ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
The proposed angular position sensor is a magnetostatic encoder based on the Hall Effect. Commercial  contactless angular sensors are composed of a two-axis sensitive Hall structure combined with rotating permanent magnets [3]. Most of these technologies provide a two-component analog output, which requires a digital signal processor to calculate the angular position of the permanent magnet (traditionally by the use of CORDIC algorithms [4]). The use of a Digital Signal Processor (DSP) increases the complexity of the surrounding electronics and limits the reliability of the sensor in harsh environment conditions. In this context, the new contactless magnetic sensor proposed here [5], based on a circular sensitive structure, provides the angle without need of a complex algorithm.  The full sensor consists of a passive magnets configuration providing a magnetic field and a sensing  element located in the plane of the field. This second element is composed of an encapsulated monolithic silicon chip that detects the direction of the magnetic field. The sensing element being aligned with the  magnetic rotation axis, this sensor is dedicated to plain shaft application where the magnetic element can be fixed on the rotating shaft and the sensing element can be held by the housing of the structure. A simple sketch of the working principle is presented thereafter:                     Figure 1. Schematic of the sensor principle (left) and sensor design (right)  This paper describes the sensor and presents the space qualification campaigns that are foreseen in the  beginning of 2008.  The first section presents the sensing principle and its associated structure. The subsequent electronic  includes in the chip to perform the basic measurement sequence along with the output information  treatment is also outlined. A second chapter introduces the magnetic configuration offering the best  combination between field homogeneity and sensor accuracy.  The development and the qualification of the sensor arise at two levels and in two steps:  /g131 A first test campaign occurs at the sensor level and is presented in the third chapter. At this level,  the electronic layout of the chip is not fully compliant with space standards, as no protection are implemented within the electronic layout with regards to radiation. This first level is a technology level and its main objective is to qualify through a test campaign the whole sensor composed of  the rotating element and the sensing element inserted within a Chip On Board (CoB) package. This activity is performed within the framework of an ESA Technology Research Program (TRP)  activity [1].  /g131 A second test campaign occurs at chip level and is presented in the fourth section. At this level,  the chip is encapsulated within a CERamic Dual In-line Package (CERDIP) and its layout  incorporates radiation hardening techniques issue from the radiation test of the first test  campaign. Those tests are undertaken at wafer and chip level according to European standards  defined for monolithic chip space qualification. 

172
Sensing structure 

The sensor consists of a sensing structure, on-chip biasing, signal conditioning circuits and readout interface. The sensing element is an n-doped ring with N contacts equally distributed on the ring surface.  Through switches each contact can be connected to the current source, to the ground or to the voltage amplifier. Many different connection combinations give information about the magnetic field. Here we present first a simple measurement sequence, with its associated sensitivity and zero-field offset, and a second sequence with a more efficient offset cancelling.          Figure 2. Integrated Hall structure and detail of a 5 Contacts Vertical Hall (5CVH) element  Sensing principle and basic measurement sequence   The measurement sequence is based on a 5 Contacts Vertical Hall element (5CVH) [6] that are  composed by 5 in-line contacts. The current is injected through the outer contacts and collected in the middle one. The potential difference between the two remaining contacts (The Hall Voltage V H) is  proportional to one component of the in-plane magnetic field:   VH/g68  Bcos(/g68) (1) 

Figure 3. One step of the acquisition of the Hall voltage of one 5CVH.  At a time t, a series of 5 neighbor contacts are connected in such way to form a 5CVH. On a perfect  device, the output voltage is proportional to Bcos(/g68), where /g68 is the angle between n(a unitary vector  normal to the middle contacts of the 5CVH) and B. At each clock time, the 5CVH element is shifted by  one contact, and the Hall voltage becomes Bcos(/g68+2/g83/n). Over a full turn, the Hall voltage exhibits a sine  function, with its amplitude proportional to the in-plane field and its phase equal to the field direction. The  information about the field direction is contained in the first harmonic over the full turn period.  173
In a real structure, because of the imperfections (in the material and in the manufacturing process), the  Hall voltage is superposed to an offset voltage. The key point is that the one-by-one shift of the 5CVH allows to compensate this offset. This can be easily understood by modeling the Hall ring by a circular array of non-identical resistors (see Figure 4). We can see that the contribution of the i th resistor is  cancelled. If a static defect induces an excess of voltage at the output at time t, the same defect causes  an opposite voltage at time t+1. In this ohmic model, the dc offset, i.e. the sum over one full turn is zero. 

Figure 4. Resistor array model. 

Zero field offset   The previous basic measurement sequence does not fully suppress the zero field offset. Even if the dc  offset vanishes, a circular array of resistors, randomly distributed, create a non-zero first harmonic. In real  devices, additional non-linear effects contribute to increase the offset. The most important one is the  junction field effect, which, by squeezing the channel according to the applied voltage causes a dynamic modification of the conductive channel. Combined with the static imperfections, it prevents the full  resistance cancellation. As a result, the sum of voltages over one cycle is not zero and degrades the  accuracy of the sensor.   Another measurement sequence for suppression of the zero field offset

Depending on the application, another sequence can be implemented for cancelling the offset. A proposed special sequence called “subspinning” can cancels the output voltage; sum over a period much shorter that the full cycle. The aim is to suppress the residual first harmonic of the randomly distributed defects. A particular subspinning sequence is given thereafter on Figure 5. 

Figure 5. Subspinning sequence for the suppression of the zero offset.  The basic element is also a 5CVH, but the two extreme contacts are shorted and connected to a single  current source, in order to make a four terminals device. At each position of the 5CVH, the four connections are circularly permuted, as for usual spinning current method. For a perfect array of resistors  the sum over these 4 steps vanishes. As a consequence, the first harmonic is strongly reduced and the  offset suppression factor is strongly reduced. Numerical simulations show that the subspinning sequence  also suppresses the offset due to junction field effect. 

Signal processing and Implementation

The selected technology for the sensor realization is a conventional CMOS 0.35-μm high-voltage  technology. The supply voltage is 3.3 V. The sensing part is composed of an n-well ring with 64 n-doped  contacts. The ring is formed by a deep n-well layer with about 6 μm of depth. The ring outer diameter is 50 μm. The ring width, contact number, size and shape were determined by optimizing the sensitivity  using finite element calculations. A logic circuit ensures the correct switching sequence. The four-phase  174
subspinning sequence presented above is implemented for the readout of the 5C segments, resulting in  256 (4 x 64) measurement steps per full measurement sequence.  Figure 6. Block diagram of the APS  The measuring principle is based on the phase measurement between the detected signal (5) and the  reference signal (2). Switches realized by NMOS transmission gates connect the sensing structure to the  bias circuit or Differential Difference Amplifier (DDA). The bias current generated in the bias circuit is derived from a bandgap cell. Oscillator, Logic and Divider blocks are realized by digital standard cells available from the foundry. The DDA, Band-Pass Filter (BPF) and Comparator (COMP) are optimized for low-noise, wide temperature range. The output signal is available in three different forms: Pulse Width Modulation (PWM), Serial Peripheral Interface (SPI) and analog output with 10 bits of resolution. Figure 7 shows the main signal waveforms in block diagram. The waveforms are cross-referenced by numbering.  175
Figure 7. Main signal waveforms (frequency of the clock and reference signal are given for  information) and view of the silicon layout. 

The Hall voltage coming from the structure (3) is sensed and amplified by a differential difference  amplifier (DDA) and buffered. The amplification gain is fixed so, that the amplified signal swing is about half of the full supply voltage range (3.3 V). The signal is further filtered through a 4th order band-pass switched capacitor (SC) filter, in order to suppress any high frequency parasitic signals induced by the Hall elements and offsets and 1/f noise caused by the DDA. The choice of the SC filter is due to its  excellent stability of the filtering frequency and input-to-output phase shift over temperature. The signal is  further filtered through a passive RC low-pass filter with cutoff frequency much higher (at least 10 x cycle frequency) in order to filter the ripple form of the signal coming from the SC filter. The filtered 1st  harmonic useful signal (waveform (4) in Figure 7) is further transformed into a square wave signal  through a comparator (waveform (5) in Figure 7). Thereby, the phase of the measured square wave  signal can be compared with the reference signal in a logic phase detector circuit COMP (6). In this way,  the analog signal is converted to PWM digital form. Such a signal can be further easily converted to a digital word using a counter. Digitalized signal is read via an SPI interface, or converted to the analog form through a DAC. In order to minimize the influence of the phase drift in temperature caused by the electronics on the measured phase, the reference signal is treated in the same way as the detected signal. In other words, the reference signal with adequate magnitude and signal level is fed through a duplicated analog path composed of DDA, SC filter and COMP. In this way both signals are exposed to  the same delay drift and the differential drift is minimized.  The sensor conditioning circuit is realized with a bandgap circuit in order to be insensitive to the supply  voltage variations and well control the temperature drift of the bias current for the sensing part (Hall  element). Since the sensing part is biased with relatively low current to keep the nonlinearity effect low,  the drop voltage over the sensing part does not overreach the working range of an N type MOS  transistor. Therefore, the sensing part is connected to the conditioning circuit and signal processing circuit via transmission gates composed only by NMOS transistor with optimized size. This allows  minimizing the charge injection feed through from a digital driving part to the signal processing path. Chip  size is of about 1.9 x 1.9 mm2. The system has 32 bonding pads with a pitch of 120 μm. The sensing part  is centered with respect to the chip outlines (see Figure 7). Supply pads of the digital and analog part are  split into two parts; in order to isolate the analog part from the digital part and prevent the clock feedthrough.  176
Magnetic source 

Requirements   The permanent magnet assembly must generate the magnetic field sensed by the detector. The field direction follows the rotation of the mechanism. This rotating element is composed of a mechanical structure that holds together the permanent magnet(s) in the desired configuration. Some of the main parameters of the magnetic source are listed thereafter.  /g131 The magnetic field must lies within the chip plane. A small tilt is not an issue since a small and  constant perpendicular component does not affects the angle reading.  /g131 The magnetic field intensity must be large as an important field at the sensor position has two  positive effects:  o It increases the signal over noise ratio, which allows reducing the sensor bias current.  This one limiting the power consumption and reducing the non linearity within the  sensitive region that is the main cause of offsets.  o It decreases the errors due to parasite external fields.  /g131 The magnetic field must be homogeneous within the whole volume where the sensor is expected  to move. This homogeneity is linked to the radius of homogeneity (HR) defined as the smallest  distance from the center where the projection of the magnetic field in the sensor plan rotates by  0.05° (see Figure 8). HR varies with the distance along the z axis. The revolution of the function HR(z) around the z-axis defines the homogeneity volume. 

Figure 8. Definition of the homogeneity radius 

/g131 The stray field distance, depending on application, must be limited to reduce the field leaking out  of the sensor region. A magnetic material (with high permeability) located inside the stray field region modifies the magnetic field distribution everywhere and thus might cause angular errors.  In addition a small stray field offers a better compatibility with other nearby devices.  /g131 The magnetic direction must be reproducible within the whole -60° to +90°C temperature range.  Small changes in the field intensity does not directly affects the sensed angle, but in a real  magnetic block, some region are usually close to demagnetization (corners, edges), and problem may arises when temperature induces a non uniform demagnetization. Therefore a magnet with  177
intensity and the homogeneity radius of a double-crown and a single-crown configuration is presented in  Figure 11.            Figure 10. Left: Halbach crown made of 8 cubes in close contact. Right: Double crown  configuration.

Figure 11. Comparison between a double and a single crown magnets configuration in terms of  homogeneity radius and field intensity.  Table 2. Magnet assembly (dimensions in mm).  The angular homogeneity produced by the assembly with the parameters defined in Table 2 in the centre  plane (z = 0) is shown in Figure 12. The homogeneity radius is close to 1 mm. Effect of displacements,  errors in cube positioning, sizes and imperfection in the magnetization show that a displacement of the  order of 0.1 mm affects the homogeneity radius by an amount of the same magnitude. The field intensity  produced by the magnet assembly is around 270 mT. This relatively high value allows limiting the sensor  bias current and thus decreasing the offsets. The stray field distance is 22 mm, i.e. about 10 mm out of the external diameter. The value is well below the values obtained for non-zero magnetic moment  assemblies (like a single block solution). 

Figure 12. Angular homogeneity in the magnet center plane (z = 0) for a double-crown  configuration. 179
Technology qualification campaign  Setup   The whole APS sensor is tested during the technology qualification campaign. The final test configuration  dedicated to the tests is illustrated on Figure 13. The rotating element is mounted on a shaft guided trough a bearing system and drive by a precision actuator. An optical encoder, offering a high accuracy, is mounted on the actuator and represents the reference sensor. A decoupling between the APS and the driving system allow keeping the same configuration in a thermal vacuum (TV) chamber where a vacuum  feedtrough is inserted between both systems. 

Figure 13. Left: APS functional and TV test setup. Right: APS setup for vibration, shock and  radiation tests. 

The technology qualification tests start at the reception of the Multiple Process Wafer run (MPW) with the plan detail thereafter. Standards procedure related to the test are also listed.   Packaging of the chip and package tests

/g131 Visual inspection [ECSS 20500]  /g131 Bond strength [MIL-STD-883]  /g131 Die shear [MIL-STD-883]  /g131 Encapsulation  /g131 Dimension check: The outline dimension and envelope of both rotating element and sensing  element are inspected according to the interface drawing.  /g131 Weight: The weight of the unit, including the flying leads shall be less than 100g according to the  sensor specifications. 

Performance functional tests   /g131 Range: The unit should be able to rotate without any limitation. 2 complete rotations are  performed in both directions.  /g131 Absolute measurement: The objective of this test is to verify that the sensor is not only an  incremental sensor and that the angular position of the magnetic field can be recovered even  after a shut-down of the power-supply.  /g131 Accuracy: Following the sensor specification, the accuracy of the APS should be closed to 0.05°.  The noise level gives a good representation of the minimum accuracy that can be reached by the sensor. However, this noise level depends on the electronic placed back along the sensor, in particular the RC filter used to convert the PWM output into an analog signal. The bit accuracy of the digital signal is most appropriate illustrate the real accuracy of the sensor. The noise of the analog output is also monitored for comparison. An angular accuracy of 0.05° corresponds to an  analog voltage noise of Vcc/7200, i.e. less than 460 /g80V. This corresponds to a digital output on  13 bits, i.e. three bits of noise on the 16 bits channel.  180
/g131 Resolution: The minimum incremental motion of the driving stage used to rotate the functional  setup is defined to 0.004°. With such a resolution, the resolution of the APS can be investigated.  /g131 Repeatability  /g131 Drift parameters: Leakage current at several level of the chip layout, bandgap voltage are some  of the drift parameters which can be influenced by radiation, EMC and temperature range and  which are monitored.  The objective of the functional tests is to verify the specifications under environmental constrains  describes in the next sections. These functional tests are repeated at reception of the chip, after the  radiation test, after the vibration and shock campaign, after the EMC test and after the lifetime test.   Radiation test

The test is performed at the Proton Irradiation Facility of the Paul Scherrer Institute (PSI) in Villigen (Switzerland). Total Dose Irradiation (TID according to ESCC 22900) test and Single Event Effect (SEE according to ESCC 25100) test is performed. During the test, the sensing element is protected by a minimum of 4 mm Aluminum inner wall (sketch on Figure 13) that allows estimating the total dose for a worst-case 15-year radiation lifetime of a geo-stationary telecom satellite. The parameters of the radiation tests are the following:  /g131 Proton Energies 6 MeV  /g131 Total dose:  300 krads  /g131 Maximum flux:  100 rad/h  During the irradiation, the sensing element is facing a static permanent magnet, which allows for the monitoring of drift parameters of the sensor such as the leakage current that is monitored at several level of the block diagram or several parity bits that allow for the SEE detection. The output of this radiation test validates the hardening of the design that is implemented in the second chip layout. 

Vibration and shock tests

The test sequence comports Sine vibration test, random vibration test and shock test. These tests are  performed on the three axes of the sensor. The vibration tests are made at room temperature, in air and  the unit is neither powered nor rotating. The APS setup (including the dummy shaft) is mounted on a  dedicated test support fixed on the shaker for the vibration tests (Figure 13). The setup is first tested  without the APS in order to identify frequencies related to the tooling itself. Vibration and shock loads are summarized in Table 3: 

Table 3. Vibration and shock loads 

181
Thermal vacuum test   The APS is installed in a thermal vacuum chamber with its rotation axis vertically mounted. The sensing element and its packaging is fixed on a thermal base plate inside the chamber in order to control the temperature of the APS mounting flange by conduction. The anodized support acts as a frame surrounding the APS in order to promote radiative exchanges. The APS is thermally cycled in vacuum (< 10 -5 Pa) according to Figure 14. 

Figure 14. Thermal cycles performed on the APS. 

The following operations occur during the thermal vacuum test:  /g131 1  Thermal balance and non-operating cycle.  /g131 2  Hot non-operational performance functional test.  /g131 3  Cold non-operational performance functional test.  /g131 4  Performance functional test at ambient temperature. Power switch on.  /g131 5  Hot operational performance functional tests (at 1 and 8th operating cycle)  /g131 6  Cold operational performance functional tests (at 1 and 8th operating cycle)  /g131 7  Performance functional test at ambient temperature. Power and rotation switched off.  The following parameters are monitored continuously during the operating cycles of the APS:  /g131 Temperature of the various thermal probes  /g131 Digital Output  /g131 Analog Output  /g131 Bandgap Voltage  /g131 Driving torque (drag torque of the APS)  /g131 Pressure 

EMC test   Electromagnetic compatibility is the ability of electrical equipment to work satisfactorily in its  electromagnetic environment without affecting this environment in an inadmissible way.  The electromagnetic compatibility of the APS is verified by means of tests performed at frequency range between 10 kHz and 18 GHz in an anechoic room. The tests consist in the measurement of the radiated  and the conducted disturbance immunity of the sensor (susceptibility) and to its emissivity in accordance  with standard ECSS-E-10-03A. 

Lifetime test

The APS sensor is thermally cycled in vacuum (< 10-5 mbar) between cold and hot operating  temperatures (-60°C/+90°C). As the sensor includes micro-electronic parts, the number of thermal cycles (100) is adapted to such electronics systems.  182