An application circuit for an ultrasound pulser-receiver for a medical ultrasoun

Question

An application circuit for an ultrasound pulser-receiver for a medical ultrasound systems is shown in the Fig. below. The MAX4805 is a new voltage-protected pre-amplifier IC that can be integrated into the head of an ultrasound transducer. Assume that the pulser produces large signals that are single cycle rectangular pulses with maximum amplitude of VPP-100V, minimum amplitude of VNN =-100V, and a baseline of 0V. Assume that received echo signals are weak (on the order of millivolts). The connection between the head probe and the main-frame is a co-axial cable. The far-left element is a symbol for a piezoelectric crystal a. b. c. Explain the role of each diode pair in the circuit below What is the maximum voltage across the pre-amp in the MAX4805? What is the maximum voltage delivered to the piezoelectric transducer? CC2 CC1 EET MAXIM MAX4805 MAX4805A SINGLE OPERATIONAL AMPLIFIER) Vcc Vcc2 Vcc OUT IN EE1 EE2 GND EN GSUB HEAD PROBE MAIN FRAME

Explanation / Answer

a. The role of diode pair in parallel to the signal is to clip the voltage to max 0.7 V so that the Amplifiers are not damaged.The role of diodes in series is to allow pulses of both direction and hence protect the signal line from high voltages due to ESD Fault.

b. Voltage across the pre-amp is 0.7 V due to the clipping circuit present in its path.

c. The volatge across the transducer is +/-100 V as the anti parallel diodes act as short.

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