Cross-Coupled Multipath Op-Amp Architecture for High Loop Gain
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Solution Overview
Problem
Multipath feedforward operational amplifiers face inefficiencies in terms of chip area and power consumption while striving for high loop gain and stability, with the parallel nature of amplification paths potentially leading to stability concerns due to increased gains and phase shifts.
Innovation Solution
The design incorporates a multipath feedforward operational amplifier architecture with capacitive input-output cross-coupling and AC coupling, allowing for efficient power delivery and reduced total capacitance, thereby achieving higher loop gains with improved stability and reduced chip area requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multipath feedforward operational amplifier architecture is used to achieve high loop gain, then loop gain is improved, but chip area and power consumption increase
Solution Approach 1:
The patent merges multiple amplification paths into a unified multipath feedforward architecture where paths share common components and nodes. This combining approach achieves high loop gain through the collective effect of parallel paths while reducing the total component count and chip area compared to implementing separate independent amplifier circuits.
Solution Approach 2:
The operational amplifier is designed with amplification paths that serve multiple functions simultaneously - providing both signal amplification and frequency compensation through the same structural elements. The feedforward paths contribute to both gain enhancement and stability improvement, eliminating the need for separate dedicated compensation components that would increase chip area.
2Power
If multipath feedforward operational amplifier architecture is used to achieve high loop gain, then loop gain is improved, but power consumption increases
Solution Approach 1:
The patent merges multiple amplification paths into a unified multipath feedforward architecture where paths share common components and nodes. This combining approach achieves high loop gain through the collective effect of parallel paths while reducing the total component count and chip area compared to implementing separate independent amplifier circuits.
Solution Approach 2:
The operational amplifier is designed with amplification paths that serve multiple functions simultaneously - providing both signal amplification and frequency compensation through the same structural elements. The feedforward paths contribute to both gain enhancement and stability improvement, eliminating the need for separate dedicated compensation components that would increase chip area.
3Power
If multipath feedforward operational amplifier architecture is used, then loop gain is improved, but stability deteriorates due to phase shifts
Solution Approach 1:
The patent implements feedforward feedback paths that anticipate and counteract phase shifts before they cause instability. The feedforward architecture introduces zero locations in the transfer function that compensate for the phase lag introduced by multiple poles, thereby maintaining stability while achieving high loop gain. This feedback mechanism actively manages the phase response to prevent oscillations.
Solution Approach 2:
The patent modifies the frequency response parameters by introducing feedforward paths with specific time constants and gain values. These parameter changes create zeros in the transfer function that counterbalance the phase lag from poles, transforming the overall phase response to maintain stability margins while achieving the desired high loop gain performance.
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 enables the operational amplifier to deliver the same frequency response and transconductance performance with a significantly smaller total capacitance value, leading to reduced chip area and power consumption, while maintaining stability and high loop gains.
Implementation Method 1
The amplifiers can include capacitive input-output cross-coupling, which can mitigate the Miller effect acting on intrinsic capacitances of the amplifier
Implementation Method 2
The cross-coupling capacitors can have capacitance values within a predetermined range of a value given by CGD (A+1)/(A−1), where CGD is an intrinsic gate-to-drain capacitance of an amplification transistor of the amplifier
Data Source
AI summary
An operational amplifier can include a plurality of amplifiers connected to form a plurality of amplification paths extending from an input terminal to an output terminal of the operational amplifier. An amplifier in one of the amplification paths can include an intrinsic amplification-transistor capacitance connected between a first amplifier input and a first amplifier output, and a cross-coupling capacitor connected between the first amplifier input and a second amplifier output. A plurality of the amplification paths can include series-connected amplifiers connected in parallel with the cross-coupled amplifier. The cross-coupling capacitor can have a capacitance value selected as a function of the intrinsic capacitance and a gain experienced between the amplifier inputs and outputs. The operational amplifier can include an AC coupling capacitor connected in series with the cross-coupled amplifier. The operational amplifier can be arranged in feedback configuration.