Clock-Switched Operational Amplifier Circuit for Flicker Noise
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Solution Overview
Problem
Flicker noise in operational amplifiers, particularly in semiconductor devices like MOS field-effect transistors, interferes with low-frequency signal applications such as audio analog-to-digital converters and direct down-conversion receivers, degrading the desired signal.
Innovation Solution
The operational amplifier employs multiple current source pairs with steering controlled by complementary logical signals, typically multi-phase clocks, to modulate flicker noise into out-of-band noise, reducing its impact on the signal integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current sources are used in the operational amplifier circuit, then the amplification function is achieved, but flicker noise is generated that degrades low-frequency signal quality
Solution Approach 1:
The patent applies periodic action by using a multi-phase clock signal to periodically switch the connection configuration of current sources. The clock signal has multiple phases (at least two) that sequentially connect different current sources to different circuit nodes, converting the continuously generated flicker noise into periodically modulated noise that can be filtered out, thereby improving signal quality while maintaining amplification function.
Solution Approach 2:
The patent implements dynamics by making the current source connections dynamic rather than static. The connection configuration changes over time based on the clock signal phases, allowing the system to adaptively manage noise distribution. This dynamic switching enables the operational amplifier to maintain its amplification function while reducing the impact of flicker noise on low-frequency signals.
2Reliability
If multiple current sources are added to reduce flicker noise impact, then signal quality improves, but hardware complexity increases
Solution Approach 1:
The patent applies universality by designing the current sources to serve multiple functions: they provide bias current for amplification and simultaneously act as noise modulation elements when switched by the clock signal. The same hardware components (current sources and switching elements) perform both signal processing and noise reduction functions, avoiding the need for separate dedicated noise reduction circuitry and thus limiting the increase in hardware complexity.
Solution Approach 2:
The patent merges the noise reduction function with the existing amplification circuitry by integrating the clock-controlled switching directly into the current source connections. Rather than adding separate noise filtering stages, the patent combines noise management with the bias current distribution function, thereby improving signal quality while minimizing additional hardware complexity.
Data Source
AI summary
A low flicker noise operational amplifier comprises two circuit branches of the same topology and a plurality of current source pairs. For each current source pair, the two current sources are commutatively steered into the two circuit branches via two sets of differential pair in a manner controlled by a pair of complementary logical signal.