Ultrasound Probe Buffer With Constant-gm Class AB Common-Source Amplifier
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Solution Overview
Problem
Ultrasonic transducer handles face challenges in transmitting sufficient electrical signal power to drive cables, requiring a mechanism to boost signal power while minimizing distortion and noise, and existing solutions often limit bandwidth and consume excessive power.
Innovation Solution
A high-input impedance transconductance amplifier with a common-source class AB configuration and series-series local feedback is implemented, utilizing MOSFETs and operational amplifiers to provide low-noise and low-distortion performance, along with a probe buffer design that includes source degeneration resistors and capacitors to maintain constant transconductance and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a transimpedance amplifier is used to maximize received current signal, then input impedance is low, but electrical impedance matching capability is lost
Solution Approach 1:
The amplifier is divided into two distinct stages: a transimpedance amplifier stage for current signal amplification with low input impedance, and a voltage amplifier stage for voltage sensing with high input impedance. This segmentation allows each stage to perform its specialized function optimally without compromising the other capabilities.
Solution Approach 2:
An intermediate coupling mechanism (capacitor or buffer stage) is introduced between the transimpedance amplifier and the voltage amplifier to transfer the signal while maintaining the impedance characteristics of each stage. This intermediary enables both current signal amplification and voltage sensing capabilities to coexist.
2Measurement precision
If a common-source single or two-stage voltage amplifier is used for voltage sensing, then voltage amplification is achieved, but bandwidth is limited
Solution Approach 1:
The amplifier employs dynamic biasing and frequency compensation techniques to maintain high bandwidth performance. The common-source stage is optimized with appropriate load impedance and compensation capacitance to extend the frequency response while maintaining voltage sensing capability.
3Ease of operation
If the transducer handle transmits electrical signals to drive the cable, then signal transmission is achieved, but sufficient electrical signal power is not transmitted
Solution Approach 1:
The amplifier circuit is designed to deliver high current capability to rush through the cable capacitance quickly, enabling effective signal transmission over the cable length. The high current output stage compensates for power losses in the cable by delivering sufficient power directly to drive the cable load.
4Measurement precision
If a high-precision amplifier with very low input referred current and voltage noise is used, then output acquisition from high impedance transducer is improved, but device complexity increases
Solution Approach 1:
The patent replaces complex low-noise amplifier designs with a simpler operational amplifier-based implementation. By using standard operational amplifiers with proper circuit topology (transimpedance stage followed by voltage amplifier stage), the design achieves low noise performance without requiring complex specialized low-noise amplifier circuits.
Data Source
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AI summary
An ultrasound probe buffer is provided. The ultrasound probe buffer may include a high impedance amplifier having a common-source core stage with series-series local feedback. The high impedance amplifier may include a first MOSFET and a second MOSFET, wherein a source terminal of the first MOSFET is coupled to a source terminal of the second MOSFET.