Differential Amplifier Gain Control Without Operating Point Shift
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Solution Overview
Problem
Conventional amplifiers face limitations in increasing gain variability while maintaining linearity, as changing degeneration resistance affects the DC operating point and requires larger transistors, leading to issues with chip size and parasitic capacitance.
Innovation Solution
A circuit configuration that includes a linearity improving transistor circuit and an operating point adjusting transistor circuit, allowing for variable degeneration by switching transistors and maintaining a constant operating point through complementary on/off control, enabling adjustable degeneration without altering the operating point.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a resistance value of a degeneration resistance is changed to adjust the amount of degeneration, then linearity can be improved, but the DC operating point changes and the variable range of gain cannot be sufficiently increased
Solution Approach 1:
The degeneration resistance function is segmented into two independent transistor circuits: a linearity improving transistor circuit (first transistor) and an operating point adjusting transistor circuit (second transistor). This segmentation allows independent control of linearity and operating point, resolving the contradiction between improving linearity and maintaining gain variability.
Solution Approach 2:
The second transistor circuit serves multiple functions: it adjusts the operating point and simultaneously enables the first transistor circuit to provide linearity improvement without operating point shifts. This multi-functionality allows the system to achieve both linearity improvement and gain variability.
2Reliability
If a resistance value of a degeneration resistance is changed, then linearity can be improved, but it is not possible to cause the amount of degeneration to be 0
Solution Approach 1:
The invention uses dynamic switching control where the control circuit can turn the first transistor circuit on or off based on operational requirements. When turned off, the amount of degeneration becomes 0, enabling full gain variability while maintaining the capability for linearity improvement when needed.
3Adaptability or versatility
If an on-resistance of the transistor is used as the degeneration resistance to increase the variable range of gain, then a transistor with a large transistor size is required, but this increases chip size and parasitic capacitance
Solution Approach 1:
The invention changes the control parameter from transistor size to switching state. Instead of using large transistors to achieve variable gain range, the system uses switching control of the transistor circuits, allowing full gain variability without requiring large transistor sizes, thus reducing chip size and parasitic capacitance.
Data Source
AI summary
An amplifier of an embodiment includes: a plurality of input transistors of a plurality of differential pairs; a plurality of first resistance circuits mutually connecting respective sources of the input transistors corresponding to the differential pairs and mutually connecting the respective sources and reference potential points; a plurality of second resistance circuits being connected between the respective sources of the plurality of input transistors and the reference potential points, respectively; and a control circuit configured to generate a control signal controlling whether or not to electrically connect the plurality of first resistance circuits and the plurality of second resistance circuits to the respective sources of the input transistors.