Digital RF Power Amplifier With Linear Gain and Impedance Stability
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Solution Overview
Problem
Existing RF power amplifiers face instability in gain control due to the influence of semiconductor process variations and operating temperature on MOS transistor on-resistance, leading to non-linear gain adjustment and instability in output impedance.
Innovation Solution
A radio frequency (RF) power amplifier design featuring a plurality of unit differential amplifiers with common inputs and outputs connected to a common adder, configured as CMOS differential cascode amplifiers, and incorporating binary gain control and attenuators with differential buffers for linear and digital control of gain and attenuation, respectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If MOS transistor on-resistance is used for gain control, then the amplification coefficient can be adjusted, but the gain control becomes unstable due to process variations and temperature influence
Solution Approach 1:
The patent changes the control parameter from MOS transistor on-resistance (which is sensitive to process and temperature) to bipolar transistor current, which provides more stable gain control. The differential amplifier uses bipolar transistors whose current can be precisely controlled through current mirrors, making the amplification coefficient stable against process variations and temperature changes.
2Manufacturing precision
If complementary CMOS and bipolar transistors are combined, then gain control linearity is improved, but circuit arrangement complexity increases
Solution Approach 1:
The patent segments the amplifier into distinct functional blocks: a differential amplifier stage using bipolar transistors for stable gain control, and a complementary CMOS amplifier stage for output buffering. This segmentation allows each stage to be optimized independently, achieving linear gain control while managing circuit complexity through modular design.
3Ease of operation
If differential amplifier outputs are cascade-connected, then gain control is achieved, but output impedance stability deteriorates
Solution Approach 1:
The patent introduces a current mirror as an intermediary between the differential amplifier stage and the complementary CMOS amplifier stage. This current mirror acts as a mediator that transfers the controlled current while maintaining output impedance stability, allowing gain control to be achieved without directly cascade-connecting the differential amplifier outputs.
Data Source
AI summary
A technology related to a power amplifier used in a wireless communication circuit is disclosed. A radio frequency (RF) power amplifier includes a plurality of unit differential amplifiers of which inputs are connected to a common input terminal and outputs are connected to a common adder, and having a gain of a weight of a corresponding bit of a binary gain control word. Each of the differential amplifiers may be configured as a complementary metal-oxide semiconductor (CMOS) differential cascode amplifier. In addition, the RF power amplifier may include a structure in which a plurality of attenuators of the same structure are cascade-connected so that an attenuation rate may be linearly and digitally controlled and an output of each attenuator is connected to an output adder through differential buffers of which turn-on and turn-off are controlled by a controller.