Differential Current Buffer Circuit for High-Voltage Wideband Sources
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Solution Overview
Problem
Existing current sources, particularly the Howland current source, are limited in their range of application, gain choice, and output current, and commercially available fully differential operational amplifiers have limitations in maximum voltage and bandwidth, making them unsuitable for high-voltage electrical stimulation and bioimpedance measurements.
Innovation Solution
A differential current buffer circuit with wide bandwidth, high accuracy, and high output impedance is designed, utilizing a differential input stage with complementary current mirrors and cascode current mirrors, connected to a DC and alternating current source with quad-feedback enhanced Howland current source configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If commercially available fully differential operational amplifiers are used, then the device complexity is reduced, but the maximum voltage and bandwidth are limited
Solution Approach 1:
The operational amplifier is divided into separate functional blocks: a differential input stage and output current mirrors. This segmentation allows each block to be optimized independently, with the input stage focusing on differential signal processing and the current mirrors handling high-voltage output and bandwidth extension, thereby achieving high bandwidth without excessive overall complexity
Solution Approach 2:
The patent extends the voltage range by adding multiple supply voltage rails (first positive, first negative, second positive, second negative supply voltages) at different hierarchical levels. This multi-dimensional voltage architecture enables the circuit to achieve high voltage output swing and wide bandwidth that cannot be obtained with conventional single-rail operational amplifiers
2Ease of operation
If commercially available fully differential operational amplifiers are used, then the ease of operation is improved, but the maximum voltage output is limited
Solution Approach 1:
The operational amplifier is segmented into a differential input stage and separate output current mirror stages. The current mirrors are configured with multiple supply voltage connections that enable high voltage output swing while maintaining the simplified operation of a single differential input stage, thus achieving high voltage capability without sacrificing ease of use
Solution Approach 2:
The patent creates a composite operational amplifier structure combining different functional elements (differential input stage, cascode current mirrors, multi-voltage supply networks) into a unified high-performance device. This composite architecture integrates the advantages of various sub-circuits to achieve both high voltage output and operational simplicity
3Measurement precision
If the Howland current source configuration is used, then the measurement precision is improved, but the range of application and gain choice are limited
Solution Approach 1:
The patent implements a fully differential operational amplifier with adjustable gain through the transimpedance amplifier configuration. The differential output stage with independent current mirrors allows dynamic adjustment of gain and output range, enabling the circuit to adapt to various application requirements while maintaining precise current control through feedback mechanisms
4Power
If discrete components are used to build operational amplifier, then the maximum voltage rating is improved, but the manufacturing precision and thermal coupling deteriorate
Solution Approach 1:
The patent merges multiple discrete components (transistors, resistors, current sources) into an integrated operational amplifier circuit. The differential input stage and current mirrors are combined in a unified architecture with shared biasing and supply networks, achieving high voltage rating through integrated design while maintaining manufacturing precision through standardized fabrication processes
Data Source
AI summary
A differential current buffer circuit comprises a differential input stage supplied from a first positive and a first negative supply voltage. The input stage has a first input circuit connected between first current paths of a first current and a second mirror connected between second positive and negative supply voltages. A second input circuit is connected between first current paths of a third and a fourth current mirror connected between the second positive and negative supply voltages. The second positive voltage is higher than the first positive supply voltage, and the second negative voltage is lower than the first negative supply voltage. A first and a second output of the differential current buffer circuit are tapped off between the respective second current paths of the first and second current mirrors and the respective second current paths of the third and fourth current mirrors, respectively.