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Evaluation Board for 2.7V to 5.25V, Micro Power, 2-Channel, 125 kSPS, 12-Bit ADC EVAL-AD7887CB

BOARD which is also available from Analog Devices. External sockets are provided for the AIN0 and AIN1 inputs.

FEATURES
Evaluation Board for 2.7V to 5.25V, Micro Power, 2-Channel, 125 kSPS, 12-Bit ADC EVAL-AD7887CB
BOARD which is also available from Analog Devices. External sockets are provided for the AIN0 and AIN1 inputs.
OPERATING THE AD7887 EVALUATION BOARD Power Supplies
Full-Featured Evaluation Board for the AD7887 EVAL-CONTROL BOARD Compatible Stand Alone Capability On-Board Analog Buffering and Reference Optional On-Board Biasing / Filter Circuit Various Linking Options PC Software for Control and Data Analysis when used with EVAL-CONTROL BOARD INTRODUCTION
When using this evaluation board with the EVAL-CONTROL BOARD all supplies are provided from the EVALCONTROL BOARD through the 96 way connector. When using the board as a stand alone unit external supplies must be provided. This evaluation board has seven power supply inputs: VDD, AGND, +12V, -12V, AGND, DVDD and DGND. +5V / +3V must be connected to the VDD input to supply the AD7887 VDD pin. +12V and -12V are used to supply the OP467 quad op-amp and the AD780 voltage reference. 0V is connected to one or both of the AGND inputs. The DVDD input can be used to supply a separate +5V for the 74LS04 and the DGND input must be tied to 0V. Alternatively the 74LS04 can be supplied from the same +5V as the AD7887 supply by inserting LK15 . The supplies are decoupled to the relevant ground plane with 10µF tantalum and 0.1µF multilayer ceramic capacitors at the point where they enter the board. The supply pins of the AD7887, quad op-amp and reference are also decoupled to AGND with 10µF tantalum and a 0.1µF ceramic capacitor. Extensive ground planes are used on this board to minimize the effect of high frequency noise interference. There are two ground planes, AGND and DGND. These are connected at one location close to the AD7887 GND pin.
This Technical Note describes the evaluation board for the AD7887, high speed, low power, 12-bit ADC that operates from a single 2.7 V to 5.25 V power supply. The AD7887 is capable of 125 ksps throughput rate. The input track-andhold acquires a signal in 500 ns and features a single ended sampling scheme. The output coding for the AD7887 is straight binary and the part is capable of converting full power signals up to 2.5MHz. Full data on the AD7887 is available in the AD7887 data sheet available from Analog Devices and should be consulted in conjunction with this Technical Note when using the Evaluation Board. On-board components include an AD780 which is a pin programmable +2.5V or +3V ultra high precision bandgap reference, an OP467 quad op-amp and a 74LS04 inverting buffer. There are various link options which are explained in detail on page 2. Interfacing to this board is through a 96-way connector. This 96-way connector is compatible with the EVAL-CONTROL
FUNCTIONAL BLOCK DIAGRAM
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EVAL-AD7887CB
LINK AND SWITCH OPTIONS
There are nine link options which must be set for the required operating setup before using the evaluation board. The functions of these options are outlined below.
Link No. Function.
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SETUP CONDITIONS
Care should be taken before applying power and signals to the evaluation board to ensure that all link positions are as per the required operating mode. Table I shows the position in which all the links are set when the evaluation board is sent out.
Table I. Initial Link and Switch Positions
Link No. LK1 LK2 LK3 LK4 LK5 LK6 LK7 LK8 LK9
Position A B B Removed A A A B A
Function. AIN0 SMB connected to the input of the AIN0 analog buffer. The input of the AIN1 analog buffer is tied to AGND. The AD780 reference voltage is applied to the AD7887 AIN1 / VREF pin. AD780 is set to provide a +2.5V reference. VREF is selected as the DC bias voltage for the optional bias-up / filter circuit. +12V supplied from EVAL-CONTROL BOARD via J1. -12V supplied from EVAL-CONTROL BOARD via J1. VDD for the AD7887 is supplied by the EVAL-CONTROL BOARD via J1. 74LS04 is powered from the same power source as the AD7887.
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EVALUATION BOARD INTERFACING Table II. 96-Way Connector Pin Functions. ROWA ROWB ROWC
Interfacing to the evaluation board is via a 96-way connector, J1. J1 is used to connect the evaluation board to the EVALCONTROL BOARD or other system. The pinout for the J1 connector is shown in Figure 2 and its pin designations are given in Table II.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 AVDD AVDD AVDD AGND -12V DGND AGND AGND AGND AGND AGND AGND DGND AGND AGND AGND AGND AGND AGND AGND AGND AGND AGND AGND +12V DGND AGND AGND AGND AGND AGND AGND DGND DGND DGND DGND DGND DGND DGND DT0 TFS0 DGND DGND DR0 RFS0 SCLK0
Figure 2. Pin Configuration for the 96-Way Connector, J1
96-Way Connector Pin Description
DTO DRO
Data Transmit Zero. This output is connected to the DIN pin of the AD7887. Data Receive Zero. This input is connected to the DOUT pin of the AD7887 via two inverting buffers. Serial Clock Zero. This serial clock is connected to the SCLK pin of the AD7887 via an inverting buffer. Transmit / Receive Frame Sync Zero. These two outputs are connected to the CS pin of the AD7887. Digital Ground. These pins are connected to the digital ground plane on the evaluation board. It allows the user to provide the digital supply via the connector along with the other digital signals. Analog Ground. These pins are connected to the analog ground plane on the evaluation board. Analog VDD Supply. These pins are connected to the VDD pin of the AD7887 via LK12. +12V Supply. This pin is connected to the V+ supply line on the board via LK13. -12V Supply. This line is connected to the V- supply line on the board via LK14.
SCLK0
TFSO / RFS0
+12V -12V
Note : The unused pins of the 96-way connector are not shown.
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SOCKETS OPERATING WITH THE EVAL-CONTROL BOARD
There are nine input sockets relevant to the operation of the AD7887 on this evaluation board. The function of these sockets is outlined in Table III.
Table III. Socket Functions
Socket J1 J2 J3 J4 J5
Function Sub-Miniature BNC Socket for AIN0 channel. Sub-Miniature BNC Socket for AIN1 channel. Sub-Miniature BNC Socket for external reference voltage input. Sub-Miniature BNC Socket for Analog input to bias-up circuit. Sub-Miniature BNC Socket for Analog output from bias-up circuit.
The evaluation board can be operated in a stand-alone mode or operated in conjunction with the EVAL-CONTROL BOARD. This EVAL-CONTROL BOARD is available from Analog Devices under the order entry "EVAL-CONTROL BOARD". When operated with this control board, all supplies and control signals to operate the AD7887 are provided by the EVAL-CONTROL BOARD when it is run under control of the AD7887 software which is provided with the AD7887 evaluation board package. This EVAL-CONTROL BOARD will also operate with all Analog Devices evaluation boards which end with the letters CB in their title. The 96-way connector on the EVAL-AD7887CB plugs directly into the 96-way connector on the EVAL-CONTROL BOARD. No power supplies are required in the system. The EVAL-CONTROL BOARD generates all the required supplies for itself and the EVAL-AD7887CB. The EVAL-CONTROL BOARD is powered from a 12V ac transformer. This is a standard 12V ac transformer capable of supplying 1A current and is available as an accessory from Analog Devices under the following part numbers: EVAL-110VAC-US: EVAL-220VAC-UK: EVAL-220VAC-EU: For use in the U.S. or Japan For use in the U.K. For use in Europe
CONNECTORS
There are four connectors on the AD7887 evaluation board as outlined in Table IV.
Table IV. Connector Functions
These transformers are also available for other suppliers including Digikey (U.S.) and Campbell Collins (U.K.). Connection between the EVAL-CONTROL BOARD and the serial port of a PC is via a standard RS-232 cable which is provided as part the EVAL-CONTROL BOARD package. Please refer to the manual which accompanies the EVAL-CONTROL BOARD for more details on the EVALCONTROL BOARD package.
Connector J6 J7 J8 J9
Function 96-Way Connector used to interface to EVALCONTROL BOARD External VDD & AGND power connector. External +12V, -12V & AGND power connector. External DVDD & DGND power connector.
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Figure 3. Main Screen
SOFTWARE DESCRIPTION
Included in the EVAL-AD7887CB evaluation board package is a PC-compatible disk which contains software for controlling and evaluating the performance of the AD7887 when it is operated with the EVAL-CONTROL BOARD. The EVAL-AD7887CB Demonstration / Evaluation Software runs under DOS 4.0 or later and requires a minimum of a 386-based machine with 400kB of base RAM and 500kB of free hard disk space. The user interface on the PC is a dedicated program written especially for the AD7887. The disk which accompanies the EVAL-AD7887CB contains several files. The user should create a new directory on the main PC drive and label this "AD7887". Then, all files on the EVAL-AD7887CB disk should be copied into this directory. The Mouse Driver on the PC should be enabled before running the software. If this has not been loaded, the program will not run. To run the software, simply make the AD7887 directory the current directory and type "go". When the evaluation program starts, the user sees the screen shown on Figure 3 (without any FFT or scope waveforms). This is the main screen and it is divided into three parts. The top part provides the main control interface for the AD7887 evaluation software. The middle part of the main screen functions as a Digital Storage Oscilloscope and the bottom part of the main screen operates as either a Digital Spectrum Analyzer or a Histogram analyzer. Each part of the screen has several buttons that can be pressed by using the mouse or the keyboard. To press a button using the mouse, simply use it to move the on-screen pointer to the button to be activated and click. To use the keyboard, simply press the appropriate key as highlighted on the button. Lower
case letters must be used. When a button is pressed, it is highlighted on the screen. The next button can be highlighted by using the Tab key or the previous button by holding down the shift key and the Tab key together. The highlighted button can also be pressed by pressing the space bar. Pressing the ESC key halts any operation currently in progress. In this document, if a button can be activated from the keyboard then the key used is shown in bold in the button name. For example, "no prog" has the "p" highlighted in bold, indicating that the button can be activated by pressing the p key. Some buttons have a red indicator. A red indicator on the button means that the function associated with that button is on. Absence of the red indicator light means that the function associated with the button is off. The on / off status of these buttons is changed simply by selecting the button.
Setting up the EVAL-CONTROL BOARD
When the software is run, the "F2 Setup" button in the top left of the screen should be selected to pop up the setup menu (see fig. 4). This menu sets up the EVAL-CONTROL BOARD for use with the EVAL-AD7887CB. Firstly, the configuration file must be loaded. The configuration file contains the default configuration information for the EVAL-CONTROL BOARD, the Digital Spectrum Analyzer and the Digital Storage Oscilloscope. It also tells the AD7887.EXE software which .HIP file to download to the ADSP-2111. The .HIP file contains the DSP code which is executed by the ADSP-2111. Normally, the "no prog" button is off, so when the configuration file is loaded, the .HIP file is automatically downloaded to the ADSP-2111. However, if the "no prog" button is on, then the .HIP file is not downloaded to the ADSP-2111. -6- REV. 0
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F7: F10:
INFORMATION WINDOWS
Figure 4. Setup Menu Screen
Single channel operation is selected by depressing the "Single" button. Dual channel operation is selected by depressing the "Dual" button. This in turn allows the user to select between the 2 input channels using the "1" and "2" buttons. When using dual channel mode, the user must ensure that the onchip reference is disabled as the AD7887 uses VDD as the reference internally.l The "Analog in" section shows the analog input range and DC offset voltage.
MAIN SCREEN
There are three information windows at the top of the main screen. The left-hand window is the configuration window and gives details about part being evaluated. It shows the name of the program that has been downloaded to the EVALCONTROL BOARD, the sampling frequency, the number of bits, the analog input range of the part and the output code format of the part. The right-hand large window is the Status window. This window provides feedback to the user as to what operations are currently being performed by the software and also displays error messages. Directly underneath the status window is a small window that shows the selected conversion sequence and the maximum and minimum values of the most recently captured samples for all channels in the conversion sequence.
The top left part of the main screen contains eight buttons which are selected using the mouse or by using the function keys from the keyboard. These buttons and the actions they perform are: F1: F2: F3: Info. This button shows information on the software. Setup. This button activates the setup menu. Samp. When this key is pressed, the software causes the AD7887 to perform a number of conversions as determined by the setup menu (see above). The data -7-
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Test Mode
DIGITAL STORAGE OSCILLOSCOPE.
When the "dual" button is on, the oscilloscope screen is divided into two parts with the sampled data display centered on one horizontal axis and the windowed data display centered on another. When the "dual" button is off, both traces are centered on the same horizontal axis. This button toggles the sampled data trace on and off. This button toggles the windowed data trace on and off.
HISTOGRAM ANALYZER
The histogram analyzer counts the number of occurrences of each code in the captured samples and displays a histogram of these counts. The most frequently occurring code is displayed in the center of the histogram. The analyzer is normally used with a dc input signal and calculates the mean and the standard deviation of the sampled data. The mean and standard deviation are displayed in both volts and in units of the lsb size of the converter. The histogram gives a good indication of the dc noise performance of the ADC. The standard deviation shows directly the noise introduced in the conversion process. Each channel is the sequence can be viewed in turn using the 4 channel select buttons on the right of the histogram screen
Figure 5 Histogram Screen
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Figure 5. AD7887 Evaluation Board Circuit Diagram
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Table V. - Eval-AD7887CB Bill Of Materails.
Qty Reference Semiconductors: 1 1 1 1 2 U1 U2 U3 U4 D1 D2
Dsrtn eci i p o
Manufacturer
AD7887BR OP467GP AD780AN 74HC04N SD103C
ADI ADI ADI Fairchild ITT / Cannon FEC 378-252
Capacitors: 3 2 12 11 C1 C2 C3 C4 C5 C6 C8 C10 C12 C13 C15 C17 C19 C21 C23 C26 C27 C7 C9 C11 C14 C16 C18 C20 C22 C24 C25 C28 10nf Multilayer Ceramic 68pf Multilayer Ceramic 0.1uF Multilayer Ceramic 10uF 16V Tantalum Philips Philips Philips AVX FEC 143-729 FEC 237-024 FEC 262-257 FEC 643-683
Miscelleanous: 7 1 1 9 5 1 2 1 36 4 LK1 LK2 LK5-9 LK3 LK4 LK1-9 J1-5 J6 J7 J9 J8 U2 U3 U4 Each Corner 2 way jumper 4 way jumper 1 way jumper Shorting shunt 50 gold SMB socket 96 pin DIN41612 rt. Angle PCB plug 2 pin terminal block 3 pin terminal block Ultra Low profile socket pins Rubber Stick-on Feet Harwin Harwin Harwin Harwin M / Acom Harting Augat Augat Harwin 3M FEC 511-833 FEC 511-833 FEC 511-833 FEC 150-410 FEC 310-682 FEC 104-986 FEC 151-789 FEC 151-790 FEC 519-959 FEC 148-922
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Figure 6. Component Side Artwork
Figure 7. Solder Side Artwork
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Figure 8. AD7887 Evaluation Board Component Placement Drawing.