ADL5511ACPZ-R7 datasheet(23/29 Pages) AD

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ADL5511

Data Sheet

Rev. B | Page 22 of 28

VRMS AND VENV OUTPUT OFFSET

The 900 MHz RF power sweeps in Figure 53 and Figure 54

show distributions of the VRMS and VENV outputs voltages

for multiple devices at 25°C. The VRMS output response

flattens out at approximately −30 dBm while the various VENV

response traces begin to fanout unpredictably (Figure 4 and

Figure 7 show this behavior at other frequencies). While these

plots suggest that operation at input levels down to −30 dBm is

feasible, account must also be taken for variations over

temperature. Figure 10 to Figure 38 show how the linearity

error starts to increase below input levels of −20 dBm (the

size of the error varies between VENV and VRMS and with

frequency).

100

1000

10000

–40

–30

–20

–10

INPUT (dBm)

Figure 53. VRMS Output vs. Input Level Distribution of 50 Devices,

900 MHz Frequency

100

1000

10000

–40

–30

–20

–10

INPUT (dBm)

Figure 54. VENV Output vs. Input Level Distribution of 50 Devices,

900 MHz Frequency

DEVICE CALIBRATION AND ERROR CALCULATION

Because slope and intercept vary from device to device,

calibration must be performed to achieve high accuracy.

In general, calibration is performed by applying two or more

known input power levels to the ADL5511 and measuring

the corresponding output voltages. The calibration points

are generally chosen to be within the linear operating range

of the device. For a two-point calibration, the conversion gain

(or slope) and intercept are calculated for VRMS and VENV using the

following equations:

Slope = (VOUT2 − VOUT1)/(VIN2 − VIN1)

(9)

Intercept = VOUT1 − (Slope × VIN1)

(10)

where:

VIN is the rms input voltage to RFIN.

VOUT is the voltage output at VRMS or VENV.

Because the gain and intercept of the rms and envelope paths

will be different, both paths should be calibrated, that is, with a

measured signal applied to RFIN, VENV, and VRMS. To ensure

that the voltage at VENV and VRMS is a steady-state value, a

constant envelope signal such as a sine wave should be used as

the source during calibration.

Once slope and intercept are calculated, an equation can be

written that allows calculation of the input rms or envelope level

using the following equations:

VINRMS = (VRMS − InterceptVRMS)/SlopeRMS

(11)

VINENV = (VENV − InterceptVENV)/SlopeVENV

(12)

The law conformance error, that is, the difference between the

actual input level (VIN_IDEAL) and the measured/calculated input

level (VMEASURED), of these calculations can be calculated using

the following equation:

Error (dB) =

20 × log [(VMEASURED − Intercept)/(Slope × VIN_IDEAL)]

(13)

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