Dynamic Differential Amplifier Tail Current Feedback for Low Common-Mode Gain
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Solution Overview
Problem
Differential amplifiers face challenges in achieving low common mode gain, which affects the performance of data converters like ADCs, particularly in balancing the low common mode rejection ratio (CMRR) of delay domain ADCs and generating noise and consuming excessive power.
Innovation Solution
The implementation of tail current control circuits in dynamic differential amplifiers, utilizing transistors and switched capacitor common-mode feedback circuits, to regulate the tail current and reduce common mode gain across a wide range of frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional differential amplifiers are used, then the amplifier can provide basic amplification function, but the common mode gain is too high which degrades CMRR performance
Solution Approach 1:
The patent implements a feedback mechanism where the common mode voltage at the input is detected and fed back through transistors M4-M6 to control the tail current. This feedback loop dynamically adjusts the tail current to counteract common mode signals, thereby reducing common mode gain and improving CMRR performance.
Solution Approach 2:
The patent changes the tail current parameter dynamically based on the common mode voltage level. By adjusting the tail current in response to common mode variations, the amplifier maintains low common mode gain across different operating conditions, improving overall CMRR performance.
2Power
If tail current is increased to improve signal amplification, then the amplification capability is enhanced, but power consumption increases excessively
Solution Approach 1:
The patent makes the tail current dynamic rather than fixed. The tail current automatically adjusts its magnitude based on the common mode voltage level, allowing the amplifier to provide sufficient amplification capability while consuming minimal power during normal operation. This dynamic adjustment resolves the trade-off between amplification strength and power consumption.
Solution Approach 2:
The patent changes the tail current parameter in response to operating conditions. By modulating the tail current based on common mode voltage, the amplifier achieves optimal amplification capability only when needed, significantly reducing average power consumption while maintaining required signal amplification performance.
3Device complexity
If conventional amplifier design is used, then the circuit structure is simple, but noise is generated excessively which degrades signal quality
Solution Approach 1:
The feedback mechanism monitors common mode voltage and adjusts tail current to minimize noise generation. By actively controlling the tail current based on common mode conditions, the circuit suppresses noise that would otherwise be generated, improving signal quality without requiring complex additional noise filtering circuits.
4Ease of manufacture
If fixed tail current is used, then the circuit is easy to design, but common mode gain cannot be reduced across wide frequency range
Solution Approach 1:
The patent transitions from a fixed tail current design to a dynamic tail current control scheme. The tail current automatically adapts to different frequency components of the common mode signal through the transistor network, enabling effective common mode rejection across a wide frequency range while adding minimal design complexity.
Solution Approach 2:
The circuit uses its own common mode voltage signal to control the tail current through the transistor feedback network. This self-service mechanism allows the amplifier to automatically adjust its operating parameters to maintain low common mode gain across frequencies without requiring external control circuits, preserving design simplicity.
Data Source
AI summary
An amplifier circuit includes a first transistor having a terminal and a second transistor having a terminal coupled to the terminal of the first transistor. A third transistor has a first terminal coupled to the terminals of the first and second transistors and has a control terminal. A fourth transistor has a control terminal coupled to the terminals of the first and second transistors and to the first terminal of the third transistor. The fourth transistor has a second terminal. A fifth transistor has a control terminal coupled to the second terminal of the fourth transistor and has second and third terminals. A sixth transistor has a control terminal coupled to the control terminal of the third transistor and to the third terminal of the fifth transistor. The sixth transistor has a second terminal coupled to the second terminal of the fifth transistor.