LED dimming or modulation of LED intensity is typically implemented using modulation schemes that use average duty cycle proportional to the desired dimming level in a fixed time period. These schemes are popularly known as pulse density modulation (PDM). Pulse-width modulator (PWM), which modulates width of pulses according to desired dimming levels, is the simplest example of PDM.

For LED dimming, the order in which individual pulses occur within a fixed time period is not important. However, the total high time or signal energy in the fixed time frame must be as configured. Cypress’ PrISM serves as an alternative to traditional modulation schemes used for LED brightness control. PrISM technology is implemented using high resolution stochastic signal density modulation (SSDM) modules.

In this application note, PrISM and SSDM are used interchangeably. Although PWM has some excellent features, it suffers from significant harmonic generation at a relatively low frequency. Sometimes it may require intense filtering to remove high frequency components. Due to high electromagnetic interference (EMI) generation from PWM waves, SSDM is used to implement PrISM.

The idea is to spread the energy at different frequencies so that it is easy to filter the higher harmonics, if required. PrISM based dimming modulation is available as a configurable hardware block in the PowerPSoC family of devices. These devices can be used to design highly integrated LED driver circuits with power supply and LED dimming.

Precision Illumination Signal Modulation (PrISM) is a Cypress technology that uses stochastic signal density modulation, which can be used for controlling the intensity of LEDs in lighting applications. This document describes the key characteristics of PrISM and its implementation using PSoC user modules.

The application note also explains the challenges faced in implementing high resolution PrISM and recommends solutions to address these issues. The attached code examples explain the implementation of 8-bit, 16-bit, and variable resolution PrISM using SSDM user modules in PowerPSoC devices.

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