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AD1380JD датащи(PDF) 7 Page - Analog Devices |
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AD1380JD датащи(HTML) 7 Page - Analog Devices |
7 / 8 page AD1380 –7– REV. B Figure 10. Analog and Power Connections for Bipolar –10 V to +10 V Input Range Other Ranges: Representative digital coding for 0 V to +10 V and –10 V to +10 V ranges is given above. Coding relationships and calibration points for 0 V to +5 V, –2.5 V to +2.5 V and – 5 V to +5 V ranges can be found by halving proportionally the corresponding code equivalents listed for the 0 V to +10 V and –10 V to +10 V ranges, respectively, as indicated in Table II. Zero and full-scale calibration can be accomplished to a preci- sion of approximately ±1/2 LSB using the static adjustment procedure described above. By summing a small sine or triangu- lar wave voltage with the signal applied to the analog input, the output can be cycled through each of the calibration codes of interest to more accurately determine the center (or end points) of each discrete quantization level. A detailed description of this dynamic calibration technique is presented in Analog-Digital Conversion Handbook, edited by D. H. Sheingold, Prentice-Hall, Inc., 1986. GROUNDING, DECOUPLING AND LAYOUT CONSIDERATIONS Many data acquisition components have two or more ground pins which are not connected together within the device. These “grounds” are usually referred to as the Logic Power Return, Analog Common (Analog Power Return) and Analog Signal Ground. These grounds (Pins 8 and 30) must be tied together at one point for the AD1380 as close as possible to the con- verter. Ideally, a single, solid analog ground plane under the converter would be desirable. Current flows through the wires and etch stripes on the circuit cards, and since these paths have resistance and inductance, hundreds of millivolts can be gener- ated between the system analog ground point and the ground pins of the AD1380. Separate wide conductor stripe ground returns should be provided for high resolution converters to minimize noise and IR losses from the current flow in the path from the converter to the system ground point. In this way AD1380 supply currents and other digital logic-gate return currents are not summed into the same return path as analog signals where they would cause measurement errors. Each of the AD1380 supply terminals should be capacitively decoupled as close to the AD1380 as possible. A large value capacitor such as 1 µF in parallel with a 0.1 µF capacitor is usually sufficient. Analog supplies are to be bypassed to the Analog Power Return pin and the logic supply is bypassed to the Logic Power Return pin. The metal cover is internally grounded with respect to the power supplies, grounds and electrical signals. Do not externally ground the cover. APPLICATION AD1380 Dynamic Performance High performance sampling analog-to-digital converters like the AD1380 require dynamic characterization to assure they meet or exceed their desired performance parameters for signal pro- cessing applications. Key dynamic parameters include signal-to- noise ratio (SNR) and total harmonic distortion (THD), which are characterized using Fast Fourier Transform (FFT) analysis techniques. The results of that characterization are shown in Figure 11. In the test a 13.2 kHz sine wave is applied as the analog input (fO) at a level of l0 dB below full scale; the AD1380 is operated at a word rate of 50 kHz (its maximum sampling frequency). Figure 11. The results of a 1024-point FFT demonstrate the exceptional performance of the converter, particularly in terms of low noise and harmonic distortion. In Figure 11, the vertical scale is based on a full-scale input referenced as 0 dB. In this way, all (frequency) energy cells can be calculated with respect to full-scale rms inputs. The resulting signal-to-noise ratio is 83.2 dB, which corresponds to a noise floor of –93.2 dB. Total harmonic distortion is calculated by adding the RMS energy of the first four harmonics and equals –97.5 dB. Increas- ing the input signal amplitude to –0.4 dB of full scale, causes THD to increase to –80.6 dB as shown in Figure 12. |
Аналогичный номер детали - AD1380JD |
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Аналогичное описание - AD1380JD |
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