No abstract

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...

Modern medical diagnostics demands point‐of‐care testing (POCT) systems for quick tests in clinical or out‐patient environments. This investigation combines the Reflectometric Interference Spectroscopy (RIfS) with thin film technology for a highly sensitive, direct optical and label‐free detection of proteins, e.g. inflammation or cardiovascular markers. Amorphous silicon (a‐Si) based thin film photodetectors replace the so far needed spectrometer and permit downsizing of the POCT system. Photodetectors with p‐i‐i‐n structure adjust their spectral sensitivity according to the applied read‐out voltage. The use of amorphous silicon carbide in the p‐type and the first intrinsic layer enhances the sensitivity through very low dark currents of the photodetectors and enables the adjustment of their absorption characteristics. Integrating the thin film photodetectors on the rear side of the RIfS substrate eliminates optical losses and distortions, as compared to the standard RIfS setup. An integrated Application Specific Integrated Circuit (ASIC) chip performs a current‐frequency conversion to accurately detect the photocurrent of up to eight parallel photodetector channels. In addition to the optimization of the photo‐detectors, this contribution presents first successful direct optical and label‐free RIfS measurements of C‐reactive protein (CRP) and D‐dimer in buffer solution in physiological relevant concentrations. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

No abstract