Operational Amplifier Flicker Noise Modulation Outside the Signal Path
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Solution Overview
Problem
Existing operational amplifiers in analog-to-digital converter (ADC) chips face challenges in reducing flicker noise, which affects the signal-to-noise ratio (SNR), as enlarging transistor area increases stray capacitance and power load, and PMOS transistors generate less noise than NMOS transistors.
Innovation Solution
Incorporating a modulating device that modulates flicker noise from current sources into a higher frequency band, separate from the signal path, to reduce low-frequency noise without affecting the desired signal, using a configuration that includes transistors and switches controlled by specific clock signals to shift flicker noise to odd harmonics of the control clocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the area of transistor is enlarged to reduce flicker noise, then the flicker noise is reduced, but the stray capacitance and chip power load increase
Solution Approach 1:
The patent extracts the flicker noise from the signal path by using a separate noise path with dedicated current sources (first and second current sources) that generate flicker noise independently. This noise path is separated from the main signal processing path, allowing noise reduction without affecting the signal quality or increasing power consumption in the signal path.
Solution Approach 2:
The patent introduces switching devices (third and fourth switching devices) as intermediaries to control the injection of flicker noise into the signal path. These switches modulate the noise at specific frequencies (odd harmonics of the control clock frequency), allowing the noise to be injected in a controlled manner that does not interfere with the desired signal bandwidth.
2Object-affected harmful factors
If the area of transistor is enlarged to reduce flicker noise, then the flicker noise is reduced, but the stray capacitance increases
Solution Approach 1:
The patent extracts the flicker noise generation function from the main signal transistors and places it in separate current sources within a dedicated noise path. This separation allows the use of smaller transistors in the signal path, reducing stray capacitance, while the noise reduction function is handled by the separate current sources.
Solution Approach 2:
The operational amplifier is segmented into distinct functional paths: a signal processing path and a noise injection path. The noise path contains dedicated current sources and switching devices that are separate from the signal transistors, allowing independent optimization of each path without compromising the other.
3Object-affected harmful factors
If PMOS transistors are used instead of NMOS transistors to reduce noise, then the noise is reduced, but the device performance is affected
Solution Approach 1:
The patent applies different transistor types in different locations within the circuit. NMOS transistors are used in the signal processing path where high performance is required, while PMOS transistors are used in the noise path current sources where noise reduction is the primary concern. This local differentiation allows each part of the circuit to be optimized for its specific function.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively reduces low-frequency noise, improving the noise figure of operational amplifiers and maintaining the integrity of the desired signal, as demonstrated by simulation results showing significant noise reduction at low frequencies when the modulating device is implemented.
Implementation Method 1
a modulating device to modulate the flicker noise from a current source into a higher frequency
Data Source
AI summary
An operational amplifier is disclosed. The operational amplifier comprises an input stage and a loading stage. The input stage receives a differential input signal pair corresponding to a first frequency band. The loading stage is coupled to the input stage. The loading stage outputs an amplified differential output at output nodes. The loading stage comprises a flicker noise source and a modulating device. The modulating device is coupled to the flicker noise source. The modulating device modulates flicker noises into a second frequency band. The modulating device is not within a signal path.