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AD7450ARZ-REEL 数据表(PDF) 11 Page - Analog Devices |
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AD7450ARZ-REEL 数据表(HTML) 11 Page - Analog Devices |
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11 / 22 page  AD7450 –11– CM* VREF p-p CM* *CM = COMMON-MODE VOLTAGE VIN+ VIN– VDD SCLK SDATA CS GND VREF SERIAL INTERFACE 3V/5V SUPPLY 1.25V/2.5V VREF 0.1 F 10 F AD7450 VREF p-p 0.1 F C/ P Figure 6. Typical Connection Diagram THE ANALOG INPUT The analog input of the AD7450 is fully differential. Differential signals have a number of benefits over single-ended signals, including noise immunity based on the device’s common-mode rejection, improvements in distortion performance, doubling of the device’s available dynamic range, and flexibility in input ranges and bias points. Figure 7 defines the fully differential analog input of the AD7450. VIN+ AD7450 VIN– VREF p-p COMMON-MODE VOLTAGE VREF p-p Figure 7. Differential Input Definition The amplitude of the differential signal is the difference between the signals applied to the VIN+ and VIN– pins (i.e., VIN+ – VIN–). VIN+ and VIN– are simultaneously driven by two signals each of amplitude VREF that are 180 ° out of phase. The amplitude of the differential signal is therefore –VREF to +VREF p-p (i.e., 2 VREF). This is regardless of the common mode (CM). The common mode is the average of the two signals, i.e., (VIN+ + VIN–)/2, and is therefore the voltage that the two inputs are centered on. This results in the span of each input being CM ± VREF/2. This voltage has to be set up externally and its range varies with VREF. As the value of VREF increases, the com- mon-mode range decreases. When driving the inputs with an amplifier, the actual common-mode range will be determined by the amplifier’s output voltage swing. Figures 8 and 9 show how the common-mode range typically varies with VREF for both a 5 V and a 3 V power supply. The common mode must be in this range to guarantee the functionality of the AD7450. For ease of use, the common mode can be set up to be equal to VREF, resulting in the differential signal being ±V REF centered on VREF. When a conversion takes place, the common mode is rejected resulting in a virtually noise free signal of amplitude –VREF to +VREF corresponding to the digital codes of 0 to 4095. VREF 5.0 0 0.25 0.75 1.75 2.25 2.75 3.25 3.50 1.25 4.5 2.0 1.5 1.0 0.5 3.5 2.5 4.0 3.0 COMMON-MODE RANGE 3.25V 1.75V Figure 8. Input Common-Mode Range vs. VREF (VDD = 5 V and VREF (Max) = 3.5 V) VREF 0 2.0 1.5 1.0 0.5 2.5 3.0 0.25 0.50 1.00 1.25 1.50 2.00 2.20 0.75 1.75 COMMON-MODE RANGE 2V 1V Figure 9. Input Common-Mode Range vs. VREF (VDD = 3 V and VREF (Max) = 2.2 V) Figure 10 shows examples of the inputs to VIN+ and VIN– for different values of VREF for VDD = 5 V. It also gives the maxi- mum and minimum common-mode voltages for each reference value according to Figure 8. Rev. A |
类似零件编号 - AD7450ARZ-REEL |
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