Controllable Power OTA with Class B Push-Pull Gain Control

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Solution Overview

Problem

Existing controllable power operational transconductance amplifiers (OTAs) face limitations in power saving, size reduction, and cost efficiency due to cross-over distortion and unnecessary power loss in class-AB amplifier stages, especially in portable devices like mobile telephone handsets, where power efficiency and compact design are crucial.

Innovation Solution

A symmetrically structured controllable input stage generates matched low power current signals for class B push-pull configured output current sources, eliminating the need for quiescent current and achieving power amplification without distortion, using diodes or MOSFET transistors for bi-directional rectification and alternating current amplification during mutually exclusive signal periods.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If class-AB amplifier stage is used to reduce power dissipation by reducing quiescent currents, then power consumption is reduced, but cross-over distortion increases beyond acceptable levels

Engineering Contradiction:

Improvepower consumptionVSAvoidlinearity of operation

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The amplifier is segmented into two distinct stages: a class-AB input stage for low-power signal processing and a class-B push-pull output stage for high-power amplification. This segmentation allows each stage to operate in its optimal mode, with the class-AB stage providing linear operation at low power and the class-B stage providing efficient high-power output without cross-over distortion.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The class-AB input stage acts as an intermediary between the signal source and the class-B output stage. It processes the input signal with high linearity and drives the class-B stage, which then provides the final power amplification. This intermediary arrangement allows the class-B stage to receive a pre-conditioned signal that eliminates cross-over distortion issues.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of operation

If variable attenuation is used to control overall gain in prior art OTAs, then gain control is achieved, but significant power is wasted as loss in the attenuator

Engineering Contradiction:

Improvegain controlVSAvoidpower loss

Core Design Contradiction:

Ease of operationVSLoss of energy

Solution Approach 1:

Instead of using attenuation to control gain (reducing signal level), the invention inverts the approach by using amplification control in the input stage. The class-AB input stage provides the gain control function through its transconductance adjustment, eliminating the need for a power-wasting attenuator in the signal path.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The overall gain of the amplifier is controlled by changing the transconductance parameter of the class-AB input stage rather than by attenuating the signal. This parameter change approach allows gain control without power loss, as the input stage operates at low power levels regardless of the gain setting.

Inventive Principle:

Principle #35Parameter changes

3Use of energy by moving object

If class B push pull configuration is used for output current sources, then power efficiency is improved by eliminating quiescent current, but distortion may increase

Engineering Contradiction:

Improvepower efficiencyVSAvoidsignal fidelity

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The class-AB input stage performs preliminary signal processing and conditioning before the signal reaches the class-B push-pull output stage. By preparing the signal with high linearity in advance, the class-B stage receives a pre-conditioned signal that minimizes distortion generation during the final power amplification stage.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS7729678B2Controllable power operational transconductance amplifier

Publication Date: 2010.06.01 SEMICON IDEAS TO MARKET ITOM

AI summary

Controllable operational transconductance power amplifier (controllable power OTA) including an input stage receiving a differential input signal (Ovin) and deriving therefrom first (i1) and second (i2) low power current signals being coupled to first (ccs1) and second (ccs2) current controlled output current sources being arranged in class B push pull configuration. To obtain an effective gain control while securing power efficiency and linearity, the overall gain of the power OTA is controlled by varying the gain or transconductance of the input stage (c15) and by the use of means for bi-directionally rectifying said first (i1) and second (io) low power current signals and providing in mutual alternation power amplification of said first (i1) and second (i2) low power current signals into first (I01) and second (Io2) mutually exclusive high power current output signals, which are supplied through a current summer to a current output (I0) of said linear power amplifier.