ADN2850BCPZ250 データシートの表示（PDF） - Analog Devices
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ADN2850BCPZ250 Datasheet PDF : 28 Pages
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ADN2850
RESISTANCE TOLERANCE, DRIFT, AND
TEMPERATURE COEFFICIENT MISMATCH
CONSIDERATIONS
In operation, such as gain control, the tolerance mismatch
between the digital resistor and the discrete resistor can cause
repeatability issues among various systems (see Figure 42).
Because of the inherent matching of the silicon process, it is
practical to apply the dual-channel device in this type of
application. As such, R1 can be replaced by one of the channels
of the digital resistor and programmed to a specific value. R2 can
be used for the adjustable gain. Although it adds cost, this approach
minimizes the tolerance and temperature coefficient mismatch
between R1 and R2. This approach also tracks the resistance
drift over time. As a result, these less than ideal parameters
become less sensitive to system variations.
B R2
W
C1
R1*
–
AD8601
VO
Vi
+
U1
* REPLACED WITH ANOTHER
CHANNEL OF RDAC
Figure 42. Linear Gain Control with Tracking Resistance Tolerance,
Drift, and Temperature Coefficient
Data Sheet
RDAC CIRCUIT SIMULATION MODEL
The internal parasitic capacitances and the external capacitive
loads dominate the ac characteristics of the RDACs. A parasitic
simulation model is shown in Figure 43.
RDAC
25kΩ
B
CB
11pF
80pF
W
Figure 43. RDAC Circuit Simulation Model (RDAC = 25 kΩ)
The following code provides a macro model net list for the
25 kΩ RDAC:
.PARAM D = 1024, RDAC = 25E3
*
.SUBCKT DPOT ( W, B)
*
CW W 0 80E-12
RWB W B {D/1024 * RDAC + 50}
CB B 0 11E-12
*
.ENDS DPOT
Rev. E | Page 24 of 28
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