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AD574A Fiches technique(PDF) 5 Page - Analog Devices |
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AD574A Fiches technique(HTML) 5 Page - Analog Devices |
5 / 12 page AD574A REV. B –5– DEFINITIONS OF SPECIFICATIONS LINEARITY ERROR Linearity error refers to the deviation of each individual code from a line drawn from “zero” through “full scale”. The point used as “zero” occurs 1/2 LSB (1.22 mV for 10 volt span) be- fore the first code transition (all zeros to only the LSB “on”). “Full scale” is defined as a level 1 1/2 LSB beyond the last code transition (to all ones). The deviation of a code from the true straight line is measured from the middle of each particular code. The AD574AK, L, T, and U grades are guaranteed for maxi- mum nonlinearity of ±1/2 LSB. For these grades, this means that an analog value which falls exactly in the center of a given code width will result in the correct digital output code. Values nearer the upper or lower transition of the code width may pro- duce the next upper or lower digital output code. The AD574AJ and S grades are guaranteed to ±1 LSB max error. For these grades, an analog value which falls within a given code width will result in either the correct code for that region or either adjacent one. Note that the linearity error is not user-adjustable. DIFFERENTIAL LINEARITY ERROR (NO MISSING CODES) A specification which guarantees no missing codes requires that every code combination appear in a monotonic increasing se- quence as the analog input level is increased. Thus every code must have a finite width. For the AD574AK, L, T, and U grades, which guarantee no missing codes to 12-bit resolution, all 4096 codes must be present over the entire operating tem- perature ranges. The AD574AJ and S grades guarantee no miss- ing codes to 11-bit resolution over temperature; this means that all code combinations of the upper 11 bits must be present; in practice very few of the 12-bit codes are missing. UNIPOLAR OFFSET The first transition should occur at a level 1/2 LSB above analog common. Unipolar offset is defined as the deviation of the actual transition from that point. This offset can be adjusted as discussed on the following two pages. The unipolar offset temperature coefficient specifies the maximum change of the transition point over temperature, with or without external adjustment. BIPOLAR OFFSET In the bipolar mode the major carry transition (0111 1111 1111 to 1000 0000 0000) should occur for an analog value 1/2 LSB below analog common. The bipolar offset error and temperature coefficient specify the initial deviation and maximum change in the error over temperature. QUANTIZATION UNCERTAINTY Analog-to-digital converters exhibit an inherent quantization uncertainty of ±1/2 LSB. This uncertainty is a fundamental characteristic of the quantization process and cannot be reduced for a converter of given resolution. LEFT-JUSTIFIED DATA The data format used in the AD574A is left-justified. This means that the data represents the analog input as a fraction of full-scale, ranging from 0 to 4095 4096 . This implies a binary point to the left of the MSB. FULL-SCALE CALIBRATION ERROR The last transition (from 1111 1111 1110 to 1111 1111 1111) should occur for an analog value 1 1/2 LSB below the nominal full scale (9.9963 volts for 10.000 volts full scale). The full-scale calibration error is the deviation of the actual level at the last transition from the ideal level. This error, which is typically 0.05% to 0.1% of full scale, can be trimmed out as shown in Figures 3 and 4. TEMPERATURE COEFFICIENTS The temperature coefficients for full-scale calibration, unipolar offset, and bipolar offset specify the maximum change from the initial (25 °C) value to the value at T MIN or TMAX. POWER SUPPLY REJECTION The standard specifications for the AD574A assume use of +5.00 V and ±15.00 V or ±12.00 V supplies. The only effect of power supply error on the performance of the device will be a small change in the full-scale calibration. This will result in a linear change in all lower order codes. The specifications show the maximum full-scale change from the initial value with the supplies at the various limits. CODE WIDTH A fundamental quantity for A/D converter specifications is the code width. This is defined as the range of analog input values for which a given digital output code will occur. The nominal value of a code width is equivalent to 1 least significant bit (LSB) of the full-scale range or 2.44 mV out of 10 volts for a 12-bit ADC. THE AD574A OFFERS GUARANTEED MAXIMUM LINEARITY ERROR OVER THE FULL OPERATING TEMPERATURE RANGE |
Numéro de pièce similaire - AD574A |
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Description similaire - AD574A |
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