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Maxim > Design Support > Technical Documents > Subsystem Boards > APP 5721

Keywords: Fremont (MAXREFDES6#), subsystem reference design, analog front-end (AFE)

SUBSYSTEM BOARD 5721

Fremont (MAXREFDES6#): 16-Bit, High-Accuracy, 0

to 100mV Input, Isolated Analog Front-End (AFE)

Sep 19, 2013

Abstract:

The Fremont (MAXREFDES6#) subsystem reference design meets the high-resolution needs of low-

voltage output sensor applications. Boards for purchase, hardware and firmware design files, and FFTs and

histograms from lab measurements provide complete system information for rapid prototyping and development.

Introduction

Smart factories, industrial, and medical

applications continue to utilize more

sensors, of various configurations. While

low-voltage sensors provide essential

data, they also require/generate high

signal-to-noise ratios, rendering many

discrete and integrated analog-to-digital

converters (ADCs) insufficient for these

applications.

The compact Fremont (MAXREFDES6#

) subsystem reference design (Figure 1) accurately measures low

voltage, 0 to 100mV, single-ended analog signals with a high-accuracy, 16-bit analog front end (AFE) complete

with an isolated data path. The design optimizes the functions of an ultra-precision low-noise buffer (MAX9632); a

highly accurate ADC (MAX11100); an ultra-high-precision 4.096V voltage reference (MAX6126); a 600V

RMS

monolithic data isolator (MAX14850); and low-dropout (LDO) regulators providing regulated +6V, +5V, and -5V

power rails (MAX1659 and MAX1735). This oneofakind AFE solution works in many applications requiring low-

voltage input, high impedance, and high-accuracy analog-to-digital conversion.

Page 1 of 9

Summary of content (9 pages)

PAGE 1
Maxim > Design Support > Technical Documents > Subsystem Boards > APP 5721 Keywords: Fremont (MAXREFDES6#), subsystem reference design, analog front-end (AFE) SUBSYSTEM BOARD 5721 Fremont (MAXREFDES6#): 16-Bit, High-Accuracy, 0 to 100mV Input, Isolated Analog Front-End (AFE) Sep 19, 2013 Abstract: The Fremont (MAXREFDES6#) subsystem reference design meets the high-resolution needs of lowvoltage output sensor applications.
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Figure 1. The Fremont subsystem design block diagram.
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Detailed Description of Hardware Fremont interfaces with field-programmable gate array (FPGA) development boards using a Pmod connector. The Pmod specification allows for both 3.3V and 5V modules as well as various pin assignments. Fremont requires a 3.3V supply voltage and uses the SPI pin assignments as illustrated here. Table 1 shows the power requirements. Table 2 shows the supported platforms and ports. Table 1.
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The firmware allows for immediate interfacing to the hardware, and for collection and saving of samples. Figure 2a shows the simple process flow. The firmware is in C, developed using the Xilinx software development kit (SDK) tool, based on the Eclipse™ open source standard. Custom Fremont-specific design functions (driver in the maximDeviceSpecificUtilities.c file) were created utilizing the standard Xilinx XSpi core version 3.03a. The SPI clock frequency is set to 3.125MHz. Figure 2a.
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The firmware allows for immediate interfacing to the hardware, for collection and saving of samples. Figure 2b shows the simple process flow. The firmware is in C, developed using the Xilinx SDK tool, based on the Eclipse™ open source standard. Custom Fremont-specific design functions (driver in the maximDeviceSpecificUtilities.c file) were created utilizing the AXI MAX11100 custom IP core. The SPI clock frequency is 4.54MHz when the sample rate is 189.4ksps. The SPI clock frequency is set to 2.
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Industrial sensor or signal source Download, read, and carefully follow each step in the appropriate Fremont Quick Start Guide: Fremont (MAXREFDES6#) Nexys 3 Quick Start Guide Fremont (MAXREFDES6#) ZedBoard Quick Start Guide Lab Measurements Equipment: HP 33120A waveform generator Voltage calibrator DVC-8500 Windows PC with two USB ports Fremont (MAXREFDES6#) board Nexys 3 development kit +7V power supply -6V power supply Take special care and use proper equipment when testing the Fremont design.
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Figure 3. AC FFT using on-board isolated power, a 0 to 100mV, 1kHz sine-wave input signal, high-impedance input, a 20ksps sample rate, and a Blackman-Harris window.
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Figure 4. DC histogram using on-board isolated power; a 50mV input signal; a 20ksps sample rate; 65,536 samples; a code spread of 19 LSBs with 95.7% of the codes falling within the nine center LSBs; and a standard deviation of 2.236. All Design Files Download All Design Files Hardware Files Schematic Bill of materials (BOM) PCB layout PCB Gerber PCB CAD (PADS 9.
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Buy Direct: Fremont (MAXREFDES6#) Or Order the Fremont reference design (MAXREFDES6#) from your local Maxim representative. ARM is a registered trademark and registered service mark of ARM Limited. AutoShutdown is a trademark of Maxim Integrated Products, Inc. Cortex is a registered trademark of ARM Limited. Eclipse is a trademark of Eclipse Foundation, Inc. MicroBlaze is a trademark of Xilinx, Inc. Nexys is a trademark of Digilent Inc. Pmod is a trademark of Digilent Inc.