REV. A
AD8304
–19–
Table V. Evaluation Board Configuration Options
Component
Function
Default Condition
VP, VN, AGND
Positive and Negative Supply and Ground Pins
Not Applicable
SW1, R10
Device Enable: When SW1 is in the “0” position, the PWDN Pin is
SW1 = Installed
connected to ground and the AD8304 is in its normal operating mode.
R10 = 10 k
(Size 0603)
R1, R2
Buffer Amplifier Gain/Slope Adjustment: The logarithmic slope
R1 = Open (Size 0603)
of the AD8304 can be altered using the buffer’s gain-setting resistors,
R2 = 0
(Size 0603)
R1 and R2.
R3, R4
Intercept Adjustment: A dc offset can be applied to the input term-
R3 = Open (Size 0603)
inals of the buffer amplifier to adjust the effective logarithmic intercept.
R4 = Open (Size 0603)
R5, R6, R7, R8, R9
Bias Adjustment: The voltage on the VSUM and INPT Pins can be
R5 = R6 = Open (Size 0603)
altered using appropriate resistor values. R9 is populated with a decoup-
R7 = R8 = Open (Size 0603)
ling capacitor to reduce noise pickup. The decoupling capacitor can be
R9 = 0.1
F (Size 0603)
removed when a fixed bias is applied to VSUM.
C1, C2, C3, C4, C9
Supply Decoupling Capacitors
C1 = C4 = 0.1
F (Size 0603)
C2 = C3 = 1 nF (Size 0603)
C9 = 10 nF (Size 0603)
C10
Photodiode Biaser Decoupling: Provides high frequency decoupling
C10 = 0.1
F (Size 0603)
of the adaptive bias output at Pin VPDB.
C5, C6, C7, C8, R11,
Output Filtering: Allows implementation of a variety of filter config-
R11 = R13 = 0
(Size 0603)
R12, R13, R14
urations, from simple RC low-pass filters to three-pole Sallen and Key.
R12 = Open (Size 0603)
C7 = C8 = Open (Size 0603)
R15, C11
Input Filtering: Provides essential HF compensation at the input
R15 = 750
(Size 0603)
Pin INPT.
C11 = 1 nF (Size 0603)
LK1, LK2
Guard/Shield Options: The shells of the SMA connectors used
LK1 = Installed
for the input and the photodiode bias can be set to the voltage on the
LK2 = Open
VSUM Pin or connected to ground.
Figure 23. Component Side Layout
Figure 24. Component Side Silkscreen
R14 = 0
(Size 0603)
C5 = C6 = Open (Size 0603)