Patent Publication Number: US-11652456-B2

Title: Trans-impedance amplifier, chip, and communications device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 16/825,708, filed on Mar. 20, 2020, which is a continuation of U.S. patent application Ser. No. 15/894,467, filed on Feb. 12, 2018, now U.S. Pat. No. 10,637,416. The U.S. patent application Ser. No. 15/894,467 claims priority to Chinese Patent Application No. 201710099963.5, filed on Feb. 23, 2017. All of the afore-mentioned patent applications are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     This application relates to the field of chip technologies, and in particular, to a trans-impedance amplifier (TIA), a chip, and a communications device. 
     BACKGROUND 
     A TIA may be configured to convert a current signal to a voltage signal, and is widely applied to a receiving part of a sensor and a radio frequency transceiver system. 
     Currently, commonly used TIAs are a TIA of a first-order active structure is shown in  FIG.  1 A  while a TIA of a second-order active structure is shown in  FIG.  1 B . Further, the TIA of the first-order active structure shown in  FIG.  1 A  includes only one operational amplifier, and has an advantage in terms of power consumption compared with the TIA of the second-order active structure shown in  FIG.  1 B . The TIA of the first-order active structure, however, has a lower filtering capability. The TIA of the second-order active structure shown in  FIG.  1 B  can perform second-order shaping filtering on an input current, and therefore has a relatively strong out-of-band interference suppression capability. 
     In conclusion, TIAs of common structures at present all have performance tradeoffs. 
     SUMMARY 
     The embodiment of the present disclosure provides a TIA, a chip, and a communications device, that reduce power consumption of a TIA while improving filtering performance. 
     According to a first aspect, a TIA is provided, including a first circuit, a second circuit, a third circuit, and an operational amplifier, where each of the first circuit, the second circuit, and the third circuit includes a passive component. The first circuit is connected to a current source, the operational amplifier, and the third circuit, and is configured to receive a first current provided by the current source, provide a third voltage to the third circuit based on the first current, perform shaping filtering on the first current and converting the processed first current to a first voltage for output, and provide the first voltage to the operational amplifier. The second circuit is connected to the current source, the operational amplifier, and the third circuit, and is configured to receive a second current provided by the current source, provide a fourth voltage to the third circuit based on the second current, perform shaping filtering on the second current and converting the processed second current to a second voltage for output, and provide the second voltage to the operational amplifier, where the first current and the second current provided by the current source are two currents in a differential current. The third circuit is configured to cooperate with the first circuit in performing shaping filtering on the first current and cooperate with the second circuit in performing shaping filtering on the second current according to the third voltage and the fourth voltage, and the operational amplifier is configured to provide a small-signal virtual ground point to the first circuit for the first current to enter the first circuit, and provide a small-signal virtual ground point to the second circuit for the second current to enter the second circuit. 
     The TIA in embodiments of this application includes only one operational amplifier, and has a smaller quantity of operational amplifiers compared with a TIA of a second-order active structure shown in  FIG.  1 B . Therefore, power consumption of the TIA in the embodiments of this application is lower. In addition, the TIA in the embodiments of this application includes the third circuit, and the third circuit can cooperate with the first circuit in performing shaping filtering on the current in the first circuit and cooperate with the second circuit in performing shaping filtering on the current in the second circuit according to the third voltage and the fourth voltage. Therefore, compared with a TIA of a first-order active structure shown in  FIG.  1 A , filtering performance of the TIA in the embodiments of this application is improved, and an out-of-band interference suppression capability thereof is further improved. 
     Based on the first aspect, in a possible design, the first circuit includes a first part and a second part, the first part and the second part are connected in parallel, one end of the parallel connection is connected to the current source and a negative input of the operational amplifier, and the other end of the parallel connection is connected to a first output of the operational amplifier, and the first part includes at least one capacitor, and the at least one capacitor is connected in series and/or in parallel, and the second part includes at least one first resistor and at least one second resistor, where the at least one first resistor is connected in series and/or in parallel, the at least one second resistor is connected in series and/or in parallel, the at least one first resistor is connected in series to the at least one second resistor, and a connection point of the series connection is connected to the third circuit. 
     According to the foregoing manner, an implementation of the first circuit is simplified. 
     Based on the first aspect, in a possible design, the second circuit includes a third part and a fourth part, the third part and the fourth part are connected in parallel, one end of the parallel connection is connected to the current source and a positive input of the operational amplifier, and the other end of the parallel connection is connected to a second output of the operational amplifier, and the third part includes at least one capacitor, and the at least one capacitor is connected in series and/or in parallel, and the fourth part includes at least one third resistor and at least one fourth resistor, where the at least one third resistor is connected in series and/or in parallel, the at least one fourth resistor is connected in series and/or in parallel, the at least one third resistor is connected in series to the at least one fourth resistor, and a connection point of the series connection is connected to the third circuit. 
     According to the foregoing manner, an implementation of the second circuit is simplified. 
     Based on the first aspect, in a possible design, the third circuit includes at least one capacitor, and the at least one capacitor is connected in series and/or in parallel. 
     According to the foregoing manner, an implementation of the third circuit is simplified. Moreover, the third circuit in the foregoing design can cooperate with the first circuit and the second circuit in order to improve a filtering capability, and further improve the out-of-band interference suppression capability of the TIA. 
     Based on the first aspect, in a possible design, the first circuit includes a first capacitor, a first resistor, and a second resistor, the first resistor and the second resistor are connected in series and then connected to the first capacitor in parallel, one end of the parallel connection is connected to the current source and a negative input of the operational amplifier, and the other end of the parallel connection is connected to a first output of the operational amplifier, and a connection point of the series connection between the first resistor and the second resistor is connected to the third circuit. 
     Based on the first aspect, in a possible design, the second circuit includes a second capacitor, a third resistor, and a fourth resistor, the third resistor and the fourth resistor are connected in series and then connected to the second capacitor in parallel, one end of the parallel connection is connected to the current source and a positive input of the operational amplifier, and the other end of the parallel connection is connected to a second output of the operational amplifier, and a connection point of the series connection between the third resistor and the fourth resistor is connected to the third circuit, and the first capacitor and the second capacitor have a same capacitance, and resistances of the first resistor, the second resistor, the third resistor, and the fourth resistor are the same. 
     Based on the first aspect, in a possible design, the third circuit includes a third capacitor, and the third circuit has a same capacitance as the first capacitor and the second capacitor. 
     According to a second aspect, a chip is provided, including the TIA in any possible design provided in the first aspect. 
     According to a third aspect, a communications device is provided, including the chip provided in the second aspect. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1 A  shows a TIA of a first-order active structure; 
         FIG.  1 B  shows a TIA of a second-order active structure; 
         FIG.  2    is a schematic structural diagram of a TIA according to an embodiment of this application; 
         FIG.  3 A  and  FIG.  3 B  are schematic structural diagrams of a first circuit according to an embodiment of this application; 
         FIG.  4 A  and  FIG.  4 B  are schematic structural diagrams of a second circuit according to an embodiment of this application; 
         FIG.  5    is a schematic structural diagram of a third circuit according to an embodiment of this application; 
         FIG.  6    is a schematic structural diagram of a TIA according to an embodiment of this application; and 
         FIG.  7    is a comparison diagram of amplitude-frequency characteristic curves of a TIA in an embodiment of this application and a TIA of a first-order active structure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The term “and/or” in the embodiments of this application describes only an association relationship for describing associated objects and represents that three relationships may exist. For example, A and/or B may represent the three cases, namely: only A exists, both A and B exist, and only B exists. In addition, the character “/” in the embodiments of this application generally indicates an “or” relationship between the associated objects. 
     The following further describes the embodiments of this application in detail with reference to the accompanying drawings. 
     A TIA is configured to convert a current signal to a voltage signal, and may be integrated into a chip and applied in a communications device, for example, applied to a receiving part of a sensor in the communications device or applied in a radio frequency transceiver system of the communications device. 
     A TIA in the embodiments of this application includes only one operational amplifier, and has a smaller quantity of operational amplifiers compared with a TIA of a second-order active structure shown in  FIG.  1 B . Therefore, power consumption of the TIA in the embodiments of this application is lower. In addition, the TIA in the embodiments of this application includes a third circuit, and the third circuit can cooperate with a first circuit in performing shaping filtering on a current in the first circuit, and cooperate with a second circuit in performing shaping filtering on a current in the second circuit according to the third voltage and the fourth voltage. Therefore, compared with a TIA of a first-order active structure shown in  FIG.  1 A , filtering performance of the TIA in the embodiments of this application is improved, and an out-of-band interference suppression capability thereof is further improved. 
     As shown in  FIG.  2   , a TIA  200  in an embodiment of this application includes a first circuit  210 , a second circuit  220 , a third circuit  230 , and an operational amplifier  240 . Each of the first circuit  210 , the second circuit  220 , and the third circuit  230  includes a passive component. 
     The first circuit  210  is connected to a current source, the operational amplifier  240 , and the third circuit  230 , and is configured to receive a first current provided by the current source, provide a third voltage to the third circuit  230  based on the first current, perform shaping filtering on the first current and converting the processed first current to a first voltage for output, and provide the first voltage to the operational amplifier  240 . 
     A first end  211  of the first circuit  210  is connected to one end of the current source and a negative input  241  of the operational amplifier  240 , a second end  212  of the first circuit  210  is connected to a first output  242  of the operational amplifier  240 , and a third end  213  of the first circuit  210  is connected to one end  231  of the third circuit  230 . The first circuit  210  is configured to receive the first current provided by the current source using the first end  211 , provide the third voltage to the end  231  of the third circuit  230  based on the first current, perform shaping filtering on the first current and converting the processed first current to the first voltage, and output the first voltage using the second end  212 . Because the second end  212  of the first circuit  210  is connected to the first output  242  of the operational amplifier  240 , a voltage of the first output  242  is set to the first voltage. 
     The second circuit  220  is connected to the current source, the operational amplifier  240 , and the third circuit  230 , and is configured to receive a second current provided by the current source, provide a fourth voltage to the third circuit  230  based on the second current, perform shaping filtering on the second current and converting the processed second current to a second voltage for output, and provide the second voltage to the operational amplifier  240 . The first current and the second current provided by the current source are two currents in a differential current. 
     A first end  221  of the second circuit  220  is connected to the other end of the current source and a positive input  243  of the operational amplifier  240 , a second end  222  of the second circuit  220  is connected to a second output  244  of the operational amplifier  240 , and a third end  223  of the second circuit  220  is connected to the other end  232  of the third circuit  230 . The second circuit  220  is configured to receive the second current provided by the current source using the first end  221  of the second circuit  220 , provide the fourth voltage to the other end  232  of the third circuit  230  based on the second current, perform shaping filtering on the second current and converting the processed second current to the second voltage, and output the second voltage using the second end  222 . Because the second output  244  of the operational amplifier  240  is connected to the second end  222 , a voltage of the second output  244  is set to the second voltage by the second circuit  220 . 
     The third circuit  230  is configured to cooperate with the first circuit  210  in performing shaping filtering on the first current and cooperate with the second circuit  220  in performing shaping filtering on the second current according to the third voltage and the fourth voltage. 
     The operational amplifier  240  is configured to provide a small-signal virtual ground point to the first circuit  210  for the first current to enter the first circuit  210 , and provide a small-signal virtual ground point to the second circuit  220  for the second current to enter the second circuit  220 . 
     The operational amplifier  240  is configured to provide the small-signal virtual ground points to the first circuit  210  and the second circuit  220 , respectively. 
     The operational amplifier  240  provides the small-signal virtual ground point to the first end  211  of the first circuit  210  using the negative input  241  to make a voltage of the first end  211  set to zero such that the first current provided by the current source enters the first circuit  210 . The operational amplifier  240  provides the small-signal virtual ground point to the first end  221  of the second circuit  220  using the positive input  243  to make a voltage of the first end  221  set to zero such that the second current provided by the current source enters the second circuit  220 . 
     It should be understood that, the passive component includes a component such as a capacitor, an inductor, and a resistor. Passive components may be used to form the first circuit  210 , the second circuit  220 , and the third circuit  230  to implement functions in this embodiment of this application. A quantity and type of the passive components are not limited herein. 
     In a possible design, the first circuit  210  includes a first part and a second part, the first part and the second part are connected in parallel, one end (that is, the first end  211 ) of the parallel connection is connected to the current source and the negative input  241  of the operational amplifier  240 , and the other end (that is, the second end  212 ) of the parallel connection is connected to the first output  242  of the operational amplifier  240 . 
     The first part includes at least one capacitor, and the at least one capacitor is connected in series and/or in parallel. The second part includes at least one first resistor and at least one second resistor, where the at least one first resistor is connected in series and/or in parallel, the at least one second resistor is connected in series and/or in parallel, the at least one first resistor is connected in series to the at least one second resistor, the at least one first resistor is connected in series to the at least one second resistor, and a connection point of the series connection is connected to the third circuit  230 . Further, the connection point of the series connection is connected to the end  231  of the third circuit  230 , and the connection point of the series connection is the third end  213  of the first circuit  210 . 
     For example, in a first circuit  210  shown in  FIG.  3 A , a first part includes three capacitors C 1 , C 2 , and C 3 , and a second part includes a first resistor R 1  and a second resistor R 2 . In a first circuit  210  shown in  FIG.  3 B , a first part includes a capacitor C 1 , and a second part includes a first resistor R 1 , a first resistor R 2 , and a second resistor R 3 . In addition to connection manners of the first circuit  210  shown in  FIG.  3 A  and  FIG.  3 B , for the first circuit  210  in this embodiment of this application, there may be another connection manner equivalent to those in  FIG.  3 A  and  FIG.  3 B . 
     In a possible implementation, for example, the second circuit  220  includes a third part and a fourth part in parallel, one end (that is, the first end  221 ) of the parallel connection is connected to the current source and the positive input  243  of the operational amplifier  240 , and the other end (that is, the second end  222 ) of the parallel connection is connected to the second output  244  of the operational amplifier  240 . 
     The third part includes at least one capacitor, and the at least one capacitor is connected in series and/or in parallel. The fourth part includes at least one third resistor and at least one fourth resistor, where the at least one third resistor is connected in series and/or in parallel, the at least one fourth resistor is connected in series and/or in parallel, the at least one third resistor is connected in series to the at least one fourth resistor, and a connection point of the series connection is connected to the third circuit  230 . Further, the connection point of the series connection is connected to the other end  232  of the third circuit  230 , and the connection point of the series connection is the third end  223  of the second circuit  220 . 
     For example, in a second circuit  220  shown in  FIG.  4 A , a third part includes four capacitors C 1 , C 2 , C 3 , and C 4 , and a fourth part includes a third resistor R 1  and a fourth resistor R 2 . In a second circuit  220  shown in  FIG.  4 B , a third part includes a capacitor C 1 , and a fourth part includes a third resistor R 1 , a third resistor R 2 , and a fourth resistor R 3 . In addition to connection manners of the second circuit  220  shown in  FIG.  4 A  and  FIG.  4 B , for the second circuit  220  in this embodiment of this application, there may be another connection manner equivalent to those in  FIG.  4 A  and  FIG.  4 B . 
     It should be understood that, the connection manners of the first circuit  210  and the second circuit  220  may be the same or may be different, and a quantity of capacitors and quantities of first resistors, second resistors, third resistors, and fourth resistors in the first circuit  210  and the second circuit  220  are not limited. 
     In a possible design, the third circuit  230  includes at least one capacitor, and the at least one capacitor is connected in series and/or in parallel. 
     For example, if the third circuit  230  includes two capacitors C 1  and C 2 , as shown in  FIGS.  5   , C 1  and C 2  are connected in parallel in the third circuit  230 . One end of the third circuit  230  is connected to the third end  213  of the first circuit  210 , and the other end of the third circuit  230  is connected to the third end  223  of the second circuit  220 . It should be understood that, a quantity of capacitors included in the third circuit  230  is not limited in this embodiment of this application. 
     It should be noted that, in this embodiment of this application, a resistance and a capacitance may be set according to an actual need, to obtain a required voltage. 
     The following uses a TIA shown in  FIG.  6    as an example and assumes that a gain of an operational amplifier within an operating frequency range is infinite to perform qualitative analysis on the TIA in the embodiments of this application using a small-signal equation. 
     As shown in  FIG.  6   , the TIA includes capacitors C 1 , C 2 , and C 3 , resistors R 1 , R 2 , R 3 , and R 4 , and an operational amplifier. A current source provides a differential current to the TIA, C 1 , R 1 , and R 2  form a first circuit, C 3  forms a third circuit, and C 2 , R 3 , and R 4  form a second circuit. A current of the differential current flows into the first circuit through p 1 , and the other current of the differential current flows into the second circuit through n 1 . 
     A negative input of the operational amplifier provides a small-signal virtual ground point to the first circuit, and a positive input of the operational amplifier provides a small-signal virtual ground point to the second circuit. It is assumed that voltages at a point a, a point b, a point p 2 , and a point n 2  shown in  FIG.  6    are Va, Vb, Vp, and Vn, respectively, a current that the current source provides to the first circuit is i 1 , and a current that the current source provides to the second circuit is i 2 , a sum of currents that flow through the point a, the point b, a point c, and a point d respectively is zero. In this case, the following formulas are obtained: 
                           (     Va   -   0     )     /   R     ⁢           ⁢   1     +         (     Va   +   Vp     )     /   R     ⁢           ⁢   2     +       (     Va   -   Vb     )     /     1     j   ⁢           ⁢   ω   ⁢           ⁢   C   ⁢           ⁢   3           =   0           (   1   )                       (     Vb   -   0     )     /   R     ⁢           ⁢   3     +         (     Vb   +   Vn     )     /   R     ⁢           ⁢   4     +       (     Vb   -   Va     )     /     1     j   ⁢           ⁢   ω   ⁢           ⁢   C   ⁢           ⁢   3           =   0           (   2   )                     -   i     ⁢           ⁢   1     +         (     0   -   Va     )     /   R     ⁢           ⁢   1     +       (     0   -   Vp     )     /     1     j   ⁢           ⁢   ω   ⁢           ⁢   C   ⁢           ⁢   1           =   0           (   3   )                       -   i     ⁢           ⁢   2     +         (     0   -   Vb     )     /   R     ⁢           ⁢   3     +       (     0   -   Vn     )     /     1     j   ⁢           ⁢   ω   ⁢           ⁢   C   ⁢           ⁢   2           =   0     ,           (   4   )               
where ω indicates an operating frequency, when R 1 =R 2 =R 3 =R 4 =R and C 1 =C 2 =C 3 =C, a transfer function is obtained as follows:
 
     
       
         
           
             
               Vout 
               Iin 
             
             = 
             
               
                 
                   Vp 
                   - 
                   Vn 
                 
                 
                   
                     i 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   - 
                   
                     i 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                 
               
               = 
               
                 
                   
                     2 
                     ⁢ 
                     
                       R 
                       ⁡ 
                       
                         ( 
                         
                           1 
                           + 
                           
                             
                               R 
                               · 
                               C 
                               · 
                               j 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             ω 
                           
                         
                         ) 
                       
                     
                   
                   
                     1 
                     + 
                     
                       2 
                       ⁢ 
                       
                         R 
                         · 
                         C 
                         · 
                         j 
                       
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       ω 
                     
                     + 
                     
                       2 
                       ⁢ 
                       
                         
                           R 
                           2 
                         
                         · 
                         
                           C 
                           2 
                         
                         · 
                         
                           
                             ( 
                             
                               j 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               ω 
                             
                             ) 
                           
                           2 
                         
                       
                     
                   
                 
                 . 
               
             
           
         
       
     
     It can be learned from the transfer function that, the transfer function includes two poles and one zero, and the zero and one pole form a zero-pole pair on a near passband. Compared with a first-order active RC structure, in-band flatness of the TIA in the embodiments of this application is improved. If a same 3 decibels (dB) corner frequency is used, the TIA in the embodiments of this application has a better out-of-band suppression characteristic compared with a TIA of a first-order active structure. As shown in  FIG.  7   , a curve  1  is an amplitude-frequency characteristic curve when R 1 =R 2 =R 3 =R 4 =R and C 1 =C 2 =C 3 =C, while a curve  2  is an amplitude-frequency characteristic curve of a TIA that is of a first-order active structure and to which C 3  is not added. It can be learned from  FIG.  7    that, the TIA in the embodiments of this application has a second-order characteristic on a near passband and has better flatness. In  FIG.  7   , 3 dB corner frequencies of the curve  1  and the curve  2  are different. The 3 dB corner frequency of the curve  1  is A, and the 3 dB corner frequency of the curve  2  is B. If the TIA in the embodiments of this application has a same 3 dB corner frequency requirement as the TIA of the first-order active structure, the amplitude-frequency characteristic curve in the embodiments of this application has a better out-of-band suppression characteristic. In addition, the TIA in the embodiments of this application uses only one operational amplifier such that power consumption of the TIA is reduced compared with a TIA of a second-order active structure. 
     In addition, the embodiments of this application further provide a chip, including any TIA provided in the embodiments of this application. 
     The embodiments of this application further provide a communications device, including the chip provided in the embodiments of this application. 
     For a connection manner of a TIA in the chip or in the communications device, refer to the connection manner of the TIA shown in  FIG.  2   . Details are not described herein. 
     Although some specific embodiments that can be implemented have been described, persons skilled in the art can make changes and modifications to these embodiments once they learn the basic inventive concept. Therefore, the following claims are intended to be construed to cover the embodiments described in this application and all changes and modifications falling within the scope of this application. 
     Obviously, persons skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. This application is intended to cover these modifications and variations of this application provided that they fall within the scope of protection defined by the following claims and their equivalent technologies.