Difference Amplifier Input Rails for Wide Common-Mode Range
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Solution Overview
Problem
Conventional difference amplifiers face challenges in handling wide common mode input ranges due to increased noise, offset, and reduced bandwidth, particularly in applications like high-power class D amplifiers and ultrasound imaging, where common mode voltages can vary significantly.
Innovation Solution
The proposed solution involves a voltage selector circuit that dynamically generates internal rail voltages based on supply voltages and input signals, allowing the input amplifier circuit to operate within a suitable range by converting differential input signals to current signals and rejecting common mode inputs, using components like diodes and comparators to manage voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If resistor dividers are used to attenuate input common mode voltage, then the amplifier can handle higher common mode voltages, but input referred noise increases
Solution Approach 1:
The patent introduces dynamic rail voltages as an intermediary mechanism between the input signal and the amplifier core. Instead of using passive resistor dividers that directly attenuate the signal, the patent uses active voltage rails that dynamically track the common mode voltage, allowing the amplifier to handle high common mode voltages without degrading the differential signal quality and maintaining low noise performance.
Solution Approach 2:
The patent dynamically changes the supply rail voltages based on the input common mode voltage level. By making the rail voltages variable rather than fixed, the amplifier can adapt its operating range to match the input signal conditions, enabling it to handle both low and high common mode voltages effectively without the noise penalty of fixed attenuators.
2Adaptability or versatility
If resistor dividers are used to attenuate input common mode voltage, then the amplifier can handle higher common mode voltages, but bandwidth is reduced
Solution Approach 1:
The dynamic rail voltage system acts as an active intermediary that responds instantaneously to common mode voltage changes without introducing the bandwidth-limiting effects of passive RC networks. The rail voltages are generated through active circuitry that can track rapid voltage changes, preserving the amplifier's bandwidth while extending its common mode voltage handling capability.
3Adaptability or versatility
If dual power supply is used to extend input range, then the amplifier can handle wider voltage ranges, but device complexity increases
Solution Approach 1:
The patent implements a self-service mechanism where the amplifier's own input signal is used to generate the dynamic rail voltages needed for operation. The common mode voltage present at the input is detected and used to adjust the supply rails accordingly, eliminating the need for external dual power supplies or complex voltage regulation circuits while still achieving wide input range capability.
Solution Approach 2:
The dynamic rail voltage generation circuit serves multiple functions simultaneously: it provides the necessary voltage rails for amplifier operation, tracks the common mode voltage level, and extends the input range. This multi-functionality eliminates the need for separate dual power supply systems, reducing overall device complexity while maintaining wide voltage range handling capability.
Data Source
AI summary
Apparatus and methods reduce increase the common mode range of a difference amplifier. A circuit uses one or more floating powers and one or more floating grounds coupled to an input stage of an amplifier to increase the common mode range of a difference amplifier. The floating power can be configured to select from the greater of the voltage level of one of the differential signals and the system power high source. The floating ground can be configured to select from the lesser of the voltage level of one of the differential signals and the system power low source.