Cross-Coupled Negative Capacitance for Differential Bandwidth Extension
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Solution Overview
Problem
Current communication systems face challenges in extending differential mode bandwidth while effectively compensating for common mode signals, leading to inefficiencies in signal transmission and reception, particularly in wireless devices.
Innovation Solution
The implementation of a transconductance (g m) circuit coupled with a negative capacitance element, which introduces negative differential capacitance to cancel parasitic capacitance and enhance differential mode bandwidth, while also providing positive common mode capacitance for stability, thereby decoupling and adjusting loop bandwidths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional transconductance circuits are used, then the circuit operates at low supply voltage, but the differential mode bandwidth is limited and common mode stability is compromised
Solution Approach 1:
The patent segments the capacitance function into two independent components: negative differential capacitance (for bandwidth extension) and positive common mode capacitance (for stability). This is achieved through a differential capacitor structure where each side has a capacitor to ground (Cgd1, Cgd2) and a cross-coupled capacitor (Cm1, Cm2), allowing independent control of differential and common mode characteristics while operating at low supply voltage
Solution Approach 2:
The patent changes the capacitance parameter by introducing negative differential capacitance through cross-coupled capacitors and buffers. The negative capacitance effect is created by configuring the differential capacitor network with specific gain conditions (|K| > 1) that generate an equivalent negative capacitance in the differential path, thereby extending bandwidth without increasing supply voltage
2Ease of manufacture
If parasitic capacitance is present in the circuit, then the circuit is simpler to manufacture, but the differential mode bandwidth is reduced and distortion increases
Solution Approach 1:
The patent converts the harmful effect of parasitic capacitance into a beneficial feature by using cross-coupled capacitors to generate negative differential capacitance that actively cancels the parasitic capacitance. The cross-coupled capacitor network, when configured with appropriate gains, creates an equivalent negative capacitance that neutralizes the bandwidth-limiting effect of parasitic elements, thereby extending differential mode bandwidth while maintaining manufacturing simplicity
3Reliability
If the common mode loop bandwidth is increased, then the common mode response is improved, but the overall system stability is reduced and distortion increases
Solution Approach 1:
The patent segments the capacitance function into two independent components: negative differential capacitance (for bandwidth extension) and positive common mode capacitance (for stability). This is achieved through a differential capacitor structure where each side has a capacitor to ground (Cgd1, Cgd2) and a cross-coupled capacitor (Cm1, Cm2), allowing independent control of differential and common mode characteristics while operating at low supply voltage
4Manufacturing precision
If output impedance is increased to reduce distortion, then signal quality improves, but the common mode loop becomes unstable
Solution Approach 1:
The patent changes the capacitance parameter by introducing negative differential capacitance through cross-coupled capacitors and buffers. The negative capacitance effect is created by configuring the differential capacitor network with specific gain conditions (|K| > 1) that generate an equivalent negative capacitance in the differential path, thereby extending bandwidth without increasing supply voltage
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 extends differential mode bandwidth, reduces distortion, and stabilizes common mode loops, improving the overall performance of wireless communication systems by boosting output impedance and maintaining low common mode loop bandwidth.
Implementation Method 1
a capacitive element coupled to the transconductance circuit, the capacitive element including a pair of cross-coupled capacitors and a pair of negative gain buffers, the negative capacitance element to introduce negative differential capacitance to cancel parasitic capacitance in the transconductance circuit
Implementation Method 2
The DAC may be coupled to a transconductance (gm) circuit. The DAC may assist in the generation of the output RF signal that is transmitted
Implementation Method 3
providing positive common mode capacitance for stability, thereby decoupling and adjusting loop bandwidths
Data Source
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AI summary
A method and apparatus are provided. The apparatus may be a capacitive element for adjusting a net capacitance of a circuit. The apparatus may be configured to be coupled to the circuit. The apparatus may be configured to adjust the net capacitance of the circuit to decouple common mode and differential loop bandwidth adjustment of the circuit. The capacitive element may include a pair of cross-coupled capacitors configured to be coupled to differential nodes of the circuit, and a pair of negative gain buffers coupled to respective capacitors.