Abstract:
The invention relates to a circuit comprising an antenna input ( 1 ), a signal input ( 2 ) and a signal output ( 3 ), and a switching unit ( 4 ), wherein the antenna input ( 1 ) is connected to a first protection device ( 6 ) against electrostatic discharges, said first protection device ( 6 ) being a band-pass filter in a π-configuration. The advantage of the first protection device ( 6 ) is that it eliminates the need for a band-pass filter in the front end module, when used in a mobile telephone. Furthermore, the band-pass filter has a very good filtering characteristic, enabling ESD-related disturbances to be effectively suppressed. The invention also relates to a switching module and to the use of the same.

Description:
TECHNICAL FIELD 
   This patent application relates to a circuit array, which has an antenna input, a signal input and a signal output. In addition, the circuit array has a switch unit that optionally connects the antenna input with the signal input or the signal output. 
   BACKGROUND 
   Circuit arrays are used as multi-band front-end modules for mobile telephones. They are connected to the antenna of a mobile telephone at the antenna input. When the antenna comes into contact with an electrically-charged user, this can result in electrostatic discharge, also known under the name “electrostatic discharge (ESD).” These electrostatic discharges can create voltage peaks that are capable of destroying the circuit array. Thus, it may be necessary to equip circuit arrays with a device that protects against ESD. 
   Printed specification WO 00/57515 discloses circuit arrays that are equipped with a protective device against ESD. The protective device comprises an electric high-pass filter in which a capacitor is connected in series and an inductor is connected in parallel to the antenna input path. 
   The ESD protective device helps reduce the ESD impulse entering the circuit array directly through the antenna. In addition to the impulse entering the circuit array directly through the antenna, an electrostatic discharge can also generate a high voltage in the circuit array through ground coupling. This can occur, for example, because the control input normally used in a circuit is arranged either on the high voltage (high) or on a low voltage (low). In this case, the high voltage (high) is defined, for example, by the fact that it lies 2.3 V above the ground voltage of the circuit array. Because, in the case of a mobile telephone, as with many other devices based on signal transmission via antennas, the signal input runs from the antenna to the system&#39;s ground, an electrostatic discharge can also directly affect the ground voltage of the circuit array in a circuit array of the type mentioned above. As a result of directly coupling a control line to ground through the “high” condition, the voltage impulse resulting from an electrostatic discharge can not only affect the path, via the antenna, but also the circuit array, via the control line. 
   A high-pass filter allows all frequency components of a signal, beginning with a certain cutoff frequency, to pass through it virtually unimpeded. In general, however, only a very narrow frequency range is relevant to the further processing of the signal received by the antenna in the mobile telephone. For example, frequencies of between 1 and 2 GHz are used in mobile telephones based on the GSM, PCN or PCS standard. All other frequencies received by the antenna tend to be interfering and, therefore, must be filtered out. 
   SUMMARY 
   A circuit array is described which contains a switch unit with an antenna input, a signal input and a signal output. The switch unit is suitable for electrically connecting the antenna input with either the signal input or the signal output. In addition, a control line that controls the switch position in the switch unit can be arranged at the switch unit. Additionally, the antenna input is connected to a first protective device against electrostatic discharges. 
   The first protective device against electrostatic discharges is a band-pass filter in a π configuration. 
   The advantage of a band-pass filter is that it has a high insertion loss below a first cutoff frequency and above a second cutoff frequency. As a result, frequencies can be effectively suppressed, especially low frequencies that contain the bulk of electrical output of the impulses generated by electrostatic discharge. By arranging a band-pass filter at the antenna input, at least the need for subsequent filters in the reception paths can be loosened, which results in a generally improved insertion loss. 
   In an embodiment, the first protective device has an antenna input and a switch output, which are connected to one another by a line. A series circuit comprising a capacitor and an inductor is connected in series to the line. Between the antenna input and the series circuit, a first parallel circuit of a capacitor and an inductor is connected in parallel to the line and connected to a ground. Between the switch output and the series circuit, a second parallel circuit comprising a capacitor and an inductor is connected in parallel to the line and connected to a ground. 
   A band-pass filter in a π configuration is achieved with the circuit array of the protective device described above. 
   In another embodiment, a capacitor can be connected in series between the switch output and the second parallel circuit. As a result, a direct current suppression is achieved that prevents DC voltage applied to the switch unit from being short-circuited against the ground. 
   In addition, a capacitor can also be connected in series to the line between the antenna input and the first parallel circuit. 
   To use the circuit array in a mobile telephone in which frequencies based on the GSM or PCS standard are used, it is advantageous for the band-pass filter to have an attenuation less than 0.5 dB between 1 and 2 GHz. Outside this frequency range, the band-pass filter should have the highest possible attenuation (e.g. &gt;20 dB at f&gt;3.4 GHz). 
   The circuit array, together with the band-pass filter, is also advantageous in that, as a result of the two capacitors connected in series to the line, a DC voltage block is achieved that prevents DC voltage applied to the switch unit from being discharged to the ground. This effectively reduces the risk of a short circuit. 
   In an embodiment, the control line is also connected to a second protective device against electrostatic discharges. The advantage of this arrangement is that ESD interference penetrating into the circuit can be effectively prevented through ground coupling via the control line. 
   The protective devices against electrostatic discharges are connected to a ground connection, into which the excess voltage from the electrostatic discharges can be discharged. 
   The switch unit can, for example, be a voltage-controlled switch, such as the type normally used in mobile telephone because of its low power consumption. In particular, a gallium-arsenide switch can be used as the switch unit. 
   The switch unit can also have multiple signal inputs and outputs. Accordingly, multiple control lines are needed. 
   The circuit array can also be provided with a decoder, which can be used to reduce the number of control lines. A decoder normally requires a power supply, which is connected via a supply line. The ESD protection of such a circuit can be improved even further by connecting the supply line to a third protective device against electrostatic discharges. 
   The decoder can also be designed so that the voltages of the control lines are generated from the voltage of the supply line. This can be accomplished by “pull-up resistors,” for example. Then ESD protection can be simplified by providing only the power supply line with a second protective device. In this case, protection of the control lines is provided through the protection of the power supply. 
   The circuit array can also contain frequency filters that are assigned to individual signal inputs or signal outputs. They are suitable for filtering the frequencies received by the antenna on a mobile telephone in such a way that the signals conducted and filtered through the signal output can be processed further by the mobile telephone. The same applies to the signal inputs of the circuit array, which, in a mobile telephone, are used to transmit the voice signals generated in the mobile telephone to a receiver via the antenna. 
   The use of a voltage-limiting element, which is connected in parallel to the control line and is also connected to the ground potential, represents another option for a second protective device against electrostatic discharges. A voltage-limiting element can be a varistor, for example. Such a varistor has very low resistance beginning at a certain cutoff voltage, so that excess voltage against ground can be diverted. Varistors with low switching voltage are suitable, because this minimizes the residual voltage that occurs in a voltage impulse and loads the circuit array. For this reason, it is advisable to use varistors with a varistor voltage of between 4 and 20 V. Accordingly, the terminal voltage in a voltage impulse that loads the circuit array is about 8 to about 50 V. As a result, the circuit array can be reliably protected against destruction in the event of an ESD impulse. 
   Another possibility is to use a switch spark gap or a Z-diode as a second protective device against electrostatic discharges. 
   Also described is a circuit array in which the antenna input is connected to an antenna, in which the signal output is connected to a receiving amplifier of a mobile telephone, and in which the signal input is connected to a transmission amplifier of a mobile telephone. 
   In addition, a circuit module is specified which contains a circuit array. The circuit module also contains a multilayer ceramic substrate with integrated passive components, which form electric frequency filters. These frequency filters are assigned to the signal inputs and/or outputs. The switch unit, which can, for example, be executed with the aid of PIN diodes or in the form of a gallium-arsenide switch, is arranged on the upper side of the multilayer ceramic substrate. In addition, the first and, if applicable, second protective device against electrostatic discharges is integrated into the circuit module. 
   An advantage of the circuit module is that, as a result of the integration of the passive components into the ceramic substrate, as well as the integration of the protective device into the circuit module, a high degree of integration is achieved, which affects the space requirements of the circuit module. The integration of the first and, if applicable, second protective device into the circuit module can occur, for example, by mounting these components onto the surface of the ceramic substrate, adjacent to the switch unit. 
   In particular, it is also advantageous to use the circuit module as a front-end module in a mobile telephone. 
   In the following, embodiments are explained in greater detail with reference to corresponding diagrams. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows, as an example, a circuit array in a basic circuit diagram. 
       FIG. 2  shows, as an example, another circuit array in a basic circuit diagram. 
       FIG. 3  shows, in a basic circuit diagram, the use of the circuit array in a mobile telephone. 
       FIG. 4  shows, as an example, the circuit module in a schematic longitudinal section. 
   

   The same reference symbols refer to the same elements in all diagrams. 
   DETAILED DESCRIPTION 
     FIG. 1  shows a circuit array with a switch unit  4 , which is provided with a ground  8 . The switch unit  4  has an antenna input  1 , which is connected to an antenna  18 . The antenna input  1  is connected to a first protective device  6  against electrostatic discharges (indicated by the lighting symbol in  FIG. 1 ). The switch unit  4  contains at least one control line  5 , which controls the switching process for connecting the antenna input  1  with the signal inputs  2  or the signal outputs  3  of the switch unit  4 . Three control lines  5  are shown in  FIG. 1 . At least one of these control lines is provided with a second protective device  7  against electrostatic discharges. These second protective device  7  is executed in the form of a varistor, which is connected to the ground  18 . 
   The switch unit  4  depicted in  FIG. 1  also has a decoder, for which a supply line  11  is required. The supply line  11  is connected to a supply voltage+Vcc. In addition, the supply line  11  is connected to a third protective device  12  against electrostatic discharges. The third protective device  12  can, for example, be a varistor that is connected to the ground  8 . 
   The first protective device  6  is implemented as a band-pass filter in a π configuration. Specifically, it can be implemented as follows: the first protective device  6  has an antenna input  111  and a switch output  112 . The antenna input  111  and the switch output  112  are connected to one another by a line  113 . A series circuit  114  comprising a capacitor C 1  and an inductor L 1  is connected in series to the line  113 . Between the antenna input  111  and the series circuit  114 , a parallel circuit  115  comprising a capacitor C 2  and an inductor L 2  is connected in parallel to the line  113 , as well as to the ground  8 . Between the switch output  112  and the series circuit  114 , a parallel circuit  116  comprising a capacitor C 3  and an inductor L 3  is also connected in parallel to the line  113 , as well as to the ground  8 . Another capacitor C 4 , which acts as a DC current suppressor, is connected between the parallel circuit  116  and the switch output  112 . Another capacitor C 5  is also connected in series to the line  113  between the antenna input  111  and the parallel circuit  115 . 
   Such a filter can have the following component data:
         L 1 =from 0.1 to 22 nH   L 2 =from 0.1 to 22 nH   L 3 =from 0.1 to 22 nH   C 1 =from 0.1 to 18 pF   C 2 =from 0.1 to 18 pF   C 3 =from 0.1 to 18 pF       

   The capacitors C 3  and/or C 2  can also be replaced with a protective element, such as a varistor. Individual or multiple combinations LiCi can also be formed by transmission lines that are coupled together. 
     FIG. 2  shows a voltage-controlled GaAs switch  9  with an antenna input  1 , to which the antenna  18  is connected. The GaAs switch  9  has transmitter inputs TX 1 , TX 2 , and receiver inputs RX 1 , RX 2 , and RX 3 . The GaAs switch  9  is controlled through control inputs S 1 , S 2 , S 3 , S 4 , and S 5 . Control takes place in that exactly one of the control inputs S 1 , S 2 , S 3 , S 4 , and S 5  is set to “high,” while the remaining control inputs are set to “low.” The number of inputs needed can be reduced using the decoder  10  connected to the GaAs switch  9 . The decoder  10  can be a 1-decoder or a 5-decoder, for example. It has control inputs E 1 , E 2 , and E 3 , as well as control outputs A 1 , A 2 , A 3 , A 4 , and A 5 . The control outputs A 1 , A 2 , A 3 , A 4 , and A 5  are connected to the control inputs S 1 , S 2 , S 3 , S 4 , and S 5  of the GaAs switch  9  through connection lines  24 . 
   The control inputs E 1 , E 2 , and E 3  of the decoder  10  are connected to the control line  5 . 
   An example of the decoding of a logical signal applied to one of the inputs E 1 , E 2 , and E 3  of the decoder  10  into signals applied to the control inputs S 1 , S 2 , S 3 , S 4 , and S 5  of the GaAs switch  9  that are suitable for controlling the GaAs switch is described by the following translation table: 
   
     
       
             
           
             
             
             
             
             
             
             
             
             
           
         
             
               TABLE 1 
             
           
           
             
                 
             
             
               Logical states of the control inputs S 1 , S 2 , S 3 , S 4 , and S 5  as 
             
             
               a factor of the logical states at the control inputs E 1 , E 2 , 
             
             
               and E 3 . 1 signifies “high” and 0 signifies “low.” 
             
           
        
         
             
               E 1   
               E 2   
               E 3   
               → 
               S 1   
               S 2   
               S 3   
               S 4   
               S 5   
             
             
                 
             
             
               0 
               0 
               0 
                 
               1 
               0 
               0 
               0 
               0 
             
             
               0 
               0 
               1 
                 
               0 
               1 
               0 
               0 
               0 
             
             
               0 
               1 
               0 
                 
               0 
               0 
               1 
               0 
               0 
             
             
               0 
               1 
               1 
                 
               0 
               0 
               0 
               1 
               0 
             
             
               1 
               0 
               0 
                 
               0 
               0 
               0 
               0 
               1 
             
             
                 
             
           
        
       
     
   
   In this case, the transmitter inputs TX 1 , TX 2  correspond to the signal inputs from  FIG. 1 . The receiver inputs RX 1 , RX 2 , and RX 3  correspond to the signal outputs  3  from  FIG. 1 . 
     FIG. 3  depicts a circuit module with a GaAs switch  9 , which has an antenna input  1  as well as two signal inputs  2  and three signal outputs  3 . In addition, the circuit module has two low-pass filters  13 ,  14 , wherein the low-pass filter  13  can be configured for the GSM frequency band and the low-pass filter  14  for the PCN/PCS frequency band. The GaAs switch  9  optionally connects one of the inputs/outputs  2 ,  3  with its antenna input  1 . The circuit module also has band-pass filters  15 ,  16 ,  17 , which are connected to the signal outputs  3 . The band-pass filter  15  is adjusted to the GSM frequency, the band-pass filter  16  to the PCN frequency, and the band-pass filter  17  to the PCS frequency. 
   The band-pass filter  15 ,  16 ,  17  at the signal output  3  can be designed to be less demanding in terms of its specifications, because a portion of filtration is assumed by the ESD protective device. This improves insertion loss on the whole. 
   The signal inputs  2  of the GaAs switch  9  are electrically connected in transmitter amplifiers  19 . The transmitter amplifiers  19 , like the low-pass filters  13 ,  14 , are adjusted to radio frequencies GSM and PCN/PCS, respectively. The signal outputs are electrically connected to receiver amplifiers  19   a  through the band-pass filters  15 ,  16 ,  17 , wherein the receiver amplifiers  19   a  are adjusted to the frequency bands GSM, PCN and PCS, respectively. The antenna input  1  of the GaAs switch  9  is connected to an antenna  18 . The signals received by the antenna  18  can now be fed, by the GaAs switch  9 , into the band-pass filter  16 , the band-pass filter  17  or the band-pass filter  18 , where they are filtered according to the radio frequency used and further processed in amplifiers  19   a.  The signals supplied by the transmitter amplifiers  19  are filtered by the low-pass filters  13 ,  14  and optionally supplied to the antenna  18  for transmission of a signal. 
     FIG. 4  shows a circuit module with a multilayer ceramic substrate  20 , into which passive components  21 ,  22 ,  23  are integrated. These passive components  21 ,  22 ,  23  can be resistors, capacitors  22 , and inductors  23 , for example. The multilayer ceramic substrate  20  can be designed in a known manner. Stacked ceramic layers  30  separated by metallic layers  31  can be used as the multilayer ceramic substrate  20 . A few of the metallic layers  31  are connected to one another through continuous contacts  32  running inside the ceramic layers  30 . A switch unit  4 , which, for example, can be a gallium-arsenide multiple switch assembled in flip chip technology, is mounted on the upper side of the ceramic substrate  20 . 
   The switch unit  4  can, for example, be secured and electrically contacted by gluing and additional wire-bonding. A GaAs multiple switch may be used as the switch unit  4 . This type of switch can have an insertion loss of 0.8 dB in the frequency range between 1 and 2 GHz. It can be an integrated circuit with FET produced on a gallium-arsenide base, with its pin surface connected to the ceramic substrate  20  by soldering. 
   The switch unit  4  can also be attached to the multilayer ceramic substrate  20  and electrically bonded by wire bonding. Bonding by soldering may be used when the switch unit  4  is to be used with an additional housing. 
   The passive components  21 ,  22 ,  23  can form the filters  13 ,  14 ,  15 ,  16 ,  17  required in accordance with  FIG. 3 . 
   In addition, the switch unit  4 , the first protective device  6  and the second protective device  7  are also mounted onto the surface of the substrate  20 . This accomplishes a high degree of integration for the circuit module, which advantageously affects the space requirements of the circuit module. 
   The individual components of the first protective device  6  can be arranged on the upper side of the ceramic substrate  20 . However, individual components, such as the capacitors C 1 , C 2 , C 3 , can also be integrated into the ceramic substrate  20 , like the passive components  21 ,  22 ,  23 . 
   The claims are not limited to the examples of the second and third protective device monitored above. In addition, the circuit array or the circuit module is not limited to applications in mobile telephones.