Ultrasound Physics
Welcome
Ultrasound Basics
Vibration and Wave
Ultrasound Parameters
Medium Acoustic Property
Ultrasound Reflection
Ultrasound Refraction
Ultrasound Scattering
Ultrasound Attenuation
Ultrasound Application
Ultrasound Transducer
Piezoelectric Effect
Transducer Cosntruction
Array Transducer
Beamforming
Ultrasound Beamformation
Beam Focus
Beam Steering
Imaging
Pulse-echo Method
Imaging Method
Imaging Resolution
Ultrasound Imaging Artifacts
Signal and Circuit
Unipolar Transmitter
Bipolar Transitter
Transceiverg
Time Gain Control
Conditioning
Preprocessing and Postprocessing
Flow Dection
Doppler Effect
Continue Wave Doppler (CW)
Pulse wave Doppler(PW)
Color Flow Imaging
Safety
Intensity
Mechanical Index
Thermal Index
Cavitation
Regulations
Ultrasound Bipolar Transmitter, Pulser
How it works:
This circuit transmits a bipolar burst and the number of cycles depends on the trigger signal. A single bipolar pulse is usually used in diagnostic applications. The circuit requires two high voltage (HV) supplies with one positive and one negative. The trigger signal has to be well controlled with one positive and one negative, having 180° phase difference. The negative trigger signal turns on MOSFET M1 sending a positive pulse on the load RL through D1. The followed positive trigger signal turns on M2 and sends a negative pulse on RL via D2.
Guideline for the Component Value Selection:
M1: Three parameters for M1 are important.
Vds: how much voltage it can handle. This parameter has to be at least 1.2 times higher than your pulse amplitude. For example, if you want to transmit a 100v peak-to-peak bipolar pulse on the transducer, the Vds for M1 & M2 should be 120 - 150 v.
Cgs, tr, tf: Switch speed. These parameters determine how fast M1 &M2 can turn on/off. Tr, tf, is determined by Cgs, and testing circuit. With a special designed driving circuit, a faster switch speed can be achieved. Normally, tr/tf should be less than a quarter of your center period. If you excite the circuit at 10MHz, the center period is 100ns, and tr+tf should be less than 50ns.
RDS(on): the on resistance. It should be less than five percent of the transducer impedance.
Diode: current rating, make sure it can handle the peak current.
Additional circuits are required to make above transmitter work properly including trigger signal coupling and MOSFET drivers. The complementary dual pulse signal can be generated from an edge signal (a single pulse with uncontrolled width).
With some modifications of the above circuit, only one positive HV is required and cost will be reduced. However, for each transmit, only one cycle bipolar pulse is transmitted and it satisfies most diagnostic applications. Transformer coupling is required to transmit a burst.
The following modules includes combinations of above functions.