Fully analog implementation of Sinusoidal Pulse Width Modulation (SPWM) using operational amplifiers — designed, simulated in LTspice, and validated through real hardware measurements.
Hardware-verified SPWM output showing duty cycle modulation with sinusoidal reference.
This project demonstrates SPWM generation using purely analog circuits, without any microcontrollers or digital control.
A low-frequency sinusoidal reference signal is compared with a high-frequency triangular carrier to generate a PWM signal whose duty cycle follows the instantaneous amplitude of the sine wave.
This technique is fundamental in Power Electronics, with applications in:
- Power Inverters
- Motor Drives
- Class-D Audio Amplifiers
-
Wien Bridge Oscillator
- Generates stable 50 Hz sine wave
- Diode-based stabilization maintains constant amplitude
-
Triangular Wave Generator
- Implemented using integrator + Schmitt trigger
- Produces ~10 kHz carrier waveform
-
Comparator
- Compares sine and triangular signals
- Generates SPWM output
- If ( V_{sine} > V_{tri} ) → Output HIGH
- If ( V_{sine} < V_{tri} ) → Output LOW
This produces PWM where:
- Duty cycle varies with sine amplitude
- Wide pulses near sine peaks
- Narrow pulses near zero crossings
LTspice schematic showing Wien Bridge oscillator, triangular generator, and comparator stages.
- Sine wave generation (~50 Hz)
- Carrier waveform (~10 kHz design target)
- SPWM duty cycle modulation
👉 Open LTspice Simulation File
- Implemented on zero PCB
- Op-Amps used: LM741 / LM324
- Power Supply: ±12V / ±15V dual rail
- Output verified using Digital Storage Oscilloscope (DSO)
- Stable SPWM waveform successfully generated
- Duty cycle accurately follows sinusoidal envelope
- Carrier frequency observed in ~5–10 kHz range
- Strong agreement between:
- Theoretical design
- LTspice simulation
- Hardware output
The observed deviation between calculated and measured frequencies highlights practical analog design limitations such as op-amp bandwidth constraints and component tolerances.
-
Wien Bridge Oscillator:
- ( f = \frac{1}{2\pi RC} )
- Designed for 50 Hz sine wave
-
Triangular Wave Generator:
- Target: ~10 kHz carrier
- Calculated: ~11.36 kHz
- Observed: ~5–10 kHz
-
Comparator:
- ( V_{sine} > V_{tri} ) → HIGH
- ( V_{sine} < V_{tri} ) → LOW
📄 Full derivations:
👉 View Detailed Calculations
Initial design calculations were performed manually before simulation and hardware implementation.
📄 Full project report (design methodology, calculations, simulation, and hardware validation):
- DC-AC Power Inverters
- Variable Frequency Motor Drives
- Class-D Audio Amplifiers
- Analog Modulation Systems
- Analog circuits require precise stability and gain control
- Component tolerances significantly affect frequency accuracy
- Diode-based stabilization is critical in oscillator design
- Analog SPWM reveals real-world non-idealities often abstracted in digital systems
- Use high-speed / precision op-amps
- Add low-pass filtering for waveform reconstruction
- Integrate with inverter stage
- Optimize PCB layout to reduce noise
/simulation → LTspice files and simulation data /hardware → PCB implementation images /images → Waveforms, diagrams, schematics /docs → Project report /calculations → Design calculations (clean + handwritten)
Arya Dinesh
B.Tech Electronics & Communication Engineering
📫 Let’s connect: www.linkedin.com/in/aryadinesh2005
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🧠 Open for collaboration or discussion on FPGA, digital design, and embedded systems.