adl5386 Analog Devices, Inc., adl5386 Datasheet - Page 24

• Manufacturer Part Number: adl5386
• Description: 50 Mhz To 2200 Mhz Quadrature Modulator With Integrated Detector And Vva
• Manufacturer: Analog Devices, Inc.

ADL5386
Figure 43 shows the resulting transfer function of the AGC
loop, that is, output power (on ATTO) vs. setpoint voltage (on
VSET) at 350 MHz. Figure 43 shows a linear-in-dB relationship
between P
plot of the linearity of the transfer function in dB. The linearity
is calculated by measuring the slope and intercept of the transfer
function using the V
0.7 and 1 V. This yields an idealized transfer function of
The error in decibels is given by
The relationship between the input level of the detector and the
voltage on V
the detector when operating in measurement mode (VSET is
connected directly to VDET). Figure 44 shows the measurement
mode relationship between the detector input level and the output
voltage at 350 MHz. Figure 44 shows that an input level of −12 dBm
produces an output of 0.6 V. In AGC mode, a setpoint voltage of
0.6 V causes the loop to adjust until the detector input level is
−12 dBm. Remembering the coupling factor of the directional
coupler, the −12 dBm level at the detector corresponds to a
power level of approximately +3 dBm at the output of the VVA.
Therefore, with a 15 dB coupling factor, a setpoint voltage of 0.6
produces an output power from the VVA of 3 dBm, as shown in
Figure 43.
–10
–15
–20
–25
–30
–35
P
ERROR (dB) = (P
–
OUT_IDEAL
5
0
5
0.5
(1 V p-p Differential Baseband Input Voltage on I and Q)
Figure 43. P
OUT
+85°C
+25°C
–40°C
0.6
VSET
and V
= SLOPE × (V
follows from the nominal transfer function of
0.7
OUT
VSET
VSET
vs. V
OUT
0.8
over at least 25 dB. It also includes a
and P
VSET
− P
0.9
Transfer Function in AGC Mode
VSET
V
OUT_IDEAL
VSET
OUT
− INTERCEPT)
1.0
data between V
(V)
)/SLOPE
1.1
1.2
VSET
1.3
levels of
1.4
–1
–2
–3
–4
4
3
2
1
0
Rev. 0 | Page 24 of 36
In general, the loop should be designed with a level of attenuation
between ATTO and INHI (detector input) that results in the
detector always seeing a power level that is within its linear
operating range. Because the power detector has a linear input
range that is larger than the attenuation range of the VVA this
is generally achievable. In addition, it is desirable to map the
desired VVA output power range into the detector’s region of
maximum linearity. In the example shown, where a maximum
output power of +3 dBm is desired, the input range to the detector
is −12 dBm to −44 dBm. Notice how the degraded linearity of
the detector below −40 dBm (see Figure 44) can also be observed
in the closed-loop transfer function at output power levels below
−25 dBm (Figure 43).
SETTING THE TADJ RESISTOR
The primary component of the temperature variation of the
V
the intercept. This temperature drift can be compensated by
connecting a resistor between TADJ (Pin 39) and ground.
The optimum resistance value for the frequencies at which the
ADL5386 is characterized has been experimentally determined to
be 22.1 kΩ. Note that the accuracy specifications of the detector
and performance plots assume that this resistance is in place.
VOUT
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
/V
0
–65 –60 –55 –50 –45 –40 –35 –30 –25 –20 –15 –10 –5
VSET
Figure 44. Measurement Mode Relationship Between
V
voltage and the detector RF input is the drift of
VOUT
/V
VSET
and Detector Input Power at 350 MHz
ERROR (dB)
P
IN
V
(dBm)
OUT
(V)
0
4
3
2
1
0
–1
–2
–3
–4