AS1506
Datasheet - Application Information
9 Application Information
The AS1506 is intended for circuits requiring digitally controlled adjustable resistance, such as LCD contrast control
(where voltage biasing adjusts the display contrast), or programmable filters with adjustable gain and/or cutoff fre-
quency.
Programmable Filter
Figure 24 shows the configuration for a 1st-order programmable filter.
The DC gain of the filter is adjusted by R2 and can be calculated as:
G = 1 + (R1/R2)
(EQ 1)
The cutoff frequency (fC) is adjusted by R3, and can be calculated as:
fC = 1/(2π x R3 x C)
(EQ 2)
Figure 24. Programmable Filter Circuit
CIN
VIN
+
–
VOUT
HIGH
R3
AS1506
WIPER
R1
LOW
HIGH
R2
AS1506
WIPER
LOW
Offset Voltage and Gain Adjustment
Connect the AS1506 to an op amp to nullify the offset voltage over the operating temperature range. Install another
AS1506 potentiometer in the feedback path to adjust the gain of the op amp (Figure 25).
Figure 25. Offset Voltage Adjustment Circuit
5V
AS1506
+
–
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