A7.4 - Offset Tracing in Hall Sensors by Integrated Temperature Coefficient Determination

Hall sensors in CMOS technologies are ever present. Modern sensors are able to measure all three orthogonal components of the magnetic flux density at approximately one point [1]. Unfortunately Hall sensors have comparative high offsets, but there are a number of known techniques to reduce the offset. The best known are the spinning current technique [2] and orthogonal coupling [3]. Using these methods reduces the offset by several magnitudes, but a residual offset always remains. Additionally, this residual offset has a non-linear temperature dependency. The compensation of the residual offset can improve the sensors’ performance. Up to now it has been necessary to measure the offset at different temperatures during the volume test. This takes a lot of time and, hence, costs money. With this proposed integrated temperature coefficient determination and a special algorithm, it is possible to trace the offset across the whole temperature range with only one required start-up point which can be measured easily and cheaply during the volume test. Fundamental idea Using an integrated heating system allows the chip to heat up by itself [4]. This temperature difference can be used to calculate the offset temperature coefficient (OTC) of the sensor. By measuring several OTCs at different temperatures, the offset characteristics across temperature could be approximated by linking up small straight lines with the according slope (OTC) as shown in figure 1. Figure 1: Fundamental idea of “offset tracing” If the chip is used for the first time, only the offset (offsetRT) and the offset temperature coefficient (OTCRT) at room temperature (RT) are already known from the volume test. With this information, only a simple Offset OTCRT-!T OTCRT+!T OTCRT