ADL5902-EVALZ AD [Analog Devices], ADL5902-EVALZ Datasheet - Page 22

• Manufacturer Part Number: ADL5902-EVALZ
• Description: 50 MHz to 9 GHz 65 dB TruPwr Detector
• Manufacturer: AD [Analog Devices]

ADL5902
Table 6. Recommended Minimum C
Modulation/Standard
W-CDMA, One-Carrier, TM1-64
W-CDMA Four-Carrier, TM1-64, TM1-32,
TM1-16, TM1-8
LTE, TM1 1CR 20 MHz (2048 Subcarriers,
QPSK Subcarrier Modulation)
OUTPUT VOLTAGE SCALING
The output voltage range of the ADL5902 (nominally 0.3 V to
3.5 V) can be easily increased or decreased. There are a number
of situations where adjustment of the output scaling makes
sense. For example, if the ADL5902 is driving an analog-to-
digital converter (ADC) with a 0 V to 5 V input range, it makes
sense to increase the detector’s nominal maximum output
voltage of 3.5 V so that it is closer to 5 V. This makes better use
of the input range of the ADC and maximizes the resolution of
the system in terms of bits/dB.
If only a part of the ADL5902’s RF input power range is being
used (for example, −10 dBm to −60 dBm), it may make sense to
increase the scaling so that this reduced input range fits into the
ADL5902’s available output swing of 0 V to 4.8 V.
The output swing can also be reduced by simply adding a
voltage divider on the output pin, as shown in Figure 49.
Reducing the output scaling may be used when interfacing the
ADL5902 to an ADC with a 0 V to 2.5 V input range.
The output voltage swing can be increased using a technique
that is analogous to setting the gain of an op amp in non-
inverting mode with the VSET pin being the equivalent of the
inverting input of the op amp.
Connecting VOUT to VSET results in the nominal 0 V to 3.5 V
swing and a slope of approximately 53 mV/dB (this varies
slightly with frequency). Figure 49 and Table 7 show the con-
figurations for increasing the slope, along with recommended
standard resistor values for particular input ranges and output
swings.
7
6
Figure 49. Decreasing and Increasing Slope
VSET
VOUT
R1
R2
LPF
7
6
Values for Various Modulation Schemes
VSET
VOUT
Peak-Envelope
Power
10.56 dB
12.08 dB
11.58 dB
R1
R2
Rev. 0 | Page 22 of 28
Signal
Bandwidth
3.84 MHz
18.84 MHz
20 MHz
Table 7. Output Voltage Range Scaling
Desired
Input Range
(dBm)
0 to −60
−10 to −50
0 to −60
−10 to −50
Equation 17 is the general function that governs this.
where:
V
through Figure 18).
V'
to 4.8 V).
R
When choosing R1 and R2, attention must be paid to the
current drive capability of the VOUT pin and the input
resistance of the VSET pin. The choice of resistors should not
result in excessive current draw out of VOUT. However, making
R1 and R2 too large is also problematic. If the value of R2 is
compatible with the input resistance of the VSET input (72 kΩ),
this input resistance, which will vary slightly from part to part,
contributes to the resulting slope and output voltage. In general,
the value of R2 should be at least ten times smaller than the
input resistance of VSET. Values for R1 and R2 should, therefore,
be in the 1 kΩ to 5 kΩ range.
It is also important to take into account part-to-part and
frequency variation in output swing along with the ADL5902
output stage’s maximum output voltage of 4.8 V. The V
distribution is well characterized at major frequencies’ bands in
the Typical Performance Characteristics section (see Figure 6
through Figure 8, Figure 12 through Figure 14, Figure 18, and
Figure 19). The resistor values in Table 7, which were calculated
based on 900 MHz performance, are conservatively chosen so
that there is no chance that the output voltages exceed the
ADL5902 output swing or the input range of a 0 V to 2.5 V and
0 V to 5 V ADC. Because the output swing does not vary much
with frequency (it does start to drop off above 3 GHz), these
values work for multiple frequencies.
IN
O
O
C
10 nF
5.6 nF
1000 pF
is the nominal maximum output voltage (see Figure 6
is the VSET input resistance (72 kΩ).
is the new maximum output voltage (for example, up
LPF
R1
(min)
=
(
R2
||
Output Noise
95 mV p-p
164 mV p-p
452 mV p-p
R
R1
(Ω)
665
1180
806
324
IN
)

 

V
V
O
O
'
R2
(Ω)
2000
2000
2000
2000
−
1

 

New
Slope
(mV/dB)
72.1
86.3
38.3
46.2
Rise/Fall Time (10% to 90%)
12/330 µs
7/200 µs
1.3/38 µs
Nominal Output
Voltage Range (V)
0.195 to 4.52
1.096 to 4.55
0.103 to 2.49
0.587 to 2.43
OUT
(17)