Evaluation Board User Guide
UG-473
Rev. 0 | Page 5 of 20
AC Signal Attenuation
The RDAC can be used to attenuate an ac signal, which must be
provided externally using the AC_INPUT connector, as shown
in Figure 3.
Depending on the voltage supply rails and the dc offset voltage
of the ac signal, various configurations can be used as described
in Table 8 and Table 9.
Table 8. AC Signal Attenuation Daughter Board Links
Link Options Description
A6
B
Connects Terminal A to A1
A7
B
Connects Terminal W to W1
A8
B
Connects Terminal B to B1
A1
IN
Closes feedback loop of second op amp in the
AD8618
The signal attenuation is defined in Equation 2.
+
×
=
AB
W
WB1
R
R
R
n
Attenuatio
log
20
)
dB
(
(2)
where:
R
W
is the wiper resistance.
R
AB
is the end-to-end resistance value.
R
WB1
is the resistor between the W1 and B1 terminals.
Table 9. AC Signal Attenuation Link Motherboard Links
Voltage
Supply
Maximum
AC Signal
Amplitude Link Options Conditions
Single
V
DD
A9
AC+
No dc offset voltage;
the ac signal is
outside the voltage
supply rails due to
the dc offset voltage;
or the dc offset
voltage ≠ V
DD
/2.
1
AC
All other conditions.
A10
BIAS
Use in conjunction
with the AC+ link.
GND
All other conditions.
Dual
V
DD
/V
SS
A9
AC+
The ac signal is
outside the voltage
supply rails due to
the dc offset voltage;
the dc offset
voltage ≠ 0 V.
1
AC
All other conditions.
A10
GND
Use in conjunction
with the AC+ link.
VSS
All other conditions.
1
Recommended to ensure optimal total harmonic distortion (THD) performance.
1
1010-
003
VOUT1
R34
R35
A1
W1
RDAC
A
B
W
AC
AC+
AGND
BIAS
B1
VSS
V
SS
BUF-W1
AC_INPUT
1kHz
HPF
V
DD
2
V
DD
2
Figure 3. AC Signal Attenuator
