Limiting Amplifier Current Feedback for Offset Suppression
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Solution Overview
Problem
Conventional limiting amplifiers face a trade-off between high gain and speed, as the high gain amplification of input offsets can lead to saturation and slow down the overall amplifier speed due to the negative feedback loop, which is ineffective for high-frequency components.
Innovation Solution
A limiting amplifier design incorporating a transconductance amplifier with a cascade arrangement of amplifier stages, where the transconductance amplifier receives a voltage signal via a high-resistance resistor and injects a current signal into the first amplifier stage via another high-resistance resistor, providing negative feedback for low-frequency offsets without loading the last amplifier stage, thus maintaining speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional feedback amplifier is used to suppress offset, then the offset suppression is effective, but the loading at circuit nodes increases and the overall speed is slowed down
Solution Approach 1:
A current feedback amplifier is introduced as an intermediary component that converts the voltage output signal to a current signal for feedback. This current signal is then converted back to voltage by a transimpedance amplifier. This intermediary conversion process allows the feedback to be applied without creating heavy voltage loading at the circuit nodes, thereby maintaining the amplifier speed while still achieving effective offset suppression.
Solution Approach 2:
The feedback mechanism changes from voltage-based feedback to current-based feedback. By converting the feedback signal to current domain and then back to voltage, the parameter representation changes, which allows the feedback to be applied without the detrimental voltage loading effects that would slow down the amplifier. This parameter transformation resolves the contradiction between offset suppression and speed maintenance.
2Power
If high gain amplification is applied to amplify the input signal, then the signal amplification is sufficient, but the input offset is also amplified to an extent that it saturates the latter stage
Solution Approach 1:
A negative feedback loop is implemented using the current feedback amplifier and transimpedance amplifier combination. The feedback loop continuously monitors the output and adjusts the input to counteract any offset amplification. This feedback mechanism allows the high gain amplification to function properly while automatically compensating for and suppressing the harmful offset signals, preventing saturation in the latter stage.
Solution Approach 2:
The current feedback amplifier acts as an intermediary that processes the feedback signal in the current domain before it is converted back to voltage. This intermediary processing allows the feedback to effectively counteract offset amplification without interfering with the high gain signal amplification function, thereby resolving the contradiction between useful signal amplification and harmful offset amplification.
Data Source
AI summary
A method including receiving an input signal; amplifying the input signal to generate an output signal using a cascade of a plurality of amplifier stages including a first amplifier stage and a last amplifier stage; generating a voltage signal by sensing the output signal in a noninvasive manner so that the sensing results in substantially no change to the output signal; generating a current signal from the voltage signal using a transconductance amplifier; and injecting the current signal into an output node of the first amplifier stage in a noninvasive manner so that the injecting results in substantially no change to an amplification function of the first amplifier stage.