Two-Stage Amplifier Biasing for Extended Linear Gain Range
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Solution Overview
Problem
Amplifiers in integrated circuits face challenges in maintaining linear operating range, especially in portable communications devices with lower voltage power supplies, leading to gain compression and distortion.
Innovation Solution
A two-stage amplifier design incorporating a gain expansion amplifier and a main amplifier with Class-B and Class-AB operation modes, coupled in parallel, to extend the linear operating range and reduce gain compression, using bias stabilization circuits to maintain predictable gain characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If lower voltage power supplies are used in portable communications devices, then power consumption is reduced, but the linear operating range of amplifiers decreases leading to gain compression
Solution Approach 1:
The amplifier is divided into two separate stages: a gain expansion stage with transistors MP1, MN1, MP2, MN2 and a main amplifier stage with transistors MP3, MN3. The gain expansion stage specifically addresses low input signal levels to extend the linear operating range, while the main amplifier handles higher signal levels. This segmentation allows each stage to be optimized for its specific function, resolving the contradiction between power consumption and linear operating range.
2Power
If the amplifier input signal falls outside the linear operating range, then the amplifier can handle higher power levels, but gain deviation and distortion increase
Solution Approach 1:
The gain expansion stage performs preliminary amplification on low-level input signals before they reach the main amplifier. By pre-expanding the gain in this initial stage, the main amplifier receives signals within its optimal linear operating range, preventing gain compression and distortion. This preliminary action ensures that the amplifier can handle higher overall power levels while maintaining gain linearity across the extended input range.
Data Source
AI summary
Techniques are disclosed for extending an amplifier's linear operating range by concatenating an amplifier exhibiting gain compression with a gain expansion stage. In an exemplary embodiment, a gain expansion stage incorporates a Class-B stage, a Class-AB stage, or a combination of the two. In an exemplary embodiment, both the gain compression stage and gain expansion stage are provided with a replica current biasing scheme to ensure stable biasing current over variations in temperature, process, and/or supply voltage. Further disclosed is an output voltage biasing scheme to set the DC output voltage to ensure maximum linear operating range.