50 dB GSM PA Controller
AD8315
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
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. 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.
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, its temperature
stability is excellent over a specified range of −30°C to +85°C.
FUNCTIONAL BLOCK DIAGRAM
VPOS
ENBL
LOW NOISE
GAIN BIAS
LOW NOISE
BAND GAP
REFERENCE
OUTPUT
ENABLE
DELAY
×1.35
VAPC
DET
RFIN
10dB
DET
DET
DET
DET
HI-Z
LOW NOISE (25nV/√Hz)
RAIL-TO-RAIL BUFFER
10dB
10dB
10dB
V-I
OFFSET
COMP’N
INTERCEPT
POSITIONING
FLTR
VSET
23mV/dB
250mV TO
1.4V = 50dB
COMM
Figure 1.
Rev. C
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responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
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©2006 Analog Devices, Inc. All rights reserved.
01520-001
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