50 dB GSM PA Controller

AD8311

Rev. 0

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FEATURES

Complete RF detector/controller function

>50 dB range at 0.9 GHz (−48 dBm to +3 dBm re 50 Ω)

Accurate scaling from 0.1 GHz to 2.5 GHz

Temperature-stable linear-in-dB response

Log slope of 23 mV/dB, intercept at −60 dBm at 0.9 GHz

True integration function in control loop

Low power: 20 mW at 2.7 V

APPLICATIONS

Single, dual, and triple band mobile handset (GSM, DCS,

EDGE)

Transmitter power control

GENERAL DESCRIPTION

The AD8311 is a complete low cost subsystem for the precise

control of RF power amplifiers operating in the frequency range

0.1 GHz to 2.5 GHz and over a typical dynamic range of 50 dB.

It is intended for use in cellular handsets and other battery-

operated wireless devices. The log amp technique provides a

much wider measurement range and better accuracy than

controllers using diode detectors. In particular, its temperature

stability is excellent over a specified range of −40°C to +85°C.

Its high sensitivity allows control at low signal levels, thus

reducing the amount of power that needs to be coupled to the

detector. For convenience, the signal is internally ac-coupled.

This high-pass coupling, with a corner at approximately

0.016 GHz, determines the lowest operating frequency. Thus,

the source can be dc-grounded.

The AD8311 provides a voltage output, VAPC, which has the

voltage range and current drive to directly connect to the gain

control pin of most handset power amplifiers. VAPC can swing

from 300 mV above ground to within 200 mV below the supply

voltage. Load currents of up to 6 mA can be supported.

The setpoint control input is applied to pin VSET and has an

operating range of 0.25 V to 1.4 V. The associated circuit

determines the slope and intercept of the linear-in-dB

measurement system; these are nominally 23.6 mV/dB and

−59.7 dBm at 0.9 GHz. Further simplifying the application of

the AD8311, the input resistance of the setpoint interface is over

35 MΩ, and the bias current is typically 0.26 µA.

The AD8311 is available in a 6-ball wafer-level chip scale

package (WLCSP), 1.0 mm × 1.5 mm, and consumes 7.6 mA

from a 2.7 V to 5.5 V supply.

FUNCTIONAL BLOCK DIAGRAM

10dB

OFFSET

COMPENSATION

INTERCEPT

POSITIONING

10dB

10dB

10dB

DET

DET

DET

DET

DET

RFIN

⋅ 1.35

HI-Z

LOW NOISE

RAIL-TO-RAIL BUFFER

VSET

23mV/dB

250mV TO

1.4V = 50dB

FLTR

VAPC

LOW NOISE

BAND GAP

REFERENCE

LOW NOISE

GAIN BIAS

COMM

VPOS

V

I

Figure 1.