Page 43 - Analog Circuit Design Art, Science, and Personalities

On Being the Machine

Figure 5-1.
Block diagram of
"recirculating
loop" mercury
acoustic memory
used in the
Univac I circa
1949.
In ti
Out

responding to a video bandwidth of about 2.5 MHz or an RF bandwidth of about 5
MHz.
On the surface, this might seem like a straightforward problem. Indeed, referring
to Figure 5-2, the initial brute force design, in part based on competent considera-
tions of practical transducers and ultrasonic attenuation characteristics, called for a
synchronously tuned system with each component of the system tuned to 11.25
MHz. It might have seemed quite obvious to cut the transducers to the frequencies
that they would be expected to vibrate at and to tune the RF amplifiers to the same
frequency. However, the designers of the system found that they could not obtain
even a close approximation to the transient rise times needed, for the mechanical
physics of the transducers established their bandwidth, and therefore, regardless of
the width of the individual stages of the RF amplifier or the number of stages em-
ployed, the desired performance could not be obtained.

Figure 5-2.
Results of "brute
force" approach
to design of
the circuit in
Figure 5-1.
I
I 11.25MHz &
Relative 1 A

I

4mplitude
Overall

w
Envelope
Translent
Response

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