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a
Evaluation Board for the AD7707 3V/5V, +/-10V Input Range, 1mW, 3Channel, 16-Bit, Sigma Delta ADC EVAL-AD7707EB
Other components on the AD7707 Evaluation Board include an AD780 (a precision 2.5V reference), an AD589 (a 1.23V precision bandgap reference), a 4.9152 MHz crystal and digital buffers to buffer signals to and from the PC.
OPERATING THE AD7707 EVAL BOARD Power Supplies
FEATURES Full-Featured Evaluation Board for the AD7707 On-Board Reference and Digital Buffers Various Linking Options PC Software for Control of AD7707 On-Board Patchwork Area INTRODUCTION
This Technical Note describes the evaluation board for the AD7707, 3V/5V, +/-10V Input Range, 1mW, 3 Channel, 16Bit, Sigma Delta ADC. The AD7707 is a complete analog front end for low frequency measurement applications. This three-channel device can accept either low level input signals directly from a transducer or high level ( 4 x VBIAS) signals and produce a serial digital output. The AD7707 operates from a single 2.7V to 3.3V or 4.75V to 5.25V supply. The AD7707 features two low level pseudo-differential analog input channels, one high level input channel and a differential reference input. Full data on the AD7707 is available in the AD7707 datasheet available from Analog Devices and should be consulted in conjunction with this Technical Note when using the evaluation board. The evaluation board interfaces to the parallel port of an IBM compatible PC. Software is available with the evaluation board which allows the user to easily program the AD7707.
This evaluation board has two analog power supply inputs: AVDD and AGND. An external +5V or +3V must be applied between these inputs which is used to provide the AVDD for the AD7707 and the reference. DGND and DVDD connections are also available. The DVDD is used to provide the DVDD for the AD7707 DVDD pin and the digital circuitry. When AVDD is set to +5V, DVDD can be +3V or +5V. When AVDD is set to +3V, DVDD can only be +3V. DVDD should never exceed AVDD. DGND and AGND are connected together under the AD7707. Therefore, it is recommended not to connect AGND and DGND elsewhere in the system. All power supplies are decoupled to their respective grounds. DV DD is decoupled using a 10F tantalum capacitor and 0.1F ceramic capacitor as close as possible to the AD7707 DVDD pin. It is again decoupled using 0.1F capacitors as close as possible to each logic device. AVDD is decoupled using a 10F tantalum capacitor and 0.1F ceramic capacitor as close as possible to the AD7707 and also at the reference.
Figure 1: Evaluation Board Setup
VREFDVDD DG ND AG N D AVD D VR EF+
AD 1580 REFERENCE
AG N D
AD 780 REFERENC E
36 -W A Y C E N T R O N IC S CO NN ECTO R
B UFFER S
AD 7707 AD C
9- W A Y D -T Y P E C O N N E C T O R
CRYST AL
M C L K IN
A IN 1
LCO M
A IN 2
A IN 3
HCOM
H B IA S
REV. A
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood. MA 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703
EVAL-AD7707EB
LINK AND SWITCH OPTIONS
There are ten link options which must be set for the required operating setup before using the evaluation board. The functions of these link options are outlined below.
Link No. Function
LK1
This option selects the master clock source for the AD7707. The master clock is generated by the on-board crystal or from an external source via SKT11. This is a double link and both links must be moved together for the correct operation of the evaluation board. With both links in position "A", the external clock option is selected and an external clock applied to SKT11 is routed to the MCLKIN pin of the AD7707. With both links in position "B", the on-board crystal is selected to provide the master clock to the AD7707. This link is used to select the on-board reference. With this link in position "A", the AD780 is selected as the on-board reference. This provides a 2.5V reference which is suitable for the AD7707 operating at +5V. With this link in position "B", the AD589 is selected as the on-board reference. This provides a 1.23V reference which is suitable for the AD7707 operating at +3V. This link is used to select the reference source for the REFIN(-) input of the AD7707. With this link in position"A", the REFIN(-) pin is connected directly to AGND. With this link in position "B", the REFIN(-) pin is connected to SKT10. An external voltage applied to SKT10 can now be used as the REFIN(-) for the AD7707. This link is used to select the With LK4 in position "A", the With LK4 in position "B", the now be used as the REFIN(+) reference source for the REFIN(+) input of the AD7707. REFIN(+) pin is connected to the output of the on-board reference. REFIN(+) pin is connected to SKT9. An external voltage applied to SKT9 can for the AD7707.
LK2
LK3
LK4
LK5
This link is in series with the AIN1 input of the AD7707. With this link in place, an analog input signal applied to SKT3 is routed directly to the AIN1 pin of the AD7707. This link may be removed so that the user can add signal conditioning circuitry if required. This link is in series with the AIN2 input of the AD7707. With this link in place, an analog input signal applied to SKT4 is routed directly to the AIN2 pin of the AD7707. This link may be removed so that the user can add signal conditioning circuitry if required. This link is in series with the AIN3 input of the AD7707. With this link in place, an analog input signal applied to SKT5 is routed directly to the AIN3 pin of the AD7707. This link may be removed so that the user can add signal conditioning circuitry if required. This With With With link this this this is used link in link in link in to select the position "A", position "B", position "C", common input for low level input channels (AIN1 and AIN2). the LCOM input is tied to AGND. the LCOM input is tied to VREF. the LCOM input is set to a voltage applied to SKT6.
LK6
LK7
LK8
LK9
This link is connected to the HBIAS pin. It used to signal condition the high level input channel (AIN3). With this link in positoin "A", the HBIAS pin is tied to the REFIN+ pin of te AD7707. With this link in position "B", a voltage applied to SKT7 is applied to the HBIAS pin. This link is connected to the HCOM pin of the AD7707. It stes the common input voltage for the high level input channel (AIN3). With this link in position "A", the HCOM input is tied to AGND. With this link in position "B", the HCOM input is tied to VREF. With this link in position "C", the HCOM input is set to a voltage applied to SKT8.
LK10
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SET-UP 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 1 shows the position in which all the links are set when the evaluation board is sent out.
Table 1: Initial Link and Switch Positions Link No. Position Function
LK1 LK2 LK3 LK4 LK5 LK6 LK7 LK8 LK9 LK10
B+B A A A IN IN IN A A A
Both links in position "B" to select the on-board crystal as the master clock for the AD7707. This selects the AD780 +2.5V output as the on-board reference. This connects the REFIN(-) input of the AD7707 to AGND. The on-board reference provides the reference voltage for the REFIN(+) input of the AD7707. The AIN1 pin on the AD7707 is tied to the analog input sockets SKT3. The AIN2 pin on the AD7707 is tied to the analog input sockets SKT4. The AIN3 pin on the AD7707 is tied to the analog input sockets SKT5. The LCOM pin on the AD7707 is tied to the AGND. The HBIAS pin of the AD7707 is tied to the REFIN+ pin. The HCOM pin on the AD7707 is tied to the AGND.
EVALUATION BOARD INTERFACING
Interfacing to the evaluation board is via either a 9-way d-type connector, SKT1 or a 36-way centronics connector, SKT2. The pin-out for the SKT1 connector is shown in Fig. 2 and its pin designations are given in Table 2. The pin-out for the SKT2 connector is shown in Fig. 3 and its pin designations are given in Table 3. SKT2 is used to connect the evaluation board to the parallel (printer) port of a PC. Connection is via a standard printer cable. SKT1 is used to connect the evaluation to any other system. The evaluation board should be powered up before a cable is connected to either of these connectors.
1
2
3
4
5
6
7
8
9
Fig. 2: Pin Configuration for the 9-Way D-Type Connector, SKT1. Table 2.: SKT1 Pin Description
1
1 2 3 4 5 6 7 8 9
1
SCLK DRDY CS DIN DGND DOUT DV DD NC
Serial Clock. The signal on this pin is buffered before being applied to the SCLK pin of the AD7707. Logic output. This is a buffered version of the signal on the AD7707 DRDY pin Chip Select. The signal on this pin is buffered before being applied to the CS pin on the AD7707. Serial Data Input. Data applied to this pin is buffered before being applied to the AD7707 DIN pin. Ground reference point for the digital circuitry. Connects to the DGND plane on the Evaluation board. Serial Data Output. This is a buffered version of the signal on the AD7707 DOUT pin. Digital Supply Voltage. If no voltage is applied to the board's DVDD input terminal then the voltage applied to this pin will supply the DVDD for the digital buffers. Not Connected.
RESET Reset Input. Data applied to this pin is buffered before being applied to the AD7707 RESET pin.
Note An explanation of the AD7707 functions mentioned here is given in Table 3 overleaf as part of the SKT2 pin descriptions.
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18 1
36
19
Fig. 3: 36-way Centronics (SKT2) Pin Configuration
Table 3: 36-Way Connector Pin Description
1 2
NC DIN
No Connect. This pin is not connected on the evaluation board. Serial Data Input. Data applied to this pin is buffered before being applied to the AD7707 DIN pin. Serial Data Input with serial data being written to the input shift register on the part. Data from this input shift register is transferred to the setup register, clock register or communications register depending on the register selection bits of the Communications Register. Reset Input. The signal on this pin is buffered before being applied to the RESET pin of the AD7707. RESET is an active low input which resets the control logic, interface logic, calibration coefficients, digital filter and analog modulator of the part to power-on status. Chip Select. The signal on this pin is buffered before being applied to the CS pin of the AD7707. CS is an active low Logic Input used to select the AD7707. With this input hard-wired low, the AD7707 can operate in its three-wire interface mode with SCLK, DIN and DOUT used to interface to the device. CS can be used to select the device in systems with more than one device on the serial bus or as a frame synchronization signal in communicating with the AD7707. Serial Clock. The signal on this pin is buffered before being applied to the SCLK pin of the AD7707. An external serial clock is applied to this input to read/write serial data from/to the AD7707. This serial clock can be continuous with all data transmitted in a continuous train of pulses. Alternatively, it can be non-continuous with the information being transmitted to the AD7707 in smaller batches of data. No Connect. These pins are not connected on the evaluation board. Digital Supply Voltage. This provides the supply voltage for the buffer chips, U3-U5, which buffer the signals between the AD7707 and SKT1/SKT2. Logic output. This is a buffered version of the signal on the AD7707 DRDY pin. A logic low on this output indicates that a new output word is available from the AD7707 data register. The DRDY pin will return high upon completion of a read operation of a full output word. If no data read has taken place between output updates, the DRDY line will return high for 500 x CLK IN cycles prior to the next output update. While DRDY is high, a read operation should not be attempted to avoid reading from the data register as it is being updated. The DRDY line will return low again when the update has taken place. DRDY is also used to indicate when the AD770-55 has completed its on-chip calibration sequence. No Connect. These pins are not connected on the evaluation board. Serial Data Output. This is a buffered version of the signal on the AD7707 DOUT pin. Serial Data Output with serial data obtained from the output shift register on the AD7707. The output shift register can contain information from the setup register, communications register, clock register or data register depending on the register selection bits of the Communications Register. No Connect. These pins are not connected on the evaluation board. Ground reference point for digital circuitry. Connects to the DGND plane on the evaluation board. No Connect. These pins are not connected on the evaluation board.
3
RESET
4
CS
5
SCLK
6-8 9 10
NC DVDD DRDY
11-12 13
NC DOUT
14-18 19-30 31-36
NC DGND NC
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SOCKETS CONNECTORS
There are eleven sockets relevant to the operation of the AD7707 on this evaluation board. The functions of these sockets are outlined in Table 4.
Table 4. Socket Functions
There are two connectors on the AD7707 evaluation board as outlined in Table 5.
Table 5. Connector Functions Functions
Connector Socket Function
J1
SKT1 SKT2 SKT3
9-way D-Type connector used to interface to other systems. 36-way centronics connector used to interface to PC via parallel printer port. Sub-Miniature BNC (SMB) Connector. The analog input signal for the AIN1 input of the AD7707 is applied to this socket. Sub-Miniature BNC (SMB) Connector. The analog input signal for the AIN2 input of the AD7707 is applied to this socket. Sub-Miniature BNC (SMB) Connector. The analog input signal for the AIN3 input of the AD7707 is applied to this socket. Sub-Miniature BNC (SMB) Connector. The analog input signal for the LCOM input of the AD7707 may be applied to this socket. Sub-Miniature BNC (SMB) Connector. The analog input signal for the HBIAS input of the AD7707 may be applied to this socket. Sub-Miniature BNC (SMB) Connector. The analog input signal for the HCOM input of the AD7707 may be applied to this socket. Sub-Miniature BNC (SMB) Connector. The reference voltage for the REFIN+ input of the AD7707 is applied to this socket when the board is configured for an externally applied reference voltage. Sub-Miniature BNC (SMB) Connector. The reference voltage for the REFIN- input of the AD7707 is applied to this socket when the board is configured for an externally applied reference voltage. Sub-Miniature BNC (SMB) Connector. The master clock signal for the MCLKIN input of the AD7707 is applied to this socket when the board is configured for an externally applied master clock.The AD7707 can be operated with internal clock frequencies in the range 500kHz to 5MHz. J2
PCB Mounting Terminal Block. The Digital Power Supply to the Evaluation Board must be provided via this Connector if it is not being supplied via SKT1 or SKT2. PCB Mounting Terminal Block. The Analog Power Supply to the Evaluation Board must be provided via this Connector.
SKT4
SWITCHES
SKT5
There is one switch on the AD7707 Evaluation board. SW1 is a push-button reset switch. Pushing this switch activates the active low RESET input on the AD7707 which resets the control logic, interface logic, calibration coefficients, digital filter and analog modulator of the part to power-on status.
SKT6
SKT7
SKT8
SKT9
SKT10
SKT11
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AD7707 SOFTWARE DESCRIPTION
The AD7707 evaluation board is shipped with a 31/2" disk containing software that can be installed onto a standard PC to control the AD7707. The software uses the printer port of the PC to communicate with the EVAL-AD7707EB, so a Centronics printer cable is used to connect the PC to the evaluation board.
Software Requirements and Installation
The software runs under Windows 3.1TM or Windows 95TM and typically requires 4Mb of RAM. To install the software the user should start Windows and use either File Manager (in Windows 3.1) or Windows Explorer (in Windows 95) to locate the file called SETUP.EXE on the floppy disk. Double clicking on this file will start the installation procedure. The user is prompted for a destination directory which is "C:\AD7707" by default. Once the directory has been selected the installation procedure will copy the files into the relevant directories on the hard drive. The installation program will create a Program Group called "Analog Devices" on the desktop for Windows 3.1 or in the "Start" taskbar for Windows95. Once the installation procedure is complete the user can double click on the AD7707 icon to start the program.
Features of the Software
1. The software will allow the user to write to and read from all the registers of the AD7707. 2. Data can be read from the AD7707 and displayed or stored for later analysis. 3. The data that has been read can be exported to other packages such as Mathcad or Excel for further analysis.
Fig. 4. The Main Screen
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What follows is a description of the various windows that appear while the software is being used. Fig. 4. shows the main screen that appears once the program has started. The printer port that will be used by the software is shown in the top left of the screen. There are three possible printer ports that can be handled by the software, LPT1 (standard), LPT2 and PRN. In the event that the PC has two printer ports the software will always select the one which is set as default by the PC. The user can change to the other printer port by using the "Select Printer Port" button on the main screen. A brief description of each of the buttons on the main screen follows: Program AD7707 Read Data Noise Analysis Reset AD7707 Read From File Write To File Select Printer Port About Quit Allows the user to program the selected register for a specific channel of the AD7707. Allows the user to read a number of samples from the AD7707. These samples can be stored for further analysis or just displayed for reference. Allows the user to perform noise analysis on the data that has been read in. Allows the user to perform a reset on the AD7707. Allows the user to read in previously stored data for display or analysis. Allows the user to write the current set of data to a file for later use. Allows the user to change which printer port the software uses (only valid for PCs with more than one printer port). Provides information about the version of software being used. Ends the program
Fig. 5. The Program AD7707 Screen
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The Program AD7707 Screen
Fig. 5. shows the screen that appears when the Program AD7707 button is selected. This screen allows the user to select which register is to be programmed. Before selecting any of the buttons on this screen the user should first choose the channel that is to be used for all the subsequent operations. The state of the Standby bit should also be selected here.
The Setup Register Screen
Fig. 6. shows the Setup Register screen. When the screen is loaded the software will read the current contents from the Setup Register of the AD7707 and change the option buttons accordingly. The setup register is used to change the operating mode of the AD7707, change the gain setting, set the part to bipolar or unipolar mode, set the part to buffered or unbuffered mode and select the state of the FSYNC bit. Every time a change is made the software will write the new conditions to the AD7707 and read back the setup register for confirmation.
Fig. 6. The Setup Screen
When the user selects a calibration, the software will start the calibration by writing to the AD7707 and then monitor the DRDY. A falling edge of the DRDY pin will indicate that the calibration has been completed. After a calibration the AD7707 returns to its normal operating mode and the program updates the screen to indicate this. The default status for the setup register on power-up is 01 (hex).
The Clock Register Screen
Fig. 7. shows the Clock Register setup screen. The Clock Register is used to control the output update rate of the AD7707. The CLKDIS bit is used to control the operation of the MCLKOUT pin. A logic 0 in this bit allows the AD7707 to function in its normal operating mode when a crystal oscillator is used as the clock source. A logic 1 disables the MCLKOUT from appearing at the pin. When disabled the MCLKOUT pin is forced low. If the AD7707 is using a crystal oscillator as the clock then disabling the MCLKOUT will stop the clock and no conversions will be done by the AD7707. The user should consult the datasheet for more information on the use of the CLKDIS bit.
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The CLKDIV is used to set the internal operating frequency of the AD7707. The user should consult the datasheet for more information on the use of the CLKDIV bit.
Fig. 7. The Clock Register Screen
The CLK bit is used in conjunction with the Output Update Rate buttons to select the output update rate. If the AD7707 is being operated with a clock of 4.9152MHz (CLKDIV=1) or 2.4576MHz (CLKDIV=0) then this bit should be set to a 1 giving a choice of 50Hz, 60Hz, 250Hz or 500Hz as an output update rate. If the AD7707 is being operated with a clock of 2MHz (CLKDIV=1) or 1MHz (CLKDIV=0) then this bit should be set to a 0 giving a choice of 20Hz, 25Hz, 100Hz or 200Hz as an output update rate. The Power-On/Reset status of this register is 05 hex.
Fig. 7. The Calibration Registers Screen
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The Calibration Registers Screen
Fig. 8. shows the Calibration Registers screen. When this screen is displayed the values of the Gain and Offset Registers are read from the AD7707 and displayed. The user has the ability to change the values of either register if required. the default value for the fullscale cal register is 5761AB hex and the default value for the zero scale cal register is 1F4000 hex.
The Read Data Screen
Fig. 9. shows the Read Data screen. This is where the user can read a number of samples from the AD7707. The user has the option of either reading data for analysis or display. When the Read For Analysis button is selected the software will read the required number of samples from the AD7707 and store them in an array so that they can be graphed or analysed later. It is possible to read upto 5000 samples at any one time although only 3000 can be displayed on a graph.
Fig. 9. The Read Data Screen
When the Read for Display button is selected the software will read one sample from the AD7707 and display its value in the Current Code text box. The software will continue to read and display the samples until a key has been pressed. It is possible to add a delay to the read cycle by checking the Use Delay Value checkbox. If the box is checked the software will wait the required number of milliseconds between reading samples. It should be noted however that the accuracy of the time delay can be affected by other programs running under Windows, therefore this method is not suitable where equidistant sampling is required.
The Noise Analysis Screen
Once data has been read from the AD7707 it is possible to perform some analysis on it. Fig. 10. shows the Noise Analysis Screen. This screen displays the maximum and minimum codes read from the AD7707 (in decimal and hexadecimal), as well as the average code, the average voltage and the RMS and Peak-Peak noise values. From this screen it is possible to display the data on a graph or as a histogram of codes. Figures 11 and 12 show the Graph and Histogram screens.
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Fig. 10. The Noise Analysis Screen
Fig. 11. The Graph Screen The Graph Screen
This screen displays the data in graph format. A rolling average feature is available by selecting the rolling average button. By default this is a 5 point rolling average but this can be changed to any integer between 1-99. The list codes button allows the user to view all the codes and the number of occurences of these codes.
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Fig. 12. The Histogram Screen
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Fig. 13. The Evaluation Board Schematic
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Table 6. Component Listing and Manufacturers INTEGRATED CIRCUITS Component Location Vendor
AD7707AR AD780AN 74HC4050N 74C08N 74HC244N AD1580 SD103C
U1 U2 U3 U4 U5 U6 D1
Analog Devices Analog Devices Philips Texas Instruments Texas Instruments Analog Devices ITT
CAPACITORS Component Location Vendor
10F 20% Tantalum (16 V) 0.1F Ceramic(X7R 20%) 0.01uF NP0 33pF 2% Ceramic
C1 C4 C5 C9 C2 C3 C6 C7 C8 C10 C15 C12 C13 C14 C16 C17
AVX- Kyocera Mftrs No TAG106MO16 Philips Mftrs No. CW20C 104M AVX-Kyocera Mftrs No. SR20X7R Philips Mftrs No. 683 34339
RESISTORS Component Location Vendor
Short Circuits 3k5% 0.25W Carbon Film 10k5% 0.25W Carbon Film 1M5%
R1 R2 R3 R5 R7 R8
---------Bourns 3k 5% Bourns 6.8k 5% Bourns 10k 5% Bourns 1M 5% 0.25W 0.25W 0.25W 0.25W
6.8k5% 0.25W Carbon Film R6 0.25W Carbon Film R9
LINK OPTIONS Component Location Vendor
Pin Headers
Lk1 Lk2 Lk8 Lk5
(4x2 way) Lk3 Lk4 Lk9(2x2 way) Lk10 (3x2 way) Lk6 Lk7 (1x2 way)
Harwin Mftrs No. M20-9993606
Shorting Plugs
Pin Headers (11 required)
Harwin Mftrs No. M7571-05
SWITCH Component Location Vendor
Sealed Push Button Switch
SW1
Omron Mftrs No. B3W1000
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SOCKETS Component Location Vendor
Miniature BNC Connectors 9-Way D-Type Connector 36 Way Centronics Connector 2 Way Terminal Block Low profile socket
SKT3-SKT11 SKT1 SKT 2 J1 J2 U2 - U5 (58 pins needed)
M/A - Com Greenpar Mftrs No. B65N07G999X99 McMurdo Mftrs No. SDE9PNTD Fujitsu Mftrs No. FCN785J036G0 Bulgin RIA Harwin Farnell No. 519-959
CRYSTAL Component
OSCILLATOR Location Vendor
4.9152 MHz Oscillator
Xtal 1
IQD Mftrs No. A127A
Fig. 14. The Evaluation Board Component Layout Diagram
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Fig. 15. The Evaluation Board Component Side Artwork.
Fig. 16. The Evaluation Board Solder Side Artwork.
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