Simultaneous Sampling
Dual 175 kSPS 14-Bit ADC
AD7863
Rev. B
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FEATURES
Two fast 14-bit ADCs
Four input channels
Simultaneous sampling and conversion
5.2 μs conversion time
Single supply operation
Selection of input ranges
±10 V for AD7863-10
±2.5 V for AD7863-3
0 V to 2.5 V for AD7863-2
High speed parallel interface
Low power, 70 mW typical
Power saving mode, 105 μW maximum
Overvoltage protection on analog inputs
14-bit lead compatible upgrade to AD7862
GENERAL DESCRIPTION
The AD7863 is a high speed, low power, dual 14-bit analog-to-
digital converter that operates from a single 5 V supply.
FUNCTIONAL BLOCK DIAGRAM
DGND
DB0
BUSY
CS
CONVST
AD7863
2kΩ
AGND AGND
DD
REF
DB13
A0
TRACK/
HOLD
TRACK/
HOLD
MUX
2.5V
REFERENCE
OUTPUT
LATCH
RD
CONVERSION
CONTROL LOGIC
SIGNAL
SCALING
SIGNAL
SCALING
SIGNAL
SCALING
MUX
14-BIT
ADC
14-BIT
ADC
CLOCK
V
A2
V
B2
V
A1
V
B1
SIGNAL
SCALING
06411-001
Figure 1.
The part contains two 5.2 μs successive approximation ADCs, two
track/hold amplifiers, an internal 2.5 V reference and a high speed
parallel interface. Four analog inputs are grouped into two channels
(A and B) selected by the A0 input. Each channel has two inputs
(V
A1
and V
A2
or V
B1
and V
B2
) that can be sampled and converted
simultaneously, thus preserving the relative phase information of
the signals on both analog inputs. The part accepts an analog input
range of ±10 V (AD7863-10), ±2.5 V (AD7863-3), and 0 V to
2.5 V (AD7863-2). Overvoltage protection on the analog inputs
for the part allows the input voltage to go to ±17 V, ±7 V, or +7 V
respectively, without causing damage.
A single conversion start signal (
CONVST
) simultaneously places
both track/holds into hold and initiates conversion on both
channels. The BUSY signal indicates the end of conversion and at
this time the conversion results for both channels are available to be
read. The first read after a conversion accesses the result from V
A1
or V
B1
, and the second read accesses the result from V
A2
or V
B2
,
depending on whether the multiplexer select (A0) is low or high,
respectively. Data is read from the part via a 14-bit parallel data bus
with standard
CS
and
RD
signals. In addition to the traditional dc
accuracy specifications such as linearity, gain, and offset errors, the
part is also specified for dynamic performance parameters
including harmonic distortion and signal-to-noise ratio.
The AD7863 is fabricated in the Analog Devices, Inc. linear
compatible CMOS (LC
2
MOS) process, a mixed technology
process that combines precision bipolar circuits with low power
CMOS logic. It is available in 28-lead SOIC_W and SSOP.
PRODUCT HIGHLIGHTS
1. The AD7863 features two complete ADC functions
allowing simultaneous sampling and conversion of two
channels. Each ADC has a two-channel input mux. The
conversion result for both channels is available 5.2 μs after
initiating conversion.
2. The AD7863 operates from a single 5 V supply and
consumes 70 mW typical. The automatic power-down
mode, where the part goes into power-down once
conversion is complete and wakes up before the next
conversion cycle, makes the AD7863 ideal for battery-
powered or portable applications.
3. The part offers a high speed parallel interface for easy
connection to microprocessors, microcontrollers, and
digital signal processors.
4. The part is offered in three versions with different analog
input ranges. The AD7863-10 offers the standard industrial
input range of ±10 V; the AD7863-3 offers the common
signal processing input range of ±2.5 V, while the AD7863-2
can be used in unipolar 0 V to 2.5 V applications.
5. The part features very tight aperture delay matching
between the two input sample and hold amplifiers.
