Continuous-Time Op-Amp CMFB Circuit for Stable Output Common Mode
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Solution Overview
Problem
Continuous time operation amplifiers face instability in output common mode due to changes in power, temperature, and noise, leading to reduced gain and signal range, which existing feedback circuits struggle to address effectively.
Innovation Solution
A continuous time op-amp with a common mode feedback (CMFB) circuit that uses capacitive coupling, switched capacitors, and switching elements to periodically recharge feedback capacitors and adjust bias feedback voltage based on a comparison between common mode voltage and reference voltage, ensuring stability through a negative feedback loop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a feedback circuit is added to stabilize output common mode, then stability is improved, but device complexity increases
Solution Approach 1:
The patent implements a common mode feedback (CMFB) circuit that continuously monitors the output common mode voltage and adjusts the bias voltage to maintain stability. The feedback path includes capacitors connected between the output nodes and the bias generation circuit, creating a closed-loop control system that automatically corrects deviations in output common mode voltage caused by power, temperature, or noise variations.
Solution Approach 2:
The patent introduces an intermediate bias voltage generation circuit that acts as a mediator between the power supply and the operational amplifier. This intermediate circuit receives the output common mode voltage through capacitive coupling and generates an adjusted bias voltage, thereby isolating the main amplifier circuit from direct feedback complexity while still achieving stability control.
2Productivity
If bias voltage is fixed to maximize swing range and gain, then amplifier performance is improved, but adaptability to changing conditions deteriorates
Solution Approach 1:
The patent transforms the static bias voltage into a dynamic quantity that automatically adjusts in response to changing operating conditions. The bias voltage is generated through a feedback mechanism that continuously adapts to variations in power supply voltage, temperature, and noise levels, allowing the amplifier to maintain optimal performance across different environmental conditions without manual intervention.
Solution Approach 2:
The amplifier circuit performs self-adjustment through the CMFB mechanism. The output common mode voltage directly influences the bias voltage generation, creating a self-regulating system that automatically compensates for drift and variations without requiring external control signals or additional sensing circuits.
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 CMFB circuit effectively stabilizes the output common mode voltage by periodically recharging charge leakage and adjusting bias feedback, maintaining a consistent level and amplitude, thus enhancing the amplifier's stability and gain.
Implementation Method 1
a common mode feedback (CMFB) circuit configured to feed a common mode voltage back to the op-amp through a feedback line in continuous time through a capacitive coupled path
Implementation Method 2
switched capacitors charged based on a common mode reference voltage
Implementation Method 3
The CMFB circuit may be configured to feed back the common mode voltage by periodically recharging, by the switching elements and the switched capacitors, a charge leakage of the feedback capacitors occurring in the capacitive coupled path
Implementation Method 4
switching elements configured to control a connection between the feedback capacitors and the switched capacitors
Implementation Method 5
The CMFB circuit may include a negative feedback loop configured to adjust a bias feedback voltage of the differential op-amp through the feedback line based on a comparison result of the common mode voltage and the common mode reference voltage
Data Source
AI summary
A continuous time op-amp includes a differential op-amp configured to produce, and output through output lines, output signals amplified based on a difference between input signals inputted to the differential op-amp, and a common mode feedback (CMFB) circuit configured to feed a common mode voltage back to the op-amp through a feedback line in continuous time through a capacitive coupled path, wherein the CMFB circuit includes: feedback capacitors connected between the output lines and the feedback line; switched capacitors charged based on a common mode reference voltage; and switching elements configured to control a connection between the feedback capacitors and the switched capacitors.