AD8364-EVAL-2140 Analog Devices Inc, AD8364-EVAL-2140 Datasheet - Page 27

• Manufacturer Part Number: AD8364-EVAL-2140
• Description: BOARD EVAL AD8364 2140MHZ
• Manufacturer: Analog Devices Inc

Specifications of AD8364-EVAL-2140

• Module/board Type: Evaluation Board
• For Use With/related Products: AD8364 2.140GHz only
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

CONSTANT OUTPUT POWER OPERATION
In controller mode, the AD8364 can be used to hold the output
power stable over a broad temperature/input power range. This
can be very useful in systems, such as a transmit module driving
a high power amplifier (HPA) in a basestation, that connect
multiple power sensitive modules together. In applications
where stable output power is needed, the RF output is
connected to Channel B using a coupler, VLVL is connected to
VREF, VSTB is used to set the power to a particular level and
can be controlled using a DAC or a dc voltage, OUTB is used to
drive the gain control of an amplifier that is capable of negative-
gain law conformance (such as the AD8367), and ADJB (set at
0 V in this example) is used to control the temperature drift.
Using this configuration, the RF input signal is down converted
to 80 MHz using the AD8343 and amplified using the AD8367.
The signal then splits and part of it is fed back to the AD8364
through Channel B, and a setpoint voltage is applied to VSTB.
This voltage corresponds to a particular power level, which is
determined by the slope of the AD8364. The power detected at
the input of the AD8364 is compared with this voltage, and the
voltage present at OUTB is adjusted up or down to match the
setpoint voltage, with the power detected on the input. The
OUTB voltage is connected to the gain control of the AD8367
VGA and increases or decreases the gain of the AD8367,
resulting in the output power being held constant, regardless of
variations in the input power. The AD8364 is able to maintain a
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fixed output power from the AD8367 even though its input
power is changing. The input power can vary over a 36 dB
range, while the output power remains constant and the drift
over temperature is less than 0.2 dB
Figure 64 shows a constant output power circuit using the
AD8364 and the AD8367 VGA. The input power was swept
from +3 dBm to −35 dBm, the output power was measured at
multiple temperatures between −40°C and +85°C, and the
power changed less than ±0.07 dB (Figure 63).
–15.0
–15.1
–15.2
–15.3
–15.4
–15.5
–15.6
–15.7
–15.8
–15.9
–16.0
–40
Figure 63. AD8364 Constant Power Performance
–35
–30
P
P
OUT
OUT
–40°C
–25
+25°C
–20
–20°C
P
IN
(dBm)
–15
P
OUT
–10
+85°C
–5
0
AD8364
5