April 1994
Revised April 1999
7
4
VH
C40
46 CMOS Phase
Lock
Loop
© 1999 Fairchild Semiconductor Corporation DS011675.prf www.fairchildsemi.com
74VHC4046
CMOS Phase Lock Loop
General Description
The VHC4046 is a low power phase lock loop utilizing
advanced silicon-gate CMOS technology to obtain high fre-
quency operation both in the phase comparator and VCO
sections. This device contains a low power linear voltage
controlled oscillator (VCO), a source follower, and three
phase comparators. The three phase comparators have a
common signal input and a common comparator input. The
signal input has a self biasing amplifier allowing signals to
be either capacitively coupled to the phase comparators
with a small signal or directly coupled with standard input
logic levels. This device is similar to the CD4046 except
that the Zener diode of the metal gate CMOS device has
been replaced with a third phase comparator.
Phase Comparator I is an exclusive OR (XOR) gate. It pro-
vides a digital error signal that maintains a 90 phase shift
between the VCO’s center frequency and the input signal
(50% duty cycle input waveforms). This phase detector is
more susceptible to locking onto harmonics of the input fre-
quency than phase comparator I, but provides better noise
rejection.
Phase comparator III is an SR flip-flop gate. It can be used
to provide the phase comparator functions and is similar to
the first comparator in performance.
Phase comparator II is an edge sensitive digital sequential
network. Two signal outputs are provided, a comparator
output and a phase pulse output. The comparator output is
a 3-STATE output that provides a signal that locks the VCO
output signal to the input signal with 0 phase shift between
them. This comparator is more susceptible to noise throw-
ing the loop out of lock, but is less likely to lock onto har-
monics than the other two comparators.
In a typical application any one of the three comparators
feed an external filter network which in turn feeds the VCO
input. This input is a very high impedance CMOS input
which also drives the source follower. The VCO’s operating
frequency is set by three external components connected
to the C1
A
, C1
B
, R
1
and R
2
pins. An inhibit pin is provided
to disable the VCO and the source follower, providing a
method of putting the IC in a low power state.
The source follower is a MOS transistor whose gate is con-
nected to the VCO input and whose drain connects the
Demodulator output. This output normally is used by tying
a resistor from pin 10 to ground, and provides a means of
looking at the VCO input without loading down modifying
the characteristics of the PLL filter.
Features
a73 Low dynamic power consumption: (V
CC
= 4.5V)
a73 Maximum VCO operating frequency: 12 MHz
(V
CC
= 4.5V)
a73 Fast comparator response time (V
CC
= 4.5V)
Comparator I: 25 ns
Comparator II: 30 ns
Comparator III: 25 ns
a73 VCO has high linearity and high temperature stability
a73 Pin and function compatible with the 74HC4046

Ordering Code:
Surface mount packages are also available on Tape and Reel. Specify by appending the suffix letter “X” to the ordering code.
Order Number Package Number Package Description
74VHC4046M M16A 16-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-012, 0.150 Narrow
74VHC4046MTC MTC16 16-Lead Thin Shrink Small Outline Package (TSSOP), JEDEC MO-153, 4.4mm Wide
74VHC4046N N16E 16-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300 Wide