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BJT Amplifiers

BJT Amplifiers

Bipolar Junction Transistors (BJTs) are pivotal components in amplifier circuits, functioning as voltage-controlled current sources in their active region. This characteristic allows them to efficiently control the collector current through variations in the base-emitter voltage. Essentially, BJTs amplify power due to their ability to take a weak input signal and output a much stronger signal.
In BJT amplifier configurations, particularly in common-emitter setups, the transistor's role extends...

Small-Signal Analysis of BJT Amplifiers

Small-Signal Analysis of BJT Amplifiers

Small signal analysis is a fundamental approach used in electronics to understand how a Bipolar Junction Transistor (BJT) amplifier processes signals. In the active region, the BJT is designed for linear amplification. The transistor's behavior under these conditions is governed by its instantaneous base-emitter voltage VBE, a sum of the DC bias VBE, and a small AC signal VBE, resulting in the collector current iC. Here, the collector current has a DC component and an AC component.

Configurations of BJT

Configurations of BJT

Bipolar Junction Transistors (BJTs) are categorized into various types based on their configurations, each with distinct characteristics and applications. The configurations are primarily differentiated by which terminal—base, emitter, or collector—is common to both the input and output circuits.
The common base configuration is noted for its high voltage gain, positioning it as an ideal choice for single-stage amplifier circuits, such as microphone pre-amplifiers. A notable characteristic of...

Working Principle of BJT

Working Principle of BJT

A Bipolar Junction Transistor (BJT), specifically a PNP transistor in a common-base configuration, effectively amplifies or switches electronic signals by controlling the flow of charge carriers. This discussion focuses on its operation in the active mode.
In the PNP configuration, the emitter is heavily doped with positive charge carriers (holes), while the base is lightly doped with negative carriers (electrons). This setup allows for a forward bias across the emitter-base junction,...

Mutual Inductance

Mutual Inductance

Inductance is the property of a device that tells us how effectively it induces an emf in another device. In other words, it is a physical quantity that expresses the effectiveness of a given device.
When two circuits carrying time-varying currents are close to one another, the magnetic flux through each circuit varies because of the changing current in the other circuit. Consequently, an emf is induced in each circuit by the changing current in the other. Therefore, this type of emf is called...

Small-Signal Analysis of MOSFET Amplifiers

Small-Signal Analysis of MOSFET Amplifiers

In small-signal analysis, a MOSFET transistor amplifier acts as a linear amplifier when operating in its saturation region. The gate-to-source voltage (VGS) of the MOSFET is the sum of the DC biasing voltage and the small time-varying input signal. This combination sets up the operating point and modulates the drain current (ID) that flows from the drain to the source. When a small AC signal is superimposed on the DC bias voltage at the gate, the instantaneous drain current comprises three...

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Related Experiment Video

Updated: May 14, 2026

MRM Microcoil Performance Calibration and Usage Demonstrated on Medicago truncatula Roots at 22 T

MRM Microcoil Performance Calibration and Usage Demonstrated on Medicago truncatula Roots at 22 T

Published on: January 16, 2021

Multi-turn transmit coil to increase b1 efficiency in current source amplification.

N Gudino¹, M A Griswold

¹Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio 44106, USA.

Magnetic Resonance in Medicine

|February 13, 2013

Summary

This summary is machine-generated.

A novel multi-turn transmit surface coil design significantly boosts B1 efficiency by nearly threefold. This advancement enhances MRI performance without increasing heat, enabling the use of lower-rated components.

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Area of Science:

Magnetic Resonance Imaging (MRI)
Electrical Engineering
Coil Design

Background:

Current MRI systems face limitations in B1 field efficiency.
Optimizing B1 efficiency is crucial for improving image quality and reducing scan times.
On-coil current source amplification presents challenges in heat dissipation and component stress.

Purpose of the Study:

To introduce and evaluate a multi-turn transmit surface coil design.
To enhance B1 efficiency in MRI transmit systems utilizing current source amplification.
To assess the impact of the new coil design on heat dissipation and component requirements.

Main Methods:

Tested three coil designs with an on-coil current-mode class-D amplifier and current envelope feedback.
Performed benchtop and 1.5 T MRI scanner imaging evaluations.
Measured power field-effect transistor case temperature to assess heat dissipation across different configurations and current levels.
Evaluated a lower power-rated transistor with the multi-turn coil to determine B1 gain potential.

Main Results:

The multi-turn surface coil achieved an almost threefold increase in B1 field strength.
This B1 gain was realized without an increase in heat dissipation at the amplifier output stage.
Similar B1 gains were observed when using a lower power-rated field-effect transistor with the multi-turn coil.

Conclusions:

The multi-turn coil design improves B1 per current efficiency, reducing heat dissipation per unit of B1.
This enhanced efficiency permits the use of field-effect transistors with lower current ratings and reduced port capacitances.
The findings suggest a potential for improved overall performance in on-coil current source transmit systems.