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No. 2D730-148E*O
4.1.2
TR
(1)
Outline
The two primary functions of this board are first, to generate and deliver the transmit
signals to the TI board, and second, to receive, amplify, and deliver the echo signals to the
RC board.
(2)
Description of functions and operation
(a)
Transmit pulser
This is the circuit which drives the piezoelectric elements inside the transducer
electrically.
The number of transmission waves and the pulse duration are controlled
by the TXPG.
The transmission
pulse (bipolar transmission waveform)
is generated
in the circuit by
increasing the low-voltage
power supply in the transformer.
In addition, this pulser has the two blocks in the transformer
primary-winding
side.
Transmission voltage switching for each rate is achieved by applying different
voltages to each of the blocks (dual pulser).
(b)
Transmit pulse generation
The transmit pulse generation section is comprised of the following subsections:
transmit control bus (TC bus), /TXCL and /TCWR signals, digital control, PECL
clocks (four blocks), PECL synchronize signals (two blocks), power supply, 64 pairs
of transmit control signals (Hout and Lout), and a transmit pulse generation
ASIC
(TXPG).
(c)
Preamplifier and variable gain amplifier (functions in RXAR ASIC)
They amplify the echo signals from the piezoelectric element.
The gain in the preamplifier is fixed to +I4 dB. The variable gain amplifier sets the
gain from 0 to +75 dB by changing the control voltage (VTGC) from 0 to 1 V.
(d)
Antialiasing filter (functions in RXAR ASIC)
This filter prevents the aliasing that occurs when the analog echo signals are
converted to digital signals in the RC board.
The cutoff frequency
can be changed from 4 to 16 MHz by changing the control
voltage (VAAC) from 0 to 1 V.
The RXAR ASIC is set as given below in the SCW mode.
The gain is fixed to 20 dB and the antialiasing filter is bypassed.
4-9
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