A practical exploration of modulation techniques for firmware engineers, starting from the obscure 7497 synchronous rate multiplier TTL chip. The post contrasts conventional PWM (fixed frequency, variable pulse width) with an accumulator-based 'synthetic division' method that is mathematically equivalent to first-order delta-sigma modulation. Code examples in C illustrate both approaches. The key tradeoff: use PWM when fixed frequency is required and switching losses matter; use delta-sigma when modulation rate is slow and you need finer resolution without a very slow PWM period. The delta-sigma approach spreads quantization noise upward in spectrum, making it easier to filter, and responds faster to duty cycle changes.
