Tunable MOSFET Pseudo Resistor for Stable Audio Band-Pass Filtering
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Solution Overview
Problem
Conventional pseudo resistors with high impedance require larger space and have limited application scope due to restrictions on signal amplitudes at their terminals, which restricts the bandwidth and stability of audio band-pass filters in medical electronics.
Innovation Solution
A pseudo resistor design featuring a pair of transistors, each with a control terminal receiving a control voltage to operate in the weak inversion region, allowing for tunable resistance and reduced signal variation effects, enabling a more extensive application scope without voltage magnitude restrictions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a resistor with high resistance is disposed outside a chip to achieve audio band-pass filter bandwidth requirements, then the filtering performance is improved, but the device occupies larger space
Solution Approach 1:
The patent merges the high resistance function with a MOSFET transistor, integrating what was previously an external discrete component into the chip itself. The MOSFET's channel resistance in the linear region provides the high resistance value needed for audio band-pass filtering, eliminating the need for external resistors and reducing overall device space.
Solution Approach 2:
The patent utilizes parameter changes by operating the MOSFET in different regions (linear region for resistance, saturation region for amplification) and adjusting gate voltage to achieve high resistance values. By controlling the gate-source voltage and drain-source voltage, the MOSFET can provide the required high resistance for filtering while maintaining compact integration.
2Area of stationary object
If MOSFETs are used to realize a pseudo resistor with high resistance for full chip integration, then the device space is reduced, but the application scope is limited due to restrictions on signal amplitudes
Solution Approach 1:
The patent employs dynamic operation by allowing the MOSFET to switch between different operating regions (linear region for resistance mode, saturation region for amplification mode) based on control signals. This dynamic capability enables the same device to function as a pseudo-resistor with high resistance while accommodating a broader range of signal amplitudes, thereby expanding application scope beyond static resistance implementations.
Solution Approach 2:
The patent achieves universality by designing the MOSFET-based pseudo-resistor to operate effectively with various signal amplitude ranges. The device can function as a high-resistance element for filtering applications while also maintaining stability across different voltage conditions, making it applicable in diverse medical electronic devices and signal processing circuits.
3Reliability
If the pseudo resistor operates in the weak inversion region with fixed control voltage, then high resistance is achieved, but signal amplitudes must be restricted to prevent excessive resistance variation
Solution Approach 1:
The patent implements dynamic control by allowing the gate voltage to vary within a controlled range rather than being fixed. This enables the MOSFET to maintain high resistance stability while accommodating a wider range of signal amplitudes. The dynamic adjustment of control voltage allows the device to adapt to different signal conditions without exceeding the weak inversion region's resistance stability requirements.
Solution Approach 2:
The patent utilizes parameter changes by adjusting the gate-source voltage and drain-source voltage ratios to maintain optimal operation in the weak inversion region. By dynamically changing these voltage parameters, the device achieves both high resistance stability and expanded signal amplitude tolerance, resolving the contradiction between stability and adaptability.
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 design achieves high resistance stability and tunability, expanding the application scope of pseudo resistors by minimizing the impact of signal variations at the terminals on resistance, thus enhancing the performance of audio band-pass filters in medical electronics.
Implementation Method 1
The first transistor is controlled by the control voltage, such that the first transistor operates in a weak inversion region
Implementation Method 2
The second transistor also operates in the weak inversion region due to an extremely small conductive current
Data Source
AI summary
A pseudo resistor with tunable resistance including a first transistor and a second transistor is provided. The first transistor has a first terminal, a second terminal and a control terminal. The first terminal of the first transistor serves as a first terminal of the pseudo resistor. The control terminal of the first transistor receives a control voltage. The first transistor is controlled by the control voltage, such that the first transistor operates in a weak inversion region. The second transistor has a first terminal, a second terminal and a control terminal. The first terminal of the second transistor is coupled to the second terminal of the first transistor. The second terminal of the second transistor and the control terminal of the second transistor are coupled to each other to serve as a second terminal of the pseudo resistor with tunable resistance. The second transistor operates in the weak inversion region.