Abstract:
A component inaccuracy correction system has a current source capable of outputting two currents with a fixed ratio, a voltage dividing circuit formed on the integrated circuit having at least an output end capable of receiving a current of the current source to output a divided voltage, a reference voltage generator capable of receiving another current of the current source to output a reference voltage, a comparison circuit electrically connected to the output end of the voltage dividing circuit for receiving the divided voltage from the voltage dividing circuit and comparing the divided voltage to the reference voltage to create a corresponding comparison signal, and a correction circuit electrically connected to the comparison circuit for correcting component inaccuracies of the integrated circuit according to the comparison signal generated by the comparison circuit.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a component inaccuracy correction system, and more particularly, to a correction system for correcting a resistance inaccuracy caused by an integrated circuit manufacturing process.  
           [0003]    2. Description of the Prior Art  
           [0004]    Integrated circuits arewidely found in day-to-day life, from watches and cellular telephones, all the way to super-computers. However, due to problems in manufacturing process controls, the characteristics of each component in an integrated circuit may deviate from the characteristics originally designed, and so the functionality of the integrated circuit may not meet the original design specifications. For example, the resistors in an integrated circuit may have inaccurate resistance values because the fabrication process is not ideal. Such process inaccuracies makes the real resistance values of all resistor components in the integrated circuit deviate from the original design values by the same ratio, i.e. the ratio of deviation from the original design value of each resistor component in the integrated circuit is the same.  
           [0005]    To avoid the above-mentioned resistance inaccuracies, U.S. Pat. No. 5,625,316 offers an inaccuracy correction system to correct resistance inaccuracies in a wave filter. Please refer to FIG. 1. FIG. 1 is a block diagram of a prior art component inaccuracy correction system  510  used to correct resistance inaccuracies of the wave filter  520 . The wave filter  520  comprises a resistor Rf and a variable capacitor  560 . The product of the two is the RC time constant that determines the bandwidth of the wave filter  520 . If the resistance of Rf is affected by the integrated circuit manufacturing process and is inaccurate, the bandwidth of the wave filter  520  may deviate from the original, designed value. To keep the bandwidth fixed, the component inaccuracy correction system  510  changes the value of the capacitor  560  to compensate for inaccuracies in the resistance of Rf.  
           [0006]    In the prior art component inaccuracy correction system  510 , Vcc provides a bias voltage for the correction system  510 . The resistorRref is an additional resistor installed outside of the integrated circuit, and so having a resistance that is not affected by the integrated circuit manufacturing process. The resistor Rc and the resistor Rf of the wave filter  520  are both made in the same integrated circuit manufacturing process, and so both of these resistors may suffer the same level of resistance inaccuracies. The correction system  510  further comprises a regulated generator  530  for producing a standard voltage Vbg, a reference voltage generator  540  for producing a reference voltage Vref according to the standard voltage Vbg, and an analog-to-digital converter (ADC)  550 .  
           [0007]    The working principle of the prior art component inaccuracy correction system  510  is described as follows. The regulated generator  530  generates a standard voltage Vbg, and the standard voltage Vbg is not only inputted into the reference voltage generator  540  to generate the reference voltage Vref, but is also linked to one end of the additional resistor Rref by way of the operational amplifierP to create a reference current Iref according to the voltage drop across Rref. That is, Iref=(Vcc-Vbg)/Rref. The reference current Iref flows through the transistor T and the resistor Rc, and generates a comparison voltage Vc. As mentioned above, the resistance values of Rc and Rf of the wave filter  520  have the same level of deviation from the designed values because both are fabricated in the same integrated circuit manufacturing process. By comparing the reference voltage Vref to the comparison voltage Vc, the resistance inaccuracies of the resistorRc and the resistor Rf of the wave filter  520  can be learned. The analog-to-digital converter  550  is used to compare the reference voltage Vref tothe comparison voltage Vc and to generate corresponding control signals to change the value of the variable capacitor  560  of the wave filter  520  to compensate for the the resistance inaccuracies.  
           [0008]    A shortcoming of the component inaccuracy correction system  510  is that both Vcc and Vbg are needed to create the standard current Iref. In some electronic devices, especially in portable electronic devices, the power supplied to the integrated circuit is generated by a battery. As battery power is consumed, the bias voltage Vcc deviates from a required value. In this situation, even though the regulated generator  530  may provide a stable voltage Vbg, the standard current Iref will nevertheless be incorrect. An incorrect reference current Iref with the resistor Rc will necessarily generate an incorrect comparison voltage Vc. When the analog-to-digital converter  550  compares the incorrect comparison voltage Vc to the correct reference voltage Vref, resistance inaccuracies cannot be properly corrected.  
         SUMMARY OF THE INVENTION  
         [0009]    It is therefore a primary objective of the present invention to provide a component inaccuracy correction system to solve the above-mentioned problem.  
           [0010]    In a preferred embodiment, the present invention provides a component inaccuracy correction system for correcting component inaccuracy in an integrated circuit. This component inaccuracy is caused by the fabrication process for making the component, which may cause characteristics of the component to deviate from an original design value. The component inaccuracy correction system has a current source capable of outputting two currents with a fixed ratio, a voltage dividing circuit formed on the integrated circuit having at least an output end capable of receiving a current of the current source to create and output a divided voltage, a reference voltage generator capable of receiving another current of the current source to create and output a reference voltage, a comparison circuit electrically connected to the output end of the voltage dividing circuit for receiving the divided voltage from the voltage dividing circuit and comparing the divided voltage to the reference voltage to create a corresponding comparison signal, and a correction circuit electrically connected to the comparison circuit for correcting the component inaccuracy on the integrated circuit according to the comparison signal generated by the comparison circuit.  
           [0011]    It is an advantage of the present invention that the component inaccuracy correction system uses a current generator to supply current respectively to an additional resistor and a set of series resistors so that the additional resistor and the series resistors generate a geometric ratio reference voltage and divided voltage to prevent the component inaccuracy correction system from incorrectly correcting resistance inaccuracies due to power changes.  
           [0012]    These and other objectives and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0013]    [0013]FIG. 1 is a circuit block diagram of a prior art component inaccuracy correction system used to correct resistance inaccuracy in a wave filter.  
         [0014]    [0014]FIG. 2 is a block diagram of the present invention component inaccuracy correction system used in a wave filter.  
         [0015]    [0015]FIG. 3 is a circuit diagram of the component inaccuracy correction system used in the wave filter as shown in FIG. 2.  
         [0016]    [0016]FIG. 4 is a functional relationship diagram of the resistance value of each node of a voltage dividing circuit of FIG. 3.  
         [0017]    [0017]FIG. 5 is a diagram of each correction circuit unit of FIG. 3 changing to ON or OFF according to related resistance inaccuracies. 
     
    
     DETAILED DESCRIPTION  
       [0018]    Please refer to FIG. 2. FIG. 2 is a block diagram of a present invention component inaccuracy correction system  10  for use with an RC wave filter  70 . The component inaccuracy correction system  10  comprises a current generator  20 . The current generator  20  generates two currents, which are respectively provided to a reference voltage generator  30  and a voltage dividing circuit  40 . The divided voltage of the voltage dividing circuit  40 , and the reference voltage generated by the reference voltage generator  30 , are respectively provided to two input ends of a comparison circuit  50 . A comparison result from the comparison circuit  50  is then provided to a correction circuit  60  such that the correction circuit  60  can correct the wave filter  70 . In the preferred embodiment, the correction circuit  60  is a variable capacitor electrically connected in parallel to the wave filter  70 . The comparison circuit  50  is an analog-to-digital converter for converting the signals from the voltage dividing circuit  40  into digital signals to control the correction circuit  60 . As shown in FIG. 2, the wave filter  70  comprises an operational amplifierQ, with the main wave filter components being a resistor Rf and a capacitor Cf. If the resistance of Rf deviates from the designed value due to deviations in the fabrication process, the product (Rf*Cf) of the resistance of Rf and the total capacitance of Cf with the variable capacitor in the correction circuit  60  is also affected. In other words, inaccuracy of the integrated circuit fabrication process changes the RC time constant of the wave filter  70 , and hence the bandwidth of the wave filter  70  is inaccurate. So the wave filter  70  does not work as originally designed. Consequently, the capacitance of the variable capacitor in the correction circuit  60  must be changed to compensate for the resistance inaccuracy of the resistor Rf so as to restore the bandwidth of the wave filter  70  to desired characteristics.  
         [0019]    Please refer to FIG. 3. FIG. 3 is a circuit diagram of the component inaccuracy correction system  10  for use with the wave filter  70  in this embodiment. The current generator  20  is a current mirror comprising two transistors MPA 11  and MPA 14 , both supplied with bias voltages of Vcc and VG 1 . The fabrication process technology for semiconductors ensures that the aspect ratio (i.e. W/L ratio) of the transistors MPA 11  and MPA 14  can be kept to M:N, so that the ratio of the currents respectively generated in both default working areas can also be kept to M:N. The reference voltage generator  30  comprises an additional resistor Rref. The additional resistor Rref is installed outside of the integrated circuit, and is electrically connected to the transistor MPA 14  of the current generator  20 , and to ground of the integrated circuit. Because the additional resistorRref is installed outside of the integrated circuit, the value of the resistance is not affected by fabrication inaccuracies of the integrated circuit manufacturing process. The inaccuracy of the resistance of such a discrete, external resistor can be between 1/1000 and 1/100 (i.e., between 0.1% and 1%), so the additional resistor Rref may serve as a standard to identify and quantify the resistance inaccuracy in the integrated circuit. The voltage across the additional resistor Rref is a reference voltage Vref.  
         [0020]    The voltage dividing circuit  40  of the present invention component inaccuracy correction system  10  is composed of a plurality of voltage dividing resistors. Please refer to FIG. 3. These voltage dividing resistors include R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 , and the nodes of the current input end of the voltage dividing resistors are respectively labeled L 15 , L 10 , L 05 , T 1 , H 05 , H 10 , and H 15 . The voltage dividing resistors R 2  to R 8 , and the resistor Rf of the wave filter  70 , are all built on the same integrated circuit, and are all fabricated in the same manufacturing process. Therefore, each voltage dividing resistor R 2  to R 8 , and the resistor Rf of the wave filter  70 , all suffer from the same resistance inaccuracy. In other words, for each resistor Rf and R 2  to R 8 , the ratio of its actual resistance to its designed resistance is fixed.  
         [0021]    As shown in FIG. 3, the comparison circuit  50  of the component inaccuracy correction system  10  comprises six comparators. Each of the six comparators has two input ends and one output end. These comparators compare the voltage of the two input ends and output a comparison result from the output end. In the six comparators of the comparison circuit  50 , the first input ends are respectively connected to the six nodes H 15 , H 10 , H 05 , L 05 , L 10 , and L 15  of the voltage dividing circuit  40 , and the second input ends are each connected to the reference voltage Vref generated by the reference voltage generator  30 . In other words, the six comparators compare the divided voltage of each node in the voltage dividing circuit  40  to the reference voltage Vref. In this manner, the comparison circuit  50  serves as an analog-to-digital converter circuit to convert the analog signals outputted from the voltage dividing circuit into suitable digital signals to control the correction circuit  60 .  
         [0022]    The output end of each comparator in the comparison circuit  50  is respectively electrically connected to one of a plurality of correction circuit units  65  in the correction circuit  60 . In the preferred embodiment, the correction circuit  60  comprises a plurality of correction circuit units  65  electrically connected in parallel with each other. Each of these correction circuit units  65  comprises a transistor S to serve as a switch, and a correction capacitor Δ C. The ON and OFF state of each transistor S is controlled by the output of the corresponding comparator in the comparison circuit  50 . If the transistor S of a correction circuit unit  65  is switched ON, the capacitor Δ C of the correction circuit unit  65  is placed in parallel with the capacitor Cf of the wave filter  70 . On the other hand, if the transistor S is OFF, the capacitor Δ C of the correction circuit unit  65  is electrically disconnected and so is not in parallel with the capacitor Cf of the wave filter  70 .  
         [0023]    This embodiment will be further described as illustrated in FIG. 4. FIG. 4 shows the relationship between the resistance value of each node H 15 , H 10 , H 05 , T 1 , L 05 , L 10 , L 15  in FIG. 3 and the relative resistance inaccuracies caused by the integrated circuit fabrication process. The relative resistance inaccuracy is defined as the ratio of the actual resistance variance of a resistor on the integrated circuit to the designed value of the resistance for this resistor. For example, when the resistance relative inaccuracy of a resistor is Δ (such as 5%), the actual resistance of the resistor is greater than the original design value by the factor Δ (i.e., by 5%). Ideally, the relative resistance inaccuracy caused by the fabrication process should be 0, in which case the divided voltage of the node T 1  is equal to the reference voltage Vref. Since the current ratio of the reference voltage generator  30  and the voltage dividing circuit  40  supplied by the current generator  20  is N:M, the total value of the resistance from the node T 1  to ground (i.e., R 2 +R 3 +R 4 +R 5 ) and the reference resistor Rref have the following relationship: M*(R 2 +R 3 +R 3 +R 5 )=N*(Rref). As shown in FIG. 4, when the relative resistance inaccuracy is 0, the total resistance from the node T 1  to ground exactly equals to (N/M)*Rref. In such a case, the total value of resistance between the nodes L 05  and ground is less than (N/M)*Rref. The total value of resistance between L 10  and ground, and between and L 15  and ground are also less than (N/M)*Rref. So the divided voltage of the nodes L 05 , L 10 , and L 15  is less than Vref. The output of the comparators electrically connected to the nodes L 05 , L 10 , and L 15  has a low potential (because the divided voltages of the three nodes are all less than Vref) so that the respective switches S are ON, and the respective capacitors Δ C in the corresponding correct circuit unit  65  are in parallel with the capacitor Cf in the wave filter. Meanwhile, in the above-mentioned situation, the total value of the resistance from the nodes H 15 , H 10 , and H 05  to ground will be greater than (N/M)*Rref, i.e. the divided voltages of the nodes H 15 , H 10 , and H 05  are all greater than Vref. The outputs of the comparators connected to the three nodes H 15 , H 10 , and H 05  have a high potential, and the respective switches S are OFF. The respective capacitors Δ C in the corresponding correct circuit unit  65  thus are electrically disconnected from being in parallel with the capacitor Cf. When the relative resistance inaccuracy is 0, the total value of the capacitance of the wave filter  70  with the correction circuit  60  is Cf+3 Δ C, and so the bandwidth of the wave filter  70  with the correction circuit  60  is the product of (Cf+3 Δ C) and Rf.  
         [0024]    When the inaccuracy caused by the fabrication process causes the resistance of each resistor to be greater than the original design value, the total value of the resistance of each node to ground is also greater, as shown in FIG. 4. Nevertheless, as previously mentioned, Rref is an additional resistor installed outside of the integrated circuit, so the resistance value of Rref is not affected by the inaccuracy of the integrated circuit fabrication process. The ratio of the two currents generated by the current generator  20  is also not affected by the resistance inaccuracy, so (N/M)*Rref serves as a stable comparison standard, shown as the horizontal dotted line in FIG. 4. If the inaccuracy caused by the fabrication process is between Δ and 2Δ, the voltage dividing circuit  40  causes the total resistance from the node L 05  to ground to be greater than (N/M)*Rref. The divided voltages of the nodes H 15 , H 10 , H 05 , and L 05  are all thus greater than Vref. The respective comparator connected to each of these nodes causes the switch S in the correction circuit unit  65  to turn OFF, and only the switches S in the correction circuit unit  65  connected to the nodes L 10  and L 15  are turned ON. Therefore, when the resistance inaccuracy is between Δ and 2Δ, the total capacitance of the wave filter  70  with the correction circuit  60  is Cf+2Δ C. In other words, when the inaccuracy caused by the fabrication process causes resistance values to be greater than the original designed resistance values, the present invention component inaccuracy correction circuit  10  causes the total value of the capacitance of the wave filter  70  to decrease so that the product of the resistance of the wave filter  70  with the total capacitance is within a limited range.  
         [0025]    When the resistance values of the nodes H 15 , H 10 , H 05 , L 05 , L 10 , and L 15  to ground are changed due to an increasing or decreasing of the relative resistance inaccuracy, the relationship diagram in FIG. 4 can be divided into eight areas labeled I to VIII. In each area, the corresponding ON/OFF states for the correction circuit unit  65  controlled by the comparators connecting to each node is listed in FIG. 5. In FIG. 5, if the comparator connecting to a node causes the corresponding switch S to be closed and the correction circuit unit  65  is electrically connected in parallel with the capacitor Cf, the corresponding switch S is labeled “ON”. If the comparator connecting to a node causes the corresponding switch S to be open and the correction circuit unit  65  is electrically disconnected from being in parallel with the capacitor Cf, the corresponding switch S is labeled “OFF”. In area I, all correction circuit units  65  are enabled, and so all capacitors Δ C are in parallel with Cf. The total value of the capacitance of the wave filter  70  with the correction circuit  60  is thus Cf+6Δ C. With comparison to FIG. 4, the value of the resistor Rf must be at least less than the original design value by 3Δ. Therefore, all correction circuit units  65  in the correction circuit  60  are enabled and electrically connected in parallel with the capacitor Cf so as to compensate for the low resistance of Rf.  
         [0026]    Similarly, in area II, the relative resistance inaccuracy is between −3Δ and −2Δ .  
         [0027]    Only the total resistance of the node H 15  with respect to ground is greater than (N/M) *Rref. The corresponding switch S for node H 15 , controlled by the corresponding comparator, is open so that the total capacitance of the wave filter  70  with the correction circuit  60  is Cf+5Δ C. In area III, the relative resistance inaccuracy is between −2Δ to −Δ, with four correction circuit units  65  enabled so that the total capacitance value of the wave filter  70  with the correction circuit  60  is Cf+4 Δ C.  
         [0028]    In area VII, the relative resistance inaccuracy is between 2Δ to 3Δ, with only one correction circuit unit  65  enabled. In this case, the resistor Rf, affected by the inaccuracies of the fabrication process to an excessive resistance value, is compensated for with the total capacitance of the wave filter  70  with the correction circuit  60  being reduced to Cf+Δ C. Finally, in area VIII, the relative resistance inaccuracy is over 3Δ, and so all correction circuit units  65  are disabled and electrically disconnected from being in parallel with Cf so that the total capacitance of the wave filter  70  with the correction circuit  60  is Cf.  
         [0029]    In short, the present invention component inaccuracy correction system  10  uses a current generator  20 , composed of current mirrors, to generate two output currents with a geometric ratio, which are then respectively input into the reference voltage generator  30  and the voltage dividing circuit  40 . Since the ratio of the two currents is fixed, the ratio of the reference voltage Vref generated by the reference voltage generator  30  with each divided voltage of the voltage dividing circuit  40  directly transfers to the ratio of the two corresponding resistances. The ratio of the two corresponding resistances may also be transferred to the ratio of the voltages. Since the resistor Rref of the reference voltage generator  30  is an additional, external resistor, whereas the voltage dividing resistors of the voltage dividing circuit  40  and the resistor Rf of the wave filter  70  all suffer from the same relative resistance inaccuracy, the resistance inaccuracy of each resistor caused by the fabrication process of the integrated circuit can be known by comparing the reference voltage of the reference voltage generator  30  with each divided voltage of the voltage dividing circuit  40 . The voltage difference caused by the resistance inaccuracy is compensated for by the comparator in the comparison circuit  50 , which controls the correction circuit  60 .  
         [0030]    The current generator of the present invention component inaccuracy correction system is composed of a current mirror. The current mirror is used to generate the reference voltage of the reference voltage generator  30  and each divided voltage of the voltage dividing circuit  40 . With this design, the present invention does not need a standard voltage and a bias voltage to generate a divided voltage for comparison, as is done in the prior art. This advantage makes the present invention useable in portable electronic products. These portable electronic products, such as cellular phones or notebooks, frequently use battery power to supply a bias voltage to the integrated circuit. As the power stored in the battery is gradually consumed, the bias voltage may drift from a designed value. In the case of an unstable power supply, prior art devices that require another system for a bias voltage to generate the divided voltage for comparison, may not function normally. In contrast to the prior art, in the present invention component inaccuracy correction system, the purpose of the current generator  20  is to supply two currents with a fixed ratio. The magnitude of the currents does not affect the operations of the component inaccuracy correction system, despite the fact that the bias voltage of the current mirror may change over time.  
         [0031]    As mentioned above, the present invention component correction system  10  compensates for resistance inaccuracies of a wave filter by changing the value of the capacitance of the wave filter. However, the functionality of the preferred embodiment is not limited to this. By changing the structure of the correction circuit  60 , the present invention may also be used in other embodiments. For example, more voltage dividing resistors in the voltage dividing circuit  40 , and more corresponding comparators and correction circuit units  65 , may be added if better accuracy is required. In this manner, the value (percentage) of Δ may be reduced. If the inaccuracy of the fabrication process can be controlled to a fixed range, the number of voltage dividing resistors and corresponding comparators and correction circuit units can also be reduced to reduce cost.  
         [0032]    Those skilled in the art will readily observe that numerous modifications and alternations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.