High Speed CMOS Logic Phase-Locked Loop with VCO and Lock Detector

The CD74HC7046A and CD74HCT7046A high-speed silicon-gate CMOS devices, specified in compliance with JEDEC Standard No. 7A, are phase-locked-loop (PLL) circuits that contain a linear voltage-controlled oscillator (VCO), two-phase comparators (PC1, PC2), and a lock detector. A signal input and a comparator input are common to each comparator. The lock detector gives a HIGH level at pin 1 (LD) when the PLL is locked. The lock detector capacitor must be connected between pin 15 (CLD) and pin 8 (Gnd). For a frequency range of 100kHz to 10MHz, the lock detector capacitor should be 1000pF to 10pF, respectively.

The signal input can be directly coupled to large voltage signals, or indirectly coupled (with a series capacitor) to small voltage signals. A self-bias input circuit keeps small voltage signals within the linear region of the input amplifiers. With a passive low-pass filter, the 7046A forms a second-order loop PLL. The excellent VCO linearity is achieved by the use of linear op-amp techniques.