Data Sheet

ADL5511

APPLICATIONS INFORMATION

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Rev. E | 22 of 26

Figure 52. VENV Response to a 20 MHz LTE Carrier with a PEP of 19 dBm

that has been Triggered to Capture the Envelope’s Peak Level

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 approx-

imately −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).

Figure 53. VRMS Output vs. Input Level Distribution of 50 Devices, 900 MHz

Frequency

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: