Segmented Transconductance Stage for Gain and DC Offset Control

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Solution Overview

Problem

Conventional transconductance stages in wireless transmitters fail to account for all baseband DC offsets, leading to inefficient gain control, noise introduction, and poor current and voltage headroom management.

Innovation Solution

A transconductance stage with an output stage comprising multiple output transistors and switch resistors, where the number of activated switch resistors determines the gain of output current signals, allowing for efficient adjustment of gain and DC offset scaling without wasting generated current or compromising voltage headroom.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If conventional gain control is implemented in the baseband portion, then gain adjustment is achieved, but baseband DC offsets cannot be fully accounted for and noise is introduced

Engineering Contradiction:

Improvegain control capabilityVSAvoidDC offset handling and noise performance

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The transconductance stage is segmented into multiple parallel branches, each with its own switch resistor and output transistors. This segmentation allows independent control of gain and DC offset compensation for each branch, enabling robust gain control while maintaining accuracy by accounting for baseband DC offsets through differential cancellation of intermediate currents.

Inventive Principle:

Principle #1Segmentation

2Adaptability or versatility

If gain is adjusted by varying output current, then gain control is achieved, but current consumption efficiency deteriorates

Engineering Contradiction:

Improvegain adjustabilityVSAvoidcurrent consumption efficiency

Core Design Contradiction:

Adaptability or versatilityVSUse of energy by moving object

Solution Approach 1:

The circuit employs dynamically controllable switch resistors that can be activated or deactivated based on the desired gain level. This dynamic configuration allows the circuit to adjust gain by selectively engaging parallel branches rather than continuously varying current, improving current consumption efficiency while maintaining full gain adjustability across different operating conditions.

Inventive Principle:

Principle #15Dynamics

3Adaptability or versatility

If conventional transconductance stage design is used, then basic gain control is provided, but voltage headroom is insufficient

Engineering Contradiction:

Improvegain control functionVSAvoidvoltage headroom

Core Design Contradiction:

Adaptability or versatilityVSStress or pressure

Solution Approach 1:

The patent introduces an additional control dimension through parallel circuit branches with switch resistors, allowing gain control to be achieved through topological reconfiguration rather than continuous voltage or current adjustment. This dimensional change in the control approach preserves voltage headroom by avoiding the need for large voltage swings while maintaining full gain control capability.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

4Reliability

If multiple output transistors and switch resistors are used, then gain control and DC offset compensation are improved, but device complexity increases

Engineering Contradiction:

Improvegain control and DC offset handlingVSAvoidcircuit structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The parallel branch structure with switch resistors serves multiple functions simultaneously: it provides gain control through selective activation, compensates for baseband DC offsets through differential current cancellation, and improves current consumption efficiency. This multi-functionality reduces the need for separate dedicated circuits, thereby mitigating the increase in device complexity while enhancing overall system performance.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS7551029B2Transconductance stage providing gain control

Publication Date: 2009.06.23 AVAGO TECHNOLOGIES INTERNATIONAL SALES PTE LTD

AI summary

A transconductance stage providing gain control includes an input stage to convert a first differential input voltage and a second differential input voltage to a first intermediate current and a second intermediate current, respectively. An output stage generates a first output current signal and a second output current signal based on the first and second intermediate currents, respectively. The output stage includes a first plurality of output transistors coupled to a first plurality of corresponding switch resistors and a second plurality of output transistors coupled to a second plurality of corresponding switch resistors. The number of activated switch resistors of the first plurality of switch resistors determines a gain of the first output current signal and a number of activated switch resistors of the second plurality of switch resistors determines a gain of the second output current signal.