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7.1 ANALOG CIRCUIT
A square wave at the desired frequency is generated by a
internal
to the microprocessor.
the input of switched capacitor filters for smoothing into a sine
wave.
The
filter
frequencies
except
Since
there are two filter output configurations, a
(switch) is used to route the sine wave to the attenuator block.
The
attenuator
resolution
by an 8 bit Digital to Analog Converter
DAC,
which is processor driven, controls the attenuator in
Normal
Mode at a resolution of 5.0 dB.
used only for calibration purposes in the Calibration Mode.
total
dynamic range of the attenuator is 112 dB.
required to
provide
overhead dB range required for calibration per frequency.
Following
the
Range extension is accomplished by increasing the gain of the OP-
Amp, which is sourced by the attenuator, by 10 dB.
The range extender circuit applies the pure tone sine wave to the
input of
the output routing switches.
signal
to either the left or right power amplifier, however, it
is
never
applied to both simultaneously.
power amplifiers, in turn, drive the left and right earphones.
7.2 DIGITAL CIRCUIT
The
heart
of
microcomputer.
power consumption.
bit programmable I/O ports,
K Bytes of ROM, 256 Bytes of RAM, 512 Bytes of EEPROM,
(A/D),
8
Counter/Timer, and Serial Port Interface.
very few external
external
EPROM
miscellaneous decodes, line multiplex, etc.
The
CPU executes the commands stored in ROM and
instructions
are
conjunction
with
pertinent
calibration data for the selected parameters.
parameters
could be:
clock
frequencies
instructions, or as simple as an ON/OFF command to a CMOS switch.
In
summary,
the digital circuitry in the GSI
analog
and
display circuitry in such a manner
panel selections are processed and acted upon accordingly.
section is programmed as Low
KHz where it is configured for
8
is a voltage controlled amplifier set to
the Normal Mode HL range as
attenuator
is a =10 dB
the
digital
This CPU was chosen for its flexibility and
Functions available from the device are (5) 8
an
8
support devices required.
(32 K Bytes), a programmable
the
result of a
look-up tables, and such,
HL calibration for a
for the switched capacitor
This square wave is applied to
The .5 dB resolution is
range
The switches
The
circuitry
is
bit analog to digital
As a result, there are
front
panel
specific
timer
Pass
for
all
Band
Pass.
multiplexer
.5
(DAC).
The
the
The
This range is
well as
the
extension
block.
apply
left and
right
a
MC
68HC11A1
converter
If there is an
timer,
EPROM.
These
command
for
the
applying
Such
frequency,
filters,
display
17 controls
that
the
front
dB
the
low
and
in
the
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