MuGFET Varactor VCO Tuning Without LC Tank Q Loss
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Solution Overview
Problem
The challenge in developing a wideband voltage-controlled oscillator (VCO) using FinFET technology is achieving a wide tuning range while addressing reliability and gate work function issues, particularly with NMOS varactors, which often result in limited frequency tuning ranges and compromised quality factors in LC tank circuits.
Innovation Solution
A voltage-controlled oscillator design incorporating a programmable current source, a coarse grain capacitor array, a varactor with MuGFETs, and a frequency scaled resistor network, where the resistance of the path for the second current is scalable with frequency, allowing for effective capacitance and resistance control to achieve a wideband frequency tuning range without degrading the quality factor of the LC tank circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If FinFET technology is used in an LC voltage controlled oscillator, then device density and integration are improved, but the tuning range is limited due to reliability and gate work function issues
Solution Approach 1:
The patent changes the work function parameter of the FinFET gate by introducing a dual-gate structure where the second gate can independently control the threshold voltage. This allows dynamic adjustment of the gate work function to compensate for reliability issues while maintaining wide tuning range capability.
Solution Approach 2:
The FinFET is segmented into multiple gates (first gate and second gate) that can be independently controlled. This segmentation allows separate optimization of different functions: the first gate controls the main current while the second gate adjusts the threshold voltage to maintain reliability across the tuning range.
2Adaptability or versatility
If NMOS varactors are used with FinFET technology, then integration is improved, but the capacitance-voltage curve is shifted to higher voltages limiting the tuning range
Solution Approach 1:
The patent changes the voltage parameter characteristics of the NMOS varactor by using the dual-gate FinFET structure to independently control the threshold voltage. This shifts the capacitance-voltage curve back to optimal positions, enabling wide frequency tuning without compromising ease of manufacture.
3Adaptability or versatility
If wideband frequency tuning is achieved, then adaptability is improved, but quality factor degradation occurs in the LC tank circuit
Solution Approach 1:
The patent introduces dynamic control of the FinFET threshold voltage through the second gate, allowing the circuit to adaptively maintain optimal operating conditions across the frequency tuning range. This dynamic adjustment prevents quality factor degradation that would otherwise occur during wideband tuning.
Solution Approach 2:
The dual-gate FinFET structure provides a feedback mechanism where the second gate can sense and compensate for changes in the LC tank circuit conditions during frequency tuning, thereby maintaining stable quality factor across the wideband operating range.
Data Source
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Figure 3~4
AI summary
Voltage-controlled oscillation (100) is described. In an apparatus therefor, an inductor (120) has a tap and has or is coupled to a positive-side output node (105) and a negative side output node (106). The tap is coupled to receive a first current. A coarse grain capacitor array (130) is coupled to the positive-side output node (105) and the negative side output node (106) and is coupled to respectively receive select signals (168). A varactor (140) is coupled to the positive-side output node (105) and the negative side output node (106) and is coupled to receive a control voltage (143). The varactor (140) includes MuGFETs (141, 142). A transconductance cell (150) is coupled to the positive- side output node (105) and the negative side output node (106), and the transconductance cell (150) has a common node (107). A frequency scaled resistor network (160) is coupled to the common node (107) and is coupled to receive the select signals (168) for a resistance for a path for a second current.