ADL5513ACPZ-R7 datasheet(20/28 Pages) AD

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ADL5513

Rev. 0 | Page 20 of 28

CONTROLLER MODE

The ADL5513 provides a controller mode feature at Pin VOUT.

Using VSET for the setpoint voltage, it is possible for the ADL5513

to control subsystems, such as power amplifiers (PAs), variable

gain amplifiers (VGAs), or variable voltage attenuators (VVAs),

which have output power that increases monotonically with

respect to their gain control signal.

To operate in controller mode, the link between VSET and VOUT

is broken. A setpoint voltage is applied to the VSET input, VOUT

is connected to the gain control terminal of the VGA, and the

RF input of the detector is connected to the output of the VGA

(usually using a directional coupler and some additional attenua-

tion). Based on the defined relationship between VOUT and the

RF input signal when the device is in measurement mode, the

ADL5513 adjusts the voltage on VOUT (VOUT is now an error

amplifier output) until the level at the RF input corresponds to

the applied VSET. When the ADL5513 operates in controller

mode, there is no defined relationship between the VSET and the

VOUT voltage; VOUT settles to a value that results in the correct input

signal level appearing at INHI/INLO.

For this output power control loop to be stable, a ground-

referenced capacitor must be connected to the CLPF pin.

This capacitor, CFLT, integrates the error signal (in the form of

a current) to set the loop bandwidth and ensure loop stability.

Further details on control loop dynamics can be found in the

AD8315 data sheet.

VGA/VVA

RFIN

INHI

INLO

VSET

CLPF

VOUT

ADL5513

DIRECTIONAL

COUPLER

52.3Ω

47nF

CFLT

DAC

GAIN

CONTROL

VOLTAGE

Figure 42. Controller Mode

CONSTANT POWER OPERATION

In controller mode, the ADL5513 can be used to hold the output

power stable over a broad temperature/input power range. This

can be useful in topologies where a transmit card is driving an

HPA or when connecting power-sensitive modules together.

Figure 44 shows a schematic of a circuit setup that holds the

output power to approximately −39 dBm at 900 MHz when the

input power is varied over a 62 dB dynamic range. Figure 43

shows the performance results. A portion of the output power is

coupled to the input of ADL5513 using a 20 dB coupler. The

VSET voltage is set to 0.65 V, which forces the ADL5513 output

voltage to control the ADL5330 to deliver −59 dBm. (If the

ADL5513 is in measurement mode and a −59 dBm input power

is applied, the output voltage is 0.65 V). A generic op amp is used

(AD8062) to invert the slope of the ADL5513 so that the gain of

the ADL5330 decreases as the ADL5513 control voltage

increases. The high end power is limited by the maximum gain

of the ADL5330 and can increase if VSET is moved so that the

ADL5513 has a higher power on its input and a VGA with

higher linearity is used. The low power is limited by the

sensitivity of the ADL5513 and can be increased with a reduction

in the coupling value of the coupler.

–35

–36

–37

–38

–39

–40

–41

–42

–43

–44

–45

–65 –60 –55 –50 –45 –40 –35 –30 –25 –20 –15 –10 –5

PIN (dBm)

+25°C

–40°C

+85°C

Figure 43. Performance of ADL5330/ADL5513

Constant Power Circuit

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