Abstract:
A structure and associated method to determine an actual resistance value of a calibration resistor within a semiconductor device. The semiconductor device comprises a capacitor, a calibration resistor, and a calibration circuit. A voltage applied to the calibration resistor produces a current flow through the calibration resistor to charge the capacitor. The calibration circuit is adapted to measure an actual time required to charge the capacitor. The calibration circuit is further adapted calculate an actual resistance value of the calibration resistor based on the actual time required to charge the capacitor and a capacitance value of the capacitor.

Description:
BACKGROUND OF INVENTION 
     1. Technical Field 
     The present invention relates to a structure and associated method to calibrate a plurality of resistors on a semiconductor device. 
     2. Related Art 
     Electronic components in a circuit typically require correct design values in order to perform a function correctly. Incorrect design values may cause a circuit to malfunction. Therefore there exists a need to provide correct design values in a circuit. 
     SUMMARY OF INVENTION 
     The present invention provides a semiconductor device, comprising: a capacitor, a calibration resistor, and a calibration circuit formed within the semiconductor device, wherein a voltage (Vin) applied to the calibration resistor is adapted to produce a current flow through the calibration resistor to charge the capacitor, wherein the calibration circuit is adapted to measure an actual time (t actual ) required to charge the capacitor, and wherein the calibration circuit is further adapted calculate an actual resistance value (R actual ) of the calibration resistor based on t actual  and a capacitance value (C) of the capacitor. 
     The present invention provides a calibration method, comprising: 
     providing a capacitor, a calibration resistor, and a calibration circuit formed within a semiconductor device; 
     providing a current flow through the calibration resistor to charge the capacitor; 
     measuring by the calibration circuit, an actual time (t actual ) required to charge the capacitor; and 
     determining by the calibration circuit, an actual resistance value (R actual) of the calibration resistor based on t actual  and a capacitance value (C) of the capacitor. 
     The present invention advantageously provides an apparatus and method to provide correct design values in a circuit. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 illustrates a block diagram of a semiconductor device comprising a circuit to determine a resistance value of a calibration resistor, in accordance with embodiments of the present invention. 
     FIG. 2 illustrates a variation of FIG. 1 showing a block diagram of a semiconductor device comprising a circuit to determine a resistance value of a variable calibration resistor, in accordance with embodiments of the present invention. 
     FIG. 3 is a flowchart depicting an algorithm for determining the expected resistance of the calibration resistor of FIG. 1, in accordance with embodiments of the present invention. 
     FIG. 4 is a flowchart depicting an algorithm for determining the expected resistance of the variable calibration resistor of FIG. 2, in accordance with embodiments of the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates a block diagram of a semiconductor device  1  comprising a circuit  2  to determine an actual resistance value (R actual ) of a calibration resistor  6 , in accordance with embodiments of the present invention. The circuit  2  is adapted to compare R actual  to an expected resistance (i.e., design resistance) value (R expected ) to determine a percentage of deviation of resistance R actual  from R expected  of the calibration resistor  6 . The semiconductor device  1  further comprises a plurality of resistors  5  located at a plurality of locations throughout the semiconductor device  1 . The plurality of resistors may be used for, inter alia, transistor biasing, phase lock loop (PLL) circuits, setting currents through charge pumps, input/output (I/O) interface circuits, digital to analog (D/A) convertors, etc. The percentage of deviation of resistance R actual  from R expected  of the calibration resistor  6  is is about equal (i.e., representative of) to a percentage of deviation of an actual resistance from an expected resistance of each of the resistance values of each of the plurality of resistors  5  within the semiconductor device  1 . R actual  and R expected  are calculated by determining a time (t) that it takes to charge a capacitor  8 . A voltage source  4  is activated to supply a voltage (Vin) to the calibration resistor  6  thereby producing a current flow through the calibration resistor  6 . The current flow through the calibration resistor  6  charges the capacitor  8 . A counter  22  using a sample clock  15  begins to count an actual time (t actual ) that it takes to charge the capacitor  8 . The rate of charge of the capacitor  8  is a function of a resistance value of the calibration resistor  6 . A charging voltage (V(t)) applied to a first input  24  of a comparator  10  increases as a function of time by the following charging equation: V(t)=Vin (1−e −t/R*C ). C in the equation is a capacitance value of the capacitor  8 . Therefore, variations of R actual  from R expected  will result in variations in the rate of charging of the capacitor  8 . A band gap reference generator  12  applies a reference voltage (Vref) to a second input  26  of the comparator  10 . Vref must be less than Vin in order for the comparator  10  to be activated. When Vref is equal to V(t) the comparator  10  is activated thereby sending a signal over link  28  to a time comparison circuit  20 . The time comparison circuit  20  compares the actual time (t actual ) that it took for the comparator to turn on to an expected time (t expected ). An expected time calculation circuit  18  calculates t expected  using the charging equation: V(t)=Vin (1−e −t/R*C ), plugging in R expected  for R, plugging in Vref for V(t), and solving for t. The expected time calculation circuit  18  transmits t expected  over link  30  to the time comparison circuit  20 . The magnitude and direction (i.e., positively or negatively) of the offset between t actual  and t expected  indicates the magnitude and direction (i.e., positively or negatively) of the percentage of deviation of resistance of R actual  from R expected  using the charging equation. If the capacitor  8  is charged more quickly than expected then R actual  is less than R expected . If the capacitor  8  is charged more slowly than expected then R actual  is greater than R expected . The time comparison circuit  20  transmits a signal (R-code) representing the time difference between t actual  and t expected  (i.e., the percentage of deviation of resistance of R actual  from R expected ) to any circuitry within the semiconductor device  1  comprising any of the plurality of resistors  5 . The percentage of deviation of resistance R actual  from R expected  of the calibration resistor  6  is is about equal to the percentage of deviation of an actual resistance from an expected resistance of each of the resistance values of each of the plurality of resistors  5 . Thus, the R-code is used to determine a change of resistance for each of the plurality of resistors  5  in order to bring each of the plurality of resistors  5  to an expected resistance. The semiconductor device  1  further comprises a bank of precision resistors  11 . Each precision resistor of the bank of precision resistors  11  is adapted to be connected in series or in parallel with each resistor of the plurality of resistors  5  such that a resistance value of a combination of a first resistor of the plurality of resistors  5  and at least one resistor of the bank of resistors  11  equals an expected resistance value of the first resistor. Each precision resistor of the bank of precision resistors  11  is adapted to be connected in series with a resistor of the plurality of resistors  5  if R actual  is less than R expected . Each precision resistor in of the bank of precision resistors  11  is adapted to be connected in parallel with a resistor of the plurality of resistors  5  if R actual  is greater than R expected . The bank of precision resistors are not utilized if R actual  equals R expected . Each resistor of the bank of resistors  5  may be connected with a resistor of the plurality of resistors  5  by any method known to a person of ordinary skill in the art including, inter alia, selectively opening or closing gates or blowing efuses to trim resistors in parallel or in series with the plurality of resistors, use of a variable field effect transistor type resistors, etc. The calibration resistor  6  may be permanently removed from the semiconductor device  1  after the R code determines the change of resistance value for each of the plurality of resistors  5 . Each of the plurality of resistors  5  may comprise a resistance value that is not equal to a resistance value of the calibration resistor  6 . 
     FIG. 2 illustrates a variation of FIG. 1 showing a block diagram view of a semiconductor device  65  comprising a circuit  42  to determine an actual resistance value (R actual ) of a variable calibration resistor  50 , in accordance with embodiments of the present invention. The circuit  42  determines a percentage of deviation of resistance R actual  from an expected resistance value (R expected ) of the variable calibration resistor  50  using much of the same circuitry as the circuit  2  of FIG.  1 . In contrast with FIG. 1, the circuit  42  comprises a feedback loop  44  to iteratively and continuously adjust a resistance of the variable calibration resistor  50 . This embodiment allows for adjusting resistance values (i.e., resistance value of the variable calibration resistor  50  or resistance values of each of the plurality of resistors  5 ) due to temperature fluctuations. The variable calibration resistor  50  may be, inter alia, a series of resistors with a bypass gate in parallel with all but one of the resistors. At the conclusion of a first iteration, some or all of the bypass gates could be open and some or all of the bypass gates could be closed. If the capacitor  8  is charged more quickly than expected then R actual  is less than R expected  (as described in the description of FIG. 1) and an additional bypass gate would be opened thereby adding resistance by adding a gate in series. If the capacitor  8  is charged more slowly than expected then R actual  is greater than R expected  (as described in the description of FIG. 1) and an additional gate would be closed thereby lowering the resistance by allowing a bypass to a resistor. When the comparator  10  is activated thereby sending the signal over link  28  to the time comparison circuit  20  (as described in the description of FIG.  1 ), the comparator  10  also sends the signal over link  46  to a reset circuit  40 . The reset circuit  40  is adapted to disable the voltage source  4  while discharging the capacitor  8  so that t actual  (i.e., the capacitor  8  charge time) and R actual  may be determined again. As described supra in the description of FIG. 1, the time comparison circuit  20  transmits the signal (R-code) representing the time difference between t actual  and t expected  (i.e., the percentage of deviation of resistance of R actual  from R expected ) to any circuitry within the semiconductor device  65  comprising any resistor of the plurality of resistors  5 . The percentage of deviation of resistance R actual  from R expected  of the variable calibration resistor  50  is is about equal to the percentage of deviation of an actual resistance from an expected resistance of each of the resistance values of each of the plurality of resistors  5 . Thus, the R-code is used to determine a change of resistance for each of the plurality of resistors  5  in order to bring each of the plurality of resistors  5  to an expected resistance. The R-code is also used to determine a change of resistance for the variable calibration resistor  50  in order to bring a resistance value of the variable calibration resistor  50  to R expected . The circuit  42  iteratively and continuously determines R-code so that the resistance value R expected  of the variable calibration resistor  50  and the resistance value of each resistor in the plurality of resistors within the semiconductor device  65  may be continuously adjusted to bring a resistance of the variable calibration resistor  50  to R and a resistance value of each of expected the plurality of resistors to an expected resistance thereby accounting for any resistance changes due to environmental factors such, as inter alia, temperature fluctuations within the semiconductor device  65 . 
     FIG. 3 is a flowchart depicting an algorithm  66  to determine the actual resistance value (R actual ) of the calibration resistor  6  of FIG. 1, in accordance with embodiments of the present invention. In step  67 , the voltage source  4  is activated and a current flow through the calibration resistor  6  charges the capacitor  8 . In step  68  while the capacitor  8  is charging, the sample clock  15  and the counter  22  count the capacitor  8  charge time (t actual ). If Vref does not equal V(t) in step  69 , then the capacitor  8  is not yet sufficiently charged and step  68  is repeated. If Vref does equal V(t) in step  69 , then the capacitor  8  is charged and the comparator  10  is activated in step  71 . In step  73 , the calculated expected charge time (t expected ) from the calculation circuit  18  is compared to t actual  and the difference is used to determine the percentage of deviation of resistance R actual  from R expected  of the calibration resistor  6  in step  75 . In step  77 , the percentage of deviation of resistance R actual  from R expected  of the calibration resistor  6  about equals a percentage of deviation of an actual resistance from an expected resistance of each of the resistance values of each of the plurality of resistors  5  within the semiconductor device  1 . Thus, a signal (R code) representing the percentage of deviation is sent to any circuits on the semiconductor device  1  that comprise at least one of the plurality of resistors  5 . In step  79 , a first resistor of the plurality of resistors  5  is combined (i.e., in parallel or series) with at least one resistor of the bank of resistors  11  such that the combination equals an expected resistance value of the first resistor of the plurality of resistors  5 . 
     FIG. 4 is a flowchart depicting an algorithm  80  for determining the actual resistance value (R actual ) of the variable calibration resistor  50  of FIG. 2, in accordance with embodiments of the present invention. In step  81 , the voltage source is activated and a current flow through the variable calibration resistor  50  charges the capacitor  8 . In step  82  while the capacitor  8  is charging, the sample clock  15  and the counter  22  count the capacitor  8  charge time (t actual ). If Vref does not equal V(t) in step  84 , then the capacitor  8  is not yet sufficiently charged and step  82  is repeated. If Vref does equal V(t) in step  84 , then the capacitor  8  is charged and the comparator is activated in step  85 . In step  87 , the calculated expected charge time (t expected) from the calculation circuit  18  is compared to t actual  and the difference is used to determine the percentage of deviation of resistance R actual  from R expected  of the variable calibration resistor  50  in step  88 . The percentage of deviation of resistance R actual  from R expected  of the variable calibration resistor  50  about equals a percentage of deviation of an actual resistance from an expected resistance of each of the resistance values of each of the plurality of resistors  5  within the semiconductor device  65 . Thus, a signal (R code) representing the percentage of deviation is sent to any circuits on the semiconductor device  65  that comprise at least one of the plurality of resistors  5  in step  89 . In step  89 , the R code is also sent to the variable calibration resistor  50 . In step  91 , a first resistor of the plurality of resistors  5  is combined (i.e., in parallel or series) with at least one resistor of the bank of resistors  11  such that the combination equals an expected resistance value of the first resistor of the plurality of resistors  5 . In step  91 , a second resistor of the plurality of resistors  5  is combined (i.e., in parallel or series) with the variable calibration resistor  50  such that the combination equals R expected  of the variable calibration resistor  50 . In step  92 , the circuit  42  is reset by disabling the voltage source  4  while discharging the capacitor  8  and upon said discharging the voltage source is enabled so that the charge time of the capacitor  8  may be determined again. The circuit  42  iteratively and continuously determines the R-code so that the resistance value R actual  of the variable calibration resistor  50  and the resistance values of the plurality of resistors within the semiconductor device  65  may be continuously adjusted to bring the variable calibration resistor  50  and the plurality of resistors to an expected resistance thereby accounting for any resistance changes due to environmental factors such, as inter alia, temperature fluctuations within the semiconductor device  65 . 
     While embodiments of the present invention have been described herein for purposes of illustration, many modifications and changes will become apparent to those skilled in the art. Accordingly, the appended claims are intended to encompass all such modifications and changes as fall within the true spirit and scope of this invention.