Evaluation Board for 3V to 5V, 200KSPS,
8-Channel, 12-Bit Sampling ADC
OPERATING THE AD7858 EVALUATION BOARD
Full-Featured Evaluation Board for the AD7858
EVAL-CONTROL BOARD Compatible
When using this evaluation board with the EVAL-CONTROL
Stand Alone Capability
B O A R D all supplies are provided from the EVAL-
Compatible with 3.3V and 5V Systems
CONTROL BOARD through the 96-way connector.
On-Board Reference and Digital Buffers
The evaluation board uses extensive ground planes to
Various Linking Options
minimise high frequency noise interference from the on-
PC Software for Control and Data Analysis when used
board clocks or any other sources. The ground plane for
with EVAL-CONTROL BOARD
the analog section is kept separate from that of the digital
section and they are joined only at the AD7858 AGND
This Technical Note describes the evaluation board for the
and DGND pins. Therefore, it is recommended not to
AD7858 8-channel, 12-Bit A/D converter. The AD7858 is
connect AGND and DGND elsewhere in the system to
a high speed, low power ADC that operates from a single
avoid ground loop problems.
+3V to +5V power supply and features throughput rates up
When using the board as a stand alone unit external supplies
to 200KSPS. It features self-calibration and system calibration
must be provided. This evaluation board has five power
options and also includes a power down mode. It incorporates
supply inputs: VAA, +12 V, -12 V, AGND and DGND. The VDD
an on chip track/hold amplifier and a versatile serial I/O
is used to to supply both the AVDD and the DVDD of the
port. This flexible serial interface allows the AD7858 to
AD7858 directly, and is also connected to the VCC pin of the
connect directly to Digital Signal Processors (ADSP-2189M,
74HC04. The +12V and -12V supply the different op amps,
TMS320C25, etc.) and Microcontrollers (8XC51, 68HC11,
biasing circuit and external reference. The AGND input is
etc.). Full data on the AD7858 is available in the AD7858
connected to the analog ground plane and the DGND input
datasheet which is available from Analog Devices and
is connected to the digital ground plane.
should be consulted in conjunction with this Technical Note
All analog supply pins are decoupled to AGND with 10?F
when using the Evaluation Board.
tantalum capacitors in parallel with 0.1?F multilayer ceramic
On-board components include an AD780 which is a pin
capacitors. These pins are the AVDD pin of the AD7858, the
programmable +2.5 V or +3 V ultra high precision bandgap
+12V and -12V pins of the op amps and SSM2141, and the
reference, two OP-467 amplifiers, two OP-07's amplifiers,
+VIN pin of the external reference. The digital supply for the
an SSM2141 line receiver and a 74HC04 quad AND gate.
AD7858 is decoupled to DGND with a 10?F tantalum
Interfacing to this board is through a 96-way connector.
capacitor in parallel with a 0.1?F disc ceramic capacitor at
This 96-way connector is compatible with the EVAL-
the power supply terminals and at the DVDD pin of the
CONTROL BOARD which is also available from Analog
AD7858. The logic chip, 74HC04, is deocupled with a DIL
Devices. External sockets are provided for the analog input,
0.02?F capacitor to DGND.
the clock input, conversion start input, external Vref and
external supplies if required.
Figure 1. FUNCTIONAL BLOCK DIAGRAM
-1 2 V
C L K IN
A IN 1
A IN 2
A D O P -4 6 7
A IN 3
A IN 4
A IN 5
A IN 6
A D O P -4 6 7
A IN 7
A IN 8
R E F IN
B ias in g c irc u it
R e fe re n c e
B IA S E D V IN
a n d s ig n a l
c o n d itio n in g
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
One Technology Way, PO. Box 9106, Norwood, MA 02062-9106, U.S.A.
infringements of patents or other rights of third parties which may result from its
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use. No license is granted by implication or otherwise under any patent or patent
Analog Devices, Inc., 2002
rights of Analog Devices.
LINK AND SWITCH OPTIONS
There are a number of link options on the evaluation board which should be set for the required operating setup before using
the evaluation board. The functions of these link options are outlined below.
These link options are used to select the input source for the eight buffer amplifiers.
With these links in position A, the input to the respective buffer amplifier is connected to the associated AINX
With these links in position B, the input to the respective buffer amplifier is connected to AGND.
This link option is in series with the AIN1 input of the AD7858.
With this link in place, the output of the amplifier A1 is connected directly to the AIN1 input.
When this link is not in place, the output of A1 is disconnected from AIN1. This is useful in association
with LK10 and LK11 in looking at the performance of the AD7858 with input shorted to ground especially
in differential mode where AIN1 and AIN2 form a differential pair. LK9 should not be in place if both LK10
and LK11 are in place (LK11 either position A or B).
This link option connects the AIN1 and AIN2 inputs of the AD7858 together.
With this link in place, the AIN1 and AIN2 inputs are connected together. LK10 should not be in place if
both LK9 and LK11 are in place (LK11 either position A or B).
When generating AIN1 from A1 and AIN2 from A2, this link should not be in place.
This link option is in series with AIN2 input of the AD7858.
With this link in position A, the output of the buffer amplifier A2 is connected directly to the AIN2 input.
With this link in position B, the AIN2 input is connected to AGND.
LK11 should not be in place if both LK9 and LK10 are in place.
This link option determines the output voltage from the AD780.
With this link in position, the reference voltage output from the AD780 is +3V.
With this link unconnected, the reference voltage output from the AD780 is +2.5V.
This link option selects the reference source for the AD7858 and for the bias circuit.
With this link in position, the reference source is the AD780 output voltage.
With this link unconnected, the reference source is the internal reference of the AD7858.
This link option adds a 50Ω termination to AGND at the VIN socket. In most applications this link will be
If a 50Ω termination is required this link should be connected. Care must be taken when connecting this link
in case the signal source driving the VIN socket cannot drive a 50Ω load.
When the signal source driving the VIN socket has a 50Ω ouput impedance it may be advantageous to connect
this link to give the correct termination to AGND.
This link option is used to select between normal mode operation and sleep mode depending on the status
of the PMGT bits of the Control Register.
With this link in position A, the SLEEP pin is tied to a logic high and normal operation results.
With this link in position B, the SLEEP pin is tied to a logic low and the part is put into sleep mode.
This link option is in series with the BUSY output to the 96-way connector.
This link has the function of connecting the BUSY output to the 96-way connector.
This link option adds a 50Ω termination to DGND to the CONVST line.
This link option should be unconnected when using the CONVST from the EVAL-CONTROL BOARD.
If a 50Ω termination is required when using an external CONVST signal this link should be connected.
This link option adds a 50Ω termination to DGND to the CLKIN line.
This link option should be unconnected when using the CLKIN from the EVAL-CONTROL BOARD.
If a 50Ω termination is required when using an external CLKIN signal this link should be connected.
This link option is in series with the SCLK1 input from the 96-way connector. When using the EVAL-
CONTROL BOARD this input supplies the clock signal for the CLKIN input of the AD7858.
This link should be connected when using the EVAL-CONTROL BOARD and no external CLKIN signal.
This link should be unconnected when using an external CLKIN signal.
This link option is in series with the FL0 input from the 96-way connector. When using the EVAL-
CONTROL BOARD this input can be used to supply the conversion start signal for the CONVST input
of the AD7858.
This link should be connected when using the EVAL-CONTROL BOARD and no external CONVST
This link should be unconnected when using an external CONVST signal.
This link option is used to tie the DIN pin to DGND or to connect it to the 96-way connector.
In position A, the DIN pin is connected to the 96-way connector and writting to the part can take place.
In position B, the DIN pin is tied to DGND and there will be no writing to the part.
When using the EVAL-CONTROL BOARD this link should be in position A.
Determines the source for the +12V required by the evaluation board.
With this link in position A, the +12V must be supplied externally at the +12V power supply terminal
With this link in position B, the +12V is supplied from the EVAL-CONTROL BOARD.
Determines the source for the -12V required by the evaluation board.
With this link in position A, the -12V must be supplied externally at the -12V power supply terminal
With this link in position B, the -12V is supplied from the EVAL-CONTROL BOARD.
This link must be unconnected if an external supply is used. This link option is used to select between an
external VDD supply and the VDD supply from the EVAL-CONTROL BOARD. The VDD supplies the AVDD
and the DVDD for the AD7858 and the VCC for the 74HC04.
With this link connected, the VDD is supplied from the EVAL-CONTROL BOARD. If this link is connected
an external supply must not be connected to the VDD power supply terminal connector.
With this link unconnected, the VDD must be supplied externally at the VDD power supply terminal connector.
This is a push button switch which is used to manually calibrate the AD7858.
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. These
links settings are consistent when operating with the EVAL-CONTROL BOARD.
Table I. Initial Link positions
Input to amplifier A1 comes from the AIN1 socket.
Input to amplifiers A2 through A8 connected to AGND.
Output of the amplifier A1 connected to the AIN1 input of the AD7858.
AIN1 and AIN2 inputs of the AD7858 not connected together.
Connects output A2 to AIN2 of AD7858.
Output of AD780 is +2.5V.
Reference source for the AD7858 and bias circuitry is AD780.
This ensures there is no 50Ω termination on the VIN line.
SLEEP pin tied to high for normal opertaion.
BUSY pin is connected to the IRQ2 pin of the 96-way connector.
This ensures there is no 50Ω termination on the CONVST line.
This ensures there is no 50Ω termination on the CLKIN line.
CLKIN pin is connected to the SCLK1 pin of the 96-way connector. Sets up the board for
the CLKIN being generated from the EVAL-CONTROL BOARD.
CONVST pin is connected to the FL0 pin of the 96- way connector. Sets up the board
for the CONVST being generated from the EVAL-CONTROL BOARD.
DIN pin is connected to the DT0 pin of the 96-way connecotr. Sets up the board for the
DIN generated from the EVAL-CONTROL BOARD.
+12V supplied via the 96-way connector. Sets up the board for +12V generated from the
-12V supplied via the 96-way connector. Sets up the board for -12V generated from the
VDD is supplied via the 96-way connector. Sets up the board for VDD generated from the
EVALUATION BOARD INTERFACING
Analog Ground. These lines are connected to
the analog ground plane on the evaluation
Interfacing to the evaluation board is via a 96-way connector,
SK4. SK4 is used to connect the evaluation board to the
Analog +3V to +5 V Supply. This line is
EVAL-CONTROL BOARD or other system. The pinout
connected to both the AVDD and DVDD (via
for the SK4 connector is shown in Figure 2 and its pin
LK24) supply lines on the board.
designations are given in Table II.
Table II. 96-Way Connector Pin Functions.
Figure 2. Pin Configuration for the 96-Way
Connector (looking in to the AD7858 evaluation board)
96-Way Connector Pin Description
Serial Clock 1. This is a logic input and is
connected to CLKIN pin on the device via
LK19. This is the master clock signal for the
device. It sets the conversion and calibration
Digital Ground. These lines 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
Data Transmit 0. This line is connected to the
DIN pin of the AD7858 via LK21. The data to
be loaded to the control register of the device is
applied to this pin in serial form.
Data Receive 0. The buffered output data from
the AD7858 is received at this pin as a 16-bit
TFS0,RFS0 Transmit Frame Synchronisation 0, Receive
Frame Synchronisation 0. These pins are tied
together on the connector and buffered from
the SYNC pin on the AD7858.
Serial Clock 0. This is a logic output and is
buffered before being applied the SCLK pin on
the device. SCLK0 is the serial clock for the
Flag Zero. This is a logic input and is
connected to the CONVST logic input on the
device via LK20. A low to high transition on
this input puts the track/hold amplifier into its
hold mode and starts a conversion.
Interrupt Request 2. This is a logic output and
is connected to the BUSY logic output on the
device via LK16. The output goes high when a
conversion begins and stays high until the
conversion is complete, at which time it goes
low. This output also indicates when the AD7858
the 96-way connector are not shown.
has completed its on-chip calibration sequence.
OPERATING WITH THE EVAL-CONTROL BOARD
There are thirteen sockets on the AD7858 evaluation board.
The evaluation board can be operated in a stand-alone mode
The functions of these sockets are outlined in Table III.
or operated in conjunction with the EVAL-CONTROL
B O A R D . The EVAL-CONTROL BOARD is available
f r o m Analog Devices under the order entry "EVAL-
Table III. Socket Functions
CONTROL BRD2". When operated with this control board,
all supplies and control signals to operate the AD7858 are
provided by the EVAL-CONTROL BOARD. Software to
AIN1-AIN8 Sub-Miniature BNC (SMB) socket for eight
communicate with the control board and AD7858 is pro-
analog input channels.
vided with the AD7858 evaluation board package. This
S u b - M i n i a t u r e BNC (SMB) socket for
EVAL-CONTROL BOARD will also operate with all Ana-
exteranl CONVST input.
log Devices evaluation boards which end with the letters CB
in their title.
S u b - M i n i a t u r e BNC (SMB) socket
external master clock input.
The 96-way connector on the EVAL-AD7858CB plugs
directly into the 96-way connector on the EVAL-CONTROL
Sub-Miniature BNC (SMB) socket which
BOARD. The EVAL-CONTROL BOARD provides all the
provides the voltage about which bipolar signals
supplies for the evaluation board. It is powered from a 12V
at the BIASED VIN output swing. This voltage
AC transformer. This is a standard 12V AC transformer
is nominally equal to one half the reference
capable of supplying 1A current and is available as an
voltage of the AD7858 (either internal or
accessory from Analog Devices under the following part
external reference). When using the BIASED
VIN voltage as the voltage for the AIN(+) of
a differential pair, this VREF/2 voltage should
For use in the U.S. or Japan
be applied to the respective AIN(-) input.
For use in the U.K.
Sub-Miniature BNC (SMB) socket for the
For use in Europe
analog input which is applied to the biasing
These transformers are also available from other suppliers
circuitry. The analog inputs of the AD7858
including Digikey (U.S.) and Campbell Collins (U.K.).
require an input voltage which is above AGND.
The biasing circuitry takes a true bipolar
Connection between the EVAL-CONTROL BOARD and
signal at VIN and generates a biased-up bipolar
the serial port of a PC is via a standard Printer port cable
signal which can be applied to the analog
which is provided as part of the EVAL-CONTROL BOARD
package. Please refer to the manual which accompanies the
EVAL-CONTROL BOARD for more details on the EVAL-
BIASED VIN Sub-Miniature BNC (SMB) socket which
CONTROL BOARD package.
provides the output of the biasing circuitry.
The BIASED VIN signal can be connected to
any of the AIN1 to AIN8 input sockets.
There are four connectors on the AD7858 evaluation board
as outlined in Table IV.
Table IV. Connector Functions
Connector for -12 V supply to the board when
using external supplies.
Connector for the +12V supply to the board
when using external supplies.
Connector for the DVDD supply to the board
when using external supplies.
96-Way Connector used to Interface to the
Figure 3. AD7858 Main Screen
The status window indicates the setup of the evaluation
Included in the EVAL-AD7858CB evaluation board pack-
board/device, number of samples taken and any information/
age is a CD ROM which contains software for controlling
error messages that are generated.
and evaluating the performance of the AD7858 when it is
The middle section of the AD7858 Main Screen is a Digital
operated with the EVAL-CONTROL BOARD. When the
Storage Oscilloscope (DSO). When samples are uploaded
CD is inserted into the PC an installation program will
from the Evaluation Control Board they are displayed here.
automatically begin. This program will install the evaluation
The samples can be displayed as either integer values or as
software onto the users machine and will also install the
voltages. Once the samples are displayed clicking any point
Technical Note for the AD7858 evaluation board as well as
on the graph will display the sample number and the value of
the datasheet for the AD7858. All literature on the CD is in
the point directly beneath the cursor. Along the axis of the
Adobe's Portable Documation format (PDF) and will require
graph are the " zoom handles ". These allow the user to zoom
Acrobat ReaderTM to be viewed or printed. The user interface
in and out to get a closer look at a particular sample if
on the PC is a dedicated program written especially for the
required. When another set of samples are taken the graph
will attempt to display all values collected unless the Hold
The software which controls the Evaluation Control Board
Zoom check box is ticked. If the Hold Zoom box is ticked
and hence the AD7858 evaluation board has three main
the graph will keep the same axis settings as for the previous
screens. The screen shown in Figure 3 shows the screen
set of data samples. There are additional check boxes in this
which appears when the software is run. The main function
section to give the user control over the vertical and horizon-
of the screen is to allow the user to read a predetermined
tal grids and data points.
number of samples from the evaluation board and display
The lowest section of the screen will show either a Fast
them in both the time and frequency domain. The screen can
Fourier Transform (FFT) of the data, or a histogram, which
be divided into three sections. The upper most section of the
shows the number of occurrences of each particular code read
screen contains the control buttons, the menu bar and the
back. The FFT (the default option) is typically used when the
status windows. The control buttons allow the user to take
user is concerned with examining an ADC's performance in
samples, reset the part and quit the program. The menu bar
the frequency domain, while the Histogram will give an
allows the user to enter the setup menu, select which printer
indication of the ADC's performance to DC signals. The
port is to be used to control the Evaluation Control Board,
option displayed can be changed by clicking on the FFT
load and save data, get information about the software, etc.
Figure 4. AD7858 Main Screen - Histogram Mode
Mode/Histogram Mode button in the top right of the screen.
SETTING UP THE EVALUATION CONTROL BOARD
Figure 4 shows how the Main Screen would look if the
The following text describes how the evaluation board,
Histogram Mode is selected.
Evaluation Control Board and software should be set up for
the user to begin using the complete system. The Evaluation
Control Board and evaluation board should be connected
together (via the 96-way connector). The power should be
The Setup Screen is responsible for allowing the user to load
applied to the Evaluation Control Board. At this stage the red
the required configuration file for the evaluation board. The
LED should be flashing which indicates that the Evaluation
configuration file will give the software detailed information
Control Board is functional and ready to receive instructions.
about the AD7858 evaluation board and part connected to the
The software, which should have been installed should be
Evaluation Control Board such as number of bits, maximum
loaded before the printer port cable is connected between the
sampling rate, output coding, maximum analog input, power
Evaluation Control Board and the PC. This will ensure that
supply requirements etc. The configuration file also tells the
the printer port has been initialized properly. The printer
software the name of the DSP program file which it should
port cable can then be connected between the PC and the
download to the Evaluation Control Board. These files are
Evaluation Control Board.
supplied by Analog Devices with the evaluation board.
Figure 5 shows the Setup Screen.
Running the Software
With the hardware set up the user is now in a position to use
the software to control the Evaluation Control Board and the
evaluation board. In the software the user should select the
File menu and click on Setup. This will display the setup
form. A window on the left of the setup form lists all the
available configuration files. The configuration files are text
based files which contain information about the particular
evaluation board to be tested. The information will cover
such things as the part name, number of samples to be taken,
Figure 5. The Setup Screen
another calibration option. Please see the AD7858 datasheet
default and maximum sampling frequency, power supply
for more information related to the Calibration selection.
settings etc. The configuration file also contains the name of
the DSP program file which is to be downloaded to the
Once all the settings have been decided, the user can click
Evaluation Control Board. The user should select the relevant
Close to return to the main form.
configuration file and click Load. The Evaluation Control
Board will be reset and the DSP program will be downloaded.
When the download has been completed the power supply
When the user clicks Sample the software will instruct the
settings indicated in the configuration file are set and the user
Evaluation Control Board to take the required number of
may hear some of the relays clicking. The pull-down menu
samples at the required frequency from the evaluation board.
items such as 'number of samples' and 'sampling frequency'
The AD7858 evaluation board will run up to 200 KSPS so
will have been set to the default values specified by the
the user can choose the sampling frequency up to this rate and
configuration file. The user is free to change these at will.
may also choose the number of samples to be taken. These
samples are then uploaded and displayed. An FFT and
Included in the Setup menu is the Channel Setup and the
Histogram are also calculated and displayed. If the user clicks
Calibration buttons. The Channel Setup button brings the
Cont Samp the software will repeat the process indefinitely
user into the Channel Setup screen. It allows the user to select
until the user clicks the button Stop Samp. While the
the mode of operation as regard the power consumption and
software is continuously sampling data the other control
the analog input channel configuration, single ended or
buttons are disabled.
pseudo-differential. By selecting SLG/DIFF=0, the input
channels will be shown as differential pairs, positive and
The Reset button will cause the Evaluation Control Board to
negative pin input respectively. If SLG/DIFF=1 is selected
perform a reset function. When this happens the power
the input channels will be configured as single ended. Figures
supplies are turned off and the program in DSP memory is
6 and 7 show the Channel Setup screen for the different input
lost. The user should repeat the setup instructions to download
another program if required.
The Quit button will exit the software, the program running
Pressing the Calibration button brings the user into the
on the Evaluation Control Board is not terminated.
Calibration Options screen. Several calibration options are
presented as shown in Figure 8. These options include Full
MENU BAR ITEMS
internal calibration, Full system calibration, Internal gain &
The main screen of the Evaluation Control Board contains a
offset calibration, System gain & offset calibration, Internal
number of options available as pull-down menu items. The
offset calibration, System offset calibration, Internal gain
functions of these are listed below.
calibration and System gain calibration. On selecting any of
the three Self calibration buttons the part is calibrated
appropriately. On selecting one of the System calibration
Setup Menu: Selecting this option displays the Setup Screen
buttons the user will be prompted by an extra pop-up window
as shown in Figure 5.
to apply the required system voltage across the AIN(+) and
Load Raw Data: Selecting this option allows the user to load
AIN(-) pins of the AD7858. Upon hitting the OK button in
data which had been saved by the software during a previous
this prompt window the part is calibrated and the software
returns to the Calibration Options menu. At this point the
Save Raw Data: Selecting this option allows the user to save
user can select OK to return to the Setup menu or select
the current set of sample data points. The data can be
Figure 7. The Channel Setup Screen,
Figure 6. The Channel Setup Screen,
Single Ended configuration
LPT2: This option selects 0x278 as the printer port address.
reloaded to the Evaluation Control Board software at a later
date or can be used by other programs for further analysis.
PRN: This option selects 0x3BC as the printer port address.
Save Binary Data: Selecting this option allows the user to
save the current set of sample data points. The data is saved
This menu item gives information about the current
in binary format as a text file. This method can be useful for
revision of software for the particular evaluation board
examining code flicker, looking for stuck bits, etc.
Save FFT Data: Selecting this option allows the user to save
the current set of FFT data points. FFT data cannot be
reloaded into the Evaluation Control Board software but can
SOFTWARE CONFIGURATION FILES
be loaded into other software packages for further analysis.
Software Configuration Files give the Evaluation Control
Exit: Quits the program.
Board software information on how the software and hardware
should perform. They contain information such as the name
of the DSP program to download, the default and maximum
sample frequencies, the number of samples to take and the
This menu item allows the user to select which printer port
power supply settings to use. A typical Software Configuration
should be used for communication with the Evaluation
File (*.cfg) is shown in Listing 1.
LPT1: This option selects 0x378 as the printer port address.
This is the default option.
;options 2scomp, binary
Figure 8. The Calibration Options Screen
Figure 7. AD7858 Evaluation Board Circuit Diagram
Table V. AD7858 Evaluation Board Bill Of Materials
D1, D2, D3, D4, D5
1?F Tantalum Bead
10?F Tantalum Bead
47?F Tantalum Bead
0.01?F Multilayer Ceramic C8,C18,C25,C27,C30,C31,
0.1?F Multilayer Ceramic C2,C4,C5,C9,C11,C13,C16,
10KΩ ?0.1% 0.25W
Welwyn RC55 Series
51Ω ?1% 0.25W
2 Pin Power Connector
96 Pin 90 DIN41612 Plug
2 Way Jumper (2x1)
2 Way Jumper (2x2)
2 Way Jumper (1x3)
50Ω Gold Plated SMB
VREF/2,Vin, Biased Vin,
8 Way Low Profile IC Socket
14 Way Low Profile IC socket
Rubber Stick-on Feet
Figure 9. Component Side Artwork
Figure 10. Solder Side Artwork
Figure 11. AD7858 Evaluation Board Component Placement Drawing.