I realized a high-res audio PWM modulator on a FPGA with I2S audio input and 384 kHz output PWM signal capable of driving a Mosfet power-stage to build up a Class-D amplifier or an audio-DAC (with RC filter behind the digital pins).
The whole system runs on a 25 MHz system-clock, the audio-input stream is 96 kHz and the signal is internally upsampled to 384 kHz with an upsampler.
The signal bit-width is reduced to only 5 bits by a multibit sigma-delta (noiseshaper) structure to feed the 5 Bit / 384 kHz audio signal into a PWM generator.
The idea behind the project was to explain how fully digital I2S Class-D amps are working internally (by modulating the PWM signal fully digital directly from the incoming data stream - without any additional analog modulators). This concept is used by many silicon vendors in especially low-power Class-D amplifiers.
The project is based on a TinyFPGA-BX board (iCE40LP8K from Lattice), a Digilent PMOD I2S2 audio adc/dac board (only ADC used), and a board with two MPS MP8040 power half-bridge drivers to drive the loudspeaker.
Before you start - please read the documentation carefully to understand how the whole system is working or just watch my YouTube video where I explained everything in detail with some real audio-tests https://youtu.be/3Jd_ZyCZeGk
Following pinout is used:
PIN24 - ADC-MCLK
PIN23 - ADC-BCLK
PIN22 - ADC-LR
PIN21 - ADC-DATA
PIN18 - PWM out inverted (PWM_n)
PIN17 - PWM out normal phase (PWM_P)
PIN16 - gain[0]
PIN15 - gain[1]
PIN14 - NoiseShaper Bypass-Control
Gain = "00" -> Gain = +0dB
Gain = "01" -> Gain = +3dB
Gain = "10" -> Gain = +6dB
Gain = "11" -> Gain = +9 dB
PIN 14 = "1" -> Noise-Shaper is active
PIN 14 = "0" -> Noise-Shaper is bypassed
