Sub-Threshold Noise Filter Circuit for Faster Audio Settling
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Solution Overview
Problem
Existing noise filter circuits face challenges with high power consumption, limited headroom in supply voltage, and slow settling time due to large transistor off-resistance, which affects audio applications and low-voltage operations.
Innovation Solution
A noise filter circuit with a transistor off-resistance control circuit that sets a controllable gate voltage for transistors to operate in the sub-threshold region, using a charge storage component and a body-biasing circuit to manage off-resistance, allowing for reduced noise interference and faster settling times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If large current dissipation is used to reduce thermal and flicker noise, then noise performance is improved, but power consumption increases
Solution Approach 1:
The patent changes the operating parameters of the transistor by applying a body bias voltage to shift the transistor into sub-threshold operation. This allows the transistor to achieve high off-resistance (reducing noise) while operating at very low currents, thereby resolving the contradiction between noise performance and power consumption.
Solution Approach 2:
The patent dynamically controls the transistor operation by adjusting the body bias voltage to maintain optimal sub-threshold operation. This dynamic control allows the system to achieve low noise performance without requiring large static current dissipation, thus reducing power consumption while maintaining noise filtering effectiveness.
2Object-affected harmful factors
If large source-degeneration is used to reduce noise, then noise performance is improved, but headroom of supply voltage shrinks
Solution Approach 1:
The patent changes the transistor's operating state by applying body bias to achieve sub-threshold operation. This parameter change enables the transistor to function as a high-value resistor without requiring large source-degeneration resistors, thereby preserving supply voltage headroom while achieving noise reduction.
3Measurement precision
If large resistance/capacitance is used in low-pass filter for low corner frequency, then audio bandwidth filtering is improved, but settling time increases
Solution Approach 1:
The patent changes the resistance parameter by using a transistor in sub-threshold operation, which provides a high effective resistance without requiring physically large resistance values. This allows the low-pass filter to achieve low corner frequency for audio bandwidth filtering while maintaining faster settling times.
Solution Approach 2:
The transistor acts as an intermediary element that provides high resistance in a compact form. By using the transistor's sub-threshold operation characteristics, the circuit achieves the filtering performance of large RC values without the associated slow settling time, effectively mediating between filtering requirements and speed requirements.
4Object-affected harmful factors
If transistor off-resistance is increased to reduce noise, then noise filtering is improved, but power efficiency decreases
Solution Approach 1:
The patent changes the transistor's operating region to sub-threshold by applying body bias voltage. In this region, the transistor achieves high off-resistance for noise filtering while consuming minimal current, thereby improving power efficiency without sacrificing noise filtering performance.
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
The solution effectively reduces transistor off-resistance, improving power efficiency, settling time, and voltage matching, making it suitable for low-voltage audio applications while minimizing interference with audio signals.
Implementation Method 1
A noise filter circuit with controllable transistor off-resistance and associated noise filtering method. The transistor off-resistance control circuit is coupled to the first transistor, and arranged to set the first control voltage for controlling the off-resistance of the first transistor
Data Source
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AI summary
A noise filter circuit includes a filter and a transistor off-resistance control circuit. The filter includes a first transistor and a charge storage component. The first transistor has off-resistance when turned off or operated under sub-threshold region. A control terminal of the first transistor is not directly tied to a reference voltage, and is used to receive a first control voltage. The charge storage component has one terminal coupled to a connection terminal of the first transistor. The transistor off-resistance control circuit is coupled to the first transistor, and arranged to set the first control voltage for controlling the off-resistance of the first transistor.