Adjustable voltage divider produced by hybrid technology

Details Adjustable voltage divider produced by hybrid technology Adjustable voltage divider produced by hybrid technology

1998-09-28

2000-08-29

Donovan, Lincoln

Electrical resistors

With mounting or supporting means

Plural resistors

338195, 338309, 338295, H01C 100

Patent

active

061114944

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to voltage dividers produced by hybrid technology.


BACKGROUND OF THE INVENTION

An adjustable voltage divider arrangement manufactured by hybrid technology for an integrated film circuit is already known from European Patent EP 93 125. FIG. 1 shows one embodiment of this known voltage divider. FIG. 2 shows the respective equivalent circuit diagram. The voltage divider comprises a first resistance layer 1 produced by thin-film or thick-film technology, with a region 11 that serves to supply power and is connected to a printed conductor 3 and with a region 12 that serves to draw off current and is connected to a printed conductor 4. The printed conductors and resistance layers are produced from conducting paste and resistance paste that are customary in hybrid technology. The tap consists of a second resistance layer 2 which overlaps with the first resistance layer 1 in a contact zone 9 and is connected to a third printed conductor 5 which is provided as a pick-off electrode. For adjustment of the voltage divider, a laser cut or sandblasted cut 10 is made in the second resistance layer, which intersects the potential lines formed during the operation of the voltage divider. The length of cut 10 is such that the potential at pick-off electrode 5 reaches the desired level. The ohmic current-carrying voltage divider resistor of the voltage divider is formed from a single, contiguous resistance region 1 with a resistance R1 which is divided into two partial resistors R1' and R1" by the pick-off, as illustrated in FIG. 2. Since partial resistors R1' and R1" which are joined together in one piece are made of the same material with the same temperature coefficient, a temperature dependence of the voltage level picked off can be largely ruled out, in contrast to the case of a voltage divider having two spatially separate resistance layers made of different materials. Furthermore, shifting the cut required for the adjustment to the second resistance layer 2 yields the result that the potential distribution within current-carrying voltage divider resistor R1 remains essentially constant.
Despite these advantages, the known voltage divider arrangement does not meet the demands in all cases. Thus, for example, in cases when a very small divider voltage is to be picked off at resistor R1, one of the two partial resistances formed must be very small, e.g., partial resistance R1", if the divider vol age is picked off at second printed conductor 4 and third printed conductor 5. Resistance ratio R1'/R1" becomes much greater than five in these cases. This leads to problems because the region required by the voltage divider arrangement within the integrated film circuit should be as small as possible (as a rule, the length of resistance layer R1 is approximately 5 mm, the width approximately 2 mm), but at the same time, partial resistors R1' and R1" must be picked off accurately to at least one percent.
Problems arise due to the fact that, given the uniformly small region requirement, the geometric dimensions of the layer structure of the second partial resistor R1" within resistance layer 1 become too small to allow tapping with the required accuracy. Since contact zone 9 of the first and second resistance layers in FIG. 1 must be extremely small in this case, cuts into these small structures cannot be made with the required accuracy when performing the adjustment with a laser. This is true even when a cut is made with the laser directly into the first resistance layer. Therefore, partial resistors R1' and R1" cannot be picked off accurately down to one percent in the cases described here. In addition, the stability of the voltage divider declines greatly over its lifetime. The only remedy is for the geometric dimensions of the first resistance layer 1 to be increased as a whole. However, this leads to a considerable increase in the space required for the voltage divider within the integrated film circuit. For example, to go from a divider ratio of R1'/R1"=5/1 to a ratio

REFERENCES:
patent: 2758256 (1956-08-01), Eisler
patent: 3601745 (1971-08-01), Helgeland
patent: 3669733 (1972-06-01), Allington
patent: 4505032 (1985-03-01), Praria
patent: 4899126 (1990-02-01), Yamada
patent: 5198794 (1993-03-01), Sato et al.

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