74hct9046a NXP Semiconductors, 74hct9046a Datasheet - Page 8

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

Philips Semiconductors
P
This is a positive edge-triggered phase and frequency
detector. When the PLL is using this comparator, the loop
is controlled by positive signal transitions and the duty
factors of SIG_IN and COMP_IN are not important.
PC2 comprises two D-type flip-flops, control gating and a
3-state output stage with sink and source transistors acting
as current sources, henceforth called charge pump output
of PC2. The circuit functions as an up-down counter (see
Fig.5) where SIG_IN causes an up-count and COMP_IN a
down count. The current switch charge pump output
allows a virtually ideal performance of PC2, due to
appliance of some pulse overlap of the up and down
signals. See Fig.8a.
2003 Oct 30
HASE COMPARATOR
PLL with band gap controlled VCO
a. At every
switches are closed simultaneously
for a short period (typically 15 ns).
=
2 (PC2)
approximately 15 ns
PC_IN
pulse overlap of
, even at zero
up
down
Fig.8 The current switch charge pump output of PC2.
I P
I P
both
V CC
PC2_OUT
C2
MBD046
8
The pump current I
voltage and is set by the internal band gap reference of
2.5 V.
Where R
ground.
The current and voltage transfer function of PC2 are
shown in Fig.9.
The phase comparator gain is:
I
K
P
p
=
=
17
------- A r
2
I
P
b
is the external bias resistor between pin RB and
2.5
------- - A
R
down
b. Comparable voltage-controlled switch.
b
up
P
V CC
is independent from the supply
R3'
I P
74HCT9046A
Product specification
C2
PC2_OUT
VC2_OUT
MBD099