AD8317

Rev. B | Page 14 of 20

INLO

INHI

GAIN

OPLO

OPHI

DIRECTIONAL

COUPLER

ATTENUATOR

VPSx

COMx

ADL5330

+5V

+5V

+5V

COMM

VOUT

VPOS

VSET

INHI

INLO

CLPF

AD8317

LOG AMP

DAC

RF OUTPUT

SIGNAL

4.12kΩ

10kΩ

SETPOINT

VOLTAGE

1nF

47nF

47nF

120nH

120nH

100pF

100pF

100pF

100pF

TADJ

18kΩ

52.3Ω

RF INPUT

SIGNAL

Figure 30. AD8317 Operating in Controller Mode to Provide Automatic Gain Control Functionality in Combination with the ADL5330

Figure 31 shows the transfer function of the output power vs.

the setpoint voltage over temperature for a 900 MHz sine wave

with an input power of −1.5 dBm. Note that the power control

corresponds to demanding a higher signal from the ADL5330,

increases gain.

The AGC loop is capable of controlling signals just under the

full 60 dB gain control range of the ADL5330. The performance

over temperature is most accurate over the highest power range,

where it is generally most critical. Across the top 40 dB range

of output power, the linear conformance error is well within

±0.5 dB over temperature.

–50

–40

–30

–10

0

10

20

30

–20

–4

–3

0

1

2

3

4

–1

–2

0.2

0.4

0.6

0.8

1.0

1.4

1.8

2.0

SETPOINT VOLTAGE (V)

1.6

1.2

For the AGC loop to remain in equilibrium, the AD8317 must

track the envelope of the ADL5330 output signal and provide

the necessary voltage levels to the ADL5330 gain control input.

Figure 32 shows an oscilloscope screenshot of the AGC loop

depicted in Figure 30. A 100 MHz sine wave with 50% AM

modulation is applied to the ADL5330. The output signal from

the VGA is a constant envelope sine wave with amplitude corre-

sponding to a setpoint voltage at the AD8317 of 1.5 V. Also

shown is the gain control response of the AD8317 to the

changing input envelope.

CH1 200mV

CH3 50.0mVΩ

A CH2

820mV

M2.00ms

T

640.00µs

1

3

2

AM MODULATED INPUT

AD8317 OUTPUT

ADL5330 OUTPUT

Figure 32. Oscilloscope Screenshot Showing an AM Modulated Input Signal

and the Response from the AD8317