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

voltage on RFIN.

(3)

where:

VCAL is the measured output voltage on the VCAL pin.

no RF input signal applied.

that is,

3

1

10

10

log













×

=

−

IN

RFIN

P

R

V

(4)

where:

R is the characteristic impedance (usually 50 Ω).

Rewriting the equation results in

























−













×

×

=

−

−

Intercept

P

R

Slope

VCAL

VCAL

IN

OFF

3

1

10

10

log

(5)

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

Equation 5 can be rewritten as

























−













×

×

=

−

−

Intercept

P

R

Slope

VIN

IN

3

1

10

10

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

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

input voltage (

LOW

RFIN

V

) and measure the voltage on the

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

associated input voltage (

HIGH

RFIN

V

) and measure the

4. Calculate the slope by using the following equation:

HIGH

RFIN

V

−

LOW

RFIN

V

)

5. Calculate the intercept by using the following equation:

When the slope and intercept are known, insert them into

which the circuit trips.

























−













×

×

=

−

−

Intercept

P

R

Slope

VIN

THRESHOLD

3

1

10

10

log