AD8311_15 Datasheet, PDF (1/24 Pages) Analog Devices – 50 dB GSM PA Controller

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.
50 dB GSM PA Controller
AD8311
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
VPOS
LOW NOISE
GAIN BIAS
LOW NOISE
BAND GAP
REFERENCE
RFIN
DET
DET
DET
DET
DET
10dB
10dB
10dB
10dB
COMM
OFFSET
COMPENSATION
INTERCEPT
POSITIONING
Figure 1.
⋅ 1.35
VAPC
HI-Z
LOW NOISE
RAIL-TO-RAIL BUFFER
FLTR
VSET
VI
23mV/dB
250mV TO
1.4V = 50dB
Rev. A
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