AD8318 datasheet(21/24 Pages) AD

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AD8318

Rev. 0| Page 21 of 24

EVALUATION BOARD

Table 6. Evaluation Board (Rev A) Configuration Options

Component

Function

Default Conditions

TP1, TP2

Supply and Ground Connections

Not Applicable

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.

SW1 = A

R3 = 10k (Size 0603)

R1, C1, C2

Input Interface: The 52.3

Ω resistor in position R1 combines with the

AD8318's internal input impedance to give a broadband input impedance

of around 50

Ω. 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 .

R1 = 52.3

Ω (Size 0402)

C1 = 1 nF (Size 0402)

C2 = 1 nF (Size 0402)

Temperature Sensor Interface: The temperature sensor output voltage is

available at J1, via the current limiting resistor, R2.

Temperature Compensation Interface: The internal temperature

compensation resistor is optimized for an input signal of 2.2 GHz when C4 is

1 k

Ω. 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.

C4 = 500 k

Ω (Size 0603)

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 = 0

Ω = (Size 0402)

R8 = open (Size 0402)

R9 = open (Size 0402

R10= 0

Ω (Size 0402)

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.

R7 = open (Size 0402)

R8 = open (Size 0402)

R9 = 0

Ω (Size 0402)

R10 = 0

Ω (Size 0402)

C5, C6, C7, C8, R5,

Power Supply Decoupling: The nominal supply decoupling consists of a

100 pF filter capacitor placed physically close to the AD8318, a 0

Ω series

resistor and a 0.1 µF capacitor placed nearer to the power supply input pin.

C6 = 100 pF (Size 0402)

C7 = 100 pF (Size 0402)

C5 = 0.1 µF (Size 0603)

C8 = 0.1 µF (Size 0603)

R5 = 0

Ω (Size 0603)

R6 = 0

Ω (Size 0603)

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.

C4 = open (Size 0603)

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