AD8315 Analog Devices, AD8315 Datasheet - Page 21

• Manufacturer Part Number: AD8315
• Description: 50 dB GSM PA Controller
• Manufacturer: Analog Devices

VSET
Figure 45. Silkscreen of Component Side (MSOP)
J3
Figure 44. Layout of Component Side (MSOP)
RFIN
J1
SW1
A
B
PWUP
LK1
EVALUATION BOARD REV A
PWDN
GND
TP2
R1
R2
C4
A1
R6
VPOS
TP1
C1
Z1
AD8315
R3
08 - 006794 REV A
COMPONENT SIDE
C3
R8
LK2
VAPC
J2
Rev. C | Page 21 of 24
For operation in controller mode, both jumpers, LK1 and LK2,
should 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 should 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 should 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.
AD8315