The 74LS14 is a Hex Schmitt-Trigger Inverter, meaning it contains six independent NOT gates with Schmitt-trigger inputs.
Unlike a standard inverter (e.g., 74LS04), the Schmitt-trigger input introduces hysteresis. This makes the IC ideal for cleaning up noisy signals or converting slow-rising/falling analog inputs into sharp digital transitions.
Part number: SN74LS14, HD74LS14, DM74LS14
Function: Hex Inverter with Schmitt Trigger Inputs
Package: DIP 14 Pin, SOIC 14 Pin
Manufacturer: Fairchild, Motorola, Texas Instruments
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Description
The 74LS14 contains logic gates / inverters which accept standard TTL input signals and provide standard TTL output levels. They are capable of transforming slowly changing input signals into sharply defined, jitter-free output signals. Additionally, they have greater noise margin than conventional inverters. Each circuit contains a Schmitt trigger followed by a Darlington level shifter and a phase splitter driving a TTL totem pole output. The Schmitt trigger uses positive feedback to effectively speed-up slow input transitions, and provide different input threshold voltages for positive and negative-going transitions. This hysteresis between the positive-going and negative-going input thresholds (typically 800 mV) is determined internally by resistor ratios and is essentially insensitive to temperature and supply voltage variations.
This device contains six independent gates each of which performs the logic INVERT function. Each input has hysteresis which increases the noise immunity and transforms a slowly changing input signal to a fast changing, jitter free output.
Pinout
How It Works — Schmitt Trigger & Hysteresis
A normal inverter switches at a single threshold voltage.
The 74LS14 Schmitt-trigger inverter switches at two different thresholds:
When input voltage rises past V_T+, the output switches LOW → HIGH.
When input falls below V_T−, the output switches HIGH → LOW.
The difference (ΔV_H = V_T+ − V_T−) ensures stable switching, rejecting small oscillations or noise around the threshold.
Features
1. Operation From Very Slow Edges
2. Improved Line-Receiving Characteristics
3. High Noise Immunity
Applications
1. HVAC Gateways
2. Residential Ductless Air Conditioning Outdoor Units
3. Robotic Controls
4. Industrial Stepper Motors
5. Power Meter and Power Analyzers
6. Digital Input Modules for Factory Automation
74LS14 Datasheet
