Single-Differential Converter Topology for Stable Common-Mode Control
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Solution Overview
Problem
Conventional single-differential converting circuits face limitations in reducing common-mode signal variations while maintaining amplification functionality, particularly at low input voltages, due to unbalanced resistance values which disrupt stable operations.
Innovation Solution
A single-differential converting circuit incorporating a fully-differential operational amplifier with equal impedance negative and positive feedback elements, and input impedance elements, allowing for reduced input voltage variations by maintaining amplification functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If resistance values R2 or R3 are set to small values to suppress common phase voltage, then common phase voltage can be reduced, but the ratio between resistance values becomes unbalanced causing disturbance of stable circuit operations
Solution Approach 1:
The patent introduces a common phase feedback circuit that detects the common phase voltage VCM and feeds it back through resistor R5 to the inverting input terminal. This feedback mechanism automatically adjusts the circuit operation to suppress common phase voltage variations without requiring extreme resistance values, thereby maintaining stable circuit operations while achieving the goal of reducing common phase voltage.
Solution Approach 2:
The patent changes the circuit configuration by adding the common phase feedback path with specifically designed resistance values. Instead of simply reducing R2 or R3 to suppress VCM, the patent introduces new parameters (R5 and the feedback path) that enable VCM suppression through a different mechanism that doesn't disrupt the balance of existing resistance ratios.
2Object-affected harmful factors
If resistance value R3 or R2 is set at 0 to make common phase voltage 0, then common phase voltage can be completely suppressed, but the circuit will not function as an amplifier
Solution Approach 1:
The common phase feedback circuit provides a controlled feedback path that suppresses common phase voltage without completely eliminating it (which would require R2 or R3 = 0). The feedback through R5 creates a virtual ground effect that reduces VCM to approximately 0 while preserving the amplification function, as the operational amplifier still operates in its linear region with proper biasing.
3Object-affected harmful factors
If resistance values are adjusted to reduce common phase voltage variations, then input voltage variations can be reduced, but amplification functionality may be compromised
Solution Approach 1:
The common phase feedback circuit independently controls the common phase voltage VCM through the feedback path involving R5. This separate control mechanism allows the circuit to suppress input voltage variations (common mode signals) without affecting the differential amplification function. The feedback acts on the common mode component while the main amplification path remains intact for differential signals.
Data Source
AI summary
There is provided a single-differential converting circuit that can reduce the variations in the input voltage of an operational amplifier sufficiently, made by changes in the voltages input from the exterior, while maintaining the function as the amplifier. The single-differential converting circuit is configured to include: an operational amplifier 104 provided with an inverting input terminal 104a and a noninverting input terminal 104c, for respectively receiving an input signal and a signal indicative of a reference voltage, a noninverting output terminal 104b and an inverting output terminal 104d having opposite polarities to each other; and a positive feedback impedance element 103a connected between one of the two input terminals and one, of the output terminals, having a same polarity with the above one of the two input terminals.