Datasheet

Evaluation Board User Guide UG-274
Rev. 0 | Page 5 of 16
In addition, R36 can be used to achieve a pseudologarithmic
attenuation. To do so, adjust the R36 resistor until a desirable
transfer function is found.
Signal Amplifier
RDAC3 can be operated as an inverting or noninverting signal
amplifier supporting linear or pseudologarithmic gains. Table 6
shows the available configurations.
Table 6. Amplifier Selection Link Options
Amplifier Gain Link Label
Noninverting Linear A27 LINEAR
A29 NON-INVERTING
A30 NON-INVERTING
Pseudologarithmic A27 PSEUDOLOG
A29 NON-INVERTING
A30 NON-INVERTING
Inverting Linear A27 LINEAR
A29 INVERTING
A30 INVERTING
Pseudologarithmic A27 PSEUDOLOG
A29 INVERTING
A30 INVERTING
The noninverting amplifier with linear gain is shown in Figure 4,
and the gain is defined in Equation 3.
R38
R
G
WB3
+=1
(3)
where R
WB3
is the resistor between the W3 and B3 terminals.
V
IN
RDAC3
B3
R42
W3
B2
W2
V
OUT
OAVOUT
C1
10nF
R41
1.7kΩ
R38
2.7kΩ
09820-004
Figure 4. Linear Noninverting Amplifier
The noninverting amplifier with pseudologarithmic gain is
shown in Figure 5, and the gain is defined in Equation 4.
AW3
WB3
R
R
G += 1
(4)
where:
R
WB3
is the resistor between the W3 and B3 terminals.
R
AW 3
is the resistor between the A3 and W3 terminals.
V
IN
RDAC3
B3A3
R42
W3
B2
W2
V
OUT
OAVOUT
A2
C1
10nF
R41
1.7kΩ
R43
09820-005
Figure 5. Pseudologarithmic Noninverting Amplifier
R43 and R42 can be used to set the maximum and minimum
gain limits.
The inverting amplifier with linear gain is shown in Figure 6,
and the gain is defined in Equation 5.
R38
R
G
WB3
−=
(5)
where R
WB3
is the resistor between the W3 and B3 terminals.
V
IN
RDAC3
B3
R42
W3
B2
W2
V
OUT
OAVOUT
C1
10nF
R41
1.7kΩ
R38
2.7kΩ
09820-006
Figure 6. Linear Inverting Amplifier
The inverting amplifier with pseudologarithmic gain is shown
in Figure 7, and the gain is defined in Equation 6.
AW3
WB3
R
R
G −=
(6)
where:
R
WB3
is the resistor between the W3 and B3 terminals.
R
AW 3
is the resistor between the A3 and W3 terminals.
V
IN
RDAC3
B3A3
R42
W3
B2
W2
V
OUT
OAVOUT
A2
C1
10nF
R41
1.7kΩ
R43
09820-007
Figure 7. Pseudologarithmic Inverting Amplifier
R43 and R42 can be used to set the maximum and minimum
gain limits.