Patent Publication Number: US-2022236755-A1

Title: Constant current generation circuit for optocoupler isolation amplifier and current precision adjustment method

Description:
TECHNICAL FIELD 
     The present disclosure relates to the technical field of designs of semiconductor integrated circuits, and in particular to a constant current generation circuit for an optocoupler isolation amplifier and a current precision adjustment method. 
     BACKGROUND ART 
     An optocoupler isolation amplifier circuit, especially one belonging to the field of designs of semiconductor integrated circuits, requires a high-performance constant current to complete biasing and output. In addition, the magnitude of current is required to be within an expected precision range; and the magnitude of current is independent of temperature changes, power supply voltage changes, change in process parameters of current sheets, etc. 
     SUMMARY 
     An object of the present disclosure is to provide a constant current generation circuit in an optocoupler isolation amplifier and a current precision adjusting method. The constant current generation circuit provides a high-performance output constant current source which is independent of temperature changes, power supply voltage changes, changes in technological parameters of current sheets, etc. 
     To achieve the above object, the present disclosure adopts the following technical solution: 
     A constant current generation circuit for an optocoupler isolation amplifier includes a start circuit, a current generation circuit and a precision adjustment and output circuit which are integrated into a same substrate, 
     where the start circuit can generate and output a first start current and a second start current; 
     the current generation circuit includes a negative temperature change rate current generation circuit and a positive temperature change rate current generation circuit, where the negative temperature change rate current generation circuit is connected with a first start current output end; the positive temperature change rate current generation circuit is connected with a second start current output end; and 
     the precision adjustment and output circuit is used for outputting a constant current meeting application requirements of the optocoupler isolation amplifier by adjusting proportional precision of two currents outputted from the current generation circuit. 
     Further, the start circuit includes a diode D 1 , a resistor R 1  and a diode D 2  which are connected with a power supply in sequence, where an anode of the diode D 1  is connected with an output end of the power supply, and a cathode is connected with one end of the resistor R 1 ; another end of the resistor R 1  is connected with a cathode of the diode D 2 ; and the first start current output end and the second start current output end are lead out from an anode of the diode D 2  via resistors R 2  and R 3 , respectively. 
     Preferably, the negative temperature change rate current generation circuit ( 21 ) comprises triodes Q 1 , Q 2 , Q 3  and Q 4  connected with each other, wherein a drain of the triode Q 1  is connected with the resistor R 2  and a gate of the triode Q 1 ; a source of the triode Q 1  is connected with a drain of the triode Q 2  and a gate of the triode Q 3 ; a source of the triode Q 2  is grounded and connected with a source of the triode Q 3  via a resistor R 4 ; a gate of the triode Q 2  is connected with a source of the triode Q 4 ; a drain of the triode Q 3  is connected with the source of the triode Q 4 ; a gate of the triode Q 4  is connected with the gate of the triode Q 1 ; and a drain of the triode Q 4  is connected with an input end of the precision adjustment and output circuit. 
     Preferably, the positive temperature change rate current generation circuit ( 22 ) comprises triodes Q 5 , Q 6 , Q 7  and Q 8  connected with each other, wherein a drain of the triode Q 5  is connected with the resistor R 3  and a gate of the triode Q 5 ; a source of the triode Q 5  is connected with a drain of the triode Q 6  and a gate of the triode Q 7 ; a source of the triode Q 6  is connected with a position between the triode Q 2  and a resistor R 4  and connected with a source of the triode Q 7  via a resistor R 5 ; a gate of the triode Q 6  is connected with a source of the triode Q 8 ; a drain of the triode Q 7  is connected with the source of the triode Q 8 ; a gate of the triode Q 8  is connected with the gate of the triode Q 5 ; and a drain of the triode Q 8  is connected with the input end of the precision adjustment and output circuit. 
     Further, the precision adjustment and output circuit ( 3 ) comprises triodes Q 9  and Q 10 , wherein a source of the triode Q 9  is connected with the output end of the power supply and a source of the triode Q 10 ; a drain of the triode Q 9  is connected with an output end of the current generation circuit and a gate of the triode Q 9 ; the gate of the triode Q 9  is connected with a gate of the triode Q 10 ; and the drain of the triode Q 10  is a constant current output end. 
     Further, the resistors R 4  and R 5  are ion implanted type resistors applied to a semiconductor integrated circuit technology; the resistor R 4  has a higher temperature coefficient than a thermal voltage of the semiconductor integrated circuit technology; and the resistor R 5  has a lower temperature coefficient than the thermal voltage of the semiconductor integrated circuit technology. 
     A precision adjustment method for a constant current generation circuit for an optocoupler isolation amplifier includes the following steps of: 
     step 1, calculating a current outputted by the current generation circuit, where a calculation formula of the current is as follows: 
     
       
         
           
             
               TC 
               
                 
                   I 
                     
                 
                 3 
               
             
             = 
             
               
                 
                   
                     I 
                     1 
                   
                   
                     
                       I 
                       1 
                     
                     + 
                     
                       I 
                       2 
                     
                   
                 
                 × 
                 
                   ( 
                   
                     
                       TCv 
                       t 
                     
                     - 
                     
                       TC 
                       
                         R 
                         4 
                       
                     
                   
                   ) 
                 
               
               + 
               
                 
                   
                     I 
                     1 
                   
                   
                     
                       I 
                       1 
                     
                     + 
                     
                       I 
                       2 
                     
                   
                 
                 × 
                 
                   ( 
                   
                     
                       TCv 
                       t 
                     
                     - 
                     
                       TC 
                       
                         R 
                         5 
                       
                     
                   
                   ) 
                 
               
             
           
         
       
     
     where I 1  represents an output current of the negative temperature coefficient current generation circuit; I 2  represents an output current of the positive temperature coefficient current generation circuit; I 3  represents an output current of the current generation circuit; TC I     3    represents a temperature coefficient of the current I 3 ; TC R     4    represents a temperature coefficient of the resistor R 4 ; TC R     5    represents a temperature coefficient of the resistor R 5 ; and TCν t  represents a temperature coefficient of the thermal voltage V t  of the semiconductor integrated circuit technology. 
     step 2, the current I 3  passes through a precision adjustment circuit, and a calculation formula of the output current is as follows: 
     
       
         
           
             
               I 
               OUT 
             
             = 
             
               
                 
                   A 
                   
                     Q 
                     9 
                   
                 
                 
                   A 
                   
                     Q 
                     
                       1 
                       ⁢ 
                       0 
                     
                   
                 
               
               × 
               
                 I 
                 3 
               
             
           
         
       
     
     where A Q     9    represents an area of an emission region of the triode Q 9 , and A Q     10    represents an area of an emission region of the triode Q 10 . 
     According to the above technical solution, the present disclosure combines and integrates the start circuit, the negative temperature change rate current generation circuit, the positive temperature change rate current generation circuit and the precision adjustment and output circuit on a single substrate to form a constant current output circuit which is independent of temperature changes, power supply voltage changes and technological parameter changes of current sheets, thereby obtaining a high-performance output constant current source. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an overall structure in accordance with the present disclosure; and 
         FIG. 2  is a schematic diagram showing circuit connection in accordance with the present disclosure. 
     
    
    
     In the figures:  1 , start circuit;  21 , negative temperature change rate current generation circuit;  22 , positive temperature change rate current generation circuit; and  3 , precision adjustment and output circuit. 
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     A preferred embodiment of the present disclosure is described in detail below with reference to the accompanying drawings. 
     As shown in  FIG. 1  and  FIG. 2 , the constant current generation circuit for an optocoupler isolation amplifier includes a start circuit  1 , a current generation circuit and a precision adjustment and output circuit  3  which are integrated into a same substrate, where the start circuit can generate and output a first start current and a second start current; the current generation circuit includes a negative temperature change rate current generation circuit  21  and a positive temperature change rate current generation circuit  22 . Further, the negative temperature change rate current generation circuit is connected with a first start current output end, and the positive temperature change rate current generation circuit is connected with a second start current output end. The precision adjustment and output circuit is used for outputting a constant current meeting application requirements of the optocoupler isolation amplifier by adjusting proportional precision of two currents outputted by the current generation circuit. 
     According to the present disclosure, a high-performance constant current source output circuit is achieved by utilizing inherent devices of a semiconductor integrated circuit technology based on the same substrate. The negative temperature change rate current generation circuit  21  can generate a current I 1  which is independent of changes in power supply voltage but related to temperature changes and changes in technological parameter of current sheets, and the current I 1  is inversely proportional to temperature changes. Similarly, the positive temperature change rate current generation circuit  22  can generate a current I 2  which is independent of changes in power supply voltage but related to temperature changes and changes in technological parameter of current sheets, and the current I 2  is proportional to temperature changes. 
     Specifically, the start circuit of the preferred embodiment includes a diode D 1 , a resistor R 1  and a diode D 2  which are connected with a power supply in sequence, where an anode of the diode D 1  is connected with an output end of the power supply, and a cathode is connected with one end of the resistor R 1 ; the other end of the resistor R 1  is connected with a cathode of the diode D 2 ; and a first start current output end and a second start current output end are lead out from an anode of the diode D 2  via resistors R 2  and R 3 , respectively. 
     The negative temperature change rate current generation circuit  21  of the preferred embodiment includes triodes Q 1 , Q 2 , Q 3  and Q 4  connected with each other, where a drain of the triode Q 1  is connected with the resistor R 2  and a gate of the triode Q 1 ; a source of the triode Q 1  is connected with a drain of the triode Q 2  and a gate of the triode Q 3 ; a source of the triode Q 2  is grounded and connected with a source of the triode Q 3  via the resistor R 4 ; a gate of the triode Q 2  is connected with a source of the triode Q 4 ; a drain of the triode Q 3  is connected with the source of the triode Q 4 ; a gate of the triode Q 4  is connected with the gate of the triode Q 1 ; and a drain of the triode Q 4  is connected with an input end of the precision adjustment and output circuit. 
     The positive temperature change rate current generation circuit  22  of the preferred embodiment includes triodes Q 5 , Q 6 , Q 7  and Q 8  connected with each other, where a drain of the triode Q 5  is connected with the resistor R 3  and a gate of the triode Q 5 ; a source of the triode Q 5  is connected with a drain of the triode Q 6  and a gate of the triode Q 7 ; a source of the triode Q 6  is connected with a position between the triode Q 2  and a resistor R 4  and connected with a source of the triode Q 7  via a resistor R 5 ; a gate of the triode Q 6  is connected with a source of the triode Q 8 ; a drain of the triode Q 7  is connected with the source of the triode Q 8 ; a gate of the triode Q 8  is connected with the gate of the triode Q 5 ; and a drain of the triode Q 8  is connected with the input end of the precision adjustment and output circuit. 
     The precision adjustment and output circuit  3  of the preferred embodiment includes triodes Q 9  and Q 10 , where a source of the triode Q 9  is connected with the output end of the power supply and a source of the triode Q 10 ; a drain of the triode Q 9  is connected with an output end of the current generation circuit and a gate of the triode Q 9 ; the gate of the triode Q 9  is connected with a gate of the triode Q 10 ; and the drain of the triode Q 10  is a constant current output end. 
     Particularly, all the above triodes have a current magnification factor far greater than 1; the resistors R 1 , R 2 , R 3  and R 4  are all ion implanted type resistors applied to the semiconductor integrated circuit technology; the resistor R 5  is a diffusion implanted type resistor applied to the semiconductor integrated circuit technology; the resistor R 4  has a higher temperature coefficient than a thermal voltage of the semiconductor integrated circuit technology; and the resistor R 5  has a lower temperature coefficient than the thermal voltage of the semiconductor integrated circuit technology. 
     A precision adjustment method for the constant current generation circuit for an optocoupler isolation amplifier of the present disclosure includes the following steps of: 
     Step 1, calculating a current outputted by the current generation circuit, where a calculation formula of the current is as follows: 
     
       
         
           
             
               TC 
               
                 
                   I 
                     
                 
                 3 
               
             
             = 
             
               
                 
                   
                     I 
                     1 
                   
                   
                     
                       I 
                       1 
                     
                     + 
                     
                       I 
                       2 
                     
                   
                 
                 × 
                 
                   ( 
                   
                     
                       TCv 
                       t 
                     
                     - 
                     
                       TC 
                       
                         R 
                         4 
                       
                     
                   
                   ) 
                 
               
               + 
               
                 
                   
                     I 
                     1 
                   
                   
                     
                       I 
                       1 
                     
                     + 
                     
                       I 
                       2 
                     
                   
                 
                 × 
                 
                   ( 
                   
                     
                       TCv 
                       t 
                     
                     - 
                     
                       TC 
                       
                         R 
                         5 
                       
                     
                   
                   ) 
                 
               
             
           
         
       
     
     where I 1  represents an output current of the negative temperature coefficient current generation circuit; I 2  represents an output current of the positive temperature coefficient current generation circuit; I 3  represents an output current of the current generation circuit; TC R     4    represents a temperature coefficient of the resistor R 4 ; TC R     5    represents a temperature coefficient of the resistor R 5 ; and TCν t  represents a temperature coefficient of the thermal voltage V t  of the semiconductor integrated circuit technology. 
     Specifically, it can be seen from the above description that a temperature change rate characteristic of the resistor R 4  satisfies TC I     1   =TCν t −TC R     1   &lt;0; a temperature change rate characteristic of the resistor R 5  satisfies TC I     2   =TCν t −TC R     2   &gt;0; in other words, the current I 1  decreases with rise of the temperature, and the current I 2  rises with rise of the temperature; a reasonable ratio of the current I 1  to the current I 2  is set through the above calculation formula, and finally the temperature coefficient TC I     3    of the current I 3  is zero, and as a result, the magnitude of the current I 3  is independent of temperature changes, and the magnitude of current I 3  is also not affected by changes of the power supply voltage V CC . 
     Step 2, in order to make the output current I OUT  meet application precision requirements of an optocoupler isolation amplifier circuit, the above current I 3  should be adjusted reasonably. The current I 3  is inputted into the precision adjustment and output circuit, and the triode Q 9  and triode Q 10  in the precision adjustment and output circuit form a current mirror relationship, that is, an output current I OUT  of the precision adjustment and output circuit is proportional to an input current I 3  of the precision adjustment and output circuit. Therefore, the current I 3  passes through a precision adjustment circuit, and a calculation formula of the output current is as follows: 
     
       
         
           
             
               I 
               OUT 
             
             = 
             
               
                 
                   A 
                   
                     Q 
                     9 
                   
                 
                 
                   A 
                   
                     Q 
                     
                       1 
                       ⁢ 
                       0 
                     
                   
                 
               
               × 
               
                 I 
                 3 
               
             
           
         
       
     
     where A Q     9    represents an area of an emission region of the triode Q 9 , and A Q     10    represents an area of an emission region of the triode Q 10 . 
     The above formula shows that the output current I OUT  of the precision adjustment and output circuit can be adjusted to an expected precision range by reasonably adjusting a ratio of the area of emission region of the triode Q 9  to the area of emission region of the triode Q 10 . Since the aforementioned current I 3  is not affected by changes of the power supply voltage V CC , the output current I OUT  is also not affected by changes of power supply voltage V CC . Moreover, since the output current I OUT  has the same temperature coefficient as the aforementioned current I 3 , and both are zero, changes of the output current I OUT  are independent of temperature changes as well, and thus the output of a high-performance constant current source is achieved. The above embodiments are merely intended to describe the preferred embodiments of the present disclosure rather than to limit the scope of the present disclosure. Various alterations and improvements made by those of ordinary skill in the art based on the technical solution of the present disclosure without departing from the design spirit of the present disclosure shall fall within the protection scope of the claims of the present disclosure.