Resistor-Based Attenuator Under-Driven Transistors
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Solution Overview
Problem
Conventional attenuators employ large transistors to minimize on-state impedance, leading to substantial size and reduced bandwidth due to high capacitance, which limits their operational efficiency, especially at high frequencies.
Innovation Solution
The attenuator system uses smaller transistors operating in under-driven modes, such as triode mode for FETs, to provide a significant portion of the total impedance, reducing size and increasing bandwidth by maintaining constant channel impedance and preventing over-driven operation through common-mode voltage extraction and biasing circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If large transistors are used to minimize on-state impedance, then the impedance accuracy is improved, but the device size increases and bandwidth is reduced
Solution Approach 1:
The patent changes the operating parameters of the transistor by introducing a common-mode voltage extraction circuit and biasing circuits that allow the transistor to operate in an under-driven mode. This parameter change enables smaller transistors to achieve the required impedance accuracy by maintaining proper voltage levels across the channel, resolving the contradiction between device size and impedance accuracy.
2Measurement precision
If large transistors are used to minimize on-state impedance, then the impedance accuracy is improved, but the bandwidth is reduced due to high capacitance
Solution Approach 1:
The patent changes the voltage parameters across the transistor channel by extracting common-mode voltage and applying appropriate biasing. This allows smaller transistors to operate in a regime where their channel impedance remains stable and accurate, while their reduced size inherently lowers capacitance and increases bandwidth, resolving the contradiction between impedance accuracy and bandwidth.
3Area of stationary object
If transistors are operated in under-driven mode, then the device size is reduced and bandwidth is increased, but the channel impedance stability must be maintained
Solution Approach 1:
The patent implements feedback through biasing circuits that monitor and adjust the voltage levels across the transistor channel. This feedback mechanism ensures that the transistor operates in the under-driven mode while maintaining stable channel impedance, resolving the contradiction between device size reduction and impedance stability.
Solution Approach 2:
The patent introduces common-mode voltage extraction circuits and biasing circuits as intermediary elements that mediate between the signal path and the transistor. These intermediaries ensure proper voltage levels are maintained across the transistor channel, enabling stable operation in under-driven mode with reduced device size.
4Speed
If smaller transistors are used, then the bandwidth is increased and size is reduced, but the on-state impedance increases
Solution Approach 1:
The patent changes the voltage parameters by extracting common-mode voltage and applying biasing circuits that ensure the transistor operates in an under-driven mode. This parameter change allows smaller transistors to achieve the required impedance accuracy by maintaining proper voltage levels across the channel, resolving the contradiction between bandwidth and impedance accuracy.
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
This approach results in a compact attenuator system with enhanced bandwidth and reduced size, as transistors contribute substantially to the overall impedance while maintaining stable operation across varying voltage conditions.
Implementation Method 1
The first transistor may be configured to operate in an under-driven mode when turned on. In the under-driven mode, a channel impedance of the first transistor may be set by the first output voltage, the channel impedance varying by less than 5% with changes to a voltage across a channel of the first transistor.
Data Source
AI summary
An attenuator system comprising a variable impedance configured to provide an impedance from among a plurality of impedance states, the variable impedance comprising a first port, a second port, a first transistor comprising first and second channel terminals coupled between the first port and the second port, and a second transistor comprising first and second channel terminals coupled between the first port and the second port, and a control circuit configured to control the variable impedance to a first impedance state of the plurality of impedance states at least in part by providing a first output voltage to a control terminal of the first transistor to turn the first transistor on, wherein the first transistor is configured to operate in an under-driven mode when turned on.