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ADA4807-2 Datasheet(PDF) 11 Page - Analog Devices |
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ADA4807-2 Datasheet(HTML) 11 Page - Analog Devices |
11 / 13 page Circuit Note CN-0385 Rev. 0 | Page 11 of 13 The mean code error increases as the voltage step size and channel switching rate increase. This increase is caused by the combined slew and settling time limitations of the components in the signal chain. Increasing the step size forces the system to settle larger changes in voltage and increasing the channel switching rate decreases the amount of time the system is given to settle these changes. At sufficiently high step sizes and switching rates, the mean code error becomes unpredictably large, as in the gain of 0.4 configuration (see Figure 17 and Figure 21). This code error is caused by the slew rate limitations of the input buffer amplifiers in the AD8251 in-amp. The performance of the system when using the ac source was evaluated by comparing its THD with respect to the channel switching rate. The AP SYS-2712 provided a full-scale sine wave input on one channel and an inverted version of the sine wave on another channel. THD was measured for various sample rates, ranging from 25 kSPS to 1.5 MSPS in 25 kSPS increments. Figure 25 shows the THD measured for each of the channels in each of the gain configurations. Figure 25. THD vs. ADG5207 Channel Switching Rate for Full-Scale 1 kHz Input The THD performance of the system begins to degrade at roughly 700 kSPS (depending on the gain configuration). The whole signal chain SNR and THD performance is mainly limited by the PGA AD8251. A smaller RC filter at the front of AD4003 also gives better THD at higher channel switching sampling rate. COMMON VARIATIONS The AD4003 ADC is pin-for-pin compatible with various other 14-bit, 16-bit, and 18-bit, 10-lead precision SAR ADCs that can be used in the CN-0385 system. The ADG1207, with wider bandwidth, can be an alternative to the ADG5207. The ADG5248F, with fault protection and detection function, can be used for single-ended inputs. The AD8475 provides a differential output signal for other differential ADCs, such as the AD7690. The ADA4805-1 op amp is an alternative for the AD8475 when driving pseudo differential or single-ended ADCs, such as the AD4000. Other Analog Devices, Inc., LDOs, such as the ADP7102 and ADP7142, can replace the ADP7118. CIRCUIT EVALUATION AND TEST This circuit uses the EVAL-CN0385-FMCZ circuit board and the EVAL-SDP-CH1Z SDP-H1 system demonstration platform controller board. The two boards have 160-pin mating connectors, allowing quick setup and evaluation of the performance of the circuit. The circuit board contains the circuit to be evaluated, as described in this circuit note, and the SDP-H1 controller board is used with the CN-0385 Evaluation Software to capture the data from the circuit board. Equipment Needed The following equipment is needed: PC with a USB port and Windows® XP or Windows Vista® (32-bit), or Windows 7 (32-bit) EVAL-CN0385-FMCZ circuit evaluation board EVAL-SDP-CH1Z SDP-H1 controller board CN-0385 Evaluation Software (download from ftp://ftp.analog.com/pub/cftl/CN0385/) 5 V to 12 V dc power supply or wall wart (9 V wall wart included with EVAL-CN0385-FMCZ board) USB to micro-USB cable Low distortion, low output impedance signal generator to provide ±10 V output Low noise, high precision dc supply to provide ±10 V output Getting Started Download the evaluation software from ftp://ftp.analog.com/ pub/cftl/CN0385/, and then install the software on the PC. Functional Block Diagram See Figure 1 for the circuit block diagram and the EVAL-CN0385- FMCZ-SCH.pdf file for the complete circuit schematic. This file is contained in the CN-0385 Design Support Package (available at www.analog.com/CN0385-DesignSupport). A functional block diagram of the test setup is shown in Figure 26. Figure 26. Test Setup Functional Block Diagram Hardware Setup Figure 27 shows the EVAL-CN0385-FMCZ evaluation hardware. Information and details regarding the SDP-H1 board can be found in the SDP-H1 User Guide. Connect the 160-pin connector on the circuit board to the J4 connector on the SDP-H1 controller board. –110 –100 –90 –80 –70 –60 –50 –40 0 200 400 600 800 CHANNEL SWITCHING RATE (kHz) GAIN = 0.4dB GAIN = 0.8dB GAIN = 1.6dB GAIN = 3.2dB EVAL-CN0385-CH1Z P1 P2/ P8 J1/P3 EVAL-SDP-CH1Z USB PC 5V TO 12V POWER AC/DC SOURCE(S) |
Similar Part No. - ADA4807-2 |
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Similar Description - ADA4807-2 |
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