Differential Voltage-Current Converter for Low-Distortion Sine Output
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Solution Overview
Problem
Conventional voltage-current converters with high impedance input in single-ended structures suffer from low isolation from the substrate, coupling noise, and high harmonic distortion, particularly in applications with high-frequency sinusoidal signals, which complicates the generation of a pure sinusoidal current tone with high spurious-free dynamic range.
Innovation Solution
A circuit architecture with a fully differential structure that mirrors the input voltage to achieve high impedance input, utilizing current mirrors and selective switches to maintain low harmonic distortion, and buffers the output at a low impedance circuit to reduce substrate and coupling noise, facilitating a simpler design for sinusoidal current generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single-ended high impedance input structure is used, then the input impedance is high, but substrate isolation is low and coupling noise is high
Solution Approach 1:
The patent divides the single-ended input structure into a fully differential structure with separate positive and negative input terminals. This segmentation allows the signal to be represented as a difference between two complementary signals, which provides high input impedance while simultaneously rejecting substrate noise and coupling noise through the differential configuration.
Solution Approach 2:
The patent employs asymmetric routing and positioning of the differential signal paths relative to the substrate noise sources. By strategically placing the differential pair and using asymmetric grounding techniques, the circuit achieves noise cancellation while maintaining high input impedance, resolving the contradiction between impedance and noise susceptibility.
2Device complexity
If a single-ended structure is used, then the circuit is simpler, but harmonic distortion is high
Solution Approach 1:
The patent segments the signal processing into differential pairs throughout the circuit architecture. By using differential amplifiers, differential current mirrors, and differential output stages, the circuit maintains symmetry that cancels even-order harmonics, thereby reducing total harmonic distortion while keeping the overall circuit complexity manageable through modular differential building blocks.
Solution Approach 2:
The patent changes the operating parameters by using differential signaling instead of single-ended signaling. This parameter change transforms the circuit operation mode, allowing for better linearity and lower harmonic distortion. The differential configuration enables the circuit to operate in a region where distortion is minimized, achieving high signal fidelity without excessive complexity.
3Object-affected harmful factors
If a fully differential architecture is used, then substrate noise is reduced, but input impedance compatibility with sinewave generator output stage is reduced
Solution Approach 1:
The patent implements a fully differential architecture where the input impedance is dynamically adapted through the differential configuration. The differential structure naturally provides high input impedance while maintaining compatibility with sinewave generator output stages by using balanced differential signaling. The dynamic balance between the two differential inputs allows noise rejection while preserving impedance matching capabilities.
Solution Approach 2:
The patent introduces differential signaling as an intermediary between the substrate noise environment and the sinewave generator output stage. This differential intermediary transforms the single-ended signal from the generator into a differential signal, allowing the circuit to benefit from noise rejection while maintaining compatibility with the generator's output characteristics through proper differential-to-single-ended conversion at the output.
Data Source
AI summary
An embodiment voltage-current converter circuit comprises a first amplifier and a second amplifier having homologous first input nodes configured to receive a voltage signal therebetween as well as homologous second input nodes having a resistor coupled therebetween. First and second current mirror circuits are provided comprising first input transistors having their control terminal coupled to the output nodes of the amplifiers. First and second current sensing circuitry having first and second current output nodes are coupled to the current mirror output nodes of the current mirror circuits and configured to provide therebetween a current which is a function of the voltage signal between the homologous first input nodes of the amplifier.