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參數資料
| 型號： | AD8316-EVAL |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | Dual Output GSM PA Controller |
| 中文描述： | 雙輸出GSM功率放大器控制器 |
| 文件頁數： | 15/20頁 |
| 文件大小： | 497K |
| 代理商： | AD8316-EVAL |
REV. C
AD8316
–15–
Enable and Power-On
The AD8316 may be disabled by pulling the ENBL pin to
ground. This reduces the supply current from its nominal level
of 8.5 mA to 3
μ
A at 2.7 V. The logic threshold for turning on
the device is at 1.8 V at 2.7 V. A plot of the enable glitch is
shown in TPC 20. Alternatively, the device can be completely
disabled by pulling the supply voltage to ground; ENBL would be
connected to VPOS. The glitch in this mode of operation is
shown on TPC 25 and TPC 26. If VPOS is applied before the
device is enabled, a narrow glitch of less than 50 mV will result.
This is shown in TPC 31.
In both situations, the voltage on V
SET
should be kept below
250 mV during power-on and power-off, preventing any unwanted
transients on V
OUT
.
Input Coupling Options
The internal 5 pF coupling capacitor of the AD8316, along with
the low frequency input impedance of 3 k
, result in a high-pass
input corner frequency of approximately 20 MHz. This sets the
minimum operating frequency. Figure 9 shows three options for
input coupling. A broadband resistive match can be implemented
by connecting a shunt resistor to ground at RFIN. This 52.3
resistor (other values can also be used to select different overall
input impedances) combines with the input impedance of the
AD8316 (3 k
1 pF) to give a broadband input impedance of
50
. While the input resistance and capacitance (C
IN
and R
IN
)
will vary by approximately
±
20% from device to device, the
dominance of the external shunt resistor means that the varia-
tion in the overall input impedance will be close to the tolerance
of the external resistor. This method of matching is most useful
in wideband applications or in multimode systems where there
is more than one operating frequency and those frequencies are
quite far apart.
A reactive match can also be implemented as shown in Figure 9b.
This is not recommended at low frequencies because device
tolerances will vary the quality of the match dramatically because
of the large input resistance. For low frequencies, Option 9a or
Option 9c is recommended.
In Figure 9b, the matching components are drawn as generic
reactances. Depending on the frequency, the input impedance
at that frequency, and the availability of standard value compo-
nents, either a capacitor or an inductor will be used. As in the
previous case, the input impedance at a particular frequency is
plotted on a Smith chart and matching components are chosen
(shunt or Series L, shunt or Series C) to move the impedance to
the center of the chart.
Figure 9c shows a third method for coupling the input signal
into the AD8316, applicable where the input signal is larger
than the input range of the log amp. A series resistor, connected
to the RF source, combines with the input impedance of the
AD8316 to resistively divide the input signal being applied to
the input. This has the advantage of very little power being
tapped off in RF power transmission applications.
Using the Chip Scale Package
On the underside of the chip scale package, there is an exposed
paddle. This paddle is internally connected to the chip’s ground.
For better electrical performance, this paddle should be soldered
down to the printed circuit board’s ground plane, even though
there is no thermal requirement to do so.
EVALUATION BOARD
Figures 10 and 11 show the schematics of the AD8316 MSOP and
LFCSP evaluation boards. Note that uninstalled components are
marked as open. The layout and silkscreen of the MSOP evalua-
tion board are shown in Figures 12 and 13. Apart from the slightly
smaller device footprint and number of pins, the LFCSP evalua-
tion board is identical to the MSOP board. The boards are
powered by a single supply in the 2.7 V to 5.5 V range. The power
supply is decoupled by a single 0.1
μ
F capacitor. Table II details
the various configuration options of the evaluation boards.
For operation in controller mode, both jumpers, LK1 and LK2,
should be removed. OUT1 and OUT2 can be selected with SW3
in Position A and Position B, respectively. The setpoint voltage
is applied to VSET, RFIN is connected to the RF source (PA
output or directional coupler), and OUT1 or OUT2 is connected
to the gain control pins of each PA. When the AD8316 is used
in controller mode, a capacitor and a resistor must be installed
in C4, C6, and R10, R11 for loop stability. For GSM/DCS
handset power amplifiers, this capacitor should typically range
from 150 pF to 300 pF. The series resistor improves the system
phase margin at low power levels, which in turn improves the
step response in the circuit. Typically, this resistor value should
be about 1.5 k
.
A quasi-measurement mode (in which the AD8316 delivers an
output voltage that is proportional to the log of the input signal)
can be implemented to establish the relationship between V
SET
and RF
IN
with the installation of 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
acts as an output. This is the simplest method for validating
operation of the evaluation board. When operated in this
mode, a large capacitor (0.01
μ
F or greater) must be installed in
C4 or C6 (set R10/R11 to 0
) to ensure loop stability.
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