ADL5330 Analog Devices, Inc., ADL5330 Datasheet - Page 16

• Manufacturer Part Number: ADL5330
• Description: 10 Mhz To 3 Ghz Vga With 60 Db Gain Control Range
• Manufacturer: Analog Devices, Inc.

ADL5330
Figure 38 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 AD8318 has a negative sense. Decreasing VSET, which
corresponds to demanding a higher signal from the ADL5330,
tends to increase 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.
The broadband noise added by the logarithmic amplifier is
negligible.
–10
–20
–30
–40
–50
30
20
10
Figure 38. ADL5330 Output Power vs. AD8318 Setpoint Voltage,
0
0.4
0.6
0.8
1.0
SETPOINT VOLTAGE (V)
P
IN
Figure 37. ADL5330 Operating in an Automatic Gain Control Loop in Combination with the AD8318
1.2
= −1.5 dBm
RF INPUT
SIGNAL
1.4
DAC
220pF
1.6
100pF
100pF
SETPOINT
1.8
VOLTAGE
2.0
INHI
INLO
412Ω
VPOS
+5V
ADL5330
VSET
CLPF
2.2
VOUT
GAIN
4
3
2
1
0
–1
–2
–3
–4
LOG AMP
AD8318
1kΩ
COMM
COMM
Rev. A | Page 16 of 24
OPLO
OPHI
VPOS
+5V
INLO
INHI
120nH
+5V
1nF
1nF
In order for the AGC loop to remain in equilibrium, the
AD8318 must track the envelope of the ADL5330 output signal
and provide the necessary voltage levels to the ADL5330’s gain
control input. Figure 39 shows an oscilloscope screenshot of the
AGC loop depicted in Figure 37. A 100 MHz sine wave with
50% AM modulation is applied to the ADL5330. The output
signal from the ADL5330 is a constant envelope sine wave with
amplitude corresponding to a setpoint voltage at the AD8318 of
1.5 V. Also shown is the gain control response of the AD8318 to
the changing input envelope.
120nH
Figure 39. Oscilloscope Screenshot Showing an AM Modulated Input Signal
100pF
100pF
1
3
CH1
CH3 250mV Ω
AM MODULATED INPUT
AD8318 OUTPUT
ADL5330 OUTPUT
DIRECTIONAL
COUPLER
250mV Ω
ATTENUATOR
RF OUTPUT
SIGNAL
T
T
M2.00ms
T
0.00000s
A CH4
1.80V