© 2003 Fairchild Semiconductor Corporation

DS011675

www.fairchildsemi.com

April 1994

Revised October 2003

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 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

s Low dynamic power consumption:

s Maximum VCO operating frequency: 12 MHz

Comparator I:

25 ns

Comparator II:

30 ns

Comparator III:

25 ns

s VCO has high linearity and high temperature stability

s 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