AMC7891_15 Datasheet, PDF (33/41 Pages) Texas Instruments – Analog Monitor and Control Circuit with 10-Bit, Multi-Channel ADC and Four DACs, Temperature Sensor, and 12 GPIOs

AMC7891
www.ti.com
SBAS518A – AUGUST 2011 – REVISED DECEMBER 2011
APPLICATION INFORMATION
BASE STATION AMPLIFIER MONITOR AND CONTROL
The AMC7891 is a highly integrated, low-power, complete analog monitoring and control system in a small
package; all of these features make the AMC7891’s an ideal low-cost, bias control circuit for modern RF
transistor modules such as the power amplifiers (PA) and low-noise amplifiers (LNA) found in RF communication
systems.
The AMC7891 is used in RF amplifier signal chains to set the transistor’s optimal bias condition as well as to
monitor for any possible malfunction. The AMC7891 four independent DAC outputs allow control of the
transistor’s gate bias voltages as well as of any variable-gain amplifiers (VGAs) in the signal chain. The
AMC7891 twelve configurable GPIOs enable digital signal control and monitoring. Additionally, the device has 8
uncommitted analog inputs driving a highly precise ADC and an accurate on-chip temperature sensor that allow
continuous monitoring of the main factors determining optimal amplifier operation such as temperature, supply
voltages as well as drain bias currents through external current shunt monitors. The use of external current shunt
monitors gives the system designer the flexibility to choose the optimal number of current measurements for the
amplifier topology as well as the accuracy, voltage range and gain setting according to the drain current level to
be measured. The Texas Instruments’ INA282 family, which includes the INA282, INA283, INA284, INA285 and
INA286 devices, are highly-accurate, wide common-mode range current shunt monitors with gains going from
50V/V to 1000V/V.
The circuit in Figure 36 shows a typical multi-stage Doherty PA monitoring and control system using the
AMC7891. The AMC7891 DAC outputs are used to set the bias gate voltage of each LDMOS transistor in the PA
as well as to set the gain of the VGA driving the PA. The AMC7891 ADC inputs are used to monitor the most
important parameters in the PA operation: supply voltages, drain bias currents as well as the TX and RX signal
power. The GPIOs give additional system flexibility. In the system example below three GPIOs are used to
address an external 8:1 multiplexer used for giving additional inputs to the AMC7891 ADC.
CS
SCLK
SDI
SPI
µController
SDO
DAV
ADC
TEMP
SENSOR
AMC7891
DAC
DAC
DAC
DAC
MUX
GPIO
Digital I/O
RF In
VDD
VGA
Pre-amplifier
Doherty Amplifier
Carrier PA
Peak PA
Bidirectional Coupler
RF Out
Figure 36. PA Monitor and Control System
Copyright © 2011, Texas Instruments Incorporated
Product Folder Link(s): AMC7891
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