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AD712KR-REEL7 bảng dữ liệu(PDF) 11 Page - Analog Devices |
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AD712KR-REEL7 bảng dữ liệu(HTML) 11 Page - Analog Devices |
11 / 15 page AD712 REV. B –11– Figures 33a and 33b show the settling time characteristics of the AD712 when used as a DAC output buffer for the AD7545. 100 10 0% 500ns 90 a. Full-Scale Positive Transition 100 10 0% 500ns 90 b. Full-Scale Negative Transition Figure 33. Settling Characteristics for AD712 with AD7545 NOISE CHARACTERISTICS The random nature of noise, particularly in the 1/f region, makes it difficult to specify in practical terms. At the same time, designers of precision instrumentation require certain guaran- teed maximum noise levels to realize the full accuracy of their equipment. The AD712C grade is specified at a maximum level of 4.0 µV p-p, in a 0.1 Hz to 10 Hz bandwidth. Each AD712C receives a 100% noise test for two 10-second intervals; devices with any excursion in excess of 4.0 µV are rejected. The screened lot is then submitted to Quality Control for verification on an AQL basis. All other grades of the AD712 are sample-tested on an AQL basis to a limit of 6 µV p-p, 0.1 Hz to 10 Hz. DRIVING THE ANALOG INPUT OF AN A/D CONVERTER An op amp driving the analog input of an A/D converter, such as that shown in Figure 34, must be capable of maintaining a constant output voltage under dynamically changing load condi- tions. In successive-approximation converters, the input current is compared to a series of switched trial currents. The compari- son point is diode clamped but may deviate several hundred millivolts resulting in high frequency modulation of A/D input current. The output impedance of a feedback amplifier is made artificially low by the loop gain. At high frequencies, where the loop gain is low, the amplifier output impedance can approach its open loop value. Most IC amplifiers exhibit a minimum open loop output impedance of 25 Ω due to current limiting resistors. +15V 1/2 AD712 0.1 F 0.1 F –15V 10V ANALOG INPUT GAIN ADJUST ANALOG COM R2 100 OFFSET ADJUST AD574 12/ 8 R1 100 CS AO R/ C CE REF IN REF OUT BIP OFF 10VIN ANA COM 20VIN STS HIGH BITS +5V DIG COM +15V –15V MIDDLE BITS LOW BITS Figure 34. AD712 as ADC Unity Gain Buffer A few hundred microamps reflected from the change in converter loading can introduce errors in instantaneous input voltage. If the A/D conversion speed is not excessive and the bandwidth of the amplifier is sufficient, the amplifier’s output will return to the nominal value before the converter makes its comparison. However, many amplifiers have relatively narrow bandwidth yielding slow recovery from output transients. The AD712 is ideally suited to drive high speed A/D converters since it offers both wide bandwidth and high open-loop gain. |
Số phần tương tự - AD712KR-REEL7 |
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Mô tả tương tự - AD712KR-REEL7 |
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