74hct9046a NXP Semiconductors, 74hct9046a Datasheet - Page 28

• Manufacturer Part Number: 74hct9046a
• Description: Pll With Bandgap Controlled Vco
• Manufacturer: NXP Semiconductors

Philips Semiconductors
Filter design considerations for PC1 and PC2 of the 74HCT9046A
Figure 30 shows some examples of passive and active filters to be used with the phase comparators of the 74HCT9046A.
Transfer functions of phase comparators and filters are given in Table 3.
Table 3 Transfer functions of phase comparators and filters.
General design consideration.
2003 Oct 30
PC1
PC2
PLL locks on
harmonics at centre
frequency
Noise rejection at
signal input
AC ripple content
when PLL is locked
COMPARATOR
PLL with band gap controlled VCO
PHASE
SUBJECT
A = 10
R3' = R
R
K
K
1
2
3
1
2
3
b
PC1
PC2
= R3
= R4
= R4
= R3'
= R4
= R4
= 25 to 250 k
PC1
PC2
PC1
PC2
PC1
PC2
EXPLANATION
=
5
=
b
= DC gain amplitude
/17;
V
---------- - V r
------ - V r
4
COMPARATOR
5
C2;
C2;
C3;
C2;
C3;
C2;
CC
PHASE
30a.
30b.
30c.
30d.
30e.
yes
no
high
low
f
f
r
r
FIGURE
= 2f
= f
i
; small ripple content at
i
; large ripple content at
28
passive filter
without damping
passive filter with
damping
active filter with
damping
passive filter with
damping
active filter with
damping
FILTER TYPE
DESIGN CONSIDERATION
PC_IN
PC_IN
A = 10
A = 10
F
F
F
F
F
j
j
j
j
j
= 0
= 90
TRANSFER FUNCTION
=
=
=
=
=
5
5
---------------------------- -
1 A
---------------------------- -
1 A
---------------------------- -
1 A
= DC gain amplitude
= DC gain amplitude
-------------------- -
1
------------------------------------- -
1
1
1
1
+
+
+
+
+
1
j
1
+
+
+
j
j
j
j
74HCT9046A
+
j
j
j
Product specification
1
j
2
2
2
1
1
1
1
+
2
1
-------------------- -
1
-------------------- -
1
-------------------- -
2
+
+
+
j
j
j
j
j
j
1
1
1
2
2
2