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Circuits from the Lab® reference designs are engineered and tested for quick and easy system integration to help solve today’s analog, mixed-signal, and RF design challenges. For more information and/or support, visit www.analog.com/CN0385. Devices Connected/Referenced AD4003 18-Bit, 2 MSPS, PulSAR®, 7.0 mW ADC in MSOP/QFN AD8251
10 MHz, 20 V/μs, G = 1, 2, 4, 8, iCMOS
Programmable Gain Instrumentation Amplifier ADuM141E Robust, Quad Channel Isolator with Output Enable and 1 Reverse Channel ADG5207 High Voltage, Latch-Up Proof, 8-Channel Differential Multiplexer AD8475 Precision, Selectable Gain, Fully Differential Amplifier ADA4807-2 3.1 nV/√Hz, 1 mA, 180 MHz, Rail-to-Rail Input/Output Dual Op Amp Isolated, Multichannel Data Acquisition System with PGIA for Single-Ended and Differential Industrial Level Signals Rev. 0 Circuits from the Lab® reference designs from Analog Devices have been designed and built by Analog Devices engineers. Standard engineering practices have been employed in the design and construction of each circuit, and their function and performance have been tested and verified in a lab environment at room temperature. However, you are solely responsible for testing the circuit and determining its suitability and applicability for your use and application. Accordingly, in no event shall Analog Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due to any cause whatsoever connected to the use of any Circuits from the Lab circuits. (Continued on last page) Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2016 Analog Devices, Inc. All rights reserved. EVALUATION AND DESIGN SUPPORT Circuit Evaluation Boards CN-0385 Circuit Evaluation Board (EVAL-CN0385-FMCZ) System Demonstration Platform (EVAL-SDP-CH1Z) Design and Integration Files Schematics, Layout Files, Bill of Materials CIRCUIT FUNCTION AND BENEFITS The circuit shown in Figure 1 is a cost effective, isolated, multi- channel data acquisition system that is compatible with standard industrial signal levels. The components are specifically selected to optimize settling time between samples, providing 18-bit performance at channel switching rates up to approximately 750 kHz. The circuit can process eight gain-independent channels and is compatible with both single-ended and differential input signals. The analog front end includes a multiplexer, programmable gain instrumentation amplifier (PGIA); precision analog-to- digital converter (ADC) driver for performing the single-ended to differential conversion; and an 18-bit, 2.0 MSPS precision PulSAR® ADC for sampling the signal on the active channel. The maximum sample rate of the system is 2 MSPS in turbo mode, and 1.5 MSPS in normal mode. The channel switching logic is synchronous to the ADC conversions, and the maximum channel switching rate is 1.5 MHz. A single channel can be sampled at up to 2 MSPS with 18-bit resolution in turbo mode. Channel switching rates up to 750 kHz also provide 18-bit performance.
Figure 1. Isolated Multichannel Data Acquisition Simplified Circuit (All Connections and Decoupling Not Shown) in potentially large voltage steps between sampling intervals. to settle to these steps before the ADC performs a conversion. propagation delay, and low dynamic power consumption. and which can be configured in the GUI. input range, which is shown in T able 1. Table 1. Input Range for Each of the Four Gain Configurations
Rev. 0 | Page 4 of 13 System Noise Analysis One of the key design goals in precision data acquisition systems is achieving a high SNR, which can be achieved by increasing the full-scale signal amplitude and/or by decreasing the noise power generated by the components in the system. The total noise power present in the system can be found by taking the root sum square (rss) of the noise power contributed by its individual components, referred to the input of the AD4003: 5,, AD4003n,AD8475nAD8251n207ADGnTOTALn vvvvv +++= The expected SNR of the system (SNREXPECTED) can then be found using TOTALn REF EXPECTED v VSNR 2log20 The expected noise contributions for each component in the system and the resulting expected SNR performance of the whole system is shown in Table 2. The total system noise calculation ignores thermal noise contributed by the passive components in the system. Noise Due to the AD4003 ADC The noise of the AD4003 ADC is a function of both its inherent quantization error and noise caused by internal components (such as passive components producing thermal noise). The rms input voltage noise of the AD4003 can be calculated from its specified SNR using ×= 20 4003 102 ADSNR REF AD4003n Vv The SNR for the AD4003 (SNRAD4003) is specified as approximately 98 dB for a 4.096 V reference. The single-pole RC filter at the input of the AD4003 limits the wideband noise from the upstream components. A smaller filter bandwidth improves SNR by further limiting noise power; however, its time constant must also be sufficiently short to settle voltage kickbacks due to charge injections that occur as the AD4003 inputs reconnect to the front-end circuitry during the acquisition phase. The appropriate bandwidth for the system is at least 5 MHz (for more information, see the Analog Dialogue article, Front-End Amplifier and RC Filter Design for a Precision SAR Analog-to-Digital Converter). Noise Due to the AD8475 Funnel Amplifier The rms noise contributed by the AD8475 (vn, AD8475) is a function of its referred to output noise spectral density (NSD) (eAD8475) and the RC filter bandwidth at the input to the AD4003 (BWRC): RCAD8475AD8475n, BWev ×π×= 2 where eAD8475 = 10 nV/√Hz. Noise Due to the AD8251 Instrumentation Amplifier The AD8251 functions as a gain stage that improves SNR for small amplitude signals by boosting their amplitude to more closely fill the ±VREF range at the input to the AD4003. Ideally, if the system gain increases by a factor of G, the SNR (in dB) of the input signal improves by ΔSNR = log10(G) This level of improvement is not achievable in reality, however, because wideband noise is also amplified by the noise gain of the circuit. Fortunately, this degradation is not as large as the improvement due to signal gain. The rms noise contributed by the AD8251 is a function of its referred to input NSD (eAD8251), its gain setting (GAD8251), the attenuation factor of the AD8475 (GAD8475), and the noise filter bandwidth at the input of the AD4003: RCAD8475AD8251ADn BWGGev ×π×××= 2 8251AD8251, The value of eAD8251 is also dependent on the AD8251 gain; the value of eAD8251 can be found in the AD8251 data sheet. Noise Due to the ADG5207 Multiplexer The NSD and resulting rms noise contributed by the ADG5207 can be found by using the Johnson/Nyquist noise equation, because the device acts like a series resistance between the source and the rest of the analog front end: ONB207ADGn, RTke ×××= 45 and RCAD8475AD8251207ADGn,207ADGn, BWGGev ×π×××= 2 The resistance of each channel (RON) can be found in the ADG5207 data sheet. A summary of the calculated noise performance of the system is shown in Table 2. The largest contributors to the total noise are the AD8251 in-amp and the AD4003 ADC.
data analysis in the time and frequency domains. www.analog.com/CN0385-UserGuide). Figure 27. EVAL-CN0385-FMCZ Evaluation Hardware
Rev. 0 | Page 13 of 13 LEARN MORE CN-0385 Design Support Package: www.analog.com/CN0385-DesignSupport UG-502. SDP-H1 User Guide. Analog Devices. Ardizzoni, John. “ A Practical Guide to High-Speed Printed-Circuit- Board Layout, ” Analog Dialogue 39-09, September 2005. Kester, Walt. “Multichannel Data Acquisition Systems” in Data Conversion Handbook, Chapter 8, Section 8.2. Elsevier. Pachchigar, Maithil. “Complete Sensor-to-Bits Solution Simplifies Industrial Data-Acquisition System Design, ” Analog Dialogue 47-04, April 2013. Pachchigar, Maithil. “Demystifying High-Performance Multiplexed Data-Acquisition Systems, ” Analog Dialogue 48-07, July 2014. W alsh, Alan. “Front-End Amplifier and RC Filter Design for a Precision SAR Analog-to-Digital Converter, ” Analog Dialogue 46-12, December 2012. Amplifiers. Analog Devices. Circuitry. Analog Devices. and Sampling Rate of a Multiplexer. Analog Devices. High Resolution Industrial Applications. Analog Devices. MT-004 Tutorial. The Good, the Bad and the Ugly Aspects of ADC Input Noise – Is No Noise Good Noise? Analog Devices. MT-046 Tutorial. Op Amp Settling Time. Analog Devices. MT-048 Tutorial. Op Amp Noise Relationships: 1/f Noise, RMS Noise and Equivalent Noise Bandwidth. Analog Devices. Data Sheets and Evaluation Boards CN-0385 Circuit Evaluation Board (EV AL-CN0385-FMCZ) System Demonstration Platform (EVAL-SDP-CH1Z) AD4003 Data Sheet AD8251 Data Sheet ADG5207 Data Sheet ADA4807-2 Data Sheet AD8475 Data Sheet ADR4540 Data Sheet ADuM141E Data Sheet ADP7118 Data Sheet ADP7182 Data Sheet ADP5070 Data Sheet ADuM3470 Data Sheet ADP2441 Data Sheet
REVISION HISTORY
10/2016—Revision 0: Initial Version (Continued from first page) Circuits from the Lab reference designs are intended only for use with Analog Devices products and are the intellectual property of Analog Devices or its licensors. While you may use the Circuits from the Lab reference designs in the design of your product, no other license is granted by implication or otherwise under any patents or other intellectual property by application or use of the Circuits from the Lab reference designs. Information furnished by Analog Devices is believed to be accurate and reliable. However, Circuits from the Lab reference designs are supplied "as is" and without warranties of any kind, express, implied, or statutory including, but not limited to, any implied warranty of merchantability, noninfringement or fitness for a particular purpose and no responsibility is assumed by Analog Devices for their use, nor for any infringements of patents or other rights of third parties that may result from their use. Analog Devices reserves the right to change any Circuits from the Lab reference designs at any time without notice but is under no obligation to do so. ©2016 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the prop erty of their respective owners. CN15142-0-10/16(0)