Data Sheet

ADL5331

Rev. A | Page 11 of 15

INLO

INHI

GAIN

OPLO

OPHI

10dB

DIRECTIONAL

COUPLER

10dB

ATTENUATOR

VPOS

COMM

ADL5331

+5V

+5V

+5V

COMM

VOUT

VPOS

VSET

INHI

INLO

CLPF

AD8319

LOG AMP

DAC

RFIN

SIGNAL

RFOUT SIGNAL

390Ω

1kΩ

SETPOINT

VOLTAGE

220pF

1nF

1nF

120nH

120nH

10nF

10nF

10nF

10nF

Figure 19. AD8319 Operating in Controller Mode to Provide Automatic Gain Control Functionality in Combination with the ADL5331

Figure 19 shows the basic connections for operating the AD8319

log detector in an automatic gain control (AGC) loop with the

ADL5331.

The gain of the ADL5331 is controlled by the output pin of the

avoid overdrive recovery issues, the AD8319 output voltage

can be scaled down using a resistive divider to interface with

the 0.1 V to 1.4 V gain control range of the ADL5331.

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 20 shows the transfer function of the output power vs.

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

which corresponds to demanding a higher signal from the

ADL5331, increases gain.

This AGC loop is capable of controlling signals of ~30 dB,

which is the gain range limitation on the ADL5331. Across

the top 25 dB range of output power, the linear conformance

error is within ±0.5 dB over temperature.

20

15

10

5

3.00

2.25

1.50

–0.75

–1.50

–2.25

–3.00

0

0.75

0

–5

–10

–15

–20

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

+85°C

+25°C

–40°C

Figure 20. ADL5331 Output Power vs. AD8319 Setpoint Voltage,