AD8315

Data Sheet

Rev. D | Page 20 of 22

Table 5. Evaluation Board Configuration Options

Component

Function

Default Condition

TP1, TP2

Supply and Ground Vector Pins.

Not Applicable

SW1

Device Enable. When in Position A, the ENBL pin is connected to VPOS and the AD8315 is

in operating mode. In Position B, the ENBL pin is grounded putting the device in power-down mode.

SW1 = A

R1, R2

Input Interface. The 52.3 Ω resistor in Position R2 combines with the AD8315 internal input

impedance to give a broadband input impedance of around 50 Ω. A reactive match can be

implemented by replacing R2 with an inductor and R1 (0 Ω) with a capacitor. Note that the

AD8315 RF input is internally ac-coupled.

R2 = 52.3 Ω (Size 0603)

R1 = 0 Ω (Size 0402)

R3, R4, C2

Output Interface. R4 and C2 can be used to check the response of VAPC to capacitive and resistive

loading. R3/R4 can be used to reduce the slope of VAPC.

R4 = C2 = Open (Size 0603)

R3 = 0 Ω (Size 0603)

C1

Power Supply Decoupling. The nominal supply decoupling consists of a 0.1 μF capacitor.

C1 = 0.1 μF (Size 0603)

C4

Filter Capacitor. The response time of VAPC can be modified by placing a capacitor between

FLTR (Pin 4) and ground.

C4 = Open (Size 0603)

LK1, LK2

Measurement Mode. A quasimeasurement mode can be implemented by installing LK1 and LK2

(connecting an inverted VAPC to VSET) to yield the nominal relationship between RFIN and VSET.

In this mode, a large capacitor (0.01 μF or greater) must be installed in C4.

LK1, LK2 = Installed

Figure 45. Layout of Component Side (MSOP)

EVALUATION BOARD REV A

PWUP GND

TP2

AD8315

VAPC

J2

VPOS

TP1

R3

C1

R2

R1

C4

Z1

R8

LK2

PWDN

A

B

SW1

RFIN

J1

J3

C3

R6

A1

LK1

VSET

08 - 006794 REV A

COMPONENT SIDE

Figure 46. Silkscreen of Component Side (MSOP)

For operation in controller mode, both jumpers, LK1 and LK2,

must be removed. The setpoint voltage is applied to VSET,

RFIN is connected to the RF source (PA output or directional

coupler), and VAPC is connected to the gain control pin of the

PA. When used in controller mode, a capacitor must be installed in

C4 for loop stability. For GSM/DCS handset power amplifiers,

this capacitor must typically range from 150 pF to 300 pF.

A quasimeasurement mode (where the AD8315 delivers an

output voltage that is proportional to the log of the input signal)

can be implemented, to establish the relationship between VSET

and RFIN, by installing the two jumpers, LK1 and LK2. This

mimics an AGC loop. To establish the transfer function of the

log amp, the RF input must be swept while the voltage on VSET

is measured, that is, the SMA connector labeled VSET now acts

as an output. This is the simplest method to validate operation

of the evaluation board. When operated in this mode, a large

capacitor (0.01 μF or greater) must be installed in C4 (filter

capacitor) to ensure loop stability.