DDC112 Datasheet, PDF (1/24 Pages) Burr-Brown (TI) – Dual Current Input 20-Bit ANALOG-TO-DIGITAL CONVERTER

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DDC112
DDC112
Dual Current Input 20-Bit
ANALOG-TO-DIGITAL CONVERTER
FEATURES
q MONOLITHIC CHARGE MEASUREMENT ADC
q DIGITAL FILTER NOISE REDUCTION:
3.2ppm, rms
q INTEGRAL LINEARITY:
±0.005% Reading ±0.5ppm FSR
q HIGH PRECISION, TRUE INTEGRATING
FUNCTION
q PROGRAMMABLE FULL SCALE
q SINGLE SUPPLY
q CASCADABLE OUTPUT
APPLICATIONS
q DIRECT PHOTOSENSOR DIGITIZATION
q CT SCANNER DAS
q INFRARED PYROMETER
q PRECISION PROCESS CONTROL
q LIQUID/GAS CHROMATOGRAPHY
q BLOOD ANALYSIS
Protected by US Patent #5841310
DESCRIPTION
The DDC112 is a dual input, wide dynamic range,
charge-digitizing analog-to-digital converter (ADC) with
20-bit resolution. Low level current output devices,
such as photosensors, can be directly connected to its
inputs. Charge integration is continuous as each input
uses two integrators; while one is being digitized, the
other is integrating.
For each of its two inputs, the DDC112 combines
current-to-voltage conversion, continuous integration,
programmable full-scale range, A/D conversion, and
digital filtering to achieve a precision, wide dynamic
range digital result. In addition to the internal program-
mable full-scale ranges, external integrating capacitors
allow an additional user-settable full-scale range of up
to 1000pC.
To provide single-supply operation, the internal ADC
utilizes a differential input, with the positive input tied
to V_REF. When the integration capacitor is reset at the
beginning of each integration cycle, the capacitor
charges to V_REF. This charge is removed in proportion
to the input current. At the end of the integration cycle,
the remaining voltage is compared to V_REF.
The high-speed serial shift register which holds the
result of the last conversion can be configured to allow
multiple DDC112 units to be cascaded, minimizing
interconnections. The DDC112 is available in a SO-28
package and is offered in two performance grades.
CAP1A
CAP1A
IN1
CAP1B
CAP1B
CAP2A
CAP2A
IN2
CAP2B
CAP2B
AV_DD AGND
CHANNEL 1
Dual
Switched
Integrator
CHANNEL 2
Dual
Switched
Integrator
V_REF
DV_DD DGND
∆Σ
Modulator
DCLK
Digital
Filter
Digital
Input/Output
DVALID
DXMIT
DOUT
DIN
Control
RANGE2
RANGE1
RANGE0
TEST CONV CLK
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©_{1997 Burr-Brown Corporation}
PDS-14121D
DDC112 ^{Printed in U.S.A. January, 2000}