Active Inductor Load With Cross-Coupled Capacitance for Wider Peaking

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Solution Overview

Problem

Active inductor circuits in programmable ICs face limitations due to gate-to-drain capacitance (Cgd), which reduces the frequency range where they behave inductively and limits their quality factor (Q), thereby restricting the achievable inductive peaking and signal swing.

Innovation Solution

The use of cross-coupled capacitive elements in active inductor loads, which cancel or reduce the effect of Cgd, extending the inductive behavior range and increasing the quality factor (Q) of each active inductor, thereby enhancing inductive peaking and allowing larger signal swings for a given power or lower power for a given signal swing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If active inductor circuits are used in programmable ICs, then inductive peaking and signal swing are achieved, but gate-to-drain capacitance (Cgd) reduces the frequency range where they behave inductively and limits the quality factor (Q)

Engineering Contradiction:

Improvefrequency range where active inductor behaves inductivelyVSAvoidgate-to-drain capacitance (Cgd)

Core Design Contradiction:

SpeedVSObject-generated harmful factors

Solution Approach 1:

The patent converts the harmful effect of gate-to-drain capacitance (Cgd) into a beneficial effect by introducing cross-coupled capacitive elements that utilize the same Cgd to extend the inductive behavior range. The cross-coupling configuration transforms the parasitic capacitance from a limiting factor into an extension of the useful capacitance, thereby extending the frequency range where the active inductor behaves inductively while maintaining circuit simplicity.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Reliability

If active inductor circuits are used, then inductive peaking is achieved, but the quality factor (Q) is limited by gate-to-drain capacitance

Engineering Contradiction:

Improvequality factor (Q)VSAvoidgate-to-drain capacitance (Cgd)

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent converts the harmful effect of gate-to-drain capacitance on quality factor into a beneficial effect. By introducing cross-coupled capacitive elements, the circuit transforms the parasitic Cgd into an extension of the useful capacitance, thereby increasing the quality factor (Q) of the active inductor. This approach maintains the inductive peaking capability while improving the reliability and performance of the circuit.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Power

If cross-coupled capacitive elements are added to active inductor loads, then inductive peaking and signal swing are enhanced, but device complexity increases

Engineering Contradiction:

Improveinductive peaking and signal swingVSAvoidcircuit structure

Core Design Contradiction:

PowerVSDevice complexity

Solution Approach 1:

The patent merges the function of additional capacitive elements with the existing gate-to-drain capacitance of the transistors. By cross-coupling the capacitive elements between the gates and drains of the active inductor transistors, the circuit combines the intrinsic parasitic capacitance with external capacitance to achieve enhanced inductive peaking and signal swing without requiring completely separate additional components, thereby limiting the increase in device complexity.

Inventive Principle:

Principle #5Merging (Combining)

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 implementation of cross-coupled capacitive elements significantly increases the inductive peaking of active inductor loads, enabling larger signal swings across the load for a given power or reducing power requirements for a given signal swing, by extending the frequency range where the active inductor behaves inductively.

Implementation Method 1

The use of cross-coupled capacitive elements in active inductor loads, which cancel or reduce the effect of Cgd, extending the inductive behavior range

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

each active inductor configured to exhibit inductive peaking in a frequency band including at least a frequency of a differential periodic signal to be applied to the pair of active inductors

Methodology Applied

Scientific EffectElectromagnetic Induction: Electromagnetic Induction

Data Source

PatentEP3371888B1Method for increasing active inductor operating range and peaking gain

Publication Date: 2020.09.02 XILINX INC

Figure 1
Figure 2A~2B
Figure 3

AI summary

Methods and apparatus are described for a differential active inductor load (500, 510) for inductive peaking in which cross-coupled capacitive elements (M3, M4, M7, M8) are used to cancel out, or at least reduce, the limiting effect of the gate-to-drain capacitance (Cgd) of transistors (M1, M2, M5, M6) in the active inductor load (500, 510). The cross-coupled capacitive elements (M3, M4, M7, M8) extend the range over which the active inductor load (500, 510) behaves inductively and increase the quality factor (Q) of each active inductor (300, 400). Therefore, the achievable inductive peaking of the load (500, 510) is significantly increased, which leads to providing larger signal swing across the load for a given power or, alternatively, lower power for a given signal swing.