Negative Capacitance Circuit for BAW Filters Above 2 GHz
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Solution Overview
Problem
Existing negative capacitance circuits are limited to frequencies below 2 GHz and cannot be effectively used for high-frequency applications, particularly in BiCMOS technology, and are not suitable for RF filters in mobile telecommunications.
Innovation Solution
A negative capacitance circuit design comprising a first and second branch with bipolar transistors, current sources, and diodes, coupled with a capacitor and linearization resistor, which can be integrated with Bulk Acoustic Wave (BAW) resonators to modify the resonant frequency, enabling high-frequency applications and RF filter implementation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional negative capacitance circuits are used, then circuit simplicity is maintained, but frequency operation is limited to below 2 GHz
Solution Approach 1:
The circuit is divided into two symmetrical branches, each containing a bipolar transistor, diode, resistor, and current source. This segmentation allows the circuit to achieve negative capacitance through the interaction of transistor transconductances while maintaining manageable complexity in each individual branch.
Solution Approach 2:
The patent combines bipolar transistors with diodes and resistors in series within each branch, and connects the two branches in parallel between Vdd and Ground. This merging of components creates the negative capacitance effect through the coupled transistor operations, enabling high-frequency operation beyond 2 GHz.
2Adaptability or versatility
If additional inductors are added to achieve filtering, then filtering functionality is improved, but device complexity and parasitic anti-resonance frequencies increase
Solution Approach 1:
The patent extracts the inductor from the traditional LC resonator design and replaces it with the negative capacitance circuit formed by the bipolar transistor branches. This extraction eliminates the need for physical inductors, reducing device complexity and avoiding parasitic anti-resonance frequencies while maintaining filtering functionality through the negative capacitance effect.
Solution Approach 2:
The patent changes the circuit parameters by using the transconductance characteristics of bipolar transistors to generate negative capacitance. By adjusting bias currents and transistor dimensions, the negative capacitance value can be tuned to achieve desired resonant frequencies and filtering characteristics without adding inductors.
3Reliability
If conventional circuits are used, then manufacturing is simpler, but quality factor of acoustic filters is reduced
Solution Approach 1:
The patent uses a composite structure combining bipolar transistors, diodes, resistors, and current sources to create an active negative capacitance circuit. This composite active circuit replaces passive LC components and provides enhanced quality factor for acoustic filters while remaining compatible with standard BiCMOS manufacturing processes.
Data Source
AI summary
A negative capacitances circuit includes first and second branches connected between a first reference voltage and a second reference voltage. The first branch includes, in series, a first biasing resistor, a first diode, a first bipolar transistor, and a first current source. The second branch includes, in series, a second biasing resistor, a second diode, a second bipolar transistor, and a second current source. The first transistor has a base coupled to a collector of the second transistor and to one input, and the second transistor has a base coupled to a collector of the first transistor and to another input. A capacitor is connected between the emitter of said first transistor and the emitter of said second transistor. A linearization resistor is coupled in parallel between the two emitters of said first and said second transistors.