Abstract:
There is provided an intermodulation (IMD) control device and method in a mobile communication system. In the IMD control device, an LNA performs low noise amplification on an input RF signal, a first switch is connected to the LNA in parallel, for switching according to a first control signal received for IMD control, a frequency converter down-converts the output of the LNA to an IF signal, an IF amplifier amplifies the IF signal, a second switch is connected in parallel to the IF amplifier, for switching according to a second IMD control signal received for IMD control, and a controller generates the IMD control signals at voltage levels determined according to an RSSI and an energy to noise ratio.

Description:
This application claims priority to an application entitled “Intermodulation Control Device and Method in Mobile Communication System” filed in the Korean Industrial Property Office on Dec. 29, 1999 and assigned Serial No. 99-64546, the contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to an IMD (Intermodulation) control device and method in a mobile communication system, and in particular, to an IMD control device and method using a switch. 
     2. Description of the Related Art 
     Single tone desensitization and intermodulation spurious response attenuation are significant factors in designing a mobile station in the RF (Radio Frequency) field. In many cases, these two factors cause current consumption in designing a receiver and increase the cost of terminal parts. Therefore, research has been made on methods of increasing the performance of a mobile station with low current consumption, to satisfy minimum performance standards related to these factors. 
     Regarding the intermodulation spurious response attenuation that falls into the field related to the present invention, its minimum performance standards (e.g., IS-98A Receiver Performance Intermodulation Spurious Response Attenuation Test shown in Table 1) are specified in three items in the table. The three items differ in frequency band. For example, only one item applies to the PCS (Personal Communication Services) frequency band and the three items apply to the CDMA (Code Division Multiple Access) frequency band, 900 MHz due to the dual mode of CDMA and AMPS (Advanced Mobile Phone System). For PCS, a circuit used for single tone desensitization also satisfies the intermodulation item. However, two of the three items must be additionally controlled for CDMA. The second item of −32 dBm can be satisfied by controlling current flowing through an IF (Intermediate Frequency) amplifier, whereas it is impossible to satisfy the third item of −21 dBM through current control alone. To satisfy the third item, it is necessary to eliminate a high level harmonic component by reducing the power level of a received signal (a dual-tone signal in the test), thus reducing the influence of the harmonic component. 
     FIGS. 1,  2 , and  3  are block diagrams of conventional IMD control devices to eliminate a high level harmonic component. The conventional IMD control device shown in FIG. 1 has a diode  124  connected between a duplexer  104  and an LNA (Low Noise Amplifier)  106  above a ground terminal to reduce the power level of an input signal. Another conventional IMD control device shown in FIG. 2 has a diode  126  connected between a SAW (Surface Acoustic Wave Filter)  108  and a mixer  116  above the ground terminal to reduce the power level of an input signal. A third conventional IMD control device shown in FIG. 3 has a switch  128  connected to the LNA  106  in parallel to reduce the power level of an input signal. The three conventional IMD control devices aim at minimization of harmonic influence caused by intermodulation between the LNA  106  and the IF amplifier  118  by reducing the power levels of input signals. 
     The above conventional IMD control devices perform IMD control only at an RF end, that is, at an LNA. The IMD control of the LNA causes great current consumption (e.g., 10 mA) at an IF amplifier and makes it impossible to optimize the performance of a mobile station. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide an IMD control device and method in a mobile communication system to overcome the problems of conventional control devices. 
     It is another object of the present invention to provide a device and method for reducing current consumption during an IMD control operation in order to minimize the influence of IMD in a mobile station. 
     It is a further object of the present invention to provide an IMD control device and method for optimizing the performance of a mobile station. 
     To achieve the above and other objects, in an IMD control device for a mobile communication system, an LNA performs low noise amplification on an input RF signal, a first switch is connected to the LNA in parallel, for switching according to a first control signal received for IMD control, a frequency converter down-converts the output of the LNA to an IF signal, an IF amplifier amplifies the IF signal, a second switch is connected in parallel to the IF amplifier, for switching according to a second IMD control signal received for IMD control, and a controller generates the IMD control signals at voltage levels determined according to an RSSI and an energy to noise ratio. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a block diagram of a conventional IMD control device; 
     FIG. 2 is a block diagram of another conventional IMD control device; 
     FIG. 3 is a block diagram of a third conventional IMD control device; 
     FIG. 4 is a block diagram of an IMD control device according to the present invention; 
     FIG. 5 is a detailed block diagram of an embodiment of a stabilizing circuit shown in FIG. 4; and 
     FIG. 6 is a detailed block diagram of another embodiment of the stabilizing circuit shown in FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment of the present invention will be described hereinbelow with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. 
     FIG. 4 is a block diagram of an IMD control device according to an embodiment of the present invention. This IMD control device performs IMD control at an IF amplifier  118  for amplifying an IF signal as well as at an LNA  128  for amplifying an RF signal in a mobile station having the LNA  128 , a mixer  116  for down-converting the amplified RF signal to the IF signal, and the IF amplifier  118 . 
     Referring to FIG. 4, the IMD control device includes a switch (SW)  128  connected to the LNA  106  in parallel and a switch (SW)  130  connected to an IF amplifier (IF AMP)  118  in parallel. The switching operations of the switches  128  and  130  are controlled by an IMD_PDM 1  signal and an IMD_PDM 2  signal received from a controller (so-called MSM chip: Mobile Station Modem chip)  134 , for IMD control. The switch  128  may be incorporated with the LNA  106  and the switch  130  may be incorporated with the IF amplifier  118 . In other words, an LNA with a switching function and an IF amplifier with a switching function may substitute for the LNA  106  and the IF amplifier  118 , respectively. A stabilizing circuit  129  is connected between the controller  134  and the switch  128  and a stabilizing circuit  132  is connected between the controller  134  and the switch  130 . The stabilizing circuits  129  and  132  can be constituted as shown in FIGS. 5 and 6. 
     FIG. 5 is a detailed block diagram of an embodiment of the stabilizing circuit  132  shown in FIG.  4 . The stabilizing circuit  129  shown in FIG. 4 can be configured in the same manner as the stabilizing circuit  132 . 
     Referring to FIG. 5, the stabilizing circuit  132  includes a loop filter  136  and a resistor R which are serially connected. The controller  134  feeds the IMD_PDM (Pulse Density Modulation) signal to the switch  130  via the loop filter  136  and the resistor R, for control of switching. In this figure, the stabilizing circuit  132  is shown to be constituted of passive devices. 
     FIG. 6 is a detailed block diagram of another embodiment of the stabilizing circuit  132  shown in FIG.  4 . 
     Referring to FIG. 6, the stabilizing circuit  132  includes the loop filter  136 , resistors R 1 , R 2 , and R 3 , and a transistor Q. The transistor Q is an NPN transistor having a collector, a base, and an emitter. The loop filter  136  has an input port connected to the controller  134 , for receiving the IMD_PDM signal, and an output port connected to an end of the resistor R 2 . The other end of the resistor R 2  is connected to the base of the transistor Q. The resistor R 1  has an end connected to the collector of the transistor Q. A power voltage VCC is applied to the other end of the resistor R 1 . The emitter of the transistor Q is connected to a ground terminal through resistor R 3  and to the switch  130  for control of switching. 
     Referring back to FIG. 4, the switch  128  is connected to the LNA  106  in parallel and the switch  130  is connected to the IF amplifier  118  in parallel for IMD control. The IMD_PDM 1  signal and the IMD_PDM 2  signal for controlling the switches  128  and  130 , respectively are provided from the controller  134 . For example, the controller  134  may be an MSM2300 chip manufactured by Qualcomm. In this case, the controller  134  is provided with RF control pins PDM 1  and PDM 2  (not shown). These control pins can be used as ones for outputting the IMD_PDM 1  and IMD_PDM 2  signals. For example, the controller  134  can output the IMD_PDM 1  signal via the control pin PDM 1  and the IMD_PDM 2  signal via the control pin PDM 2 . The controller  134  reads an RSSI (Received Signal Strength Indicator) and an energy-to-noise ratio (Eb/Nt) and generates the IMD_PDM  1  and IMD_PDM 2  signals at voltage levels corresponding to the present IMD situation. The RSSI and the energy-to-noise ratio can be measured in an RSSI measurer (not shown) and an energy-to-noise ratio measurer (not shown) as well known. The IMD_PDM 1  signal has a voltage level that determines whether the switch  128  is turned on or off and the IMD_PDM 2  signal has a voltage level that determines whether the switch  130  is turned on or off. If the stabilizing circuit  132  is constituted as shown in FIG. 5, the voltage level of the IMD PDM signal can be determined considering the difference between the voltage levels of input and output signals of the loop filter  136  and a voltage decrement by the resistor R. On the other hand, if the stabilizing circuit  32  is constituted as shown in FIG. 6, the voltage level of the IMD_PDM can be determined considering the difference between the voltage levels of the input and output signals of the loop filter  136  and the difference between the voltage levels of signals at the emitter and at the base of the transistor Q upon application of a signal to the base. The voltage level difference between the base and the emitter of the transistor Q is controllable according to the values of the resistors R 1 , R 2 , and R 3 . 
     In the IMD control device according to the embodiment of the present invention, the LAN  106  is connected to the switch  128  in parallel, the IF amplifier  118  is connected to the switch  130  and the controller  134  senses the IMD situation and feeds the IMD_PDM 1  and IMS_PDM 2  signals to the switch  130  Particularly, use of amplifiers with a switching function as the LNA  106  and the IF amplifier  118  will facilitate designing of the IMD control device. That is, the IMD problem is readily solved by applying the IMD_PDM 1  and IMD_PDM 2  signals at voltage levels suitable for switching the switches  128  and  130 . Furthermore, only if impedance at both sides of the switches  128  and  130  are matched, ripples can be eliminated because an input signal passes through the switches  128  and  130 . 
     Prior to describing the operation of the IMD control device shown in FIGS. 4,  5 , and  6 , Table 1 below lists items related to CDMA and PCS in the intermodulation spurious response attenuation test. 
     
       
         
               
             
               
               
               
             
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 IS98-A Receiver Performance Intermodulation Spurious Response 
               
               
                 Attenuation Test 
               
             
          
           
               
                   
                 Ior 
                 Mobile Station Class II, III 
               
             
          
           
               
                 Parameter 
                 (dBm/1.23 MHz) 
                 Test 1 
                 Test 2 
               
               
                   
               
             
          
           
               
                 Tone 1 offset from 
                   
                 +900 
                 KHz 
                 −900 
                 KHz 
               
               
                 carrier 
               
               
                 Tone power 1 
                 −101 (1)  
                 −43 
                 dBm 
                 −43 
                 dBm 
               
               
                   
                 −90 (2) 
                 −32 
                 dBm 
                 −32 
                 dBm 
               
               
                   
                 −79 (3) 
                 −21 
                 dBm 
                 −21 
                 dBm 
               
               
                 Tone 2 offset from 
                   
                 +1700 
                 KHz 
                 −1700 
                 KHz 
               
               
                 carrier 
               
               
                 Tone power 2 
                 −101 (1)  
                 −43 
                 dBm 
                 −43 
                 dBm 
               
               
                   
                 −90 (2) 
                 −32 
                 dBm 
                 −32 
                 dBm 
               
               
                   
                 −79 (3) 
                 −21 
                 dBm 
                 −21 
                 dBm 
               
               
                 Pilot Ec/Ior 
                   
                 −7 
                 dBm 
                 −7 
                 dBm 
               
               
                 Traffic Ec/Ior 
                   
                 −15.6 
                 dBm 
                 −15.6 
                 dBm 
               
               
                   
               
             
          
         
       
     
     In Table 1, the three items ( 1 ), ( 2 ), and ( 3 ) are all related to CDMA, and only the first of them is related to PCS. Here, a tone  1  offset from a carrier is 900 KHs, a tone  2  offset from the carrier is 1700 KHz, and Ior is the power of a signal received from a base station to which the mobile station belongs to. In test  1 , a +900-KHz tone  1  and a +1700-KHz tone  2  are generated and these tones and a signal from the base station are received at an antenna of the mobile station via a so-called jammer. In test  2 . A −900-KHz tone and a −1700-KHz tone  2  are generated and theses tones and the signal from the base station are received at the antenna of the mobile station via the jammer. Here, the power of the signal from the base station varies with the items. 
     The operation of the novel IMD control device according to the present invention will be described below. 
     The LNA  106  shown in FIG. 4 is designed to satisfy single tone desensitization. If the single tone desensitization is satisfied, the first item (−43 dBm) is also satisfied. Thus, the second and third items are notable considerations. As described above, RF interface control pins for an MSM2300 chip made by Qualcomm that can be used as the controller  134  are PDM 1  and PDM 2 . A user can selectively use these control pins, for IMD control. Therefore, about 260 PDM signals can be generated depending on the RSSI and Eb/No of a mobile station. That is, a desired voltage can be applied to the switch  130  by empirically setting the voltage of the IDM_PDM signal so that the switch  130  may output a signal at an intended level. 
     If a jamming signal is applied to an antenna  102  shown in FIG. 4, it means that signals stronger than an intended signal of the mobile station are received. In view of the design of the LNA  106  for satisfying single tone desensitization, it is not reasonable to expect a further performance increase from the LNA  106 . In reality, dual tone-caused intermodulation occurs in the IF amplifier  118 . A dual tone signal is amplified in the same manner as the intended signal of the mobile station across the RF SAW filter  108  to the mixer  116  and a higher level signal than an input signal of the LNA  106  is applied to the input of the IF amplifier  118 . As a result, the IF amplifier  118  having a lower ICP 1  (Input Compression Point 1 dB) than that of the LNA  106  is highly susceptible to the influence of dual tone-caused intermodulation spurious response. Therefore, if the controller  134  generates the IMD_PDM signals at intended voltage levels and switches on the switch  130  upon receipt of the jamming signal via the antenna  102 , a signal received at the IF amplifier  118  via the LNA  106 , the SAW filter  108 , and the mixer  116  does not experience intermodulation and most signals are removed as they pass through an IF filter  120 . Consequently, the influence of the dual tone is minimized. 
     As described above, the IMD control device of the present invention controls IMD at an IF amplifier as well as at an LNA. As compared to the case that an IMD control is performed only at the LNA, current consumption at the IF amplifier can be decreased. Furthermore, IMD control at both sides of a receiver makes the performance of a mobile station optimal. 
     While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.