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Using the MCP4728 12bit DAC for LDMOS amplifier bias control applications

Posted: 23 Jun 2010 ?? ?Print Version ?Bookmark and Share

Keywords:12bit DAC? LDMOS amplifier? power amplifier module?

The LDMOS transistors are CMOS devices, designed for high frequency and high power operation. These devices are widely used for RF power amplifier applications such as GSM and CDMA cellular base stations, radar, CATV and portable radio devices. A limiting factor of these devices is the significant drifts of quiescent current (IDQ) at a fixed gate bias voltage (VGS) over temperature, due to the charge build-up in the Drain-Gate region, that is caused by hot carrier injection effects.

The IDQ changes proportionally with both the gate bias voltage and temperature. To maintain the maximum output power with high linearity, the IDQ needs to be constant over time across all operating temperature ranges. To achieve this goal, the gate bias voltage needs to be adjusted during operation to compensate the temperature changes.

The DAC is favourably used in the bias control circuit for the base station power amplifier module (PAM). In practical applications, the bias control circuit maintains the IDQ within a 4 percent range. This application note shows an example of how the DAC converter is used for this purpose.

View the PDF document for more information.

Click here to view related datasheets.

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