參數(shù)資料
型號(hào)： AD8315ARM-REEL7
廠商： ANALOG DEVICES INC
元件分類： 通信及網(wǎng)絡(luò)
英文描述： 50 dB GSM PA Controller
中文描述： SPECIALTY TELECOM CIRCUIT, PDSO8
封裝： MO-187AA, MSOP-8
文件頁(yè)數(shù)： 11/20頁(yè)
文件大?。?/td> 1787K
代理商： AD8315ARM-REEL7
REV. B
AD8315
–11–
Check:
The power range is 50 dB, which should correspond
to a voltage change in
V
SET
of 50
dB
￥
24
mV
/
dB
= 1.2
V
,
which agrees.
Now, the value of V
APC
is of interest, although it is a dependent
parameter, inside the loop. It depends on the characteristics of
the power amplifier, and the value of the carrier amplitude
V
CW
.
Using the control values derived above, that is,
G
O
= 0.316 and
V
GBC
= 1 V, and assuming the applied power is fixed at –7
dBm
(so
V
CW
= 100 mV rms), the following is true using Equation 11:
V
V
(
( .
1 44
3 0
V
V
kG V
V
/
.
0 316
V
V
APC
SET
GBC
￥
1 0 48
0 5
SLP
CW
￥
Z
(
)
)/
– log
– log (0 0316
)/ .
=
. /
0 1 316
)
. – .
.
max
=
=
=
￥
10
2 5
m
(15)
both of which results are consistent with the assumptions made
about the amplifier control function. Note that the second term
is independent of the delivered power and a fixed function of
the drive power.
V
V
(
(0 24
. – .
0 5
V
V
kG V
0 0316
V
/
.
0 316
V
zero
APC
SET
GBC
￥
1 0 48
0 5
SLP
CW
￥
Z
(
)
)/
– log
– log ( .
)/ .
=
. /
0 1 316
)
min
=
=
=
￥
10
m
(16)
RF PA
DIRECTIONAL COUPLER
V
RF
V
CW
RF DRIVE: UP
TO 2.5GHz
AD8315
V
SET
V
IN
= kV
RF
C
FLT
RESPONSE-SHAPING
OF OVERALL CONTROL-
LOOP (EXTERNAL CAP)
V
APC
Figure 4. Idealized Control Loop for Analysis
Finally, using the loop time constant for these parameters and
an illustrative value of 2 nF for the filter capacitor C
FLT
:
Practical Loop
At the present time, power amplifiers, or VGAs preceding such
amplifiers, do not provide an exponential gain characteristic. It
follows that the loop dynamics (the effective time constant) will
vary with the setpoint, since the exponential function is unique
in providing constant dynamics. The procedure must, therefore,
be as follows. Beginning with the curve usually provided for the
power output versus the APC voltage, draw a tangent at the
point on this curve where the slope is highest (see Figure 5).
Using this line, calculate the effective
minimum
value of the
variable V
GBC
and use it in Equation 17 to determine the time
constant. Note that the minimum in V
GBC
corresponds to the
maximum rate of change in the output power versus V
APC
.
For example, suppose it is found that, for a given drive power,
the amplifier generates an output power of P
1
at V
APC
= V
1
and
P
2
at V
APC
= V
2
. Then, it is readily shown that:
T
V
(
1 0 48 3 07
V
/
T
s
nF
s
O
GBC
SLP
) .
=
=
￥
=
)
(
)
.
2
12 8
m
m
(17)
V
This should be used to calculate the filter capacitance. The
response time at high and low power levels (on the “shoulders”
V
(
V
P
P
GBC
=
20
2
1
2
1
–
)/(
–
)
(18)
of the curve shown in Figure 5) will be slower. Note also that it
is sometimes useful to add a zero in the closed-loop response by
placing a resistor in series with C
FLT
. For more about these
matters, refer to the Applications section.
V
APC
– V
33
0
P
R
–
23
13
3
0.5
1.0
1.5
2.0
2.5
–7
V
2
, P
2
V
1
, P
1
Figure 5. Typical Power-Control Curve
A Note About Power Equivalency
In using the AD8315, it must be understood that log amps do not
fundamentally respond to power. It is for this reason that dBV
(decibels above 1 V rms) are used rather than the commonly used
metric of dBm. The dBV scaling is fixed, independent of termi-
nation impedance, while the corresponding power level is not.
For example, 224 mV rms is always –13 dBV (with one further
condition of an assumed sinusoidal waveform; see the AD640
data sheet for more information about the effect of waveform on
logarithmic intercept), and this corresponds to a power of 0 dBm
when the net impedance at the input is 50
W
. When this impedance
is altered to 200
W
, however, the same voltage corresponds to a
power level that is four times smaller (
P
=
V
2
/
R
) or –6 dBm. A
dBV level may be converted to dBm in the special case of a 50
W
system and a sinusoidal signal by simply adding 13 dB (0 dBV
is then, and only then, equivalent to 13 dBm).
Therefore, the external termination added ahead of the AD8315
determines the effective power scaling. This will often take the
form of a simple resistor (52.3
W
will provide a net 50
W
input),
but more elaborate matching networks may be used. The choice
of impedance determines the logarithmic intercept, that is, the
input power for which the V
SET
versus P
IN
function would
cross the baseline if that relationship were continuous for all
values of V
IN
. This is never the case for a practical log amp; the
intercept (so many dBV) refers to the value obtained by the
minimum error straight line fit to the actual graph of V
SET
versus
P
IN
(more generally, V
IN
). Where the modulation is complex, as
in CDMA, the calibration of the power response needs to be
adjusted; the intercept will remain stable for any given arbitrary
waveform. When a true power (waveform independent) response is
needed, a mean-responding detector, such as the AD8361,
should be considered.
The logarithmic slope, V
SLP
in Equation 1, which is the amount
by which the setpoint voltage needs to be changed for each decibel
of input change (voltage or power), is, in principle, independent
of waveform or termination impedance. In practice, it usually
falls off somewhat at higher frequencies, due to the declining
gain of the amplifier stages and other effects in the detector
cells (see TPC 13).
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AD8315ARMZ 功能描述:IC RF PA CTRLR 50DB GSM 8MSOP RoHS:是 類別:RF/IF 和 RFID >> RF 電源控制器 IC 系列:- 標(biāo)準(zhǔn)包裝:3,000 系列:- RF 型:GSM 頻率:450MHz ~ 2GHz 特點(diǎn):四頻帶 封裝/外殼:8-VFBGA 供應(yīng)商設(shè)備封裝:8-MicroSMD（1.51x1.51） 包裝:帶卷 (TR) 其它名稱:LMV243BLX
AD8315ARMZ-RL 功能描述:IC RF PA CTRLR 50DB GSM 8MSOP RoHS:是 類別:RF/IF 和 RFID >> RF 電源控制器 IC 系列:- 標(biāo)準(zhǔn)包裝:3,000 系列:- RF 型:GSM 頻率:450MHz ~ 2GHz 特點(diǎn):四頻帶 封裝/外殼:8-VFBGA 供應(yīng)商設(shè)備封裝:8-MicroSMD（1.51x1.51） 包裝:帶卷 (TR) 其它名稱:LMV243BLX
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