LM318 Op-Amp Signal Generator (Triangle, Square, and Sine Waves)

This project implements a signal generator capable of producing triangle, square, and sine waveforms using LM318 high-speed op-amps. The design is built around a voltage-controlled oscillator (VCO) with an adjustable DC control input and a dedicated sine-shaping stage.

Note: The repository previously included an LM324N-based relaxation oscillator prototype (Multisim Live + early LTspice replication). That version is being deprecated and will be removed once the LM318 design and PCB release are finalized.

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Overview

Stage 1 — Voltage-Controlled Oscillator (VCO)

• Generates triangle and square waveforms.
• Frequency is controlled by an adjustable DC input (control voltage).
• Migrated from LM324N to LM318 to support:
  • faster switching behavior (better comparator-like transitions when used in the loop),
  • improved high-frequency performance,
  • cleaner waveform edges and reduced distortion at higher oscillation rates.

Stage 2 — Sine Wave Shaper

• Converts the triangle waveform into a sine-like output.
• Integrated to work seamlessly with the LM318 VCO output levels and biasing.

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What’s New (LM318 Revision)

Improvements vs. the earlier LM324N prototype

• LM318-based VCO for higher speed and more reliable operation over a wider frequency range.
• Adjustable DC control input for straightforward frequency tuning.
• Improved biasing (cleaner operating points and better repeatability).
• Increased stability in simulation (reliable startup and reduced sensitivity to small parameter changes).

PCB Roadmap

A USB-C powered PCB is planned that integrates both stages:

• VCO + sine shaper on one board
• power architecture designed around USB-C input
• improved layout + decoupling to support the LM318’s speed and stability

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Simulation Status

LTspice (Current / Primary)

The LM318 design is being developed and verified in LTspice:

• Frequency tuning via DC control input
• Triangle + square generation in the VCO
• Sine shaping integrated downstream

Oscillators may require startup conditions in simulation (e.g., startup in transient analysis) to break symmetry and ensure oscillation from initial conditions.

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Legacy Reference (LM324N Prototype — Deprecated)

The following images are preserved as a historical reference to the original LM324N design and early simulation results. This implementation is being phased out in favor of the LM318 revision.

Multisim Simulation — Square & Triangle Wave Generator

Circuit:

Output:

Multisim Simulation — Sine Wave Generator

Circuit:

Output:

LTspice Simulation (Legacy Full Circuit)

Full Circuit: