Philips 50 T Series, Руководство по обслуживанию

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Chapter 9 - Theory of Operation
Theory of Operation
Transmitter Functional Blocks
US Gating
The US Gating circuitry generates the gated 1 MHz bursts for the US driver
and the US receiver necessary in a pulsed doppler system.
The burst repetition rate is 3.2 kHz. The US driver burst has a duration of
96
µ
sec. The burst for the Receiver’s demodulator, which also has a duration
of 96
µ
sec, follows the driver bursts with a delay of 32
µ
sec. This timing gives
a sensitive depth range from 2.4cm up to 16.8cm (with a sound velocity in
human tissue of 1500 m/sec.)
US Driver
The US Driver circuitry drives the ultrasound transducer crystals with the
bursts delivered by the US Gating module. The output amplitude is 4V peak
to peak. The drivers output goes to a high impedance state when the driving
burst is inactive.
US Receiver
The US Receiver consists of three submodules:
• Preamplifier
• Demodulator
• Bandpass filter with amplification
The preamplifier amplifies the small doppler shifted 1MHz signals from the
transducer. These are converted to the low frequency baseband by the