AD670JP ,Low Cost Signal Conditioning 8-Bit ADCSpecifications subject to change without notice.–2– REV. AAD670Model AD670A AD670B AD670SMin Typ Ma ..
AD670KN ,Low Cost Signal Conditioning 8-Bit ADCfeatures a differential instrumenta-The device is configured with input scaling resistors to permit ..
AD670KP ,Low Cost Signal Conditioning 8-Bit ADCspecificationsare guaranteed, although only those shown in boldface are tested on all production un ..
AD671JD-750 ,Monolithic 12-Bit 2 MHz A/D ConverterSPECIFICATIONS unless otherwise noted)AD671J/S-750 AD671K-750Parameter Min Typ Max Min ..
AD671KD-500 ,Monolithic 12-Bit 2 MHz A/D ConverterFEATURES12-Bit ResolutionAIN BPO/UPO ENCODE REF IN ACOM DCO ..
AD673JD ,8-Bit A/D Converterspecifications.from –55°C to +125°C.Two package configurations are offered. All versions are also o ..
ADC0838BCN ,8-Bit Serial I/O A/D Converter with Multiplexer OptionADC0831/ADC0832/ADC0834/ADC0838 8-Bit Serial I/O A/D Converters with Multiplexer OptionsJuly 2002AD ..
ADC0838BCV ,8-Bit Serial I/O A/D Converter with Multiplexer OptionGeneral Descriptionn No zero or full-scale adjust requiredTheADC0831seriesare8-bitsuccessiveapproxi ..
ADC0838BCV ,8-Bit Serial I/O A/D Converter with Multiplexer OptionADC0831/ADC0832/ADC0834/ADC0838 8-Bit Serial I/O A/D Converters with Multiplexer OptionsJuly 2002AD ..
ADC0838BCV ,8-Bit Serial I/O A/D Converter with Multiplexer OptionADC0831/ADC0832/ADC0834/ADC0838 8-Bit Serial I/O A/D Converters with Multiplexer OptionsJuly 2002AD ..
ADC0838CCJ ,8-Bit Serial I/O A/D Converter with Multiplexer OptionGeneral Descriptionn No zero or full-scale adjust requiredTheADC0831seriesare8-bitsuccessiveapproxi ..
ADC0838CCN ,Serial I/O 8-Bit A/D Converters with Multiplexer OptionsGeneral Descriptionn No zero or full-scale adjust requiredTheADC0831seriesare8-bitsuccessiveapproxi ..
AD670BD-AD670JN-AD670JP-AD670KN-AD670KP
Low Cost Signal Conditioning 8-Bit ADC
FUNCTIONAL BLOCK DIAGRAMREV.A
Low Cost Signal
Conditioning 8-Bit ADC
FEATURES
Complete 8-Bit Signal Conditioning A/D Converter
Including Instrumentation Amp and Reference
Microprocessor Bus Interface
10 ms Conversion Speed
Flexible Input Stage: Instrumentation Amp Front End
Provides Differential Inputs and High Common-Mode
Rejection
No User Trims Required
No Missing Codes Over Temperature
Single +5 V Supply Operation
Convenient Input Ranges
20-Pin DIP or Surface-Mount Package
Low Cost Monolithic Construction
MIL-STD-883B Compliant Versions Available
GENERAL DESCRIPTIONThe AD670 is a complete 8-bit signal conditioning analog-
to-digital converter. It consists of an instrumentation amplifier
front end along with a DAC, comparator, successive approxima-
tion register (SAR), precision voltage reference, and a three-
state output buffer on a single monolithic chip. No external
components or user trims are required to interface, with full
accuracy, an analog system to an 8-bit data bus. The AD670
will operate on the +5 V system supply. The input stage pro-
vides differential inputs with excellent common-mode rejection
and allows direct interface to a variety of transducers.
The device is configured with input scaling resistors to permit
two input ranges: 0 mV to 255 mV (1 mV/LSB) and 0 to 2.55 V
(10 mV/LSB). The AD670 can be configured for both unipolar
and bipolar inputs over these ranges. The differential inputs and
common-mode rejection of this front end are useful in applica-
tions such as conversion of transducer signals superimposed on
common-mode voltages.
The AD670 incorporates advanced circuit design and proven
processing technology. The successive approximation function
is implemented with I2L (integrated injection logic). Thin-film
SiCr resistors provide the stability required to prevent missing
codes over the entire operating temperature range while laser
wafer trimming of the resistor ladder permits calibration of the
device to within ±1 LSB. Thus, no user trims for gain or offset
are required. Conversion time of the device is 10 μs.
The AD670 is available in four package types and five grades.
The J and K grades are specified over 0°C to +70°C and come
in 20-pin plastic DIP packages or 20-terminal PLCC packages.
The A and B grades (–40°C to +85°C) and the S grade (–55°C
to +125°C) come in 20-pin ceramic DIP packages.
The S grade is also available with optional processing to
MIL-STD-883 in 20-pin ceramic DIP or 20-terminal LCC
packages. The Analog Devices Military Products Databook
should be consulted for detailed specifications.
PRODUCT HIGHLIGHTSThe AD670 is a complete 8-bit A/D including three-state
outputs and microprocessor control for direct connection to
8-bit data buses. No external components are required to
perform a conversion.The flexible input stage features a differential instrumenta-
tion amp input with excellent common-mode rejection. This
allows direct interface to a variety of transducers without
preamplification.No user trims are required for 8-bit accurate performance.Operation from a single +5 V supply allows the AD670 to
run off of the microprocessor’s supply.Four convenient input ranges (two unipolar and two bipolar)
are available through internal scaling resistors: 0 mV to
255 mV (1 mV/LSB) and 0 V to 2.55 V (10 mV/LSB).Software control of the output mode is provided. The user
can easily select unipolar or bipolar inputs and binary or 2s
complement output codes.
GAIN ACCURACY
BIAS CURRENT (255 mV RANGE)
NOTES
AD670–SPECIFICATIONS(@ VCC = +5 V and +258C, unless otherwise noted)
RELATIVE ACCURACY
2.55 V RANGE FULL-SCALE MATCH
DIGITAL INPUT CURRENT
AD670
AD670
ORDERING GUIDENOTESFor details on grade and package offerings screened in accordance with MIL-STD-883 refer to the Analog Devices
Military Products Databook.D = Ceramic DIP; N = Plastic DIP; P = Plastic Leaded Chip Carrier.
Figure 1.AD670 Block Diagram and Terminal
Configuration (AII Packages)
ABSOLUTE MAXIMUM RATINGS*VCC to Ground . . . . . . . . . . . . . . . . . . . . . . . . . . .0 V to +7.5 V
Digital Inputs (Pins 11–15) . . . . . . . . . . .–0.5 V to VCC +0.5 V
Digital Outputs (Pins 1–9) .Momentary Short to VCC or Ground
Analog Inputs (Pins 16–19) . . . . . . . . . . . . . . .–30 V to +30 V
Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . .450 mW
Storage Temperature Range . . . . . . . . . . . . .–65°C to +150°C
Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . . .+300°C
*Stresses above those listed under “Absolute Maximum Ratings” may cause
permanent damage to the device. This is a stress rating only and functional
operation of the device at them or any other conditions above those indicated in
the operational sections of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect device reliability.
CIRCUIT OPERATION/FUNCTIONAL DESCRIPTIONThe AD670 is a functionally complete 8-bit signal conditioning
A/D converter with microprocessor compatibility. The input
section uses an instrumentation amplifier to accomplish the
voltage to current conversion. This front end provides a high
impedance, low bias current differential amplifier. The com-
mon-mode range allows the user to directly interface the device
to a variety of transducers.
The AID conversions are controlled by R/W, CS, and CE. The
R/W line directs the converter to read or start a conversion. A
minimum write/start pulse of 300 ns is required on either CE or
CS. The STATUS line goes high, indicating that a conversion is
in process. The conversion thus begun, the internal 8-bit DAC
is sequenced from MSB to LSB using a novel successive ap-
proximation technique. In conventional designs, the DAC is
stepped through the bits by a clock. This can be thought of as a
static design since the speed at which the DAC is sequenced is
determined solely by the clock. No clock is used in the AD670.
Instead, a “dynamic SAR” is created consisting of a string of in-
verters with taps along the delay line. Sections of the delay line
between taps act as one shots. The pulses are used to set and re-
set the DAC’s bits and strobe the comparator. When strobed,
accuracy. Ease of implementation and reduced dependence on
process related variables make this an attractive approach to a
successive approximation design.
The SAR provides an end-of-conversion signal to the control
logic which then brings the STATUS line low. Data outputs re-
main in a high impedance state until R/W is brought high with
CE and CS low and allows the converter to be read. Bringing
CE or CS high during the valid data period ends the read cycle.
The output buffers cannot be enabled during a conversion. Any
convert start commands will be ignored until the conversion
cycle is completed; once a conversion cycle has been started it
cannot be stopped or restarted.
The AD670 provides the user with a great deal of flexibility by
offering two input spans and formats and a choice of output
codes. Input format and input range can each be selected. The
BPO/UPO pin controls a switch which injects a bipolar offset
current of a value equal to the MSB less 1/2 LSB into the sum-
ming node of the comparator to offset the DAC output. Two
precision 10 to 1 attenuators are included on board to provide
input range selection of 0 V to 2.55 V or 0 mV to 255 mV. Ad-
ditional ranges of –1.28 V to 1.27 V and –128 mV to 127 mV
are possible if the BPO/UPO switch is high when the conversion
CONNECTING THE AD670The AD670 has been designed for ease of use. All active com-
ponents required to perform a complete A/D conversion are on
board and are connected internally. In addition, all calibration
trims are performed at the factory, assuring specified accuracy
without user trims. There are, however, a number of options
and connections that should be considered to obtain maximum
flexibility from the part.
INPUT CONNECTIONSStandard connections are shown in the figures that follow. An
input range of 0 V to 2.55 V may be configured as shown in Fig-
ure 2a. This will provide a one LSB change for each 10 mV of
input change. The input range of 0 mV to 255 mV is configured
as shown in Figure 2b. In this case, each LSB represents 1 mV
of input change. When unipolar input signals are used, Pin 11,
BPO/UPO, should be grounded. Pin 11 selects the input format
for either unipolar or bipolar signals. Figures 3a and 3b show
the input connections for bipolar signals. Pin 11 should be tied
to +VCC for bipolar inputs.
Although the instrumentation amplifier has a differential input,
there must be a return path to ground for the bias currents. If it
is not provided, these currents will charge stray capacitances
and cause internal circuit nodes to drift uncontrollably causing
the digital output to change. Such a return path is provided in
Figures 2a and 3a (larger input ranges) since the 1k resistor leg
is tied to ground. This is not the case for Figures 2b and 3b (the
lower input ranges). When connecting the AD670 inputs to
floating sources, such as transformers and ac-coupled sources,
there must still be a dc path from each input to common. This
can be accomplished by connecting a 10 kΩ resistor from each
input to ground.
2a.0 V to 2.55 V (10 mV/LSB)
2b.0 mV to 255 mV (1 mV/LSB)
NOTE: PIN 11, BPO/UPO SHOULD BE LOW WHEN
CONVERSION IS STARTED.3a.±1.28 V Range
3b.±128 mV Range
NOTE: PIN 11, BPO/UPO SHOULD BE HIGH WHEN
CONVERSION IS STARTED.Figure 3.Bipolar Input Connections
Bipolar OperationThrough special design of the instrumentation amplifier, the
AD670 accommodates input signal excursions below ground,
even though it operates from a single 5 V supply. To the user,
this means that true bipolar input signals can be used without
the need for any additional external components. Bipolar signals
can be applied differentially across both inputs, or one of the in-
puts can be grounded and a bipolar signal applied to the other.
Common-Mode PerformanceThe AD670 is designed to reject dc and ac common-mode volt-
ages. In some applications it is useful to apply a differential in-
put signal VIN in the presence of a dc common-mode voltage
VCM. The user must observe the absolute input signal limits
listed in the specifications, which represent the maximum volt-
age VIN + VCM that can be applied to either input without affect-
ing proper operation. Exceeding these limits (within the range of
absolute maximum ratings), however, will not cause permanent
damage.
The excellent common-mode rejection of the AD670 is due to
the instrumentation amplifier front end, which maintains the
differential signal until it reaches the output of the comparator.
In contrast to a standard operational amplifier, the instrumenta-
tion amplifier front end provides significantly improved CMRR
over a wide frequency range (Figure 4a).
AD670
Table I. AD670 Input Selection/Output Format Truth TableFigure 5a. Unipolar Output Codes (Low Range)
Figure 5b. Bipolar Output Codes (Low Range)
CalibrationBecause of its precise factory calibration, the AD670 is intended
to be operated without user trims for gun and offset; therefore,
no provisions have been made for such user trims. Figures 6a,
6b, and 6c show the transfer curves at zero and full scale for the
unipolar and bipolar modes. The code transitions are positioned
so that the desired value is centered at that code. The first LSB
transition for the unipolar mode occurs for an input of +1/2 LSB
(5 mV or 0.5 mV). Similarly, the MSB transition for the bipolar
mode is set at –1/2 LSB (–5 mV or –0.5 mV). The full scale
transition is located at the full scale value –1 1/2 LSB. These
values are 2.545 V and 254.5 mV.
Figure 4a.CMRR Over Frequency
Figure 4b.AD670 Input Rejects Common-Mode
Ground Noise
Good common-mode performance is useful in a number of situ-
ations. In bridge-type transducer applications, such performance
facilitates the recovery of differential analog signals in the pres-
ence of a dc common-mode or a noisy electrical environment.
High frequency CMRR also becomes important when the ana-
log signal is referred to a noisy, remote digital ground. In each
case, the CMRR specification of the AD670 allows the integrity
of the input signal to be preserved.
The AD670’s common-mode voltage tolerance allows great
flexibility in circuit layout. Most other A/D converters require
the establishment of one point as the analog reference point.
This is necessary in order to minimize the effects of parasitic
voltages. The AD670, however, eliminates the need to make the
analog ground reference point and A/D analog ground one and
the same. Instead, a system such as that shown in Figure 4b is
possible as a result of the AD670’s common-mode performance.
The resistors and inductors in the ground return represent un-
avoidable system parasitic impedances.
Input/Output OptionsData output coding (2s complement vs. straight binary) is
selected using Pin 12, the FORMAT pin. The selection of
input format (bipolar vs. unipolar) is controlled using Pin 11,
BPO/UPO. Prior to a write/convert, the state of FORMAT and
BPO/UPO should be available to the converter. These lines may
be tied to the data bus and may be changed with each conver-
sion if desired. The configurations are shown in Table I. Output
coding for representative signals in each of these configurations
is shown in Figure 5.
