ADL5507ACBZ-R7 datasheet(30/34 Pages) AD

30 / 34 page

Data Sheet

ADL5507

APPLICATIONS INFORMATION

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Rev. 0 | 30 of 34

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Each operating frequency

To achieve the best accuracy, it is recommended to determine

SLOPE and INTERCEPT for each individual unit, requiring a two-

point factory calibration. When temperature drift effects are to be

included, SLOPE and INTERCEPT need to be determined at differ-

ent operating temperatures and the system needs to incorporate a

temperature sensor to determine which parameter values to use for

the current operating temperature.

The logarithmic conformance error curves in the Typical Perform-

ance Characteristics section were obtained using linear regression

applied to the response of the individual detector devices over

−45 dBm to −10 dBm input power at TA = 25°C. The calculated

SLOPE and INTERCEPT numbers are displayed in the tables

under Specifications.

At measurement temperatures other than TA = 25°C, the logarith-

mic response deviates slightly. A better measurement accuracy is

achieved if detector response at the actual device temperature is

used. The log conformance error deviation from TA = 25°C, the

temperature drift error, equals:

Temperature Drift Error=VVLOGT −VVLOG25°C

SLOPE25°C

(5)

INPUT COUPLING OPTIONS

The internal 25 pF coupling capacitor of the ADL5507, along

with the low frequency input impedance, gives a high-pass input

corner frequency of approximately 4 MHz. This sets the minimum

operating frequency. Figure 84 to Figure 86 show three options for

input coupling. A broadband resistive match can be implemented

by connecting a shunt resistor to ground at RFIN (see Figure 84).

This 51 Ω resistor (other values can also be used to select different

overall input impedance) combines with the input impedance of the

ADL5507 to give a broadband input impedance of 50 Ω. While

the input resistance and capacitance (RIN and CIN) varies by a max-

imum of approximately ±20% from device to device, the dominance

of the external shunt resistor means that the variation in the overall

input impedance is close to the tolerance of the external resistor.

Achieve better return loss by placing the 51 Ω shunt resistor as

near the device under test (DUT) as possible.

A reactive match can also be implemented, as shown in Figure

85. This is not recommended at low frequencies because device

tolerances dramatically vary the quality of the match due to the

large input resistance. For low frequencies, the option shown in

Figure 84 or Figure 86 is recommended.

In Figure 85, the matching components are drawn as general

reactants. Depending on the frequency, the input impedance at that

frequency and the availability of standard value components, either

a capacitor or an inductor, is used. As in the previous case, the

input impedance at a particular frequency is plotted on a Smith

Chart and matching components are chosen (Shunt or Series L,

or Shunt or Series C) to move the impedance to the center of

the chart. Matching components for specific frequencies can be

calculated using the Smith Chart.

Figure 84. Broadband Resistive Method for Input Coupling

Figure 85. Narrow-Band Reactive Method for Input Coupling

Figure 86. Series Attenuation Method for Input Coupling

Figure 86 shows a third method for coupling the input signal into

the ADL5507 in applications where the input signal is larger than

the input range of the log amp. A series resistor, connected to the

RF source, combines with the input impedance of the ADL5507 to

resistively divide the input signal being applied to the input. This

has the advantage of very little power being tapped off in RF power

transmission applications.

Table 4. Input Impedance with 51 Ω Shunt for Select Frequency

Frequency

S11

Impedance Ω

(GHz)

Real

Imaginary

(Series)

0.01

-0.006

-0.009

49.35 - j0.85

0.1

-0.011

-0.006

48.88 - j0.60

0.5

-0.010

-0.026

48.90 - j2.57

-0.010

-0.054

48.72 - j5.27

-0.008

-0.113

47.96 - j11.01

-0.003

-0.179

46.64 - j17.30

+0.006

-0.250

44.67 - j23.79

+0.012

-0.323

41.49 - j29.90

-0.006

-0.392

36.30 - j33.57

-0.063

-0.464

29.04 - j34.48

-0.204

-0.504

20.67 - j29.59

-0.354

-0.545

13.55 - j25.59

-0.593

-0.459

7.98 - j16.70

-0.616

-0.326

9.45 - j12.01

-0.760

-0.274

5.48 - j8.64

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