Differential Amplifier Dynamic Rail Selection for Wide Common-Mode Range
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Solution Overview
Problem
Current shunt amplifiers have limitations in common mode input range, requiring large die size and being inefficient near zero differential input voltage, with high noise and limited bidirectional current measurement capabilities beyond the power supply voltage.
Innovation Solution
A differential amplifier with a maximum voltage selector circuit that uses the larger of the supply voltage or the common mode input voltage to power the input amplifier, allowing operation beyond the power supply voltage and enabling bidirectional measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a current shunt amplifier uses traditional operational amplifier topology with fixed power supply voltage, then the circuit is simple to implement, but the common mode input range is limited to within the power supply voltage
Solution Approach 1:
The patent implements dynamic voltage selection by automatically switching between a first power supply voltage (for low common mode input voltages) and a second power supply voltage (for high common mode input voltages). This dynamic adaptation allows the amplifier to handle a wide common mode input range spanning from near ground to beyond the traditional power supply voltage, resolving the contradiction between input range and circuit complexity.
2Adaptability or versatility
If the amplifier is designed to handle high common mode input voltages, then the common mode input range is extended, but the die size increases
Solution Approach 1:
The patent creates a multi-functional power supply system where a single amplifier circuit can operate with different power supply voltages depending on the input conditions. By making the power supply configuration adaptable rather than fixed, the same hardware implementation serves multiple voltage range requirements, avoiding the need for separate amplifier designs for different voltage ranges and thus reducing overall die size.
3Reliability
If traditional current shunt amplifier topology is used, then the circuit implementation is straightforward, but the amplifier does not function well when differential input voltage is near 0 volts
Solution Approach 1:
The patent changes the operating parameters of the amplifier by dynamically adjusting the power supply voltage based on the common mode input voltage level. When the common mode input voltage is high, a higher power supply voltage is applied, which improves the amplifier's ability to resolve small differential signals near 0 volts by providing sufficient voltage headroom for the internal transistor operations, thereby enhancing reliability without complicating the basic circuit topology.
Data Source
AI summary
A differential amplifier (1D) includes circuitry (5,R1,R2,52) coupling a common mode component of an input voltage (Vin+−Vin−) to a maximum voltage selector circuit (53) that produces an internal voltage (VRAIL-TOP) equal to the larger of a first supply voltage (VREG) and the common mode component. An input amplifier circuit (46) of the differential amplifier is powered by the internal voltage. The input voltage (Vin+−Vin−) is coupled to inputs (41A,B) of the input amplifier circuit (46). Outputs (64A,B) of the input amplifier circuit (46) are amplified by an output amplifier (50).