Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01C—RESISTORS
  • H01C17/00—Apparatus or processes specially adapted for manufacturing resistors
  • H01C17/22—Apparatus or processes specially adapted for manufacturing resistors adapted for trimming
  • H01C17/232—Adjusting the temperature coefficient; Adjusting value of resistance by adjusting temperature coefficient of resistance
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01C—RESISTORS
  • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
  • H01C7/06—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material including means to minimise changes in resistance with changes in temperature

Definitions

• the invention relates to resistors and resistor networks which are electro-thermally trimmable, and more specifically, to thermal trimming of these resistors to adjust resistance, temperature coefficient of resistance and relative temperature coefficient of resistance.
• resistors In working with resistors referred to as “precision resistors", it is advantageous to have the capability to precisely adjust the resistance value. It is also advantageous to precisely adjust the temperature coefficient of resistance (TCR) of such a resistor.
• TCR temperature coefficient of resistance
• the bulk resistor material remain substantially constant during this trimming process, since only the shapes of the resistor portions are being trimmed.
• Another non-laser trimming technique is known to adjust the resistance of thin film resistors. This technique is based on thermal trimming of a resistor
• Resistor trimming is achieved by heating using electric current pulses passed through the resistor itself or through an adjacent auxiliary heater (US Patents 4210996, 5635893,
• thermal trimming directly modifies the 0 physical properties of the material such as resistivity and TCR.
• TCT Temporal Coefficient of Trimming
• Non-zero TCT generates a new problem (not existing in typical cutting- based trimming techniques), which can be illustrated by the following example.
• a resistor divider consisting of two trimmable resistors with 14836-19PCT
• TCT ⁇ OOOppm/K/trim-fraction. If the resistance ratio is adjusted by trimming one of the resistors "down” by 10%, the accompanying change in relative TCR (RTCR) may reach 200ppm/K. While resistance matching can potentially be done very precisely using thermal 5 trimming (better than 0.01 -0.1%), variation of ambient temperature in the range of ⁇ 50°C can make the divider voltage very unstable, with resistance ratio drift reaching ⁇ 1 %.
• near-zero TCR of the resistor is often desirable because it gives near-zero resistance drift with variation of ambient temperature, resistance 0 modulation due to self-heating in operation also should be minimized to avoid signal distortions in analog circuits.
• One of the problems of compound resistors consisting of two portions with positive and negative TCR is that near-zero TCR of the whole resistor does not mean zero resistance modulation due to self-heating.
• a compound resistor with the 5 first portion having resistance of 1 OK ohm and TCR of 100ppm/K and the second portion (connected in series) having resistance of 1 K ohm and TCR of -1000ppm/K has zero net TCR.
• Electric current passing through the compound resistor results in power dissipated in the first portion 10 times higher than in the second portion. If the thermal isolation of the two portions is 0 the same, the first portion is heated to a temperature rise 10 times greater than the second. Assume that the overheating temperature of the first portion is 10 0 C and the overheating temperature of the second portion is 1 0 C. As a result, the first resistance increases by 0.1 % or 10 Ohm while the second resistance decreases by 0.1 % or 1 Ohm. Absolute resistance change of the 5 compound resistor equals 9 Ohm. The same relative resistance change of two portions gives a different absolute change of their resistance values. As a result, the total resistance will no longer be constant.
• An embodiment of the present invention compensates (or minimizes) RTCR (TCR mismatch) resulting from non-zero TCT of a thermally trimmable resistor network by constructing a compound resistor from at least two 5 resistive portions having different resistance and TCR values.
• An embodiment of the present invention achieves independent adjustment of resistance ratio and RTCR of a thermally trimmable resistor network, the RTCR being adjusted to near-zero or intentionally to a non-zero value.
• a trimmable resistor network with adjustable non-zero RTCR can be o used in various different applications where temperature drift of circuit parameters (offset, gain, sensitivity and others) is needed.
• An embodiment of the present invention reduces the influence of self- heating on resistance modulation of a compound resistor containing two portions with positive and negative TCR.
• a method for providing a trimmable resistive component having a predetermined behavior of temperature coefficient of resistance (TCR) as a function of trimming comprising: selecting materials to form a compound resistor having at least a first portion and a second portion, at least 0 said first portion including a first resistor that is thermally trimmable and has a first resistivity, a first temperature coefficient of resistance value ⁇ 0 , and a value of trimming-induced shift of temperature coefficient ⁇ x , which defines a change in said ⁇ 0 per fraction of trimming x of said first resistivity, said second portion including at least a second resistor having a second resistivity value, 5 and a second temperature coefficient of resistance value ⁇ 0 ; determining how said TCR value of said resistive component changes as at least said first portion is trimmed, by generating a function of said TCR versus trim-fraction x, with Ri and R 2 as variable parameters and ⁇ 0 ,
• a trimmable resistive component having a predetermined behavior of temperature coefficient of resistance (TCR) as a function of trimming comprising: a first portion composed of a first resistor that is thermally trimmable and has a first resistivity, a first temperature coefficient of resistance value ⁇ 0 , and a value of trimming-induced shift of temperature o coefficient ⁇ ⁇ , which defines a change in said ⁇ 0 per fraction of trimming x of said first resistivity; and a second portion composed of at least a second resistor having a second resistivity value and a second temperature coefficient of resistance value ⁇ 0 , said first portion and said second portion having specific values for Ri and R 2 or Ri/R 2 to provide said compound 5 resistor with said predetermined behavior of said TCR value; wherein said predetermined behavior of said TCR is defined by a function of said TCR versus trim-fraction x, with R 1 and R 2 as variable parameters and ⁇ 0 , ⁇ o,
• an application specific circuit having an adjustable parameter of the circuit and an adjustable temperature coefficient of said parameter, the circuit comprising: at least one compound resistor including: a first portion composed of a first resistor that is thermally trimmable and has a first 5 resistivity, a first temperature coefficient of resistance (TCR) value ⁇ o, and a value of trimming-induced shift of temperature coefficient ⁇ x , which defines a change in said ⁇ 0 per fraction of trimming x of said first resistivity; and a second portion composed of a second resistor having a second resistivity value and a second TCR value ⁇ 0 , said first portion and said second portion 14836-19PCT
• circuit shown in figure 23a can be implemented with an Ri_comp and R 2 _com P as per the prior art.
• trimming algorithms such as those disclosed in PCT publications WO04/097859, WO04/097860, and
• WO04/083840 are used.
• control circuitry such as that described in 5 PCT publications WO03/023794 and WO04/097859 to trim resistors is also preferred.
• a method for providing a resistor having a predetermined resistance value and temperature coefficient of resistance value comprising: providing a trimmable resistive component having a predetermined behavior of temperature coefficient of resistance (TCR) as a function of trimming, the method comprising: selecting materials to form a compound resistor having at least a first portion and a second portion, at least said first portion including a first resistor that is thermally trimmable and has a 5 first resistivity, a first temperature coefficient of resistance value ⁇ 0 , and a value of trimming-induced shift of temperature coefficient ⁇ ⁇ , which defines a change in said ⁇ 0 per fraction of trimming x of said first resistivity, said second portion including at least a second resistor having a second resistivity value, 14836-19PCT
• An embodiment of the present invention can be used for making precision adjustable resistors and resistor networks. Electro-thermal trimming used for the adjustment in general changes not only resistance value but also TCR of trimmable material. The proposed solutions allow the designer/user to achieve:
• compound resistor is to be . understood as a resistor composed of more than one identifiable resistor, which can have the same or different resistances, resistivity, sheet resistances, trim amounts, and other 5 physical properties.
• a “resistive component” can be a single resistance, a network of resistances, multiple resistances where some of the multiple resistances are 14836-19PCT
• the analysis done to generate the function can be numerical (when 5 computer-based simulation tools are used), analytical (based on classic electricity laws), or experimental (when set of curves TCR(x) is generated experimentally) and should not be limited to any one of these techniques.
• basic electrical laws to be used in generating the function as described above can o be Ohm's Law (relating current, voltage and resistance in a resistor), Kirchoff's current law (for summing of currents at a node), Kirchoff's voltage law (regarding the sum of voltages around a closed electrical loop), and equations describing how the, component values of electrical components (e.g. resistance) vary with temperature.
• resistivity units: ohm-cm
• sheet resistance units: ohms/square
• trim-fraction and “fraction of trimming” are used interchangeably to mean the fraction of the as-manufactured resistance by which the trim reduces the resistance.
• Fig. 1 is a schematic of a compound resistor consisting of two parts connected in series, as per an embodiment of the present invention
• Fig. 2 is a comparative graph of the TCR of a single trimmable resistor
• Fig. 3 is a graph showing TCR of a compound resistor configured as shown in Fig. 1 vs. relative trimming of its resistance value, for several different ratios of R ⁇ i/Rio,
• Fig. 4 is a schematic of a compound resistor in a parallel configuration, as per another embodiment of the present invention.
• Fig. 5 is a comparative graph of the TCR of a single trimmable resistor R 1 and the TCR of a compound resistor as in fig 4;
• Fig. 6 is a graph which shows the dependence of the TCR of a 0 compound resistor R COm p, composed of two trimmable portions in series, Ri(x), R 2 (W, as a function of relative trimming of the compound resistor;
• Fig. 7 shows a series connection of two compound resistors, each compound resistor consisting of two trimmable resistors; 14836-19PCT
• Fig. 8 shows a series connection of a compound resistor as in Fig. 1 , along with a third resistor which is trimmable;
• Fig. 9 shows an alternative circuit configuration for a compound resistor, with two resistors forming the first portion and one resistor forming 5 the second portion;
• Fig. 10 shows a full Wheatstone bridge, R b1 , Rb ⁇ , Rb3, Rb4, each with a trimmable compound resistor, R comp i, Rcomp ⁇ , Rcom P 3, Rcom P 4, connected in parallel, and a simplified representation where each bridge resistor and its associated compound resistor is combined and represented as Rb_compi, 0 rib_comp2, r ⁇ b_comp3, r ⁇ b_comp4,
• Fig. 11 shows two different configurations of trimmable compound resistors, one where Ri(x) and R ⁇ iy) are connected in series, and the other where Ri(x) and R 2 (y) are connected in parallel;
• Fig. 12 is a graph of overall TCR of an example of one Rb_com P 5 compound resistor having a series connection, as a function of its own normalized resistance, as one of the trimmable portions is trimmed down, where trimming R 2 (y) increases the TCR while trimming Ri(x) decreases the
• Fig. 13 is a graph of overall TCR of an example of one Rb_ C omp 0 compound resistor having a series connection, as a function of its own normalized resistance, as one of the trimmable portions is trimmed down, where trimming R 2 (y) changes the TCR by a much larger amount than does trimming Ri(x);
• Fig. 14 is a graph of overall TCR of an example of one Rb_ C o mP 5 compound resistor having a series connection, as a function of its own normalized resistance, as one of the trimmable portions is trimmed down, 14836-19PCT
• trimming R 1 (X) decreases the TCR by a larger amount than the increase caused by trimming R 2 (y);
• Fig. 15 is a graph of overall TCR of an example of one Rb_com P compound resistor having a parallel connection, as a function of its own
• Fig. 16 is a graph of overall TCR of an example of one Rb_com P compound resistor having a parallel connection, as a function of its own 0 normalized resistance, as one of the trimmable portions is trimmed down, where the magnitudes of the changes in TCR are smaller than those in figure
• Fig. 17 is a graph of overall TCR of an example of one Rb_com P compound resistor having a parallel connection, as a function of its own 5 normalized resistance, as one of the trimmable portions is trimmed down, where trimming R 2 (y) causes a larger increase in TCR than the decrease in
• Fig. 18 shows the trimming behavior of one compound resistor Rb_co mP having several different values of the nominal TCR ( ⁇ b ) of the bridge resistor 0 (R b ), where the changes in TCR and relative resistance remain almost the same, for the three different values of yS ⁇ ;
• Fig. 19 shows a scheme of TCR compensation of the bridge as a whole, where the trimmable compound resistor R 5 is connected in parallel with the whole bridge, such that it experiences the entire voltage applied to the 5 bridge, U b ⁇
• Fig. 20 shows an example of trimming the TCR of the overall bridge using resistor R 5 , connected in parallel with the entire bridge; 14836-19PCT
• Fig. 21 shows another scheme of TCR compensation of the bridge as a whole, where the trimmabie compound resistor Re is connected in series with the whole bridge, such that it experiences the same current as that applied to the bridge;
• Fig. 22 shows the temperature coefficient of bridge voltage (upper graph), and the ratio Ut/U (lower graph, where U is the excitation voltage of the circuit shown in Fig. 21), as functions of normalized resistance of the trimmabie resistor R 6 (x)from Fig. 21 ;
• Fig. 23a shows a schematic of a single module containing a resistor o bridge with two trimmabie compound resistors Ri_ CO m P and R2_com P on one side of the bridge, and an amplifier having gain and
• Fig. 1 shows a schematic of the compound resistor consisting of two parts connected in series, a trimmabie resistor Ri with TCR ceo, negative TCT 0 ⁇ i and ballast resistor R ⁇ o (non-trimmable) with TCR ⁇ o.
• resistor Ri is trimmabie in the range of +15% from its middle resistance value R ⁇ 0 :
• R 1 (X) R 10 (I + X) (1) .
• the resistance and TCR of the compound resistor can be expressed as:
• Fig 2 depicts the TCR of a single trimmable resistor Ri and the TCR of a compound resistor (such as shown in Fig. 1 ), as a function of resistance trimming relative to its middle value RIQ.
• the resistance 5 value of the resistor R 2 used for TCT compensation was calculated from eq.
• TCT compensation for a resistor having negative TCT is possible only in the case when the ballast resistor R 2 o has a more negative TCR than the trimmable resistor.
• ⁇ o -12OOppm/K
• ⁇ -3000ppm/K/trim-fraction and /? 0 ⁇ -4200ppm/K.
• a simple guideline for this is to use resistor materials with low TCT ⁇ i and high TCR difference a 0 - ⁇ o.
• Application-specific cases where an intentionally narrow trimming range of the compound resistor is needed also may exist. Equations (4,5) can be used to make a proper choice of the 5 resistor materials.
• Fig. 3 is a graph which shows the TCR of the compound resistor vs. relative trimming of its resistance value.
• a procedure for implementing an embodiment of the method of the present invention is as follows (for a circuit as shown in Fig. 1):
• the materials are chosen for the two portions of the resistor (with specific sheet resistance and TCR for both portions, and TCT for the first 0 portion).
• the as-manufactured resistance ratio of two portions is defined (based on the known sheet resistances, TCR's and TCT), such that the compound resistor reaches ideal TCT-compensation (defined by eq.(4)) 5 approximately at the middle of the desired trimming range, thus providing relatively "flat" TCR vs. trimming in that entire desired trimming range.
• the resistive portions are distributed 5 within the chip (and/or suspended microstructures) such that their thermal isolation provides self-heating of two portions (with positive and negative TCR) such that the net resistance modulation is minimized in operation.
• Fig. 4 shows the schematic of the analogous compound resistor with two resistive parts connected in parallel.
• the resistance of the compound 0 resistor and its TCR can be found as:
• the compound resistor has a trimming range narrower than that of a 0 single trimmable resistor by a factor of k/(1+k). Therefore, to maintain a substantial trimming range for the compound resistor, it is again preferable to choose materials with high TCR difference ⁇ o-ao so as to maximize the parameter k. 14836-19PCT
• Fig. 5 plots the TCR of a single trimmable resistor R 1 and the TCR of a compound resistor composed of two resistors connected in parallel, as a function of resistance trimming relative to its middle value R 10 .
• the resistance value of the resistor R ⁇ o used for TCT compensation and calculated from eq. (7) equals 0.6R 10 .
• the described compound trimmable resistors with compensated TCT can be used in designing various resistor networks.
• a resistor divider can be built from two TCT-compensated trimmable resistors. Resistance ratio adjustment of this divider can be performed with near-zero RTCR variations as will be explained further below.
• thermally mutable materials for example polysilicon doped with different types of dopants, may have significantly different TCT.
• polysilicon doped with Boron has much lower TCT than poiysilicon doped with Arsenic (D. Feldbaumer, J. Babcock, C. Chen, Pulse Current Trimming of Polysilicon Resistors, Trans, on 0 Electron Devices, vol. 42 (1995), pp. 689-696).
• Polysilicon samples doped with one type of dopant but at different doping levels also may have different TCT (US patent 6306718).
• Thermally trimmable single resistors with different TCR and TCT are proposed to be used in a compound resistor to provide independent 5 adjustment of resistance value and TCR.
• Fig. 6 shows the dependence of the TCR of this series-connected compound resistor R C om P as a function of its relative trimming.
• resistor R 1 (X) is trimmed by fraction x
• the TCR of the compound resistor remains 0 almost constant while its total resistance, f? comp , changes.
• trimming of the resistor R 2 (y) by fraction y results in a significant change in the TCR of Rcomp, with a slope of approximately -40ppm/K per 1 % of trimming of the compound resistor, or -13ppm/K per 1 % of trimming of the resistor R 2 .
• the possibility of trimming the resistance value of the compound resistor with 5 different slopes of TCR vs. R COm p trimming fraction is useful " for building resistor networks with independent adjustment of resistance ratio and RTCR.
• Resistors R 11 and R 21 are the "first" resistors within each of the two compound resistors, and are made from the same material with resistance where X 1 and X 2 are relative trimming fractions for each of the "first" resistors in each compound pair.
• the resistance and TCR of resistors R 12 5 and R 22 (the "second" resistors in each compound pair), can be expressed as where y 1 and y 2 are relative trimming fractions for each of the "second" resistors in each compound pair.
• R 2comp R 1 (1 + ⁇ 2 ) + R 2 (1 + y 2 ) (9c)
• Resistor R 22 (whose trimming significantly changes the TCR of the compound resistor), can be used for this purpose.
• the trimming targets are farther deviated from the initial conditions, as compared to the four previous examples. The same resistor positions were chosen for trimming as in the previous examples.
• the necessity to adjust the resistance ratio of two trimmable 5 resistors and their RTCR may exist not only for the resistor divider circuit as described in the examples, but also for other resistor networks where two trimmable resistors are not necessarily connected in series.
• the principle of the adjustment of such a circuit remains the same as described in the examples 1 - 8.
• the overall circuit output may depend on (a) 0 ratio(s) (or relationship) of a number of resistors, not necessarily in a simple series or parallel combination (not necessarily connected directly to each other). The main idea is that the compound resistor behaves differently when we trim one or the other, provided that they have different TCT.
• Fig. 8 shows a schematic of a resistor divider consisting of a compound 5 TCT-compensated trimmable resistor R C om P plus a single trimmable resistor
• R 3 connected in series.
• the circuit can be used in applications where one needs essentially non-zero RTCR of the voltage divider.
• 14836-19PCT 14836-19PCT
• the divider 0 resistance ratio can be adjusted by trimming of the TCT-compensated compound resistor R? comp without significant RTCR changes, as was described above (e.g. in Fig. 6).
• the as-manufactured resistance value of R 3 should be chosen intentionally 10% higher, so that subsequent 5 trimming down by -10% allows both the required RTCR adjustment and the required, resistance ratio.
• the present invention is suitable in a broad range ' of cases where thermal trimming of thermally-mutable resistance is possible. This does not necessarily require special thermal isolation of the resistors beyond what 0 is typically found in standard integrated circuit host processes.
• the present invention does not necessarily require bidirectional trimming, and can function effectively even if individual resistors are trimmed largely only in a downward direction. It can also function effectively in cases where the range is limited for trimming upwards from a trimmed-down value. Since thermal trimming is 5 typically much faster in the downward direction than in the upward direction, the required trim signals may be short enough that special thermal isolation is
• the available trimming precision and efficiency may be enhanced by using devices having greater thermal isolation. However this raises the question of self-heating of the trimmable resistors during operation.
• the analysis below addresses accompanying techniques for managing resistance
• AT 1 and AT 2 are overheating temperatures of each of the two 5 portions due to power I 2 R 1 and / 2 R 2 dissipated in them.
• a practical example of a specially designed TCT-compensated compound resistor with near-zero TCR and near-zero resistance modulation due to self-heating may be constructed as follows.
• a compound resistor with parameters analogous to those given in examples 5 - 8 is chosen 5
• Fig. 8 shows one possible configuration of the compound resistor.
• the first portion R ? consists of two sub-portions, each having resistance R/2. In this case, each sub-portion, and the second portion R 2 , have the same thermal isolation. This condition is fulfilled if all three parts of the compound 0 resistor have approximately the same area, and their thermal contact with the substrate or other heat sink is the same.
• microstructures such as MEMS-type structures, such as those seen in PCT publication PCT/CA02/01366, it is preferable to use identical supporting microstructures with the same thermal isolation from the substrate. Electric 5 current passing through the series connection heats all three parts up to the 14836-19PCT
• the power dissipated in the first portion is twice as great as that dissipated in the second portion.
• the overall thermal isolation of the resistor R 1 needed to be two times lower than the thermal isolation of resistor R ⁇ .
• the negative shift of 5 resistance R 2 is twice as great as the positive shift of each of two sub-portions of the resistor R 1 .
• the net resistance deviation of the compound resistor remains zero even when operated at varying power levels.
• the single resistor R 2 in the compound resistor shown in Fig. 9 can be trimmable ("active") or not ("passive").
• the invention can be used in a variety of applications, such as for zero compensation of a Wheatstone bridge.
• a Wheatstone bridge built from four resistors (which are commonly all nominally equal, but which may not be in some configurations).
• R b each of the equal resistors
• "Zero offset" of a Wheatstone bridge can be translated into a relative resistance mismatch ⁇ R t /R b , of one of the four resistors, and a mismatch of the TCR of that resistor with respect to the others (which nominally have identical TCR's). If the voltage drop across the entire bridge is U, and one of the four nominally-identical resistors has an undesired 0 resistance shift of ⁇ R b , then the zero offset is equal to:
• the scheme depicted in Fig.10 is an example of the invented method applied for zero compensation (compensation of zero offset and temperature coefficient of zero offset) of the Wheatstone bridge.
• Four trimmable compound resistors R ⁇ m P i, Rcomp ⁇ , Rcom P 3, Rcomp4 are each connected in parallel to the corresponding bridge resistors RM, Rb ⁇ , Rb3, Rw-
• Each pair of resistors thus o forms a new compound resistor, represented in the figure by R b _co mP i, ⁇ b_comp2, ⁇ ⁇ b_comp3 ⁇ r ⁇ b_comp4-
• trimmable compound resistors each consisting of two trimmable portions Ri(x) and R 2 (Y) made from different materials (where x and y are the trimming fractions of each 5 single resistor within a compound resistor). These portions can be connected in series or in parallel, as shown in Fig. 11. Each resistive portion is independently trimmable:
• R 1 (X) R 10 (H- X) (17a)
• R 2 (y) R 20 (I + y) (17b) where R 10 and R 20 are as-manufactured resistance values.
• Rb_comp as a function of its own normalized resistance (R_,_ comp ).
• R b by itself
• R COmP normalized resistance
• the overall TCR of the resultant R b _co mP is approximately 1275ppm/K.
• the resistance value of the compound resistor, R comp is approximately 5 times (Figs. 12 and 13), and 0 10 times (Fig. 14), greater than the resistance of the bridge resistor R b .
• the trimming-induced ⁇ TCR in R b _com P i is about -70ppm/K
• the trimming-induced ⁇ TCR in Rb_c omP 3, on the opposite side of the bridge is about +50ppm/K, for a total ⁇ TCR having magnitude approximately 120ppm/K.
• these trimming operations did 5 not change the state of bridge resistance match (or mismatch), since Rb_compi and Rb_comp3, in corresponding positions on opposite arms of the bridge, were each reduced by the same 3%. Only the relative TCRs were changed in such a way that the effective temperature coefficient of zero was changed by 120ppm/K, which corresponds to a temperature coefficient of zero of 0 approximately 3OuVMK.
• the range of bridge zero offset adjustment can be further doubled if the corresponding (same-numbered) single resistors Ri or R 2 in pair R CO m P i, Rcomp4, and in pair R CO m P 2, Rcom P 3, are trimmed simultaneously. For example, one would trim down Ri in R CO mpi and R CO mp4, and trim down R 2 in R comP 2 and
• Figs. 15 - 17 show examples similar to those shown in Figs. 12 - 14, where the single trimmable resistors Ri and R 2 are connected in parallel instead of in series. Again the overall (net) TCR of the compound resistor 14836-19PCT
• Rb_co m p is shown as a function of normalized resistance Rb__ C o mP when single trimmable resistors R 1 and R 2 are trimmed down.
• Fig. 18 shows the trimming behaviour of compound resistor Rb_com P with several different values of the nominal TCR ( ⁇ b ) of each of the four bridge resistors (R b ). Note that in Fig. 18 the slope of this overall bridge TCR with 5 trimming depends on the value of ⁇ b while trimming range of ⁇ TCR and relative resistance change remains almost the same, for each of the three values of ⁇ b .
• trimming-compensation circuit consisting of four compound resistors with resistance value of approximately 5 times higher 0 than resistance of resistors of the bridge allows RTCR adjustment in the range of ⁇ 240ppm/K (2 x 120ppm/K) and relative resistance adjustment of
• Some sensor-based applications where the sensing element(s) is/are configured in a Wheatstone bridge, require increasing the bridge-voltage (e.g.
• Bridge TCR compensation scheme (trimmable resistor in parallel with the bridge): First, note that the shift of the bridge TCR (shown in Figs. 12-17) caused by connection of "zero-offset-compensation" compound resistors Rco m pi-Rcomp 4 (Fig.10), must be included into consideration. Assume that the 5 "zero-offset-compensated" bridge with parameters shown in Fig. 15 is to be “TCR-compensated” using the scheme depicted in Fig. 19. In this case, the bridge TCR is already shifted (prior to any trimming), from its initial 1600ppm/K to approximately 1450ppm/K.
• Fig. 22 shows bridge voltage tempco and ratio Ut/U (where U is the excitation voltage) as functions of normalized resistance of the trimmable resistor R 6 (x).
• U is the excitation voltage
• the effectiveness of the compensation scheme substantially depends on the as-manufactured TCR oco and trimming-induced shift of TCR 5 per trimming fraction ⁇ ot the trimmable resistor.
• a trimmable resistor having constant, nominally-zero TCR it must be trimmed from 0 to 85%-down from its as-manufactured resistance, in order to cover a particular desired bridge voltage temperature coefficient range between 1100 and 1500ppm/K. It is 0 also important to note that the as-manufactured resistance value of the trimmable resistor, 15 times greater than the bridge resistance, results in reduction of ratio Ut/U to 0.1 - 0.3, with corresponding reduction in sensor sensitivity. Therefore, a desired normal operating bridge voltage of, say, 1V requires 3-10V of excitation voltage.
• TCR and TCT values of the single trimmable resistors used in the 0 above analysis correspond to the following materials:
• Compound resistor R comp consisting of two single trimmable resistors Ri and R 2 connected in series (Fig. 11) and bridge resistor Rb (Fig. 11) form net 0 compound resistor f?i,_ comp .
• Resistance and TCR of single resistors are functions of their trimming fraction x and y correspondently:
• R 1 (X) R 10 (I + X) (19a)
• R 2 (Y) R 20 (I + y) (19b)
• R 10 , R ⁇ o, a 0 , ⁇ o, ⁇ i, 72 are as-manufactured resistance, TCR and TCT values of single resistors.
• Resistance of the compound resistor Rb_ comP equals:
• ⁇ b is TCR of the resistor Rb.
• Figs. 12 - 14 show TCR cc b _ C omp (eq.(23)) vs. normalized resistance
• 0 TCR of the compound resistor can be expressed as:
• a circuit for compensation of non-linear temperature variations may be built.
• Such a circuit generates an output voltage as a polynomial function of temperature T. It could be used, for example, for temperature compensation of crystal oscillators (US Patent 4560959). Typically such generation of higher-order 0 temperature compensation is done with analog multiplication using bipolar 14836-19PCT
• CMOS complementary metal-oxide-semiconductor
• Figs. 23a, 23b the circuitry shown in Figs. 23a, 23b can be more- easily implemented in a CMOS process, (without requiring a BiCMOS process).
• Fig. 23a shows a schematic of a single module containing a resistor o bridge with two compound trimmable resistors Ri_ CO m P and R2_com P (analogous to those described above), and an amplifier with gain Ki.
• the resistors Ri and R 2 on the opposite side of the bridge, are not necessarily trimmable.
• the output voltage of the module, with the bridge initially balanced at ambient temperature T 0 (zero output voltage), equals:
• output voltages of the first and second modules can also be used to generate the polynomial function of temperature by summing all 0 three output voltages.
• the number of modules can be different from three.
• the resistor bridges in the modules can be initially intentionally unbalanced to simplify generation of the desired polynomial function of temperature.
• the scheme shown in Fig. 23b may 5 have the first module with an initial (as-manufactured) bridge being unbalanced, which generates an output voltage as a linear function of 14836-19PCT

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• 2005
  • 2005-09-21 WO PCT/CA2005/001440 patent/WO2006032142A1/en active Application Filing
  • 2005-09-21 JP JP2007531559A patent/JP2008513981A/ja active Pending
  • 2005-09-21 EP EP05787857A patent/EP1800319A1/de not_active Withdrawn
  • 2005-09-21 CA CA002581284A patent/CA2581284A1/en not_active Abandoned

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