waveguide in response to received acoustic energy is shown. When no acoustic energy is received, the section  20  does not vibrate. As a result, the received light at the waveguide groove  24  on the receive section  22  is maximized. In response to acoustic energy, however, the vibration section  20  vibrates, moving up and down as designated by the positions A and B, relative to the receive section  22 . As a result of these vibrations, the amount or degree of optical coupling between the waveguide groove  24  on the vibration section  20  and the receive section  22  is reduced. 
         [0021]    The spatial distribution waveform  30  shows the distribution of received light, depending on the position of the vibrating section  20 . When there is no acoustic energy input and the vibrating section  20  is stationary, the amount of received light has the largest magnitude, as designated by the light intensity distribution curve  32 . On the other hand, when the section  20  is vibrating between positions A and B for example, the amount of received light is decreased, as designated by the light intensity distribution curves  34  and  36  respectively. Thus, as the vibrating section  20  vibrates in response to the received acoustic energy, the light received by the receive section  22  is proportionally modulated. 
         [0022]    Referring to  FIG. 3 , a polymer waveguide used as a microphone according to another embodiment is shown. In this embodiment, lenses  38  and  40  are provided at the terminal ends of the waveguide groove  24  on both the vibrating section  20  and the receive section  22 . The lenses  38  and  40  tend to increase the optical coupling between the two sections of the waveguide groove  24 . 
         [0023]    Referring to  FIG. 4 , a diagram of the light transmitter  12  according to one embodiment is shown. The light transmitter  12  includes a Pulse Width Modulation (PWM) driver  42  and a Light Emitting Diode (LED)  44 . The output of the LED  44  is optically coupled to the input of the waveguide groove  24  of the transmit section  18 . During operation, the PWM driver  42  controls the delivery of power to the LED. In response, the LED  44  generates light, which is optically coupled to the waveguide groove  24  of the transmit section  18 . In an alternative embodiment, a Vertical Cavity Surface Emitting Laser (VCSEL) may be used in place of the LED. 
         [0024]    Referring to  FIG. 5 , a circuit diagram of the receiver  14  according to one embodiment of the invention is shown. The receiver  14  includes a first switch SW 1 , a photo diode  52 , a second switch SW 2 , and a charge-to-voltage converter  54 . The switch SWI is coupled between voltage Vreset and the cathode of the photodiode  52  at node A. The anode of the photodiode  52  is connected to ground. The switch SW 2  is connected between node A and the input of the charge-to-voltage converter  54 . The photodiode  52  is positioned adjacent to and is configured to receive the light exiting the waveguide groove  24  of the receive section  22  of the waveguide  16 . 
         [0025]    The photodiode  52 , which acts as a capacitor in this circuit configuration, tends to leak current from ground to Vreset when exposed to light. The amount of current leakage is proportional to the intensity of the light from the waveguide groove  24  of the receive section  22 . In other words, the greater the intensity of light, the more current leakage and the smaller the capacitance. Alternatively, when the intensity of the received light is small, there is less current leakage, and more capacitive charge is stored on the photodiode  52 . The capacitive charge is therefore inversely proportional to the intensity of light received by the receive section  22  from the vibration section  20  of the waveguide  16 . 
         [0026]    During operation of the receiver  14 , the switch SW 1  is initially closed, causing node A and the cathode of the photodiode  52  to charge up to Vreset. In response to received light, the diode  52  leaks current. As discussed above, the charge at node A is therefore inversely proportional to the intensity of the light from the waveguide groove  24  of the receive section  22 . Switch SW 2  is opened and closed at a predetermined sampling rate. Each time the switch SW 2  is closed, the capacitance at node A is provided to the input of the charge-to-voltage converter  54 . A voltage signal that is indicative of the acoustic energy received by the microphone  10  is therefore generated at the node Vout. In various embodiments, the sampling rate may be 8 Khz or less, between 8 to 16 Khz, between 16 to 44 Khz, or more than 44 Khz. 
         [0027]    Referring to  FIG. 6 , a polymer waveguide having an extended dynamic range according to another embodiment of the present invention is shown. In this embodiment, the vibrating section  20  of the waveguide actually includes a plurality of vibrating sections  62 A- 62 N, each capable of independently vibrating with respect to one another. Each of the vibrating sections  62  includes a waveguide groove  24  in optical alignment with the same on the transmit section  18 . In the embodiment shown, the vibrating sections  62  are each a different length and have a different stiffness. For example, the vibrating section  62 A is shorter in length and stiffer, compared to the vibrating section  62 N, which is longer and more flimsy. The various lengths of the vibrating sections  62  each have a different sensitivity to acoustic energy. The dynamic range of the microphone  10  can therefore be extended. For example, by using shorter and stiffer vibrating sections  62 , the sensitivity can be decreased. With longer less-stiff sections such as  62 N, the sensitivity is increased, which vibrates more in response to the same amount of acoustic energy. A plurality of receivers  14  is provided with each vibrating section  62 A- 62 N respectively. 
         [0028]    Referring to  FIG. 7 , a multi-phase light receiver circuit  70  used with a polymer waveguide having a plurality of vibrating elements, such as illustrated in  FIG. 6  above, is shown. In this embodiment, receiver circuits  14 A- 14 N are each coupled to the input of a charge-to-voltage converter  54 . Each of the receiver circuits  14 A- 14 N, which each include switches SW 1 a-n and SW 2 a-n, and photodiodes  52 A-N respectively, are essentially the same as described above, and therefore are not described in detail herein. A phase control circuit  72  is coupled the switches SW 1 a-n and SW 2 a-n of each of the receiver circuits  14 A- 14 N respectively. The phase control circuit  72  sequentially the switches SW 1 a-n and SW 2 a-n of each circuit  14 A- 14 N out of phase with respect to one another. As a result, the charge of only one photodiode  52 A- 52 N of a selected circuit  14  is connected to the input of the charge-to-voltage converter  54  at a time. In this manner, a single charge-to-voltage converter  54  and analog-to-digital converter (ADC)  74  can be shared among multiple receiver circuits  14 A- 14 N. In one embodiment, each receiver circuit  14 A- 14 N is equally out of phase. For example, if there is N circuits  14 , then they would be N/360 degrees out of phase with respect to one another. 
         [0029]    Polymer waveguides  16  can be made in a number of known methods. See for example U.S. patent application Ser. Nos. 11/498,356, 10/861,251, 10/923,550, 10/923,274, 10/923,567, 10/862,003, 10/862,007, 10/758,759 and 10/816,639, all incorporated herein by reference for all purposes. 
         [0030]    Referring to  FIG. 8 , a diagram which illustrates a method of making a polymer waveguide  16  with transmit section  18 , vibrating section  20  and a receive section  22  is shown. In the Figure, a waveguide  16  is shown, including the waveguide groove  24 , fabricated in a manner described in one of the above applications incorporated by reference. To form the sections  18 ,  20  and  22 , the waveguide  16  is cut along the pattern defined by element  82 . In various embodiments, the waveguide  16  may be cut using a laser, stamped using a stamping tool that removes the polymer material in the shape of element  82 , or patterned using conventional semiconductor photolithography techniques. Regardless of how the waveguide is cut, the resulting structure includes the three sections  18 ,  20  and  22  as illustrated in  FIG. 1  for example. 
         [0031]    While this invention has been described in terms of several preferred embodiments, there are alteration, permutations, and equivalents, which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present invention. For example, the steps of the present invention may be used to form a plurality of high value inductors  10  across many die on a semiconductor wafer. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations and equivalents as fall within the true spirit and scope of the present invention.