Differential Amplifier Source Degeneration for High-Power Linearity
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Solution Overview
Problem
Conventional differential amplifying circuits face challenges in maintaining linearity at high operating frequencies and output powers due to second harmonic feedback effects, which are exacerbated by the sensitivity of shared source degeneration resistor structures to operating conditions and variations.
Innovation Solution
A differential amplifying circuit with separate source degeneration resistors for main and auxiliary transistors, where the second-order derivatives of transconductances are properly offset and cancelled out, and additional common degeneration resistors are used to enhance linearity, particularly at high output power regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a shared source degeneration resistor structure is used, then device complexity is reduced, but linearity deteriorates at high operating frequencies and output powers due to second harmonic feedback effects
Solution Approach 1:
The patent divides the previously shared source degeneration resistor into separate resistors for each transistor (main and auxiliary transistors). This segmentation allows independent optimization of each resistor to cancel second harmonic feedback specific to each transistor, thereby improving linearity at high operating frequencies and output powers while accepting increased device complexity.
2Reliability
If separate source degeneration resistors are used for main and auxiliary transistors, then linearity is improved by suppressing second harmonic feedback, but device complexity increases
Solution Approach 1:
The patent applies different resistance values to different source degeneration resistors based on the specific requirements of each transistor. The main transistor has one source degeneration resistor value while the auxiliary transistor has a different source degeneration resistor value, allowing each to be locally optimized for second harmonic feedback cancellation, thereby improving overall linearity.
3Power
If operating frequency and output power are increased, then amplifier performance is improved, but second harmonic feedback effects are exacerbated causing linearity to deteriorate
Solution Approach 1:
The patent applies source degeneration resistors that are specifically designed to preemptively counteract the second harmonic feedback effects that occur at high operating frequencies and output powers. By carefully selecting the resistance values before operation, the circuit is pre-configured to cancel the harmful feedback effects that would otherwise deteriorate linearity under high-power conditions.
Data Source
AI summary
There is provided a highly linear differential amplifying circuit. The highly linear differential amplifying circuit includes: a differential amplifying unit including a main differential amplifying unit having a differential pair of transistors for amplifying a difference of two input signals and an auxiliary amplifying unit connected in parallel with the main differential amplifying unit, wherein second-order derivatives of transconductances of the main differential amplifying unit and the auxiliary differential amplifying unit are properly set to have an offset; and a source degeneration resistor unit including a first source degeneration resistor to a fourth source degeneration resistor. Accordingly, the linearity of the differential amplifying circuit is improved at a wide output power region.