Patent Publication Number: US-2002003447-A1

Title: Trimming circuit of semiconductor integrated device

Description:
BACKGROUND OF THE INVENTION  
       [0001] The present invention relates to semiconductor devices, and more particularly, to a trimming circuit that adjusts the resistance of a semiconductor integrated device.  
       [0002] The resistance of a semiconductor integrated circuit is adjusted so that it matches a target resistance value. To adjust the resistance with high accuracy, the semiconductor integrated circuit is provided with a highly accurate trimming circuit.  
       [0003]FIG. 1 illustrates a first prior art example of a two-bit Zener zap trimming circuit E used in a semiconductor integrated circuit. The trimming circuit E is connected between resistors R 0 , R 3  and includes two parallel circuits connected between the resistors R 0 , R 3  and three trimming terminals T 1 , T 2 , T 3 . In more detail, the first parallel circuit includes an upstream resistor R 1  and a first Zener diode Z 2 , which is connected in parallel to the upstream resistor R 1 . The second parallel circuit includes a downstream resistor R 2  and a second Zener diode Z 2 , which is connected in parallel to the downstream resistor R 2 . The four resistors R 0 , R 1 , R 2 , R 3  are connected in series. When a high voltage is applied to two of the trimming terminals T 1 , T 2 , T 3 , a breakdown occurs in the associated one of the first and second Zener diodes Z 1 , Z 2 . This causes the associated one of the first and second Zener diodes Z 1 , Z 2  to become conductive.  
       [0004] When adjusting the resistance of the semiconductor integrated circuit, the breakdown voltage is applied to one or both of the first and second Zener diodes Z 1 , Z 2 . This causes the first and second Zener diodes Z 1 , Z 2 , to which the breakdown voltage is applied, to become conductive and decreases the voltage of the trimming circuit E.  
       [0005]FIG. 2 illustrates a second prior art example of a two-bit fuse trimming circuit F used in a semiconductor integrated circuit. The trimming circuit F includes a first fuse F 1  and a second fuse F 2  in lieu of the Zener diodes Z 1 , Z 2  of the trimming circuit E of FIG. 1. The resistance of the first fuse F 1  is significantly lower than that of an upstream resistor R 1 , and the resistance of the second fuse F 2  is significantly lower than that of a downstream resistor R 2 .  
       [0006] When adjusting the resistance of the semiconductor integrated circuit, a fusing current is supplied to at least one of the first and second fuses F 1 , F 2 . This breaks the at least one of the fuses F 1 , F 2  and increases the resistance of the trimming circuit F.  
       [0007] The Zener ZAP trimming circuit E of FIG. 1 is capable of only decreasing the resistance. Thus, the initial resistance of the trimming circuit E is set higher than the target resistance.  
       [0008] On the other hand, the fuse trimming circuit F of FIG. 2 is capable of only increasing the resistance. Thus, the initial resistance of the trimming circuit F is set lower than the target resistance.  
       [0009] Accordingly, the trimming circuits E, F of FIGS. 1 and 2 are capable of either increasing or decreasing the resistance. However, the trimming circuits E, F are not capable of adjusting the resistance in both increasing and decreasing directions. Further, the initial resistance is always greater than or less that the target resistance to enable trimming. As a result, trimming must always be performed to adjust the resistance.  
       SUMMARY OF THE INVENTION  
       [0010] It is an object of the present invention to provide a trimming circuit capable of increasing and decreasing the resistance.  
       [0011] To achieve the above object, the present invention provides a trimming circuit having an initial resistance. The trimming circuit has a first circuit, which includes a first resistor and a first resistance adjustment device connected in parallel to the first resistor, and a second circuit, which includes a second resistor and a second resistance adjustment device connected in parallel to the second resistor. The second circuit is connected in series to the first circuit. The resistance of the trimming circuit is decreased to a value lower than the initial resistance by performing trimming with the first resistance adjustment device and is increased to a value higher than the initial resistance by performing trimming with the second resistance adjustment device.  
       [0012] The present invention also provides a trimming circuit having an initial resistance. The trimming circuit has a first resistor and a first circuit connected in parallel to the first resistor. The first circuit includes a first auxiliary resistor and a first resistance adjustment device that are connected in series. The trimming circuit also has a second resistor and a second circuit connected in parallel to the second resistor. The second circuit includes a second auxiliary resistor and a second resistance adjustment device that are connected in series. The resistance of the trimming circuit is decreased to a value lower than the initial resistance by performing trimming with the first resistance adjustment device and is increased to a value higher than the initial resistance by performing trimming with the second resistance adjustment device.  
       [0013] The present invention further provides a semiconductor integrated circuit device including a trimming circuit having an initial resistance. The trimming circuit has a first circuit, which includes a first resistor and a first resistance adjustment device connected in parallel to the first resistor, and a second circuit, which includes a second resistor and a second resistance adjustment device connected in parallel to the second resistor. The second circuit is connected in series to the first circuit. The resistance of the trimming circuit is decreased to a value lower than the initial resistance by performing trimming with the first resistance adjustment device and is increased to a value higher than the initial resistance by performing trimming with the second resistance adjustment device.  
       [0014] The present invention further provides a trimming circuit having an initial resistance. The trimming circuit has a plurality of trimming terminals including a first trimming terminal, a second trimming terminal, and a third trimming terminal. A first resistor is connected between the first trimming terminal and the second trimming terminal. A Zener diode is connected in parallel to the first resistor between the first and second trimming terminals. A second resistor is connected in series to the first resistor between the second trimming terminal and the third trimming terminal. A fuse is connected in parallel to the second resistor and in series to the Zener diode between the second and third trimming terminals. The resistance of the trimming circuit is decreased to a value lower than the initial resistance by applying a breakdown voltage of the Zener diode between the first and second trimming terminals, and the resistance of the trimming circuit is increased to a value higher than the initial resistance by supplying a fusing current of the fuse between the second and third trimming terminals.  
       [0015] Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0016] The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:  
     [0017]FIG. 1 is a schematic circuit diagram of a prior art Zener zap trimming circuit;  
     [0018]FIG. 2 is a schematic circuit diagram of a prior art fuse trimming circuit;  
     [0019]FIG. 3 is a schematic circuit diagram of a trimming circuit according to a first embodiment the present invention;  
     [0020]FIG. 4 is a schematic circuit diagram of a trimming circuit according to a second embodiment of the present invention;  
     [0021]FIG. 5 is a schematic circuit diagram of a trimming circuit according to a third embodiment of the present invention; and  
     [0022]FIG. 6 is a schematic circuit diagram of a trimming circuit according to a fourth embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0023] With reference to FIG. 3, a trimming circuit A according to a first embodiment of the present invention includes a first resistor R 1 , a second resistor R 2 , a Zener diode Z 1 , which functions as a first resistance adjustment device, and a fuse F 1 , which functions as a second resistance adjustment device. The Zener diode Z 1  is connected in parallel to the first resistor R 1 . The fuse F 1  is connected in parallel to the second resistor R 2 . The two parallel circuits are connected in series between two resistors R 0 , R 3 . Application of a breakdown voltage to the Zener diode Z 1  causes the Zener diode Z 1  to be conductive. The supply of a fusing current to the fuse F 1  breaks and causes the fuse F 1  to be non-conductive.  
     [0024] The trimming circuit A enables the total resistance of the trimming circuit A to increase and decrease. More specifically, when the resistance of the trimming circuit A prior to trimming is higher than a desired resistance, a breakdown voltage is applied to the Zener diode Z 1 . If the resistance of the trimming circuit A prior to trimming is lower than a desired resistance, a fusing current is supplied to the fuse F 1 . Accordingly, the trimming circuit A of the first embodiment adjusts the resistance of the trimming circuit A in both increasing and decreasing directions. Thus, the resistance is variable in a bidirectional manner.  
     [0025] A trimming circuit B according to a second embodiment of the present invention will now be discussed with reference to FIG. 4.  
     [0026] The trimming circuit B has an upstream circuit and a downstream circuit connected in series between a resistor R 0  and a resistor R 3 . The upstream circuit includes a first resistor R 1 , a Zener diode Z 1 , and an upstream resistor R 1   a , which is connected in series between the first resistor R 1  and the Zener diode Z 1 . The downstream circuit includes a second resistor R 2 , a fuse F 1 , and a downstream resistor R 2   a , which is connected in series between the second resistor R 2  and the fuse F 1 . The resistance of the fuse F 1  is significantly smaller than the resistances of the resistors R 2 , R 2   a . The resistor R 1  is connected to the resistor R 0 , and the resistor R 2  is connected to the resistor R 3 . The application of a breakdown voltage between the trimming terminals T 1 , T 2  results in breakdown of the Zener diode Z 1  and causes the Zener diode Z 1  to become conductive. The supply of a fusing current to the fuse F 1  breaks the fuse F 1 . This causes the fuse F 1  to become non-conductive.  
     [0027] Prior to trimming, that is, in an untrimmed state, the Zener diode Z 1  is non-conductive and the fuse F 1  is conductive.  
     [0028] When the resistances of the resistors R 1 , R 1   a , R 2 , R 2   a , and the fuse F 1  are represented by r 1 , r 1   a , r 2 , r 2   a , f 1  (f 1 &lt;&lt;r 2 , r 2   a ), respectively, and the resistance f 1  is so small that it can be ignored, the resistance (initial resistance) of the trimming circuit B in an untrimmed state is expressed by formula (1). 
       r   1 +( r   2 × r   2   a )÷( r   2 + r   2   a )  (1) 
     [0029] To decrease the resistance of the trimming circuit B, a breakdown voltage is applied to the Zener diode Z 1 . This causes the Zener diode Z 1  to become conductive. In this case, the resistance of the trimming circuit B subsequent to trimming is expressed by formula (2). 
     ( r   1 × r   1   a )÷( r   1 + r   1   a )+( r   2 × r   2   a )÷( r   2 + r   2   a )  (2) 
     [0030] To increase the resistance of the trimming circuit B, a fusing current is supplied to the fuse F 1 . This breaks the fuse F 1  and causes the fuse F 1  to be non-conductive. In this case, the resistance of the trimming circuit B subsequent to trimming is expressed by formula (3). 
       r   1 + r   2   (3) 
     [0031] When finely adjusting the initial resistance, a breakdown voltage is applied to the Zener diode Z 1  to cause the Zener diode Z 1  to become conductive, and a fusing current is supplied to the fuse F 1  to break and cause the fuse F 1  to become non-conductive. In this case, the resistance of the trimming circuit subsequent to trimming is expressed by formula (4). 
     ( r   1 × r   1   a )÷( r   1 + r   1   a )+ r   2   (4) 
     [0032] The trimming circuit B of the second embodiment has the advantages described below.  
     [0033] (1) In the trimming circuit B, the fuse  1  increases the resistance from the initial resistance and the Zener diode Z 1  decreases the resistance from the initial resistance. Thus, the fuse  1  and the Zener diode Z 1  enable the initial resistance to be set to substantially match the target resistance from the beginning. If the initial resistance matches the target resistance, trimming need not be performed. Further, the fuse  1  and the Zener diode Z 1  enable the resistance to be varied from the initial resistance when necessary.  
     [0034] (2) By performing trimming with the Zener diode Z 1  and the fuse F 1 , fine adjustment of the resistance with the upstream resistor R 1   a , which is series-connected to the Zener diode Z 1 , is enabled.  
     [0035] (3) Since the resistance can be varied (increased and decreased) as desired, semiconductor integrated circuit devices are manufactured with improved accuracy and an increased yield. Further, the testing time required until completing incorporation to, for example, a power supply IC circuit is decreased.  
     [0036] A trimming circuit C according to a third embodiment of the present invention will now be discussed with reference to FIG. 5. The trimming circuit C uses an intermediate resistor Ra in lieu of the upstream and downstream resistors R 1   a , R 2   a  of the second embodiment. The intermediate resistor Ra is connected between a trimming terminal T 2  and a node between resistors R 1 , R 2 . The resistance of the intermediate resistor Ra is significantly greater than the resistance of the fuse F 1 .  
     [0037] When the resistance of the intermediate resistor Ra is represented by ra and the resistance of the fuse F 1  is so small that it can be ignored, the initial resistance of the trimming circuit C is expressed by formula (5). 
       r   1 +( r   2 × ra )÷( r   2 + ra )  (5) 
     [0038] To decrease the resistance, trimming is performed with the Zener diode Z 1 . This causes the resistance of the trimming circuit C to be substantially null.  
     [0039] To increase the resistance, trimming is performed with the fuse F 1 . In this case, the resistance of the trimming circuit C subsequent to the trimming is expressed by formula (6). 
       r   1 + r   2   (6) 
     [0040] To finely adjust the resistance of the trimming circuit C, trimming is performed with the Zener diode Z 1  and the fuse F 1 . In this case, the resistance of the trimming circuit C is expressed by formula (7). 
     ( r   2 × ra )÷( r   1 + ra )+ r   2   (7) 
     [0041] The trimming circuit C of the third embodiment has the advantages described below.  
     [0042] (1) Trimming may be performed with the Zener diode Z 1 . This enables the resistance of the trimming circuit C to become substantially null.  
     [0043] (2) Trimming may be performed with the Zener diode Z 1  and the fuse F 1 . This enables fine adjustment of the resistance with the intermediate resistor Ra, which is series-connected to the Zener diode Z 1 .  
     [0044] A trimming circuit D according to a fourth embodiment of the present invention will now be discussed with reference to FIG. 6. The trimming circuit D is connected to a reference voltage circuit  100 . The reference voltage circuit  100  includes PNP transistors Tr 1 , Tr 2 , NPN transistors Tr 3 -Tr 6 , and resistors R 0 , R 5 , R 6 . The trimming circuit D is connected between the resistors R 0 , R 5 .  
     [0045] The trimming circuit D is a two-bit trimming circuit configured by a two-bit Zener zap trimming circuit and a two-bit fuse trimming circuit. The Zener zap trimming circuit includes a first resistor R 1 , a second resistor R 2 , a first Zener diode Z 1 , and a second Zener diode Z 2 . The fuse trimming circuit includes a third resistor R 3 , a fourth resistor R 4 , a first fuse F 1 , and a second fuse F 2 .  
     [0046] The resistance of the first fuse F 1  is significantly lower than the resistance of the third resistor R 3 . The resistance of the second fuse F 2  is significantly lower than the resistance of the fourth resistor R 4 . Application of a breakdown voltage between the trimming terminals T 1 , T 2  causes the first Zener diode Z 1  to become conductive. Application of a breakdown voltage between the trimming terminals T 2 , T 3  causes the second Zener diode Z 2  to become conductive. The supply of a fusing current between the trimming terminals T 3 , T 4  breaks and causes the first fuse F 1  to become non-conductive. The supply of a fusing current between the trimming terminals T 4 , T 5  breaks and causes the second fuse F 2  to become non-conductive.  
     [0047] When the resistances of the resistors R 1 , R 2 , R 3 , R 4  are represented by  4 r, r,  2 r,  8 r, respectively, and the resistance f 1  of the fuse F 1  and the resistance f 2  of the fuse F 2  are so small that they can be ignored, the initial resistance of the trimming circuit D is expressed by equations (8) to (22).  
     [0048] The resistance of the trimming circuit D when performing trimming with the fuses F 1 , F 2  is expressed by equation (8). 
       R   1 + R   2 + R   3 + R   4 = 15   r   (8) 
     [0049] The resistance of the trimming circuit D when performing trimming with the fuses F 1 , F 2  and the Zener diode Z 2  is expressed by equation (9). 
       R   1 + R   3 + R   4 = 14   r   (9) 
     [0050] The resistance of the trimming circuit D when performing trimming with the fuse F 2  is expressed by equation (10). 
       R   1 + R   2 + R   4 = 13   r   (10) 
     [0051] The resistance of the trimming circuit D when performing trimming with the fuse F 2  and the Zener diode Z 2  is expressed by equation (11). 
       R   1 + R   4 = 12   r   (11) 
     [0052] The resistance of the trimming circuit D when performing trimming with the fuses F 1 , F 2  and the Zener diode Z 1  is expressed by equation (12). 
       R   2 + R   3 + R   4 = 11   r   (12) 
     [0053] The resistance of the trimming circuit D when performing trimming with the fuses F 1 , F 2  and the Zener diodes Z 1 , Z 2  is expressed by equation (13). 
       R   3 + R   4 = 10   r   (13) 
     [0054] The resistance of the trimming circuit D when performing trimming with the fuse F 2  and the Zener diode Z 1  is expressed by equation (14). 
       R   2 + R   4 = 9   r   (14) 
     [0055] The resistance of the trimming circuit D when performing trimming with the fuse F 2  and the Zener diodes Z 1 , Z 2  is expressed by equation (15). 
       R   4 = 8   r   (15) 
     [0056] The resistance of the trimming circuit D when performing trimming with the fuse F 1  is expressed by equation (16). 
       R   1 + R   2 + R   3 = 7   r   (16) 
     [0057] The resistance of the trimming circuit D when performing trimming with the fuse F 1  and the Zener diode Z 2  is expressed by equation (17). 
       R   1 + R   3 = 6   r   (17) 
     [0058] The resistance of the trimming circuit D in an untrimmed state is expressed by equation (18). 
       R   1 + R   2 = 5   r   (18) 
     [0059] The resistance of the trimming circuit D when performing trimming with the Zener diode Z 2  is expressed by equation (19). 
       R   1 = 4   r   (19) 
     [0060] The resistance of the trimming circuit D when performing trimming with the fuse F 1  and the Zener diode Z 1  is expressed by equation (20). 
       R   2 + R   3 = 3   r   (20) 
     [0061] The resistance of the trimming circuit D when performing trimming with the fuse F 1  and the Zener diodes Z 1 , Z 2  is expressed by equation (21). 
       R   3 = 2   r   (21) 
     [0062] The resistance of the trimming circuit D when performing trimming with the Zener diode Z 1  is expressed by equation (22). 
       R   2 = r   (22) 
     [0063] When trimming is performed with the Zener diodes Z 1 , Z 2 , the resistance of the trimming circuit D is substantially null. Accordingly, the resistance of the trimming circuit D is adjustable in sixteen ways.  
     [0064] The trimming circuit D of the fourth embodiment has the advantages described below.  
     [0065] (1) The combination of the two-bit fuse trimming circuit and the two-bit Zener zap trimming circuit in addition to the employment of resistors having different resistances enable fine adjustment of the resistance of the trimming circuit D. In other words, the trimming circuit D is highly accurate.  
     [0066] (2) Trimming may be performed with the Zener diodes Z 1 , Z 2 . This enables the resistance of the trimming circuit D to become substantially null.  
     [0067] It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms.  
     [0068] The resistance of each of the resistors used in the above embodiments may be changed as required.  
     [0069] In the fourth embodiment, the resistance of each of the resistors may be changed such that the resistance of the trimming circuit D is increased by performing trimming with the fuses f 1 , f 2  and the resistance of the timing circuit D is decreased by performing trimming with the Zener diodes Z 1 , Z 2 .  
     [0070] The number of fuses and Zener diodes may be varied. An increased number of fuses and Zener diodes enables finer adjustment of the resistance when matching the resistance of the semiconductor integrated circuit with the target resistance.  
     [0071] The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.