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LTC2622 数据表(PDF) 14 Page - Linear Technology |
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LTC2622 数据表(HTML) 14 Page - Linear Technology |
14 / 26 page LTC2323-16 14 232316fc For more information www.linear.com/LTC2323-16 APPLICATIONS INFORMATION Single-Ended-to-Differential Conversion While single-ended signals can be directly digitized as previously discussed, single-ended to differential conver- sion circuits may also be used when higher dynamic range is desired. By producing a differential signal at the inputs of the LTC2323-16, the signal swing presented to the ADC is maximized, thus increasing the achievable SNR. The LT®1819 high speed dual operational amplifier is recommended for performing single-ended-to-differen- tial conversions, as shown in Figure 8. In this case, the first amplifier is configured as a unity-gain buffer and the single-ended input signal directly drives the high imped- ance input of this amplifier. Fully-Differential Inputs ToachievethefulldistortionperformanceoftheLTC2323-16, a low distortion fully-differential signal source driven through the LT1819 configured as two unity-gain buffers, as shown in Figure 9, can be used. This circuit achieves the full data sheet THD specification of –85dB at input frequencies of 500kHz and less. Data sheet typical perfor- mance curves taken at higher frequencies used a harmonic rejection filter between the ADC and the signal source to eliminate the op amp as the dominant source of distortion. The fully-differential configuration yields an analog input span (AIN+ – AIN–) of ±REFOUT1,2. In this configuration, the input signal is driven on each AIN pin, typically at equal spans but opposite polarity. This yields a high com- mon mode rejection on the input signals. The common mode voltage of the analog input can be anywhere within the VDD input range, but will be limited by the peak swing of the full-range input signal. For example, if the internal reference is used with VDD = 5VDC, the full-range input span will be ±4.096V. Half of the input span is typically driven on each AIN pin, yielding a signal span for each AIN pin of 4.096VP-P. This leaves ~0.9V of common mode variation tolerance. When using external references, it is possible to increase common mode tolerance by com- pressing the ADC full-range codes into a tighter range. For example, using an external 2.048V reference with VDD = 5V the total span would be ±2.048V and each AIN span would be limited to 2.048VP-P allowing a common mode range of ~3V. Compressing the input span would incur a SNR penalty of approximately 2dB. Input span compres- sion may be useful if single-supply analog input drivers Figure 8. Single-Ended to Differential Driver Figure 9. LT1819 Buffering a Fully-Differential Signal Source VREF 0V VREF 0V VREF 0V VREF/2 + – + – 200 200 LT1819 232316 F08 VREF 0V VREF 0V VREF 0V VREF 0V + – + – LT1819 232316 F09 |
类似零件编号 - LTC2622 |
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类似说明 - LTC2622 |
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