Data Sheet

ADL5511

Rev. C | Page 23 of 29

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

(9)

(10)

where:

Because the gain and intercept of the rms and envelope paths

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

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:

(11)

(12)

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

the following equation:

Error (dB) =

(13)

Figure 55 is a plot of this error for VENV at 1900 MHz for a

multiple devices at +25°C, +85°C, and −40°C with calibration

performed at two points, −14 dBm and +5 dBm (notice how

the error at 25°C at the calibration points is zero). These error

plots for all temperatures are calculated using the 25°C slope

and intercept. This is consistent with calibration in a mass

production environment where calibration at temperature is

generally not practical.

Figure 55. VENV Linearity Error vs. Input Level and Temperature Using a

Two-Point Calibration at 1900 MHz

By adding a third calibration point, the linearity of the ADL5511

can be enhanced at lower power levels. With a three-point

calibration, calibration coefficients (slope and intercept) are

calculated for each segment (thus, there will be two slopes and

two intercepts).

Figure 56 shows the same data as Figure 55, but with a three-

point calibration (calibration points at −26 dBm, −15 dBm, and

+5 dBm. This helps to extend the usable operating range of the

ADL5511 well below −25 dBm.

Figure 56. VENV Linearity Error vs. Input Level and Temperature Using a Three-

Point Calibration at 1900 MHz

–3

–2

–1

0

1

2

3

–30

–25

–20

–15

–10

–5

0

5

10

15

–40°C

+25°C

+85°C

–3

–2

–1

0

1

2

3

–30

–25

–20

–15

–10

–5

0

5

10

15

–40°C

+25°C

+85°C