ADL5910ACPZN-R7 datasheet(15/22 Pages) AD

15 / 22 page

Data Sheet

ADL5910

Rev. 0 | Page 15 of 22

Alternatively, by measuring the voltage on the VCAL output pin

with and without RF power applied, an equation can be derived

that establishes a precise relationship between the VIN− voltage

and the associated RF input power trip point.

Within the linear operating range of the ADL5910, there is a

linear relationship between VCAL − VCALOFF and the input

voltage on RFIN.

VCAL − VCALOFF = Slope × (VRFIN − Intercept)

(3)

where:

VCAL is the measured output voltage on the VCAL pin.

VCALOFF is the measured output voltage on the VCAL pin with

no RF input signal applied.

VRFIN is the RF input power (in dBm) converted into volts rms,

that is,

log













−

RFIN

(4)

where:

R is the characteristic impedance (usually 50 Ω).

PIN is the RF input power on the RFIN pin in dBm.

Rewriting the equation results in

















−













−

Intercept

Slope

VCAL

OFF

log

(5)

The voltage that must be applied to the VIN− pin for a particular

input power is equal to (VCAL − VCALOFF). Therefore,

Equation 5 can be rewritten as

















−













−

Intercept

Slope

VIN

log

(6)

Use a two-point or a three-point calibration to establish the

slope and intercept values in Equation 6. The procedure for a two-

point calibration follows:

1. With no RF input signal applied, measure the voltage on

the VCAL pin (VCALOFF).

2. Apply an RF input power that is toward the minimum limit

of the RF input range (RFINLOW). Calculate the associated

input voltage (

LOW

RFIN

) and measure the voltage on the

VCAL pin (VCALLOW).

3. Apply an RF input power that is toward the maximum

limit of the RF input range (RFINHIGH). Calculate the

associated input voltage (

HIGH

RFIN

) and measure the

voltage on the VCAL pin (VCALHIGH) pin.

4. Calculate the slope by using the following equation:

Slope = (VCALHIGH − VCALLOW)/(

HIGH

RFIN

−

LOW

RFIN

)

5. Calculate the intercept by using the following equation:

Intercept = VRFIN − (VCAL − VCALOFF)/Slope

When the slope and intercept are known, insert them into

Equation 6, where PTHRESHOLD is the desired RF power level at

which the circuit trips.

















−













−

Intercept

Slope

VIN

THRESHOLD

log

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