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参数资料
| 型号： | AD8316ACP-EVAL |
| 厂商： | Analog Devices, Inc. |
| 英文描述： | Dual Output GSM PA Controller |
| 中文描述： | 双输出GSM功率放大器控制器 |
| 文件页数： | 10/20页 |
| 文件大小： | 497K |
| 代理商： | AD8316ACP-EVAL |
REV. C
–10–
AD8316
Further details about the structure and function of log amps are
provided in data sheets for other log amps produced by Analog
Devices. The AD640 and AD8307 include detailed discussions
of the basic principles of operation and explain why the intercept
depends on waveform, an important consideration when complex
modulation is imposed on an RF carrier.
The intercept need not correspond to a physically realizable part
of the signal range for the log amp. Thus, for the AD8316, the
specified intercept is –62 dBm at 0.9 GHz, whereas the lowest
acceptable input for accurate measurement (+1 dB error) is
–48 dBm. At 2.5 GHz, the +1 dB error point shifts to –52 dBm.
This positioning of the intercept is deliberate and ensures that
the VSET voltage is within the capabilities of certain DACs,
whose outputs cannot swing below 200 mV. Figure 2 shows the
0.9 GHz response of the AD8316; the vertical axis represents
the value required at the power control pin VSET to null the
control loop rather than the voltage at the OUT1 or OUT2
pins.
P
IN
0.5V
–67dBm
V
S
0
1.5V
1.0V
80dBV
V
IN
, dBV
IN
10mV
40dBV
1mV
60dBV
100mV
20dBV
1V (rms)
0dBV
–47dBm
–27dBm
–7dBm
+13dBm
–62dBm
SLOPE=22mVdB
IDEAL
0.308V AT –48dBm
ACTUAL
1.408V AT +2dBm
Figure 2. Basic Calibration of the AD8316 at 0.9 GHz
Controller-Mode Log Amps
The AD8316 combines the two key functions required for the
measurement and control of the power level over a moder-
ately wide dynamic range. First, it provides the amplification
needed to respond to small signals with a chain of four ampli-
fier/limiter cells, each with a small signal gain of 10 dB and a
bandwidth of approximately 4 GHz (see Figure 1). At the
output of each of these amplifier stages is a full-wave recti-
fier, essentially a square-law detector cell that converts the
RF signal voltages to a fluctuating current having an average
value that increases with signal level. A passive detector stage is
added ahead of the first stage. These five detectors are separated
by 10 dB, spanning 50 dB of dynamic range. Their outputs are
in the form of a differential current, making summation a
simple matter. It is readily shown that the summed output can
closely approximate a logarithmic function. The overall accu-
racy at the extremes of the total range, viewed as the deviation
from an ideal logarithmic response, that is, the law-conformance
error, can be judged by referring to TPC 4, which shows that
errors across the central 40 dB are moderate. Other perfor-
mance curves show how conformance to an ideal logarithmic
function varies with supply voltage, temperature, and frequency.
In a device intended for measurement applications, this current
would be converted to an equivalent voltage to provide the
log(V
IN
) function shown in Equation 1. However, the design of
the AD8316 differs from standard practice in that its output
needs to be a low noise control voltage for an RF power ampli-
fier, not a direct measure of the input level. Further, it is highly
desirable that this voltage be proportional to the time integral of
the error between the actual input V
IN
and a dc voltage V
SET
(applied to Pin 3, VSET) that defines the setpoint, that is, a
target value for the power level, typically generated by a DAC.
This is achieved by converting the difference between the sum
of the detector outputs (still in current form) and an internally
generated current proportional to VSET to a single-sided
current-mode signal. This, in turn, is converted to a voltage
(at FLT1 or FLT2, the low-pass filter capacitor nodes) to
provide a close approximation to an exact integration of the
error between the power present in the termination at the input
of the AD8316 and the setpoint voltage. Finally, the voltages
developed across the ground referenced filter capacitors C
FLT
are buffered by a special low noise amplifier of low voltage
gain (
×
1.35) and presented at OUT2 or OUT1 for use as the
control voltage for the appropriate RF power amplifier. This
buffer can provide rail-to-rail swings and can drive a substan-
tial load current, including large capacitors. Note:
The RF
power delivered by the power amplifier is assumed to increase mono-
tonically with an increasingly positive voltage on its APC control pin.
Band selection in the AD8316 relies on the fact that dual-band/
dual-mode amplifier systems require only one active amplifier at
a time. This allows both amplifier outputs to share the RF input
of the AD8316 (Pin 1, RFIN) as long as the inactive amplifier is
disabled, i.e., it is not delivering RF power. In this case, power
control is directed solely through the selected amplifier. The
AD8316 ensures that the output control pin associated with the
unselected amplifier pulls its APC pin to ground. It is assumed
that the amplifier is essentially disabled when its APC pin is
grounded.
Control Loop Dynamics
To understand how the AD8316 behaves in a complete control
loop, it is necessary to develop an expression for the current in
the integration capacitor as a function of the input V
IN
and the
setpoint voltage V
SET
. Refer to Figure 3.
1.35
C
FLT
4
FLT1
9
VOUT1
V
SET
V
IN
I
DET
SETPOINT
INTERFACE
3
RFIN
1
LOGARITHMIC
RF DETECTION
SUBSYSTEM
I
ERR
VSET
I
SET
= V
SET
/ 4.15k
I
DET
= I
SLP
log
10
(V
IN
/V
Z
)
Figure 3. Behavioral Model for the AD8316 with
OUT1 Selected
First, write the summed detector currents as a function of the
input:
=
log
(
/
10
I
I
V
V
DET
SLP
IN
Z
)
(3)
where
I
DET
is the partially filtered demodulated signal, whose
exact average value will be extracted through the subsequent
integration step;
I
SLP
is the current-mode slope, and has a value
of 106 mA per decade (that is, 5.3 mA/dB);
V
IN
is the input in
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| AD8316ACP-REEL7 | Dual Output GSM PA Controller |
| AD8316ARM | Dual Output GSM PA Controller |
| AD8316ARM-REEL7 | Dual Output GSM PA Controller |
| AD8318ACPZ-WP | 1 MHz - 8 GHz, 60 dB Logarithmic Detector/Controller |
相关代理商/技术参数 |
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|---|---|
| AD8316ACP-REEL | 制造商:Rochester Electronics LLC 功能描述:- Tape and Reel |
| AD8316ACP-REEL7 | 制造商:Analog Devices 功能描述:DUAL OUTPUT GSM PA CNTRLR 16LFCSP EP - Tape and Reel 制造商:Rochester Electronics LLC 功能描述:DUAL OUTPUT GSM PA CONTROLLER - Tape and Reel |
| AD8316ARM | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| AD8316ARM-REEL7 | 制造商:Rochester Electronics LLC 功能描述:- Tape and Reel |
| AD8316-EVAL | 制造商:Analog Devices 功能描述:- Bulk |
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