Bidirectional thermal trimming of electrical resistance

Abstract

There are described various methods and circuits for trimming the parameter value of a thermally mutable electrical component in two directions. A sequence of heat pulses is selected as a function of thermal history using an adaptive trimming algorithm, where parameters of the sequence of heat pulses are based on a resulting impact of previous heating pulses. Direction of trimming, trimming increment, and remaining trimming distance can all be used to determine the parameters of succeeding heat pulses, wherein the parameters of the pulses can be, for example, amplitude, duration, and time interval between pulses.

1 . An apparatus for adjusting a parameter of a resistor made from a thermally mutable material, the apparatus comprising:
 a substrate having a portion for thermally-isolating said resistor;   heating circuitry having a decision-making module for applying a sequence of heat pulses as a function of thermal history, said decision-making module applying an adaptive trimming algorithm where parameters of said heat pulses are selected based on a resulting impact of previous heating pulses, said resulting impact including a direction of trimming caused by said previous heating pulses; and   measuring circuitry for measuring said parameter of said resistor.   
   
   
       2 . An apparatus as claimed in  claim 1 , wherein said parameters of said heat pulses are amplitude, duration, and a time interval before a succeeding heat pulse. 
   
   
       3 . An apparatus as claimed in  claim 1 , wherein said parameter is resistance. 
   
   
       4 . An apparatus as claimed in  claim 1 , wherein said component is part of a bridge circuit and said parameter is a balanced state of said bridge circuit. 
   
   
       5 . An apparatus as claimed in  claim 1 , wherein said portion of said substrate comprises a thermally-isolated micro-platform for thermally-isolating said resistor. 
   
   
       6 . An apparatus as claimed in  claim 5 , wherein said heating circuitry comprises a heating element for heating said resistor. 
   
   
       7 . An apparatus as claimed in  claim 6 , wherein said heating element is on said thermally isolated micro-platform. 
   
   
       8 . An apparatus as claimed in  claim 6 , wherein said heating element is on a second thermally isolated micro-platform in close proximity to said resistor. 
   
   
       9 . An apparatus as claimed in  claim 1 , wherein said resulting impact also includes a trimming increment resulting from said previous heating pulses. 
   
   
       10 . An apparatus as claimed in  claim 1 , wherein said resulting impact also includes a remaining distance to a target parameter value. 
   
   
       11 . A method for trimming a parameter of a resistor made from a thermally mutable material to a target value, the method comprising:
 thermally-isolating said component on a portion of a substrate;   selecting a sequence of heat pulses as a function of thermal history using an adaptive trimming algorithm, where parameters of said sequence of heat pulses are selected based on a resulting impact of previous heating pulses, said resulting impact including a direction of trimming resulting from said previous heating pulses; and   applying said sequence of heat pulses to said component to trim to said target value.   
   
   
       12 . A method as claimed in  claim 11 , wherein said resulting impact also includes a trimming increment resulting from said previous heating pulses. 
   
   
       13 . A method as claimed in  claim 11 , wherein said resulting impact also includes a remaining distance to a target parameter value. 
   
   
       14 . A method as claimed in  claim 11 , wherein said parameters of said heat pulses comprise amplitude, duration, and time interval between succeeding heat pulses. 
   
   
       15 . A method as claimed in  claim 11 , wherein pulse amplitude is changed while pulse duration remains constant in a sequence of heat pulses having increasing amplitudes. 
   
   
       16 . A method as claimed in  claim 11 , wherein amplitude and duration vary in a sequence of heat pulses having decreasing amplitudes. 
   
   
       17 . A method as claimed in  claim 11 , wherein said parameters of said heat pulses are selected to optimize a total trimming time. 
   
   
       18 . A method as claimed in  claim 11 , further comprising regularly returning said resistor to a predetermined ambient temperature and measuring the parameter. 
   
   
       19 . A method as claimed in  claim 11 , wherein said sequence of heat pulses comprises heat pulses to trim said parameter value in a first direction and heat pulses to trim said parameter value in an opposite direction. 
   
   
       20 . A method as claimed in  claim 11 , wherein said resistor is provided on a thermally isolated micro-platform. 
   
   
       21 . A method as claimed in  claim 11 , wherein said resistor is provided on a thermally isolated micro-platform, and said heat pulses are directed to said micro-platform. 
   
   
       22 . A method as claimed in  claim 11 , wherein said resistor is made of polysilicon. 
   
   
       23 . A method as claimed in  claim 11 , wherein said parameter is resistance.