AD8362-EVALZ Analog Devices Inc, AD8362-EVALZ Datasheet - Page 20

• Manufacturer Part Number: AD8362-EVALZ
• Description: BOARD EVAL FOR AD8362
• Manufacturer: Analog Devices Inc
• Series: TruePower™r
• Type: Detector, CDMAr

Specifications of AD8362-EVALZ

• Frequency: 50Hz ~ 3.8GHz
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• For Use With/related Products: AD8362
• Other names: Q3199218

AD8362
An external 100 Ω shunt resistor combines with the internal
100 Ω single-ended input impedance to provide a broadband
50 Ω match. The unused input (in this case, INLO) is ac-coupled
to ground. Figure 49 shows the transfer function of the AD8362
at various frequencies when the RF input is driven single-
ended. The results show that transfer function linearity at the
top end of the range is degraded by the single-ended drive.
For operation at frequencies ≥2.7 GHz, some additional
components are required to match the AD8362 input to
50 Ω (see Figure 50). As the operating frequency increases,
there is also corresponding shifting in the operating power
range (see Figure 51).
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
Figure 50. Input Matching for Operation at Frequencies ≥2.7 GHz
–55
RF INPUT
Figure 49. Transfer Function at Various Frequencies when the
–50 –45 –40 –35 –30 –25 –20 –15 –10 –5
450MHz
1900MHz
2500MHz
900MHz
2140MHz
4.7nH
2.7nH
RF Input is Driven Single-Ended
1nF
PIN (dBm)
0.01µF
1nF
1nF
1nF
1
2
3
4
5
6
7
8
COMM
CHPF
DECL
INHI
INLO
DECL
PWDN
COMM
AD8362
0
ACOM
ACOM
VPOS
VOUT
VREF
VTGT
VSET
CLPF
5
10
16
15
14
13
12
11
10
2.0
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
9
Rev. D | Page 20 of 32
OPERATION AT LOW FREQUENCIES
In conventional rms-to-dc converters based on junction tech-
niques, the effective signal bandwidth is proportional to the
signal amplitude. In contrast, the 3.5 GHz VGA bandwidth in
the AD8362 is independent of its gain. Because this amplifier is
internally dc-coupled, the system is also used as a high accuracy
rms voltmeter at low frequencies, retaining its temperature-
stable, decibel-scaled output (for example, in seismic, audio,
and sonar instrumentation).
While the AD8362 can be operated at arbitrarily low frequencies,
an ac-coupled input interface must be maintained. In such cases,
the input coupling capacitors should be large enough so that the
lowest frequency components of the signal to be included in the
measurement are minimally attenuated. For example, for a 3 dB
reduction at 1.5 kHz, capacitances of 1 μF are needed because the
input resistance is 100 Ω at each input pin (200 Ω differentially),
and the calculation is 1/(2π × 1.5 kΩ × 100) = 1 μF. In addition, to
lower the high-pass corner frequency of the VGA, a large capaci-
tor must be connected between the CHPF pin and ground (see
the Choosing a Value for CHPF section).
More information on the operation of the AD8362 and other RF
power detectors at low frequency is available in Application Note
AN-691: Operation of RF Detector Products at Low Frequency.
3.00
2.75
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
Figure 51. Transfer Function at Various Frequencies ≥2.7 GHz when
0
–60 –55
–50
–45
the RF Input is Driven Single-Ended
–40
INPUT AMPLITUDE (dBm)
–35
–30
–25
2.8GHz
3.45GHz
3.65GHz
–20
–15
–10
–5
0
5
10
15
3.0
2.5
2.0
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
–2.5
–3.0