Multistage Current Driver Circuit for Multi-Muscle Stimulation
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Solution Overview
Problem
Current neuromuscular stimulation devices face limitations due to the need for expensive, high-voltage rated operational amplifiers in conventional Howland pump designs and the inability to simultaneously stimulate multiple muscles efficiently, as they require multiple channels and high power consumption.
Innovation Solution
A multistage driver circuit using a voltage-controlled current source (VCCS) with low-cost components and a bidirectional current mirror circuit, employing folded-cascode topology and low-voltage rated op-amps, allows for high-voltage compliance and simultaneous stimulation of multiple muscles using a single VCCS with adjustable current intensities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If conventional Howland pump design is used with high-voltage rated operational amplifiers, then high-voltage compliance is achieved, but device cost and power consumption increase significantly
Solution Approach 1:
The patent divides the voltage compliance function into two separate stages: a low-voltage Howland pump stage for precise current control and a high-voltage current mirror stage for voltage compliance. This segmentation allows each stage to operate at optimal voltage levels, avoiding the need for expensive high-voltage op-amps while achieving the required voltage compliance capability.
Solution Approach 2:
The patent introduces a folded-cascode current mirror circuit as an intermediary between the low-voltage Howland pump and the tissue load. This current mirror acts as a buffer that translates the low-voltage control signal into high-voltage compliant output, enabling voltage compliance without requiring the operational amplifier to directly handle high voltages.
2Adaptability or versatility
If multiple channels are used to stimulate multiple muscles simultaneously, then stimulation capability is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent makes the return lead of the first muscle channel serve multiple functions: it acts as both the return path for the first muscle and the drive lead for the second muscle. This multi-functionality allows a single VCCS channel to control multiple muscles simultaneously, eliminating the need for separate channels and reducing device complexity.
Solution Approach 2:
The patent merges the return lead of the first muscle channel with the drive lead of the second muscle channel into a single electrical conductor. This consolidation reduces the number of required VCCS channels from multiple independent channels to a single shared channel, simplifying the overall device architecture while maintaining the ability to stimulate multiple muscles.
3Ease of manufacture
If bootstrapped Howland pump is used to reduce cost, then component cost decreases, but common-mode latch-up issues arise requiring wide common-mode input range
Solution Approach 1:
The patent segments the operational amplifier requirements by using a low-voltage rated op-amp exclusively for the Howland pump stage, which operates at low voltages. The high-voltage compliance function is handled by the current mirror stage using inexpensive high-voltage transistors, eliminating the need for expensive wide-common-mode op-amps while maintaining system functionality.
Data Source
AI summary
Neuromuscular stimulation is widely used for rehabilitation and movement assist devices, due to its safety, efficacy, and ease of operation. For repeatable and accurate muscular contractions, a voltage controlled current sources (VCCS) with high compliance is required. Conventional VCCS design requires high-voltage rated operational amplifiers, which are expensive and consume large power. Moreover, conventional stimulators are not viable for simultaneous stimulation of muscle synergies, as they require multiple VCCS operating at the same time. This invention presents a neuromuscular stimulator with a multistage driver circuit wherein, a VCCS connected to an output driving stage comprising of folded-cascode transistor buffers and a bidirectional current mirror circuit. The multistage driver circuit uses inexpensive low-voltage rated operational amplifiers that consume 95% less power. Additionally, we disclose a stimulation method wherein only a single current source drives several output drivers connected in series or parallel to simultaneously stimulate multiple muscles or muscle synergies.