Non-Inverting Differential Amplifier With Reduced Common-Mode Gain
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Solution Overview
Problem
Conventional differential amplifier circuits face challenges in achieving low noise factor and high input impedance while maintaining a common-mode output voltage independent of the common-mode input voltage, which is essential for certain applications.
Innovation Solution
A non-inverting fully differential amplifier circuit design incorporating a transconductance amplifier to set the common-mode output voltage independently of the common-mode input voltage, with infinite differential input impedance and a noise factor of 1, ensuring low noise and high input impedance across all differential gains.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a conventional non-inverting differential amplifier circuit is used, then high input impedance is achieved, but the common-mode output voltage depends on the common-mode input voltage (common-mode gain = 1)
Solution Approach 1:
A third amplifier is introduced as an intermediary component to sense the common-mode voltage and generate a compensating signal that is subtracted from the differential input signals. This mediator amplifier enables the common-mode output voltage to be independent of the common-mode input voltage while preserving the high input impedance特性 of the non-inverting configuration.
2Adaptability or versatility
If a conventional inverting differential amplifier circuit is used, then common-mode output voltage is independent of common-mode input voltage, but noise factor is high and input impedance is limited
Solution Approach 1:
The patent inverts the conventional approach by using a non-inverting configuration with an additional amplifier to achieve common-mode rejection, rather than using the traditional inverting configuration. This inversion allows the circuit to achieve both high input impedance and low noise factor while maintaining common-mode output voltage independence.
3Power
If differential gain is increased in a non-inverting amplifier, then signal amplification is improved, but noise factor increases
Solution Approach 1:
The amplification function is segmented between two amplifiers: the first amplifier provides the primary differential gain, while the third amplifier handles common-mode voltage sensing and compensation. This segmentation allows the differential gain to be increased without proportionally increasing the noise factor, as the common-mode rejection function is separated into a dedicated component.
Data Source
AI summary
An embodiment of an amplifier circuit includes first, second, and third amplifiers. The first and second amplifiers are configured to amplify a differential input signal with a non-inverting gain. And the third amplifier, which can be a transconductance amplifier, is configured to cause the first and second amplifiers to amplify a common-mode input signal with a gain that is less than unity. The third amplifier can also be configured to cause the first and second amplifiers to generate a common-mode output voltage that is substantially independent of the common-mode input voltage. Consequently, in addition to presenting a high input impedance and a low noise factor, such an amplifier circuit has a configurable common-mode output voltage and has a lower common-mode gain (e.g., less than unity, approaching zero) than other non-inverting differential amplifiers.