AD8364ACPZ-R2 datasheet(27/44 Pages) AD

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Data Sheet

AD8364

Rev. C | Page 27 of 44

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 base station, 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 fixed output power from the

AD8367 even though the 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).

PIN (dBm)

–40

–35

–30

–20

–15

–25

–10

–5

–15.0

–15.2

–15.3

–15.1

–15.4

–15.5

–15.7

–15.6

–15.8

–15.9

–16.0

POUT +25°C

–20°C

POUT –40°C

POUT +85°C

Figure 63. AD8364 Constant Power Performance

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