AD7293 datasheet(76/79 Pages) AD

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AD7293

Data Sheet

Rev. D | Page 76 of 79

APPLICATIONS INFORMATION

The AD7293 contains all the functions required for general-

purpose monitoring and control of current, voltage, and

temperature. With its 60 V maximum common-mode range,

the device is useful in applications where current sensing in the

presence of a high common-mode voltage is required. Closed-

loop mode is designed for monitoring and controlling, for

example, the power amplifier in a cellular base station.

BASE STATION POWER AMPLIFIER CONTROL

The AD7293 is used in a signal chain to achieve the optimal

bias conditioning for enhancement mode or depletion mode

power amplifiers. The main factors influencing the bias

conditions are temperature, supply voltage, gate voltage drift,

and general processing parameters. The overall performance of

a power amplifier configuration is determined by the inherent

trade-offs required in efficiency, gain, and linearity. The high

level of integration as well as the intelligent features offered by

the AD7293 allows the use of a single chip to dynamically

control the drain bias current to maintain a constant value over

temperature and time, thus significantly improving the overall

performance of the power amplifier. The AD7293 incorporates

the functionality of eight discrete components, providing

considerable board area savings over discrete solutions.

The circuit shown in Figure 59 is the typical power amplifier

control application diagram for the AD7293. The device

monitors and controls the overall performance of four final

stage amplifiers. The gain control and phase adjustment of the

driver stage are incorporated in the application and are carried

out by the four available uncommitted outputs of the AD7293.

The high-side current sensor measures the amount of current

on the respective final stage amplifiers while the closed-loop

system maintains the programmed current across the sense

resistor. Furthermore, the PA_ON provides optional control for

a cutoff switch on the supply. The ALERTx pins can be configured

to trigger when current readings are more than a specified limit

and the RF input signal can be switched off by the ALERTx pin.

The alert feature can also be routed internally to clamp the DAC

outputs and turn off the power.

By measuring the transmitted (Tx) power and the received (Rx)

power, the device can dynamically change the drivers and PA

signal to optimize performance.

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