
AD8318
EVALUATION BOARD
Table 6. Evaluation Board (Rev A) Configuration Options
Component
Function
TP1, TP2
Supply and Ground Connections
SW1
Device Enable: When in position A, the ENBL pin is connected to VP and the
AD8318 is in operating mode. In position B, the ENBL pin is grounded
through R3, putting the device in power-down mode. The
ENBL pin may be
exercised by a pulse generator connected to J3 with SW1 in position B.
R1, C1, C2
Input Interface: The 52.3
resistor in position R1 combines with the
AD8318's internal input impedance to give a broadband input impedance
of around 50
. Capacitors C1 and C2 are DC blocking capacitors. A reactive
impedance match can be implemented by replacing R1 with an inductor
and C1 and C2 with appropriately-valued capacitors .
R2
Temperature Sensor Interface: The temperature sensor output voltage is
available at J1, via the current limiting resistor, R2.
C4
Temperature Compensation Interface: The internal temperature
compensation resistor is optimized for an input signal of 2.2 GHz when C4 is
1 k
. This circuit can be adjusted to optimize performance for other input
frequencies by changing the value of the resistor in position C4. Note that
the designation C4 on the evaluation board is a typographical error as this
pad will always be populated with a resistor. This error will be corrected on
the Rev B revision of the board.
R7, R8, R9, R10
Output Interface—Measurement Mode: In measurement mode, a portion of
the output voltage is fed back to pin VSET via R7. The magnitude of the
slope of the VOUT output voltage response may be increased by reducing
the portion of VOUT that is fed back to VSET. R10 can be used as a back-
terminating resistor or as part of a single-pole low-pass filter.
R7, R8, R9, R10
Output Interface—Controller Mode: In this mode, R7 must be open. In
controller mode, the AD8318 can control the gain of an external
component. A setpoint voltage is applied to pin VSET, the value of which
corresponds to the desired RF input signal level applied to the AD8318 RF
input. A sample of the RF output signal from this variable-gain component is
selected, typically via a directional coupler, and applied to AD8318 RF input.
The voltage at pin VOUT is applied to the gain control of the variable gain
element. A control voltage is applied to pin VSET via R9 and R8. The
magnitude of the control voltage may optionally be attenuated via the
voltage divider comprised of R8 and R9, or a capacitor may be installed in
position R8 to form a low-pass filter along with R9.
C5, C6, C7, C8, R5,
R6
100 pF filter capacitor placed physically close to the AD8318, a 0
series
resistor and a 0.1 μF capacitor placed nearer to the power supply input pin.
Rev. 0| Page 21 of 24
Default Conditions
Not Applicable
SW1 = A
R3 = 10k (Size 0603)
R1 = 52.3
(Size 0402)
C1 = 1 nF (Size 0402)
C2 = 1 nF (Size 0402)
C4 = 500 k
(Size 0603)
R7 = 0
= (Size 0402)
R8 = open (Size 0402)
R9 = open (Size 0402
R10= 0
(Size 0402)
R7 = open (Size 0402)
R8 = open (Size 0402)
R9 = 0
(Size 0402)
R10 = 0
(Size 0402)
Power Supply Decoupling: The nominal supply decoupling consists of a
C6 = 100 pF (Size 0402)
C7 = 100 pF (Size 0402)
C5 = 0.1 μF (Size 0603)
C8 = 0.1 μF (Size 0603)
R5 = 0
(Size 0603)
R6 = 0
(Size 0603)
C4 = open (Size 0603)
C9
Filter Capacitor: The low-pass corner frequency of the circuit that drives pin
VOUT can be lowered by placing a capacitor between CLPF and ground.