CG/CB RF Transmitter Current Steering for Wideband Linearity

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Solution Overview

Problem

Current RF transmitters for high-speed, high-frequency, and high-linear wideband RF power applications face challenges in achieving energy efficiency and linearity due to non-linear trans-conductance and power-hungry digital pre-distortion (DPD) requirements, especially in low to medium power wireless systems like Wi-Fi and 5G mMIMO base stations.

Innovation Solution

The implementation of a digitally controlled current source with a current diversion path in common-gate (CG) or common-base (CB) configured output stages, which provides optimized current waveforms to drive these stages in a class-A like operation, avoiding the need for DPD and enhancing efficiency and linearity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If digital pre-distortion (DPD) is used to improve linearity, then linearity is improved, but power consumption increases and device complexity increases

Engineering Contradiction:

ImprovelinearityVSAvoidpower consumption

Core Design Contradiction:

Manufacturing precisionVSUse of energy by moving object

Solution Approach 1:

The patent extracts the DPD function entirely from the system by using a current-mode CG/CB output stage that inherently provides linear operation without requiring digital pre-distortion correction algorithms, thereby eliminating the power consumption and complexity associated with DPD while maintaining high linearity

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the digital signal processing approach (DPD) with an analog current-mode approach using CG/CB transistors, substituting a complex digital correction system with a simpler analog circuit topology that achieves linearity through its inherent operating characteristics rather than through computational correction

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Manufacturing precision

If digital pre-distortion (DPD) is used to improve linearity, then linearity is improved, but device complexity increases

Engineering Contradiction:

ImprovelinearityVSAvoiddevice complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent removes the DPD processing block entirely from the transmitter architecture, achieving linearity through the intrinsic properties of the current-mode CG/CB output stage rather than through additional digital processing circuits, thereby reducing device complexity while maintaining linearity performance

Inventive Principle:

Principle #2Taking out (Extraction)

3Use of energy by moving object

If current sources are switched off to save power, then power consumption is reduced, but linearity deteriorates due to non-linear trans-conductance

Engineering Contradiction:

Improvepower consumptionVSAvoidlinearity

Core Design Contradiction:

Use of energy by moving objectVSManufacturing precision

Solution Approach 1:

The patent implements dynamic power management where current sources are selectively activated or deactivated based on the instantaneous signal requirements, using the current-mode CG/CB topology to maintain linearity during active operation while minimizing power consumption during low-activity periods, achieving both energy efficiency and linearity through dynamic control of the output stage

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the operating parameters of the current sources by utilizing the unique trans-conductance characteristics of CG/CB configured transistors, which maintain more linear behavior across a wider operating range compared to conventional CS/CE stages, allowing for more aggressive power management while preserving linearity

Inventive Principle:

Principle #35Parameter changes

4Power

If common-source (CS) or common-emitter (CE) configured output stages are used, then gain is improved, but linearity deteriorates due to non-linear trans-conductance

Engineering Contradiction:

ImprovegainVSAvoidlinearity

Core Design Contradiction:

PowerVSManufacturing precision

Solution Approach 1:

The patent inverts the conventional amplifier topology by using common-gate (CG) or common-base (CB) configurations instead of the more common common-source (CS) or common-emitter (CE) stages. This topological inversion fundamentally changes the trans-conductance characteristics, providing inherently more linear operation while maintaining the necessary gain through the current-mode operation and circuit topology

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentUS11996839B2Digital transmitter with high linearity for wideband signals

Publication Date: 2024.05.28 TECH UNIV DELFT

AI summary

An RF transmitter having one or more common-gate, CG, or common-base, CB, configured output stages, and a digitally controlled current source having a plurality of unit cells connected to the output stages, each of the plurality of unit cells comprising a current source. The digitally controlled current source is configured for driving the output stages with respective driving currents originating from the associated current source in each of the plurality of unit cells, in dependence of one or more input signals. The digitally controlled current source further comprises a current diversion path in each of the plurality of unit cells for providing a diversion current to a voltage source having a voltage lower than drain/collector terminals of transistors provided in the CG/CB configured output stages.