A 10kHz bandwidth 50Amax current sensor using a Hall effect gradiometer without magnetic core provides 80kHz update rate with a digital interface. Very low un-calibrated offset of 30mA (1σ) and after calibration typical 10mA over temperature is accomplished by a chopped multi-bit feedback continuous-time 3rd order ΔΣ-ADC. This also realizes low noise of 13mA rms in 1kHz signal bandwidth. The ADC uses enhanced chopping techniques and additional digital feedback loops to avoid chopper ripple. New analog and digital stresscompensation circuits with lateral and vertical n-doped resistors achieve lifetime gain drifts below 1% and temperature compensation. Auto-zeroing ping-pong comparators offer a fast over-current detection of 1...2µs on a dedicated output pin. The monolithic integrated sensor chip and the 4kV galvanic isolated current rail fit into a very small 7x7x1mm 3 package.

Silicon Hall sensors are known to suffer from a long-term drift in the magnetic sensitivity between 1% and 4%, depending on the degree of moisture in the mold compound of the package. This drift is mainly caused by changes of mechanical stress exerted by the plastic package onto the die. We present a system, which continuously measures the relevant stress components, estimates the sensitivity drift, and corrects for it digitally. An individual precalibration versus temperature is necessary to achieve the required level of accuracy. Results from laboratory characterization with pressure cells and lifetime drift during qualification runs show that this system can keep the drift of magnetic sensitivity well below 1%.

Accurate voltage references are key building blocks for almost all electronic systems. Specifically, fuel gauge applications benefit from very high precision references to allow for extremely precise measurement of battery voltage and current in order to provide an accurate measurement of the state of charge of the battery.In this work a digitally assisted single-point-trimmed CMOS bandgap voltage reference is presented. Compared to previous art [1][2][3][4], this work achieves a low inaccuracy of ±0.08% (3σ) from -40°C to +120°C. The residual temperature drift is as low as 7 ppm/°C. The key idea is to keep the analog bandgap core simple and only compensate non-PTAT related effects (like offset) by using chopping techniques. The remaining PTAT and chip-to-chip variations can then be cancelled out using a single-point trim. Compared to [1], this work avoids the need for a bulky analog notch filter by minimizing offset using a DAC and a simple digital calibration loop. Finally, the remaining curvature, temperature drift, and stress effects are compensated in the digital domain by means of a temperature sensor, a stress sensor and a lookup table (LUT). In summary, the high precision of the reference voltage is achieved by reducing the analog portion to a minimum and combining this with digital compensation. As a consequence, the analog output voltage of the reference is not fully compensated (but also not needed in our system).Figure 5.8.1 shows a system overview of the voltage reference in the context of a fuel gauge system. The core of the reference is a CMOS bandgap circuit providing an analog reference voltage, V BG . This voltage is used as reference for the high accuracy ΣΔ-ADC [5], which measures the battery cell voltage (or current via a shunt resistor). Since V BG is compensated for non-PTAT errors only, the remaining error also affects the uncorrected ADC result in the digital domain. Here the remaining errors are compensated using a LUT, which is based on correction values from the measured V BG at room temperature (single-point trim). In addition, the LUT is used to provide curvature correction, since this effect is quite stable for devices in a given technology [7]. During calibration, the analog V BG output is passed via a 1 st -order lowpass filter to an on-chip chopped buffer (not shown) to provide a low impedance signal source to the tester. The temperature is measured by an on-chip temperature sensor with ±0.5°C accuracy. Finally, stress effects caused by packaging or aging are compensated for by using a stress sensor [6] and calculating the final corrected ADC result used by the fuel gauge algorithms. Combining all of these techniques, a single-point calibration at wafer level is sufficient to achieve the required accuracy of the overall system. Figure 5.8.2 shows a block diagram of the used bandgap subsystem. PNP transistors Q 1 and Q 2 and resistors R 1 , R 2 , and R 3 form a classical bandgap structure. The common node of the core is driven by M P1 , which is in common source configuration. Wit...

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Accurate magnetic sensors with digital signal processing and means for individual adjustment are required for many automotive and industrial applications. Previous magnetic sensors have used separate choppers, preamps, anti-aliasing filters and switched capacitor converters, but the compact magnetic sensor presented here combines the spinning-current Hall probe and a chopped 3 rd -order continuous-time ∆Σ-converter (CT-∆Σ-ADC) with multibit feedback to optimize noise and EMI performance at minimum chip area and power (Fig 16.6.1). The improved architecture of the CT-ADC includes an additional digital tracking loop and range switching in the feedback DAC (Fig. 16.6.2) to increase the robustness and the DR to 90dB in a bandwidth of 4kHz.

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