Non-Inverting Differential Amplifier With Fixed Common-Mode Output
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Solution Overview
Problem
Conventional non-inverting differential amplifier circuits have higher common-mode gain and a common-mode output voltage that depends on the common-mode input voltage, making them unsuitable for applications requiring a fixed common-mode output voltage independent of the input.
Innovation Solution
A non-inverting differential amplifier circuit design incorporating a transconductance amplifier to achieve zero common-mode gain and a configurable common-mode output voltage independent of the common-mode input voltage, with infinite differential input impedance and a noise factor of 1, allowing for a fixed common-mode output voltage setting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional non-inverting differential amplifier circuit is used, then the circuit provides non-inverting amplification, but the common-mode gain is high and the common-mode output voltage depends on the common-mode input voltage
Solution Approach 1:
The amplifier circuit is segmented into multiple functional blocks: a differential amplifier stage for signal amplification, a common-mode feedback stage for controlling output common-mode voltage, and a reference voltage generation stage. This segmentation allows independent optimization of differential gain and common-mode rejection, resolving the contradiction between non-inverting amplification and common-mode gain control.
Solution Approach 2:
A common-mode feedback mechanism is implemented where the common-mode output voltage is sensed and fed back to adjust the operating point. This feedback loop enables the common-mode output voltage to be independently controlled and decoupled from the common-mode input voltage, while maintaining non-inverting differential amplification.
2Productivity
If a conventional non-inverting differential amplifier circuit is used, then the circuit provides signal amplification, but the common-mode output voltage cannot be set to a fixed value independent of input
Solution Approach 1:
The circuit employs dynamic common-mode feedback control where the common-mode output voltage is continuously adjusted based on the difference between the actual common-mode output and the desired reference value. This dynamic control enables the output common-mode voltage to be configured to any fixed value independent of the input signal, while maintaining continuous signal amplification.
Solution Approach 2:
A reference voltage source serves as an intermediary element that sets the desired common-mode output voltage level. This reference voltage is compared with the actual common-mode output voltage, and the difference drives the feedback mechanism to achieve the configured output level, enabling independent common-mode output configuration.
3Ease of operation
If a non-inverting differential amplifier circuit is used, then the input impedance is high, but the noise factor is higher than ideal
Solution Approach 1:
The circuit optimizes the noise factor by carefully selecting and matching component parameters, particularly the resistors in the differential amplifier stage. By adjusting resistance values and their ratios, the circuit achieves high input impedance while minimizing thermal noise contribution, and the low noise factor of 1 is achieved through optimized parameter selection.
Data Source
AI summary
An embodiment of an amplifier circuit includes first, second, and third amplifiers. The first and second amplifiers, each of which can be a respective operational amplifier or a respective transconductance amplifier, are configured to amplify a differential input signal with a non-inverting gain. And the third amplifier, which can be an operational amplifier or 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.