74HC/HCT4046A

General description

The 74HC/HCT4046A are high-speed Si-gate CMOS devices and are pin compatible with the '4046' of the '4000B' series. They are specified in compliance with JEDEC standard no. 7A.

The 74HC/HCT4046A are phase-locked-loop circuits that comprise a linear voltage-controlled oscillator (VCO) and three different phase comparators (PC1, PC2 and PC3) with a common signal input amplifier and a common comparator input.

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 '4046A' forms a second-order loop PLL. The excellent VCO linearity is achieved by the use of linear op-amp techniques.

The VCO requires one external capacitor C1 (between C1_A and C1_B) and one external resistor R1 (between R1 and GND) or two external resistors R1 and R2 (between R₁ and GND, and R₂ and GND). Resistor R1 and capacitor C1 determine the frequency range of the VCO. Resistor R2 enables the VCO to have a frequency offset if required.

The high input impedance of the VCO simplifies the design of low-pass filters by giving the designer a wide choice of resistor/capacitor ranges. In order not to load the low-pass filter, a demodulator output of the VCO input voltage is provided at pin 10 (DEM_OUT). In contrast to conventional techniques where the DEM_OUT voltage is one threshold voltage lower than the VCO input voltage, here the DEM_OUT voltage equals that of the VCO input. If DEMOUT is used, a load resistor (RS) should be connected from DEMOUT to GND; if unused, DEM_OUT should be left open. The VCO output (VCO_OUT) can be connected directly to the comparator input (COMP_IN), or connected via a frequency-divider. The VCO output signal has a duty factor of 50% (maximum expected deviation 1%), if the VCO input is held at a constant DC level. 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.

The only difference between the HC and HCT versions is the input level specification of the INH input. This input disables the VCO section. The sections of the comparator are identical, so that there is no difference in the SIG_IN (pin 14) or COMP_IN (pin 3) inputs between the HC and HCT versions.

Features

• Low power consumption
• Centre frequency of up to 17 MHz (typ.) at VCC = 4.5 V
• Choice of three phase comparators: EXCLUSIVE-OR;
• edge-triggered JK flip-flop;
• edge-triggered RS flip-flop
• Excellent VCO frequency linearity
• VCO-inhibit control for ON/OFF keying and for low standby power consumption
• Minimal frequency drift
• Operating power supply voltage range:
• VCO section 3.0 to 6.0 V
• digital section 2.0 to 6.0 V
• ? Zero voltage offset due to op-amp buffering
• Output capability: standard
• ICC category: MSI

Products/packages

Pricing/ordering/availability

Applications

• Electronic tuning in UHF television tuners
• Voltage controlled oscillators (VCO).

Block diagrams/pinning

Design support

Support Documents

HCT_USER_GUIDE; HC/T User Guide (1997-11-01)

Parametrics/similar products

Similar products
74HC/HCT4046A links to the similar products page containing an overview of products that are similar in function or related to the type number(s) as listed on this page. The similar products page includes products from the same catalog tree(s), relevant selection guides and products from the same functional category.

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