系统板 5896

MAXREFDES39#:通过MAX11300 PIXI实现功率放大器偏置



MAXREFDES39#系统板 MAXREFDES39#系统板 放大+

概述

MAXREFDES39#功率放大器(PA)偏置参考设计使用MAX11300,可用来偏置和监测射频基站系统应用中的功率放大器。本例中使用的是Infineon的 PTMA210152M-20W,但可使用任意其它功率放大器。MAX11300为射频功率放大器偏置基础设施提供高度集成的方案。设计全部使用MAX11300的模拟外设,只需要一片MAX11300即可偏置和监测2级射频功率放大器。参考设计的特性如下:

  • 频分双工(FDD)和时分双工(TDD)射频(RF)功率放大器监测、偏压配置和控制。
  • 监测功能
    • 高精度测量电压和电流
    • 通过Maxim的电流检测放大器(MAX44285)测量电流
    • 一级和二级放大器的漏极电压和电流
    • 两个外部和一个内部温度监测器
    • 一级和二级放大器的栅极偏置
  • 控制功能
    • RF PA快速开/关
    • 同步TDD功能
    • 高效率、可调节漏极电压电源
    • LED信号和报警
    • 自动控制功能

  • 图1. MAXREFDES39#系统方框图

    连接微控制器的USB接口以及连接MAX11300的串口都通过MAX14850与主电路隔离。微控制器部分通过USB供电,而其它电路部分则由独立的36V直流电源供电。图1也包括RF PA的电源控制和监测。

Introduction

The MAXREFDES39# power amplifier (PA) bias reference design uses the MAX11300, also called a programmable mixed-signal I/O (PIXI), to bias and monitor a power amplifier for an RF base station application. In this case, an Infineon PTMA210152M-20W is used but any Power Amplifier can be used. The MAX11300 provides a highly integrated solution for the RF power amplifier biasing infrastructure. The design utilizes all of the MAX11300’s analog peripherals, while only requiring one MAX11300 device to both bias and monitor a 2-stage RF power amp. All the features of this reference design are listed below.

  • Monitor, biasing, and control for frequency division duplex (FDD) and time division duplex (TDD) radio frequency (RF) power amplifiers.
  • Monitoring function
    • Accurate voltage and current measurement
    • Current measurement through Maxim current-sense amplifier (MAX44285)
    • Drain voltage and current of first- and second-stage amplifiers
    • Two external and one internal temperature monitors
    • Gate biasing of first-stage and second-stage amplifiers
  • Control function
    • Fast RF PA on/off
    • Synchronized TDD function
    • Efficient, adjustable drain voltage supply
    • LED signaling and alarm
    • Automatic control function


Figure 1. The MAXREFDES39# system block diagram.

The USB interface to the microcontroller and serial interface to the MAX11300 are digitally isolated from the main circuit through the MAX14850. The microcontroller section is powered through USB power, whereas the rest of the circuit is powered by a separate 36V DC supply. Figure 1 also shows power control and monitoring for RF PA.

Design Details

The design uses the highly configurable input/output capability of the MAX11300 to bias an Infineon PTAM210152M; 15W, two-stage, LDMOS power amp. The MAX11300 internal design as used in this PA bias reference design is shown in Figure 2. It consists of six single-ended ADCs, four DACs, two switches, and two GPOs.

Internal schematic of MAX11300 for PA biasing.
Figure 2. Internal schematic of MAX11300 for PA biasing.

In Figure 2, three of the ADCs are configured for 0 to 2.5V input range for current-sense measurement and the other three are configured for 0 to 10V input range for supply voltage detection. Two of the DACs are configured to regulate MAX17503 DC-DC converter for optimal power output for the PA. The other two DACs are used to bias stage 1 and stage 2 of the PA. GPI-controlled analog switches can be used for fast switching of DAC outputs for TDD application. If fast switching is not required, these can be left connected internally or through an isolated GPIO of microcontroller (see schematic for more details).

Input power is supplied through a 36V, 150W DC power supply. MAX17503 DC-DC converters are used to regulate 15V to 28V for PA. Their main characteristics are 4.5 to 60V input range and up to 2.5A output. As mentioned above, DAC outputs regulate the FB input of these converters, as shown in Figure 3.

DC-DC converter circuit.
Figure 3. DC-DC converter circuit.

MAX44285 current-sense amplifiers (CSAs) are used to measure bias current of stage 1 and stage 2 of the PA. The CSA output range is designed to vary from 0 to 2.5V for 0 to 1A current with a 0.05Ω sensor resistor, and a gain of 50. Therefore, the ADC range of 0 to 2.5V is selected for all ADCs used to monitor current.

To measure PA’s temperature, an external diode is attached to the PA using thermal paste and connected to the MAX11300 EXT Temp 1 pins. Another diode is attached to the PA board and connected to the MAX11300 EXT Temp 2 pins, as shown in Figure 4.

External temperature sensor connection scheme.
Figure 4. External temperature sensor connection scheme.

Quick Start

Required equipment:

Steps to test the MAXREFDES39# hardware:

  • Download and install the MAXREFDES39# software. 
  • Connect 36V power supply to the DC jack J9
  • Connect the MAXREFDES39# board through mini USB cable to PC
  • Once the automatic driver software installation is complete, run the software by opening its icon in the Start Menu
  • Through the Configuration Tab, load the MAX11300 configuration file (MAXREFDES39#_config_file.csv) that comes with the software
  • Upon visual validation, write the file to the MAX11300 device
  • Through the Control / Monitor tab, read the ADCs. The results should be close to the results shown in Figure 5.

    Screenshot of expected ADC values during initial startup of the PA bias reference design.
    Figure 5. Screenshot of expected ADC values during initial startup of the PA bias reference design.

  • Change DAC voltages of PORT0 and PORT10 from 1V–9V and measure the change in voltage from 28V to 12V at V1 and V2, respectively as shown in Figure 6.

    Screenshot of DAC values in the PA bias GUI.
    Figure 6. Screenshot of DAC values in the PA bias GUI.

  • If the above tests pass, then connect the Power Amplifier EV kit as shown in Figure 7.


    Figure 7. Connections of the MAXREFDES39# board with the PTMA210152M EV kit.

  • The gain of the Stage 1 and Stage 2 of the power amplifier can be adjusted through changing the DAC voltages from 2V to 3V at PORT6 and PORT14 respectively, as PTMA210152M requires this voltage range for biasing.
  • The gain and offset errors can be calibrated for all DAC and ADC configured ports from the Calibration tab.

Software flow:

The software provides all required features including

  • Configuration of the MAX11300 device by reading the register map file generated by the MAX11300 configuration software
  • Control/monitoring feature of all analog peripherals including DAC, ADC, etc.
  • Calibration of DACs and ADCs

The Configuration tab provides the option to load the MAX11300 configuration file generated by the MAX11300 configuration software. Once the file is loaded, users can view whole configuration for the device, as shown below in Figure 8. If the configuration matches Figure 8, it can be written to the MAX11300 device. This configuration can also be used with other 2-stage power amplifiers instead of PTMA210152M.


Figure 8. Screenshot of the MAXREFDES39# software - Configuration Tab.

The Control / Monitor tab provides features to set the voltages of all DAC configured ports and read the data of all ADC configured ports. Instantaneous output of ADC ports as well as averaged output can be read. The software also calculates the standard deviation of the averaged data as shown in Figure 5 and in Figure 9.


Figure 9. Screenshot of MAXREFDES39# software – Control / Monitor tab.

The Calibration tab (Figure 10) is used to calibrate the ADC and DAC gain and offset errors. The values of gain and offset error compensation are set on this tab and the effect can be seen on the ADC and DAC configured ports when data is read or written to the MAX11300 device through the Control / Monitor tab. As an example, if gain is set to 0.5 for a DAC configured on port 0 and output is set to 10V, then actual output will be 5V.


Figure 10. Screenshot of MAXREFDES39# software – Calibration tab.

Lab Measurements

The power amplifier is biased by using the MAXREDES39# board with a 2.1GHz RF input connected to the PTMA210152M EV kit. The output of the EV kit is connected to a spectrum analyzer through an RF attenuator. The power amplifier is biased through the DAC configured ports, port 6 and port 14. The spectrum analyzer result is shown in Figure 11.

Spectrum of power amp output when biased with the MAX11300.
Figure 11. Spectrum of power amp output when biased with the MAX11300.

The output in Figure 11 does not show any spikes added by the MAX11300 within 100kHz span, whereas the DAC update rate is 25kHz.

 
Status:
Package:
Temperature:

MAX11300
PIXI、20端口可编程混合信号I/O,带有12位ADC、12位DAC、模拟开关和GPIO

  • 多达20路12位ADC输入,单端或差分
  • ADC输入绝对电压范围
  • 可编程采样平均,每个ADC端口均可

MAX44285
双通道,高精度,高压,电流检测放大器

  • 2.7V至76V通用输入模式
  • 低12µV (max)输入补偿电压
  • 低0.1% (max)增益误差

MAX17503
4.5V-60V、2.5A、高效、同步降压型DC-DC转换器,带内部补偿

  • 无需外部元件,降低总体成本
  • 缩减DC-DC调节器物料单
  • 降低功耗

MAX14850
六通道数字隔离器

  • 高压保护
  • 完整的数字隔离方案
  • 兼容多种接口标准

MAXQ622
具有红外模块和USB (可选)功能的16位微控制器

  • 高性能、低功耗16位RISC核
  • 在整个工作电压范围内支持直流至12MHz工作频率
  • 1.70V至3.6V工作电压范围