Feedback Amplifier Gain Range Using Segmented Voltage Divider
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Solution Overview
Problem
Conventional feedback amplifiers face issues with gain offset due to parasitic resistance and high current consumption, particularly in achieving a wide range of gain from −57 dB to 6 dB, which degrades noise performance and increases chip area usage.
Innovation Solution
A feedback amplifier design that couples a voltage divider with an operational amplifier, using resistors R1 and R2, and adjustable resistances R3 and R4, allowing for a wide range of gain through the formula 20*log(R2/R1)+20*log(R4/(R3+R4), with R2 being twice R1, and R4/(R3+R4) adjustable for optimal gain settings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single-stage feedback amplifier uses a small resistance r2 to achieve low gain (−57 dB), then the gain range is extended, but parasitic resistance increases causing gain offset and high current consumption is required
Solution Approach 1:
The feedback path is segmented into two parallel branches: one with resistor r2 and another with series combination of resistors r3 and r4. This segmentation allows the amplifier to achieve low gain values without requiring extremely small resistance values, thereby reducing parasitic resistance effects and improving gain accuracy while maintaining the extended gain range capability
2Adaptability or versatility
If a two-stage feedback amplifier is used to achieve wide gain range (63 dB), then the gain coverage is improved, but chip area increases and more currents are consumed
Solution Approach 1:
The patent merges the feedback functions of two stages into a single operational amplifier by providing two parallel feedback paths. This combining approach achieves the wide gain range capability of a two-stage amplifier while using only one operational amplifier, thereby reducing chip area and current consumption
3Adaptability or versatility
If a two-stage feedback amplifier is used to achieve wide gain range (63 dB), then the gain coverage is improved, but noise performance degrades due to more noise sources
Solution Approach 1:
The patent combines the feedback functionality of two stages into a single operational amplifier with parallel feedback paths. This eliminates the need for a second operational amplifier, thereby reducing the number of noise sources while maintaining the wide gain range capability
Data Source
AI summary
A feedback amplifier includes an operational amplifier having an input end and an output end. A first resistor is coupled with the input end of the operational amplifier. A second resistor has a first end coupled with the input end of the operational amplifier and a second end coupled with the output end of the amplifier. A voltage divider has a first end being operably coupled with the output end of the operational amplifier and a second end being analog grounded. In an embodiment, the feedback amplifier further includes a first switch coupled to the first end of the voltage divider and the output end of the operational amplifier, and a second switch coupled to an internal node of the voltage divider. In an embodiment, the feedback amplifier is configured to provide attenuation when the first switch is open and second switch is closed.