Philips Semiconductors
Product specification
Programmable divide-by-n counter
74HC/HCT4059
APPLICATION INFORMATION
Fig.10 Example showing the application of the PC74HC/HCT4059 in a phase-locked-loop (PLL) for a FM band
synthesizer.
Calculating the minimum and maximum divide-by-n
values:
Figure 11 shows a BCD switch compatible arrangement
suitable for divide-by-5 and divide-by-8 modes, which can
be adapted (with minimal changes) to the other
Output frequency range = 87.6 to 103.8 MHz
(CCIR band 2)
divide-by-modes. In order to be able to preset to any
number from 3 to 256 000, while preserving the BCD
switch compatible character of the JAM inputs, a rather
complex cascading scheme is necessary because the
“4059” can never be preset to count less than 3. Logic
circuitry is required to detect a condition where one of the
numbers to be preset in the “4059” is < 3. In order to
simplify the detection logic, only that condition is detected
where the JAM inputs to terminals 6, 7 and 9 would be
LOW during one count. If such a condition is detected, and
if at least 1 is expected to be jammed into the MSB
counter, the detection logic removes one from the number
to be jammed into the MSB counter (with a place value of
2 000 times the divide-by-mode) and jams the same 2 000
into the “4059” by forcing pins 6, 7 and 9 HIGH.
Channel spacing frequency (fc) = 300 kHz
Division factor prescaler (k) = 10
fc
300
---------
10
Reference frequency (fr) =
=
= 30 kHz
---
k
103.8 MHz
----------------------------
300 kHz
Maximum divide-by-n value =
Minimum divide-by-n value =
= 346
87.6 MHz
= 292
-------------------------
300 kHz
3 MHz
Fixed divide-by-n value =
= 100
------------------
30 kHz
The general circuit in Fig.11 can be simplified considerably
if the range of the cascaded counters do not start at a very
low value.
Application of the “4059” as divide-by-n counter allows
programming of the channel spacing (shown in equations
as 300 kHz). A channel in the CCIR band 2 is selected by
the divide-by-n counter as follows:
Figure 12 shows an arrangement in the divide-by-4 mode,
where the counting range extends in a BCD switch
compatible manner from 99 003 to 114 999.
channel = n − 290
1998 Jul 08
12
NXP [ NXP ]
