Sensor signals are, their nature, perfect must corrected with suitable
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Signal Conditioning Circuits Sensors Frame ASICs* Modular Signal Conditioning
Sensor signals are, their nature, perfect must corrected with suitable techniques such that target error levels achieved. method calibrate compensate sensor signal with digital components. market, there existing integrated solutions which allow such electronic correction. often these flexible enough simply practical sensor applications. This article shows electronic correction sensor system possible clear separation analog digital components thereby achieving target accuracy very cost (labour material) eliminating weaknesses monolithic solutions.
*The term Frame ASIC describes class integrated analog signal conditioning circuits sensor technology. Frame ASIC name given whose input, output analog peripheral functions surround digital correction facilities sensor system integrated processor like frame (see Figure idea Frame ASICs evolved from concept Modular Signal Conditioning, enabling applications devised simply flexibly sensible budget.
Approaches Signal Conditioning date there have been various approaches correction sensors whose transfer function deviates from ideal characteristic curve required. These include procedures such trimming resistors correction network (e.g. laser compensation), current compensation (e.g. pressure sensors with constant current excitation) compensation processes which involve active components such transistors diodes. past years Definitions correction been suggested which correction absolute values, such offbased advances semiconductor Calibration: span. technology which already been introduced number companies Compensation: correction induced disturbance variables, such temperature coefficients form 2-chip solutions offset drift. monolithic ICs. This approach involves Linearisation: correction measuring system transelectronic digital correction which characteristic which dependent calibrate, compensate disturbance variables. linearise imperfect sensor signal.
analog microelectronics
Analog Microelectronics GmbH Fahrt 55124 Mainz Phone: (0)6131/91 Fax: (0)6131/91 E-Mail: info@analogmicro.de
August 2000
Frame ASICs Modular Signal Conditioning
monolithic solutions centring electronic correction introduced thus have their specific problems, meaning that widespread breakthrough circuits this kind been achieved. Where company have difficulties with surface area chip (price/device), another's difficulties unsuitable programming production. Others manufacture chips which require many external components others still make promises fail meet them beyond data sheet. Analog Microelectronics GmbH devised simple cost-effective approach problem which both tried-and-tested, functional, flexible, cost effective: Modular Signal Conditioning with Frame ASICs. Concept Modular Signal Conditioning assume that analog front signal processing sensing element output) almost always fulfil same conditions that back usually provide normed output values, then reach conclusion that analog front back circuits implemented using structures which recur time again. This means that circuit components such these reduced down small number variations prerequisite production), making integration inexpensive operation. Requirements regarding accuracy, temperature range compensation range particular necessary adaptation individual sensing elements are, however, manifold applications they govern sensing elements used. This calls great flexibility with regard relevant digital correction functions correction elements, feature which makes integration economically praxis unviable.
Supply Sensing Element Output Stages
Amplifier
Electronic Correction
Analog Output
AM400
Protection Functions
Figure Frame ASIC concept
analog microelectronics
August 2000
Frame ASICs Modular Signal Conditioning
Bearing various requirements correction mind, then take close look range processors controllers currently available consider that this market rapidly moving towards devices which smaller, cheaper have more features, then becomes obvious that sensor signal conditioning solution Modular Signal Conditioning. Solution: take suitable analog input circuit (instrumentation amplifier) standardised output circuit (e.g. 0.10V), peripheral functions, such temperature detection, voltage reference, protective circuits, current source sensing element, want accommodate them inexpensive integrated circuit, then device need Frame ASIC. suitable standard processor controller correction purposes will have signal conditioning system which functions principle Modular Signal Conditioning. last have favourable solution, more technological limitations high performance sensor system. Basic Conditions Digital Correction general rule, digital correction prove sensible option used optimum effect, basic conditions must observed: first basic condition fulfilled that signal indirectly directly modified using controller microprocessor. There essentially ways doing this using Frame ASICs manufactured Analog Microelectronics GmbH: Indirect Modification This solution requires external access integrated circuit components (e.g. amplifier) which alter offset span (programming functions). Here, analog signal path signal remains unimpaired either conversion. combination Frame ASIC microprocessor make signal conditioning system which performs tasks "analog sensor signal processor" (see Figure path uncut, analog signal modified indirectly resolution signal nearly unlimited (only noise). Direct Modification this approach controller (with converters) connected between analog front back end. This form signal correction more extensive gives user greater degrees freedom permits influence overall signal directly. quantisation error, resolution degree intervention largely determined digital elements. combination Frame ASIC microprocessor with converters make signal conditioning system could refer "digital sensor signal processor" (see Figure
analog microelectronics
August 2000
Frame ASICs Modular Signal Conditioning
Sensing Element Pre-amplifier Adjustable Amplifier
Output Stage
D/A-Wandler
Analog Output
Converter
Converter Sensing Element Temperature Pre-amplifier Processor
EEPROM
Figure schematic circuit diagram analog sensor signal processor
Sensing Element Pre-amplifier Converter Converter Output Stage
Sensing Element Temperature Pre-amplifier Converter
Analog Output
Processor
Digital Output
EEPROM
Figure schematic circuit diagram digital sensor signal processor
analog microelectronics
August 2000
Frame ASICs Modular Signal Conditioning
second basic condition governing efficient correction requires that sensor components (sensor element signal conditioning electronics) compensated individually that sensor circuit complete system corrected target output values assembled state. Traditional compensation methods entail adding together errors individual sensor components, whereas overall compensation system entirety involves correcting resultant error. This undoubtedly more exact method, total error corrected until production line. Compensating finished systems also ties with demands production keen eradicate influences exerted assembling packaging technology compensate sensors once they have been compiled. Processors Controllers only corrections necessary those calibration temperature compensation analog output signal required simple 8-bit risc processor connected Frame ASICs electronic (digital) signal correction accordance with Modular Signal Conditioning. this instance combined Frame ASICs processor function analog sensor signal processor (see Figure Should linearisation, high degree accuracy (e.g. 0.5% wide temperature range), other functions required, then normally more complex microcontroller used which enables suitable application-specific algorithms implemented. This system detection functions digital sensor signal processor (see Figure Frame ASICs standard controllers processors enables inexpensive problem-specific solutions created form stand-alone products. Here, specifically, this digitally compensated sensor with standard analog output and/or digital output necessary protective circuitry. With regard aspects outlined here, principle Modular Signal Conditioning ideally applied when parent system sensor integrated into processor operation. this processor able correct transfer characteristic sensor, which usually case, then need additional components thus cost project considerably reduced. Existing Frame ASICs Based concept Modular Signal Conditioning range Frame ASICs currently available from Analog Microelectronics GmbH includes following ICs: AM400 differential input signals industrial voltage/current output AM401/11 differential input signals industrial voltage output AM402/42 differential input signals industrial current output
Figure various Frame ASICs
analog microelectronics
August 2000
Frame ASICs Modular Signal Conditioning
CAN404 CAV414 capacitive input signals Namur output capacitive input signals industrial voltage output
Tried-and-Tested Examples Taking AM400 example, concept Modular Signal Conditioning with Frame ASICs shall demonstrated here. tiny processor which indirectly influences analog path connected AM400 create analog sensor signal processor (see Figure this combination, offset span entire sensor system (sensing element ASIC) corrected influencing current voltage source adjustable input amplifier Frame ASIC. method correction would calculate correction values from look-up table stored controller. Other methods also possible, depending processor performance.
AM400
VOUT
IOUT
EEPROM
Figure AM400 controller analog sensor signal processor
analog microelectronics
August 2000
Frame ASICs Modular Signal Conditioning
order assemble digital sensor signal processor, AM400 analog signal path behind amplifier unit front analog output stage). Here there analog output (max. value reference voltage, voltage-limited protect converter input following which used activate microcontroller ADC. Depending profile application, microcontroller signal processed digitally, compensated and, necessary, linearised before being converted back into required industrial output signals analog AM400 (see Figure using conversion. sensing element power supply, input output protection circuits output area settings voltage current outputs included AM400 Frame ASIC reduce number discrete components needed. With latter combination user free standard controller adapt digital complexity suit required signal correction level additional functions and/or existing controllers processors parent system.
AM400
VOUT
IOUT
Pressure
EEPROM
DOUT
Figure AM400 microprocessor digital sensor signal processor applications requiring high degrees accuracy with digital analog signal output.
analog microelectronics
August 2000
Frame ASICs Modular Signal Conditioning
Analog Microelectronics GmbH continuing focus concept Frame ASICs series ASSPs (application-specific standard products). AM400 integrated circuit such example. Capable being modified specific applications, Frame ASICs tailored suit range customer requirements. entire Modular Signal Conditioning package from Analog Microelectronics GmbH also offered customised design required. Detailed data sheets giving dimensional specifications application notes available from Analog Microelectronics GmbH website Internet: www.analogmicro.de Authors: Dipl.-Phys. Helmut Kremer, Systems Design Manager Dipl.-Ing. Roland Fischer, Project Manager Pressure Sensor Technology
analog microelectronics
August 2000
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