Motorola CMOS Logic, Руководство пользователя, Страница: 162 / 571

MOTOROLA CMOS LOGIC DATA MC14046B
6–124
Typical Low–Pass Filters
NOTE: Sometimes R3 is split into two series resistors each R3
÷
2. A capacitor CC is then placed from the midpoint to ground. The value for
CC should be such that the corner frequency of this network does not significantly affect
ω
n. In Figure B, the ratio of R3 to R4 sets the
damping, R4
^
(0.1)(R3) for optimum results.
Figure 3. General Phase–Locked Loop Connections and Waveforms
Waveforms
Note: for further information, see:
(1) F. Gardner, “Phase–Lock Techniques”, John Wiley and Son, New York, 1966.
(2) G. S. Moschytz, “Miniature RC Filters Using Phase–Locked Loop”, BSTJ, May, 1965.
(3) Garth Nash, “Phase–Lock Loop Design Fundamentals”, AN–535, Motorola Inc.
(4) A. B. Przedpelski, “Phase–Locked Loop Design Articles”, AR254, reprinted by Motorola Inc.
PCAin
@ FREQUENCY f
′
PCBin
14
3
PHASE
COMPARATOR
EXTERNAL
LOW–PASS
FILTER
VCO
2 OR 13
PC1out
OR
PC2out
VCOin
9
9
10
4
EXTERNAL
÷
N
COUNTER
R1 R2
11 12 6 7
CIA CIB
CI
SFout
RSF
VCOout
@ FREQUENCY Nf
′
= f
(a)
INPUT
R3
OUTPUT
C2
2fC
[
1
p
2
p
fL
R3 C2
Ǹ
(a)
INPUT
R3
OUTPUT
R4
C2
Typically:
R4 C2
+
6N
fmax
–
N
2
p D
f
(R3
)
3, 000
W
) C2
+
100N
D
f
fmax2
– R4 C2
∆
f = fmax – fmin
Definitions: N = Total division ratio in feedback loop
K
φ
= VDD/
π
for Phase Comparator 1
K
φ
= VDD/4
π
for Phase Comparator 2
KVCO
+
2
p D
fVCO
VDD – 2 V
2
p
fr
10
for a typical design
ω
n
^
(at phase detector input)
ζ
^
0.707
LOW–PASS FILTER
Filter A Filter B
w
n
+
K
f
KVCO
NR3C2
Ǹ
z +
N
w
n
2K f KVCO
F(s)
+
1
R3C2S
)
1
w
n
+
K
f
KVCO
NC2(R3
)
R4)
Ǹ
z +
0.5
w
n (R3C2
)
N
K f KVCO
)
F(s)
+
R3C2S
)
1
S(R3C2
)
R4C2)
)
1
PCAin
PCBin
PC1out
VCOin
VDD
VSS
VOH
VOL
VOH
VOL
VOH
VOL
PCAin
PCBin
PC2out
VCOin
LD
VDD
VSS
VOH
VOL
VOH
VOL
VOH
VOL
VOL
VOH
Phase Comparator 1 Phase Comparator 2
SOURCE
FOLLOWER