UNISONIC TECHNOLOGIES CO., LTD

U74HCT7046

CMOS IC

www.unisonic.com.tw

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Copyright © 2012 Unisonic Technologies Co., Ltd

QW-R502-851.A

PHASE LOCKED LOOP WITH VCO &

LOCK DETECTOR

DESCRIPTION

The U74HCT7046 is phase-locked-loop circuit that comprise a linear

voltage-controlled oscillator (VCO), two-phase comparators (PC1, PC2),

a lock detector, a common signal input amplifier and a common

comparator input.

The lock detector capacitor should be connected between pin

15(CLD) and pin 8(GND).For a frequency range of 100kHz to 10MHz,the

lock detector capacitor must be 1000pF to 10pF,respectively.

The signal can be directly coupled to large voltage signals, or with a

series capacitor coupled to small signals. Small voltage signals can be

kept within the linear region of the input amplifiers with a self-bias input

circuit. The U74HCT7046 and a passive low-pass filter form a

second-order loop PLL. With a linear op-amp, the VCO achieves

excellent linearity.

The VCO requires external capacitor and resistor. R1 (between R1

and GND) and capacitor C1 (between C1A and C1B) determine the

frequency range of the VCO. R2 (between R2 and GND) enables the

VCO to have a frequency offset if required.

For the high input impedance of the VCO, the design of low-pass filters is simplified, and the designer has a wide

(maximum expected deviation 1%). A LOW level at the inhibit input (INH) enables the VCO and demodulator, while

a HIGH level turns both off to minimize standby power consumption.

FEATURES

* Operating Power Supply Voltage Range: Digital Section 4.5 to 5.5 V

VCO Section 4.5 to 5.5 V

* VCO-Inhibit Control For ON/OFF Keying and for Low Standby Power Consumption

* Minimal Frequency Drift

* Zero Voltage Offset due to OP-Amp Buffering