ADL5507ACBZ-R7 datasheet(29/34 Pages) AD

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Data Sheet

ADL5507

APPLICATIONS INFORMATION

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Rev. 0 | 29 of 34

BASIC CONNECTIONS

Figure 82 shows the basic connections for measurement mode.

A supply voltage of 2.7 V to 3.45 V is required. Decouple the

supply to the VPOS pin with a low inductance 0.1 µF surface-mount

ceramic capacitor. A series resistor of about 10 Ω can be added;

this resistor slightly reduces the supply voltage to the ADL5507 and

depends on the load resistance at the output to ground. Avoid its

use in applications where the power supply voltage is very low. A

series inductor provides similar power supply filtering with minimal

drop in supply voltage.

Figure 82. Basic Connections

The ADL5507 has an internal input coupling capacitor. This elim-

inates the need for external AC coupling. In this example, a

broadband input match is achieved by connecting a 51 Ω resistor

between RFIN and ground. This resistance combines with the inter-

nal input impedance to give an overall broadband input resistance

of 50 Ω. Several other coupling methods are possible; these are

described in the Input Coupling Options section.

Figure 83 shows the typical logarithmic conformance at 3.6 GHz.

Figure 83. VVLOG and Log Conformance Error vs. Input Level at 3.6 GHz

TRANSFER FUNCTION IN TERMS OF SLOPE

AND INTERCEPT

The transfer function of the ADL5507 is characterized in terms of its

slope and intercept. The logarithmic slope is defined as the change

in the VLOG output voltage for a 1 dB change in RF power level at

the RF input. For the ADL5507, the slope is nominally 18.7 mV/dB

in positive slope response mode. Therefore, a 10 dB change at

the input results in a change at the output of approximately 187

mV. Figure 83 shows the range over which the device maintains

its constant slope. The dynamic range can be defined as the range

over which the error remains within a certain band, usually ±1 dB

or ±3 dB. In Figure 83 for example, the ±1 dB dynamic range is

approximately 55 dB (from −56 dBm to −1 dBm), and the ±3 dB

dynamic range is approximately 62 dB (from −60.5 dBm to +1.5

dBm).

The intercept is the point at which the extrapolated linear response

intersects the horizontal axis (see Figure 83). Using the slope and

intercept, calculate the output voltage for any input level within the

specified input range, or calculate the input level from the output

voltage by the following complementary equations:

VVLOG=SLOPE× PIN−INTERCEPT (1)

PIN=VVLOGSLOPE+INTERCEPT

(2)

where:

VVLOG is the power detector output voltage, in millivolts.

PIN is the input signal level, expressed in decibels relative to some

reference level (dBm in this case).

SLOPE is the logarithmic slope, expressed in mV/dB.

INTERCEPT is the logarithmic intercept, expressed in decibels

relative to the same reference level.

For example, at an input level of −25 dBm, the VLOG output

voltage is VVLOG = 18.7mV/dB × [−25 dBm −(−64.4 dBm)] = 737mV.

LOG CONFORMANCE ERROR CALCULATION

Log conformance error is expressed in terms of the deviation in

the output voltage between the measured VVLOG and the VVLOG

calculated with an ideal log transformation function. Ideally, the

measured VVLOG output at a particular input power, as plotted in

Figure 83, must not deviate from the calculated value of VVLOG at

that same input power. Setting the measured VVLOG to the right side

of the preceding equation and rearranging yields

VV LOG, MEASURED PIN

SLOPE

− PIN + INTERCEPT = 0

(3)

In actuality, this does not always calculate to zero. The finite

calculation that results is the log conformance error, as follows:

Error PIN =

VV LOG, MEASURED PIN

SLOPE

− PIN

+ INT ERCEPT

(4)

where Error is in dB.

The parameters SLOPE and INTERCEPT are best obtained from

the actual detector response using linear regression over a suitable

power range (where the detector response is close to linear). Better

accuracy/smaller errors are obtained if SLOPE and INTERCEPT

are determined for:

►

Each detector device individually

►

Each operating temperature

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