DDC118 Datasheet, PDF (8/30 Pages) Burr-Brown (TI) – Octal Current Input 20-Bit Analog-To-Digital Converter

DDC118
SBAS325A − JUNE 2004 − REVISED JUNE 2005
THEORY OF OPERATION
The block diagram of the DDC118 is shown in Figure 1.
The device contains eight identical input channels that
perform the function of current-to-voltage integration
followed by a multiplexed A/D conversion. Each input has
two integrators so that the current-to-voltage integration
can be continuous in time. The output of the sixteen
integrators are switched to four delta-sigma (∆Σ)
converters via four four-input multiplexers. With the
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DDC118 in the continuous integration mode, the output of
the integrators from one side of the inputs will be digitized
while the other eight integrators are in the integration
mode, as illustrated in the timing diagram in Figure 2. This
integration and A/D conversion process is controlled by
the system clock, CLK. The results from side A and side
B of each signal input are stored in a serial output shift
register. The DVALID output goes low when the shift
register contains valid data.
AVDD
IN1
Dual
Switched
Integrator
IN3
Dual
Sw itche d
Integrator
IN2
Dual
Switched
Integrator
IN4
Dual
Switched
Integrator
IN5
Dual
Switched
Integrator
IN7
Dual
Sw itche d
Integrator
IN6
Dual
Switched
Integrator
IN8
Dual
Sw itche d
Integrator
AGND
VREF DVDD
∆Σ
M odulator
Digital
Filter
C ontro l
CLK
CONV
RANGE0
RANGE1
RANGE2
TEST
CLK_4X
HISPD/LOPWR
RESET
∆Σ
M odulator
Digital
Filter
FORMAT
DCLK
DCLK
∆Σ
M odulator
Digital
Filter
Dig ital
In pu t/Output
DVALID
DOUT
DOUT
DIN
DIN
∆Σ
Digital
M odulator
Filter
DGND
Figure 1. DDC118 Block Diagram
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