AD8319

Rev. A | Page 14 of 20

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

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

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 gener-

ally 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

1.2

1.4

SETPOINT VOLTAGE (V)

1.3

1.1

0.3

0.5

0.7

0.9

1.5 1.6

Figure 31. ADL5330 Output Power vs. AD8319 Setpoint Voltage,

For the AGC loop to remain in equilibrium, the AD8319 must

track the envelope of the output signal of the ADL5330 and

provide the necessary voltage levels to the gain control input of

the ADL5330. 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 corresponding to a setpoint voltage at the AD8319 of

1.3 V. Also shown is the gain control response of the AD8319 to

the changing input envelope.

CH1 200mV

A Ch2

1.03V

M2.00ms

T

0.00000 s

1

AM MODULATED INPUT

AD8319 OUTPUT

2

3

ADL5330 OUTPUT

Figure 32. Oscilloscope Screenshot Showing an AM Modulated Input Signal

and the Response from the AD8319

Figure 33 shows the response of the AGC RF output to a pulse

responds with an RF burst. In this configuration, the input signal to

the ADL5330 is a 1 GHz sine wave at a power level of −15 dBm.

A Ch1

2.60V

T

179.800µs

AD8319 VSET PULSE

ADL5330 OUTPUT

3

1

M10.µs

Ch1 2.00V

T

Figure 33. Oscilloscope Screenshot Showing the

Response Time of the AGC Loop

Response time and the amount of signal integration are

feedback capacitor around an integrating amplifier. While it is

values under 1 nF provide sufficient filtering.

Calibration in controller mode is similar to the method used in

measurement mode. A simple 2-point calibration can be done

measuring the output power from the VGA. Slope and intercept

can then be calculated by:

(8)

(9)

(10)

More information on the use of the ADL5330 in AGC applications

can be found in the ADL5330 data sheet.