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AD8319

Data Sheet

Rev. D | Page 14 of 19

INLO

INHI

GAIN

OPLO

OPHI

DIRECTIONAL

COUPLER

ATTENUATOR

VPOS

COMM

ADL5330

+5V

COMM

VOUT

VPOS

VSET

INHI

INLO

CLPF

AD8319

LOG AMP

DAC

RF OUTPUT

SIGNAL

4.12kΩ

10kΩ

SETPOINT

VOLTAGE

1nF

47nF

120nH

100pF

TADJ

18kΩ

52.3Ω

RF INPUT

SIGNAL

Figure 30. AD8319 Operating in Controller Mode to Provide Automatic Gain Control Functionality in Combination with the ADL5330

The basic connections for operating the AD8319 in an automatic

gain control (AGC) loop with the ADL5330 are shown in

Figure 30. The ADL5330 is a 10 MHz to 3 GHz VGA. It offers a

large gain control range of 60 dB with ±0.5 dB gain stability.

This configuration is similar to Figure 29.

The gain of the ADL5330 is controlled by the output pin of the

AD8319. This voltage, VOUT, has a range of 0 V to near VPOS. To

avoid overdrive recovery issues, the AD8319 output voltage can

be scaled down using a resistive divider to interface with the 0 V

to 1.4 V gain control range of the ADL5330.

A coupler/attenuation of 21 dB is used to match the desired

maximum output power from the VGA to the top end of the

linear operating range of the AD8319 (approximately −5 dBm

at 900 MHz).

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

the VSET voltage over temperature for a 900 MHz sine wave with

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

AD8319 has a negative sense. Decreasing VSET, which corresponds

to demanding a higher signal from the ADL5330, increases gain.

The AGC loop is capable of controlling signals of ~40 dB. This

range limitation is due to the dynamic range of the AD8319.

Using a wider dynamic range detector, such as the AD8317,

AD8318, or AD8362, allows for the full 60 dB range of the

ADL5330 to be used. 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

–20

–4

–3

–1

–2

0.2

0.4

0.6

0.8

1.0

1.2

1.4

SETPOINT VOLTAGE (V)

1.3

1.1

0.30.50.70.9

1.5 1.6

Figure 31. ADL5330 Output Power vs. AD8319 Setpoint Voltage, PIN = −1.5 dBm

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