50 dB GSM PA Controller

Data Sheet

AD8315

Rev. D

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FEATURES

Complete RF detector/controller function

>50 dB range at 0.9 GHz (−49 dBm to +2 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, 38 mW at 5 V

Power-down to 10.8 μW

APPLICATIONS

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

Transmitter power control

GENERAL DESCRIPTION

The AD8315 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, the temperature stability is

excellent over a specified range of −30°C to +85°C.

Its high sensitivity allows control at low signal levels, thus

reducing the amount of power that must 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. Therefore, the

source can be dc grounded.

The AD8315 provides a voltage output, VAPC, that has the

voltage range and current drive to directly connect to most

handset power amplifiers’ gain control pin. VAPC can swing

from 250 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 the VSET pin 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 mV/dB and

−60 dBm for a 50 Ω termination (−73 dBV) at 0.9 GHz.

Further simplifying the application of the AD8315, the input

resistance of the setpoint interface is over 100 MΩ, and the bias

current is typically 0.5 μA.

The AD8315 is available in MSOP and LFCSP packages and

consumes 8.5 mA from a 2.7 V to 5.5 V supply. When powered

down, the sleep current is 4 μA.

FUNCTIONAL BLOCK DIAGRAM

VPOS

ENBL

RFIN

COMM

DET

10dB

DET

10dB

DET

DET

DET

10dB

10dB

OFFSET

COMP’N

INTERCEPT

POSITIONING

LOW NOISE

GAIN BIAS

LOW NOISE

BAND GAP

REFERENCE

OUTPUT

ENABLE

DELAY

×1.35

VAPC

HI-Z

LOW NOISE (25nV/√Hz)

RAIL-TO-RAIL BUFFER

FLTR

VSET

V-I

23mV/dB

250mV TO

1.4V = 50dB

Figure 1.