ITT - Index of

SAH190
MOS TONE GENERATOR
next identically designed divider with the input
frequency divided by 44/37.
L-__ .--J Clock pulses: ••
and soon
Fig. 9-Block circuit diagram of a 44/1 or
44/37 divider
The divider shown in Fig. 9 consists of two
counters, A and B, and a suppression circuit
U. Counter A counts the clock pulses and each
time when it is reset to its initial position it
emits a pulse to the suppression circuit and to
counter B.
Counter B has the end position 7. It counts
the output pulses of counter A and also controls
the final position of the latter. If counter
B is in the position 1, 2, 3, 5, or 6, counter
A counts up to six. When counter B is in
position 4 or 7, counter A counts up to seven.
Counter B therefore emits an output pulse on
every 44th clock pulse. Each output pulse of
counter A suppresses a clock pulse in the
suppression circuit. At the output of the suppression
circuit, which leads to the input of
the next divider, only 37 output pulses appear
from the 44 clock pulses. The pulse frequency
at the output of the suppression circuit of the
second divider is also reduced by the factor
44/37 with reference to the value at the output
of the suppression circuit of the first divider.
The fraction 44/37 is a good approximation for
the frequency ratio 12v'~
That is the interval of three semitones, a minor
third.
Switchable output dividers are driven from the
outputs of counters B. Oepending on whether
the highest octave is the third or fourth octave
above middle C, a divider ratio of 8 or 4 is
set. These switchable output dividers give
a square wave signal with the pulse duty factor
of 0.5, having a sufficiently small amount of
jitter.
The divider chain A (Fig. 8) generates four
notes at an interval of a minor third in each
case, that is the notes C, A, F* and 0*. The
notes B, G*, F and 0 are generated in divider
chain B. This chain also has four 44/37
dividers, which have a 196/185 divider con_
nected in front of them, reducing the clock
frequency and hence all output frequencies of
divider chain B by the amount of one semitone.
The notes A *, G, E and C* which are still
missing are generated by divider chain C.
A preliminary divider is required here to lower
the clock frequency and hence the four output
frequencies of divider chain C by an amount
equal to one whole tone. This corresponds to
a frequency ratio "~~
The fraction 55/49 is a good approximation
for this value. The preliminary dividers also
operate on the basis of the suppression principle
explained using Fig. 9.
Splitting the divider system into three chains,
each producing four tones, is very advantageous
for integration. The SAH190 (Fig. 10)
which is constructed according to the principle
described, contains a chain with four 44/37
dividers with the associated switchable output
dividers and the two 55/49 and 196/185 preliminary
dividers. By switching over the connection
Option I externally, it is possible to
select one of the two preliminary dividers
or to put both of them out of service. Three
SAH190 units are required to build up a complete
twelve tone generator, as shown in Fig.
2. The following Table 1 shows the exact numerical
values of a twelve tone generator in
accordance with Fig. 2.
Fig. 10-Block circuit diagram of the SAH190
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