AMC7891 datasheet(33/43 Pages) TI2

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AMC7891

µController

SCLK

SDI

SDO

DAV

SPI

MUX

ADC

TEMP

SENSOR

DAC

GPIO

RF Out

Bidirectional Coupler

VGA

Pre-amplifier

Doherty Amplifier

Carrier PA

Peak PA

VDD

RF In

Digital I/O

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.

Figure 36. PA Monitor and Control System

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