Amplifier Lowpass Feedback Using Miller Capacitance for Offset Suppression
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Solution Overview
Problem
Amplifiers designed for high-frequency signal components face issues with significant input offset due to small transistor dimensions, leading to undesirable steady components in the output signal, which can reach half of the dynamic range.
Innovation Solution
A feedback unit with lowpass characteristics and Miller capacitance is implemented to reduce the offset fraction by feeding the output signal back to the input after lowpass filtering, utilizing an additional amplifier stage to enhance capacitance without increasing silicon area, allowing for effective compensation of steady components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large capacitor is used in the feedback path to achieve lowpass filtering with adequate limiting frequency, then the steady component can be effectively filtered, but the silicon area required increases significantly
Solution Approach 1:
An additional amplifier stage is introduced as an intermediary element in the feedback path. This amplifier stage works together with a small Miller capacitor to generate the necessary lowpass filtering effect, replacing the need for a large capacitor. The amplifier stage mediates between the feedback signal and the Miller capacitor, enabling effective offset suppression with minimal silicon area.
Solution Approach 2:
The invention changes the parameters of the feedback path by introducing an amplifier stage with specific gain characteristics. By adjusting the gain of the additional amplifier stage and the value of the Miller capacitor, the limiting frequency of the lowpass filter is optimized to effectively suppress the steady component while maintaining small component dimensions.
2Speed
If transistors are dimensioned very small to amplify high-frequency signal components, then the amplifier can handle gigahertz range frequencies, but significant fluctuations in transistor threshold voltages occur, resulting in large input offset
Solution Approach 1:
A feedback path is implemented that feeds back a portion of the output signal to the input of the amplifier. This feedback mechanism detects the steady component generated by input offset and automatically adjusts the input signal to compensate for it, thereby reducing the overall input offset effect while preserving the high-frequency response capability.
Solution Approach 2:
The invention extracts and separates the steady component (offset) from the dynamic signal components. By using lowpass filtering in the feedback path, only the steady component is fed back for compensation, while the dynamic high-frequency signal components are preserved and amplified without the harmful offset effect.
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 solution significantly reduces the steady component in the output signal, improving the utilization of the dynamic range and reducing the space and cost requirements for capacitors, while maintaining a small and cost-effective design.
Implementation Method 1
at least one Miller capacitance connected between an input and an output of the amplifier stage... an additional amplifier stage is provided, between whose inputs and outputs at least one Miller capacitor of comparatively small dimensions is connected. Since the amplifier stage amplifies an applied voltage by an amplification factor, hereinafter referred to as A2, and since to this extent a significantly higher voltage is present at the connections of the Miller capacitor, the relatively small-dimensioned Miller capacitor can store a charge quantity which corresponds to the charge of a capacitor that is larger by the factor (1+A2).
Data Source
AI summary
An amplifier is described which amplifies an input signal according to a defined amplification factor, and which generates an output signal. To reduce an offset fraction of the output signal the amplifier comprises a feedback path which has lowpass characteristics and which returns the output signal in a lowpass-filtered state to an input of the amplifier. The feedback path comprises an amplifier stage as well as at least one Miller capacitance connected between an input and an output of the amplifier stage.