Ramp Generator - MCi JH-400B Series Technical Manual

3.7.1
RAMP GENERATOR
(See Schematic, Figure 29, Page 10-21)
Two "one shot" multivibrators alternately trigger each other and
clock a BCD COU~JTER through each step from 0000 to 1001
(0 through 9),
resets, then repeats the sequence. The counter drives a BCD TO
DECIMAL DECODER whose decimal outputs go LOW as the equivalent
binary input is fed to it.
The DECODER drives a D/A
(Digital
to
Analog)
CONVERTER which is
contoured to produce a logarithmic change in ten steps. The
VOLTAGE DIVIDER, R3-Rl2, feeds a signal voltage to IC5 which varies
from +15 volts to +7.5 volts, depending on which output of the
DECODER is ?Ulled to ground potential.
The
RA~1P
output is a positive-going, 15 volt, 10 step, logarithmic
shaped wave, with a repetition rate of about 5 to 6 kHz.
The BCD information developed by the COUNTER ·is also fed into buses
to be used by all of the Channel Cards.
3.7.2
CHANNEL BOARDS
(See Schematic, Figure28, Page 10-19)
The incoming AUDIO SIGHAL is rectified and filtered to produce a
changing DC voltage which is equivalent to the AUDIO LEVEL. This
level is compared to the RAMP coming from the MASTER CONTROL BOARD.
When the RAMP exceeds the AUDIO SIGNAL level, the cm1PARATOR output
switches to the positive rail and sends a signal to the QUAD LATCH.
The QUAD LATCH receives as its input signal, BCD information from
the MASTER
CO~TROL
BOARD. This BCD information is IN STEP with the
RAMP
(since the BCD drives the D/A converter which produces the RAMP).
When
the COHPARATOR switches, the QUAD LATCH is clocked, and its cutout
matches the input it is receiving at the moment.
NOTE:
The QUAD LATCH CLOCK works ONLY on the POSITIVE-GOING EDGE of the signal •
I t will not resp:::>nd
to
either a HI level or a LO level signal.
The DIGITAL "WORD" on the out?Ut of the QUAD LATCH is held until a
new CLOCK PULSE is received from the COMPARATOR.
The output of the QUAD LATCH drives a BCD TO DECIMAL DECODER. The
decimal output corresponding to the digital "WORD" goes to ground
potential and turns ON its light.
NOTE:
Outputs corresponding to "0" and "1" have not been supplied with a
light· This means that the DISPLAY is unlighted when the AUDIO SIGNAL
is at its lowest level.
A NEW LEVEL COMPARISON IS COMPLETED EVERY
0.2
MILLISECONDS,
JH-400B Page 3-9