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전자부품 데이터시트 검색엔진 |
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전자부품 데이터시트 검색엔진 |
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AD73311L 데이터시트(PDF) 24 Page - Analog Devices |
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AD73311L 데이터시트(HTML) 24 Page - Analog Devices |
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24 / 37 page  REV. A AD73311L –23– The dc biasing of the analog input signal is accomplished with an on-chip voltage reference. If the input signal is not biased at the internal reference level (via REFOUT), it must be ac-coupled with external coupling capacitors. CIN should be 0.1 µF or larger. The dc biasing of the input can then be accomplished using resistors to REFOUT as in Figures 27 through 29. REFCAP REFOUT REFERENCE 0/38dB PGA OPTIONAL BUFFER 0.1 F VREF AD73311L VINP VINN VOUTP VOUTN +6/15dB PGA CONTINUOUS TIME LOW-PASS FILTER Figure 26. Analog Input (DC-Coupled) Using External Amplifiers The AD73311L’s ADC inputs are biased about the internal reference level (REFCAP level), therefore it may be neces- sary to bias external signals to this level using the buffered REFOUT level as the reference. This is applicable in either dc- or ac-coupled configurations. In the case of dc coupling, the signal (biased to REFOUT) may be applied directly to the inputs (using amplifier bypass), as shown in Figure 25, or it may be conditioned in an external op amp where it can also be biased to the reference level using the buffered REFOUT signal as shown in Figure 26. In the case of ac-coupling, a capacitor is used to couple the signal to the input of the ADC. The ADC input must be biased to the internal reference (REFCAP) level which is done by connecting the input to the REFOUT pin through a 10 k Ω resistor as shown in Figure 27. CONTINUOUS TIME LOW-PASS FILTER REFOUT REFERENCE VREF REFCAP 0.1 F 10k VOUTP VOUTN VINP 0.047 F 100 0.1 F 10k VINN 0.047 F 100 0.1 F 0/38dB PGA AD73311L +6/–15dB PGA Figure 27. Analog Input (AC-Coupled) Differential If the ADC is being connected in single-ended mode, the AD73311L should be programmed for single-ended mode using the SEEN and INV bits of CRF, and the inputs connected as shown in Figure 28. When operated in single-ended input mode, the AD73311L can multiplex one of the two inputs to the ADC input, as shown in Figures 28 and 29. CONTINUOUS TIME LOW-PASS FILTER REFOUT REFERENCE 0/38dB PGA VREF REFCAP 0.1 F VINN VINP 0.047 F 100 0.1 F VOUTP VOUTN 10k AD73311L +6/–15dB PGA Figure 28. Analog Input (AC-Coupled) Single-Ended CONTINUOUS TIME LOW-PASS FILTER REFOUT REFERENCE 0/38dB PGA VREF REFCAP 0.1 F VINN VINP 0.047 F 100 0.1 F VOUTP VOUTN 10k AD73311L +6/15dB PGA Figure 29. Analog Input (AC-Coupled) Single-Ended (Alternate Input) Interfacing to an Electret Microphone Figure 30 details an interface for an electret microphone which may be used in some voice applications. Electret microphones typically feature a FET amplifier whose output is accessed on the same lead that supplies power to the microphone; therefore, this output signal must be capacitively coupled to remove the power supply (dc) component. In this circuit the AD73311L input channel is being used in single-ended mode where the internal inverting amplifier provides suitable gain to scale the input signal relative to the ADC’s full-scale input range. The buffered internal reference level at REFOUT is used via an external buffer to provide power to the electret microphone. This provides a quiet, stable supply for the microphone. If this is not a concern, the microphone can be powered from the system power supply. |
유사한 부품 번호 - AD73311L_17 |
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유사한 설명 - AD73311L_17 |
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