Abstract:
A frequency conversion circuit includes a first mixer for performing frequency conversion of a received signal having components disposed at first frequency intervals into a first intermediate frequency signal which has a frequency lower than that of the received signal and which has components disposed at predetermined frequency intervals, two second mixers for performing frequency conversion of the first intermediate frequency signal into a second intermediate frequency signal having a frequency lower than that of the first intermediate frequency signal. A first local oscillation signal changing at second frequency intervals different from the first frequency intervals is supplied to the firs mixer, and a second local oscillation signal having a frequency which is the reciprocal of an integer of the frequency of the first local oscillation signal is supplied to the second mixers.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a frequency conversion circuit suitable for use in a transceiver employing the next-generation 5-GHz mobile communication system called the “Multimedia Mobile Access Communication System (MMAC)” 
           [0003]    2. Description of the Related Art  
           [0004]    A common frequency conversion circuit of the prior art is shown in FIG. 6. An input/output end of a switching device  31  is connected to an antenna (not shown), and a frequency conversion circuit  32  in a receiver circuit is connected to the output end of the switching device  31 . A received signal RX is input to a low noise amplifier  32   a  in the frequency conversion circuit  32 . A first mixer  32   b  is connected in the next stage to the low noise amplifier  32   a , and a first local oscillation signal L 1  is supplied from a first local oscillator  32   c  to the first mixer  32   b . An intermediate frequency amplifier  32   d  is connected in the next stage to the first local oscillator  32   b , and a second mixer  32   e  is connected in the next stage to the intermediate frequency amplifier  32   d . A second local oscillation signal L 2  is supplied from the second local oscillator  32   f  to the second mixer  32   e.    
           [0005]    In addition, a frequency conversion circuit  33  in a transmitter circuit is connected to the input end of the switching device  31 . A second intermediate frequency signal IF 2  on which a base-band signal to be transmitted is superimposed is input to a third mixer  33   a  in the frequency conversion circuit  33 . A third local oscillation signal L 3  is supplied from a third local oscillator  33   b  to the third mixer  33   a . An intermediate frequency amplifier  33   c  is connected in the next stage to the third mixer  33   a , and a fourth mixer  33   d  is connected in the next stage to the intermediate frequency amplifier  33   c . A fourth local oscillation signal L 4  is supplied from a fourth local oscillator  33   e  to the fourth mixer  33   d . A power amplifier  33   f  is connected in the next stage to the fourth mixer  33   d , and the output end of the power amplifier  33   f  is connected to the input end of the switching device  31 .  
           [0006]    In the above-described construction, as FIG. 7 shows, from the frequency spectrum between the received signal RX and the first local oscillation signal L 1  which are input to the first mixer  32   b , it is found that the received signal RX is lower and the first local oscillation signal L 1  is higher. The frequency range of the received signal RX is equal to the frequency range of the first local oscillation signal L 1 , and the frequency of the first local oscillation signal L 1  changes correspondingly to the frequency of the received signal RX. As shown in FIG. 7, the first intermediate frequency signal IF 1  has a constant frequency because the first mixer  32  outputs the first intermediate frequency signal IF 1 , which is the difference in frequency between the received signal RX and the first local oscillation signal L 1 .  
           [0007]    As shown in FIG. 7, the second local oscillation signal L 2  supplied to the second mixer  32   e  has a frequency higher than that of the first intermediate frequency signal IF 1 , and the second mixer  32   e  outputs the second intermediate frequency signal IF 2 , which is the difference in frequency between the second local oscillation signal L 2  and the first intermediate frequency signal IF 1 . The second intermediate frequency signal IF 2  is processed by another circuit provided after the stage of the second mixer  32   e.    
           [0008]    In the transmitter circuit, the second intermediate frequency signal IF 2  input to the third mixer  33   a  has a central frequency identical to that of a second intermediate frequency signal output from the second mixer  32   e  in the receiver circuit, and the third local oscillation signal L 3  supplied to the third mixer  33   a  has a frequency identical to that of the second local oscillation signal L 2 . Accordingly, the third mixer  33   a  outputs the first intermediate frequency signal IF 1 . The fourth local oscillation signal L 4  supplied to the fourth mixer  33   d  has a frequency identical to that of the first local oscillation signal L 1 . Accordingly, the fourth mixer  33   d  outputs a transmission signal TX having a frequency identical to that of the received signal RX. Therefore, the frequency spectrum of each portion of the frequency conversion circuit  33  in the transmitter circuit is as shown in FIG. 7.  
           [0009]    In the above-described construction, the first local oscillation signal L 1  and the fourth local oscillation signal L 4  are identical in frequency range, and the second local oscillation signal L 2  and the third local oscillation signal L 3  are identical in frequency. Thus, one of the first local oscillator  32   c  and the fourth local oscillator  33   e  can be used in common, with the other one eliminated. In addition, one of the second local oscillator  32   f  and the third local oscillator  33   b  can be used in common, with the other one eliminated.  
           [0010]    The structure of the frequency conversion circuit of the prior art causes beat interference between local oscillation signals because two local oscillators having different oscillation frequencies are used.  
         SUMMARY OF THE INVENTION  
         [0011]    It is an object of the present invention to prevent occurrence of beat interference caused by two local oscillation signals when frequency conversion is performed twice.  
           [0012]    To this end, according to an aspect of the present invention, a frequency conversion circuit is provided which includes a first mixer for performing frequency conversion of a received signal which has components disposed at first frequency intervals into a first intermediate frequency signal having a frequency lower than that of the received signal, and which has components disposed at predetermined frequency intervals, second mixers for performing frequency conversion of the first intermediate frequency signal into a second intermediate frequency signal having a frequency lower than that of the first intermediate frequency signal. A first local oscillation signal changing at second frequency intervals different from the first frequency intervals is supplied to the first mixer, and a second local oscillation signal having a frequency which is the reciprocal of an integer of the frequency of the first local oscillation signal is supplied to the second mixers.  
           [0013]    Preferably, the frequency conversion circuit further includes a local oscillator for supplying the first local oscillation signal to the first mixer. The second local oscillation signal is generated by performing frequency division on the first local oscillation signal.  
           [0014]    The frequency of the first local oscillation signal may be set to be higher than that of the received signal, and the frequency division factor of the frequency division on the first local oscillation signal may be set to 6.  
           [0015]    The frequency of the first local oscillation signal may be set to be lower than that of the received signal, and the frequency division factor of the frequency division on the first local oscillation signal may be set to 4.  
           [0016]    The lowest central frequency of the received signal may be set to 5170 MHz, and the central frequency of the second intermediate frequency signal may be set to 20 MHz.  
           [0017]    According to the present invention, the beat interference between two local oscillation signals is prevented from occurring.  
           [0018]    Since frequency conversion is performed twice, the signal can be amplified by amplifiers in stages prior to the first and second mixers. Thus, the amplifiers can be prevented from abnormally oscillating, even if the signal is amplified to the required level.  
           [0019]    According to the present invention, the frequency of the second local oscillation signal can easily be reduced to the reciprocal of an integer of the frequency of the first local oscillation signal.  
           [0020]    According to the present invention, the local division factor can easily be set without setting the frequency of the first local oscillation signal not to be so high.  
           [0021]    According to the present invention, the ratio of the image frequency to the received signal frequency is large. This is advantageous in coping with image interference.  
           [0022]    According to the present invention, by setting the lowest central frequency of the received signal to 5170 MHz, and setting the central frequency of the baseband signal to 20 MHz, the endurance against image interference of the receiver unit of a transceiver using the 5-GHz band can be enhanced.  
           [0023]    According to another aspect of the present invention, a frequency conversion circuit is provided which includes third mixers for performing frequency conversion of a second intermediate frequency signal into a first intermediate frequency signal which has a frequency higher than that of the second intermediate frequency signal and which has components disposed at one type of frequency intervals among plural types of predetermined frequency intervals, and a fourth mixer for performing frequency conversion of the first intermediate frequency signal into any one of transmission signals which each have a frequency higher than that of the first intermediate frequency signal and which each have components disposed at first frequency intervals. A first local oscillation signal changing at second frequency intervals different from the first frequency intervals is supplied to the fourth mixer, and a second local oscillation signal having a frequency which is the reciprocal of an integer of the first local oscillation signal is supplied to the third mixers.  
           [0024]    Preferably, the frequency conversion circuit further includes a local oscillator for supplying the first local oscillation signal to the fourth mixer, and the second local oscillation signal is generated by performing the frequency division on the first local oscillation signal.  
           [0025]    The frequency of the first local oscillation signal may be set to be higher than that of the transmission signal, and the frequency division factor of the frequency division on the first local oscillation signal may be set to 6.  
           [0026]    The frequency of the first local oscillation signal may be set to be lower than that of the transmission signal, and the frequency division factor of the frequency division on the first local oscillation signal may be set to 4.  
           [0027]    The lowest central frequency of the transmission signal may be set to 5170 MHz, and the central frequency of the second intermediate frequency signal may be set to 20 MHz.  
           [0028]    The frequency of the second local oscillation signal may be set to be higher than that of the first intermediate frequency signal.  
           [0029]    The frequency of the second local oscillation signal may be set to be higher than that of the first intermediate frequency signal.  
           [0030]    The frequency of the second local oscillation signal may be set to be higher than that of the first intermediate frequency signal.  
           [0031]    The frequency of the second local oscillation signal may be set to be higher than that of the first intermediate frequency signal.  
           [0032]    According to the present invention, the beat interference between two local oscillation signals is prevented from occurring.  
           [0033]    Since frequency conversion is performed twice, the signal can be amplified by amplifiers in stages prior to the first and third mixers. Thus, the amplifiers can be prevented from abnormally oscillating, even if the signal is amplified to the required level.  
           [0034]    According to the present invention, the frequency of the second local oscillation signal can easily be reduced to the reciprocal of an integer of the frequency of the first local oscillation signal.  
           [0035]    According to the present invention, the local division factor can easily be set without setting the frequency of the first local oscillation signal not to be so high.  
           [0036]    According to the present invention, the ratio of the image frequency to the received signal frequency is large. This is advantageous in coping with image interference.  
           [0037]    According to the present invention, by setting the lowest central frequency of the transmission signal to 5170 MHz, and setting the central frequency of the second intermediate frequency signal to 20 MHz, the endurance against image interference of the receiver unit of a transceiver using the 5-GHz band can be enhanced.  
           [0038]    In addition, according to the present invention, the load on a mixer to which a first intermediate frequency signal is input can be reduced because the frequency of a second local oscillation signal is set to be higher than the frequency of the first intermediate frequency signal. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0039]    [0039]FIG. 1 is a transceiver block diagram illustrating a frequency conversion circuit of the present invention;  
         [0040]    [0040]FIG. 2 is a first frequency spectrum graph illustrating the operation of the frequency conversion circuit shown in FIG. 1;  
         [0041]    [0041]FIG. 3 is a second frequency spectrum graph illustrating the operation of the frequency conversion circuit shown in FIG. 1;  
         [0042]    [0042]FIG. 4 is a third frequency spectrum graph illustrating the operation of the frequency conversion circuit shown in FIG. 1;  
         [0043]    [0043]FIG. 5 is a fourth frequency spectrum graph illustrating the operation of the frequency conversion circuit shown in FIG. 1;  
         [0044]    [0044]FIG. 6 is a circuit diagram of a transceiver which illustrates a frequency conversion circuit of the prior art; and  
         [0045]    [0045]FIG. 7 is a frequency spectrum graph illustrating the operation of the frequency conversion circuit shown in FIG. 6. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0046]    A frequency conversion circuit of the present invention is described below with reference to the accompanying drawings. FIG. 1 is a transceiver block diagram illustrating the frequency conversion circuit of the present invention. FIGS.  2  to  5  are frequency spectrum graphs illustrating operations.  
         [0047]    Referring to FIG. 1, the input/output end of a switching device  1  is connected to an antenna (not shown), and a frequency conversion circuit  2  in a receiver circuit is connected to the output end of the switching device  1 . A received signal RX is obtained by orthogonal frequency division multiplexing (OFDM) and has first frequency intervals each having 10 MHz. The received signal RX is amplified by two stages formed by low noise amplifiers  2   a  and  2   b  in the frequency conversion circuit  2 . The frequency range of the signal received by each amplifier is approximately 20 MHz.  
         [0048]    A first mixer  2   c  is connected in the next stage to the low noise amplifier  2   b , and a first local oscillation signal L 1  is supplied from a local oscillator  3  to the first mixer  2   c . The frequency of the first local oscillation signal L 1  changes at second frequency intervals correspondingly to the frequency of the received signal. However, the second frequency intervals differ from the first frequency intervals. The oscillation frequency of a local oscillator  3  is controlled by a phase-locked loop (PLL) circuit  4 . Data SDA and a clock SCL for controlling the oscillation frequency are input to the PLL circuit  4 .  
         [0049]    A bandpass filter  2   d  and an intermediate frequency amplifier  2   e  are cascade-connected in the next state to the first mixer  2   c . Two second mixers  2   f  and  2   g  are connected in parallel in the next stage to the intermediate frequency amplifier  2   e . A second local oscillation signal L 2  is supplied to the second mixers  2   f  and  2   g . The second local oscillation signal L 2  is generated by using a frequency divider  5  to perform frequency division on the first local oscillation signal L 1  output from the local oscillator  3 . Accordingly, the second local oscillation signal L 2  changes at frequency intervals which are smaller than the second frequency intervals. In this case, the phases of the second local oscillation signal L 2  supplied to the two second mixers  2   f  and  2   g  are orthogonal to each other (differ in 90 degrees).  
         [0050]    Bandpass filters  2   h  and  2   i  are connected in the next stage to the second mixers  2   f  and  2   g , respectively. Each of the bandpass filters  2   h  and  2   i  has a central passband frequency of approximately 10 to 25 MHz.  
         [0051]    A frequency conversion circuit  6  in a transmitter circuit is connected to the input end of the switching device  1 . Second intermediate frequency signals (I signal and Q signal the phases of which are orthogonal to each other) to be transmitted are input to two third mixers  6   a  and  6   b  in the frequency conversion circuit  6  through bandpass filters  6   c  and  6   d  connected to the third mixers  6   a  and  6   b . The bandpass filters  6   c  and  6   d  are identical to the bandpass filters  2   h  and  2   i  in structure and characteristics. Second local oscillation signal L 2  the phases of which are orthogonal to each other are supplied to the third mixers  6   a  and  6   b . An adder  6   e  is connected in the next stage to the third mixers  6   a  and  6   b . A bandpass filter  6   f  is connected to the adder  6   e . The bandpass filter  6   f  is also identical to the bandpass filter  2   d  in structure and characteristics. A fourth mixer  6   g  is connected in the next stage to the bandpass filter  6   f , and the first local oscillation signal L 1  is supplied to the fourth mixer  6   g.    
         [0052]    A bandpass filter  6   h  and a power amplifier  6   i  are cascade-connected in the next stage to the fourth mixer  6   g , and the output end of the power amplifier  6   i  is connected to the switching device  1 .  
         [0053]    In the above construction, the first mixer  2   c  outputs a first intermediate frequency signal IF 1  that is the difference in frequency between the received signal RX and the first local oscillation signal L 1 . The second mixers  2   f  and  2   g  output second intermediate frequency signals IF 2  (I signal and Q signal the phases of which are orthogonal to each other). Each of the second intermediate frequency signals IF 2  is the difference in frequency between the first local oscillation signal L 1  and the second local oscillation signal L 2 .  
         [0054]    Here, assuming that the frequency of the received signal RX be R+kS R  (where R represents the central frequency of the lowest frequency band of the received signal RX, k represents a positive integer up to 15 including 0, and S R  represents the first frequency interval), the frequency of the first local oscillation signal L 1  be L+kS L  (where L represents the lowest frequency of the first local oscillation signal L 1  which corresponds to the received signal RX, and S L  represents the second frequency interval), the frequency division factor of the frequency divider  5  be N, and the central frequency of the second intermediate frequency signal IF 2  be 12, the following expression holds:  
                      (     R   -     kS   R       )     -     (     L   +     kS   L       )            =         L   +     kS   L       N     ±     I   2               (   1   )                               
 
         [0055]    By substituting 0 and 1 for k in expression (1), two equations (not shown) are obtained. From the two equations, the lowest frequency L of the first local oscillation signal L 1  and the frequency dividing factor N can be found.  
         [0056]    First, in a first combination case in which the frequency of the first local oscillation signal L 1  is set to be higher than that of the received signal RX, and the frequency of the second local oscillation signal L 2  is set to be higher than that of the second local oscillation signal L 2 , the lowest frequency of the first local oscillation signal L 1  and the frequency dividing factor N are as shown in the following expressions:  
             L   =         S   L          (     R   -     I   2       )         S   R               (   2   )               N   =       S   L         S   L     -     S   R                 (   3   )                               
 
         [0057]    [0057] 
         [0058]    When specific values, R=5170, S R =10, and I 2 =20, in expressions (2) and (3), L=515S L , and N=S L /(S L −10). Accordingly, the second frequency interval S L  is a value that is not less than 10, and the lowest frequency L of the first local oscillation signal L 1  and the frequency dividing factor N can be found. For example, when the second frequency interval S L  is set to 11, 12, 15, and 20, the frequency dividing factor is 11, 6, 3, and 2, respectively, and the lowest frequency of the first local oscillation signal L 1  is 5665, 6180, 7725, 10300 MHz, respectively. Nevertheless, from the stability of the oscillating frequency and ease of the frequency dividing factor N, it is preferable that the second frequency interval S L  be 12 MHz.  
         [0059]    The frequency spectrum obtained when the second frequency interval S L  is set to 12 MHz is shown in FIG. 2. For a received signal changes at intervals of 10 MHz in the 150-MHz frequency range from 5170 MHz to 5320 MHz, the first local oscillation signal L 1  changes at intervals of 12 MHz in the 180-MHz frequency range from 6180 MHz to 6360 MHz. The first intermediate frequency signal IF 1  changes at intervals of 2 MHz in the 30-MHz frequency range from 1010 MHz to 1040 MHz.  
         [0060]    Next, in a second combination case in which the frequency of the first local oscillation signal L 1  is set to be higher than that of the received signal RX, and the frequency of the second local oscillation signal L 2  is set to be lower than that of the first intermediate frequency signal IF 1 , the lowest frequency L of the first local oscillation signal L 1  is as shown in the following expression. Expression (3) is unchanged and applied to the frequency dividing factor N.  
             L   =         S   L          (     R   -     I   2       )         S   R               (   4   )                               
 
         [0061]    Similarly, when the above specific values are used, L=519S L , N=S L /(S L −10). Also in this case, the second frequency interval S L  is a value that is not less than 10, and the lowest frequency L of the first local oscillation signal L 1  and the frequency dividing factor N can be found for the value of S L . For example, when the second frequency interval S L  is set to 11, 12, 15, and 20, the lowest frequency of the first local oscillation signal L 1  is 5709, 6228, 7785, and 10380 MHz, respectively. Nevertheless, from the stability of the oscillating frequency and ease of setting the frequency dividing factor N, it is preferable that the second frequency interval S L  be 12 MHz.  
         [0062]    A frequency spectrum obtained when the second frequency interval S L  is set to 12 MHz is shown in FIG. 3. The first local oscillation signal L 1  changes at intervals of 12 MHz in the 180-MHz frequency range from 6228 MHz to 6408 MHz. The first intermediate frequency signal IF 1  changes at intervals of 2 MHz in the 30-MHz frequency range from 1058 MHz to 1088 MHz.  
         [0063]    Next, in a third combination case in which the first local oscillation signal L 1  is set to be lower than that of the received signal RX, and the frequency of the second local oscillation signal L 2  is set to be higher than that of the first intermediate frequency signal IF 1 , the frequency dividing factor N is represented by the following expression, and expression (4) is applied to the lowest frequency of the first local oscillation signal L 1 .  
             N   =       S   L         S   R     -     S   L                 (   5   )                               
 
         [0064]    When the above specific values are used, L=519S L , and N=S L /(10−S L ). In this case, the second frequency interval S L  is a value that is not greater than 10. For example, when the second frequency interval S L  is set to 9, 8, and 5, the frequency dividing factor N is 9, 4, and 1, respectively, and the lowest frequency of the first local oscillation signal L 1  is 4671, 4152, and 2595 MHz, respectively. Nevertheless, from the stability of the oscillating frequency and ease of the frequency dividing factor N, it is preferable that the second frequency interval S L  be 8 MHz.  
         [0065]    A frequency spectrum obtained when the second frequency interval S L  is set to 8 MHz is shown in FIG. 4. The first local oscillation signal L 1  changes at intervals of 8 MHz in the 120-MHz frequency range from 4152 MHz to 4272 MHz. The first intermediate frequency signal IF 1  changes at intervals of 2 MHz in the 30-MHz frequency range from 1018 MHz to 1048 MHz.  
         [0066]    Finally, in a fourth combination case in which the frequency of the first local oscillation signal L 1  is set to be lower than that of the received signal RX, and the frequency of the second local oscillation signal L 2  is also set to be lower than that of the first intermediate frequency signal IF 1 , expression (2) is applied to the first local oscillation signal L 1 , and expression (5) is applied to the frequency dividing factor N.  
         [0067]    When the specific values are used, L=515S L , and N=S L /(10−S L ). When the second frequency interval S L  is set to 9, 8, and 5, the frequency dividing factor N is 9, 4, and 1, respectively, and the lowest frequency L of the first local oscillation signal L 1  is 4635 MHz, 4120 MHz, and 2575 MHz, respectively. Nevertheless, from the stability of the oscillating frequency and ease of the frequency dividing factor N, it is preferable that the second frequency interval S L  be 8 MHz.  
         [0068]    A frequency spectrum obtained when the second frequency interval S L  is set to 8 MHz is shown in FIG. 5. The first local oscillation signal L 1  changes at intervals of 8 MHz in the 120-MHz frequency range from 4120 MHz to 4240 MHz. The first intermediate frequency signal IF 1  change at intervals of 2 MHz in the 30-MHz frequency range from 1050 MHz to 1080 MHz.  
         [0069]    Among the above-described four cases, the third and fourth cases in which an image signal frequency is lower than the frequency of the received signal RX are advantageous in order to reduce image interference. From the perspective that there are small loads on the second mixers  2   f  and  2   g  because preferable band characteristics are obtained based on the low frequency of the first intermediate frequency signal IF 1 , the first and third cases are advantageous in that the second local oscillation signal L 2  is higher than that of the first intermediate frequency signal IF 1 .  
         [0070]    Next, the operation of the frequency conversion circuit  6  in the transmitter circuit is described below.  
         [0071]    The two third mixers  6   a  and  6   b  output the first intermediate frequency signal IF 1  which has the sum or difference in frequency between the input second intermediate frequency signal IF 2  and the second local oscillation signal L 2 . The fourth mixer  6   g  outputs the transmission signal TX which has the sum or difference in frequency between the first intermediate frequency signal IF 1  and the first local oscillation signal L 1 .  
         [0072]    Also, in this case, expressions (1) to (5) are directly applied to frequency relationships among the signals, and the frequency band of the received signal RX and the frequency band of the transmission signal TX are similar to each other.  
         [0073]    When the third mixers  6   a  and  6   b  output the first intermediate frequency signal IF 1  which has the difference in frequency between the second intermediate frequency signal IF 2  and the second local oscillation signal L 2 , and the fourth mixer  6   g  outputs the transmission signal TX which has the difference in frequency between the first intermediate frequency signal IF 1  and the first local oscillation signal L 1 , the first case is applied.  
         [0074]    In addition, when the third mixers  6   a  and  6   b  output the first intermediate frequency signal IF 1  which has the sum in frequency between the second intermediate frequency signal IF 2  and the second local oscillation signal L 2 , and the fourth mixer  6   g  outputs the transmission signal TX which has the difference in frequency between the first intermediate frequency signal IF 1  and the first local oscillation signal L 1 , the second case is applied. When the third mixers  6   a  and  6   b  output the first intermediate frequency signal IF 1  which has the difference in frequency between the second intermediate frequency signal IF 2  and the second local oscillation signal L 2 , and the fourth mixer  6   g  outputs the transmission signal TX which has the sum in frequency between the first intermediate frequency signal IF 1  and the first local oscillation signal L 1 , the third case is applied.  
         [0075]    In addition, when the third mixers  6   a  and  6   b  output the first intermediate frequency signal IF 1  which has the sum in frequency between the second intermediate frequency signal IF 2  and the second local oscillation signal L 2 , and the fourth mixer  6   g  outputs the transmission signal TX which has the sum in frequency between the first intermediate frequency signal IF 1  and the first local oscillation signal L 1 , the fourth case is applied.