STPAC01F1

3/6

Coupler

GND2

Out

GND1

STPAC01F1

RF input

Thermal

compensation

Low pass

filter

RF detector

-

+

APPLICATION DIAGRAM

The STPAC01 is the first part of the power amplifier stage and provides both RF power and die

temperature measurements. The above figure gives the basic circuit of RF detector.

A coupler located on the line between RF amplifier output and the antenna takes a part of the available

power and applies it to STPAC01 RF input.

The RF detector and the low pass filter provide a DC voltage depending on the input power. Thermal

compensation provides a DC voltage depending on the ambient temperature. As the detection system and

the thermal compensation are based on the same topology, VDCout will have the same temperature

variation as Vtemp. Connected to a differential amplifier, the output will be a voltage directly linked to the

RF input power. VDCout and Vtemp must be bias with 50µA DC current.

This topology offers the most accurate output value as it is 100% compensated.

RF in

DC output

voltage

RF generator

Power

supply

Current

generator

STPAC

test board

Multimeter

0.8

1

1.2

1.4

1.6

1.8

2

-20

-15

-10

-5

0

5

10

Pin (dBm)

VDCout

850MHz

1850MHz

Tamb = 25°C

Ibias = 50µA

Vbias = 2.7V