Tiny Tapeout > Tiny Tapeout Chips > Tiny Tapeout GF 0p3 > 452 PolyWave

452 PolyWave

452 : PolyWave

Author: Riccardo Pellegrini
Description: Mixed-signal four-channel waveform source with a compact digital engine driving four 16-bit R-2R DACs.
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Clock: 50000000 Hz

PolyWave

PolyWave is a four-channel mixed-signal waveform source. A compact digital engine generates four 16-bit sample streams, and the custom GF180 layout converts those streams to analog voltages with four R-2R DAC ladders.

The design is intended as a small multi-output waveform lab for synchronized signals, modulation experiments, DAC characterization and mixed-signal Tiny Tapeout demonstrations.

How it works

The digital engine contains four 20-bit phase accumulators, a shared 16-bit LFSR/noise source, a 4-bit sequencer and four 16-bit DAC sample registers. It can run autonomously in generated-waveform mode, or it can accept direct byte writes to any DAC channel.

The four DAC sample registers drive inverted 16-bit layout buses named R2R_Bn_0, R2R_Bn_1, R2R_Bn_2 and R2R_Bn_3. These buses feed the four physical R-2R ladders in the custom GDS. The analog DAC outputs are exposed on ua[0] to ua[3].

This repository uses the Tiny Tapeout custom GDS path. The prebuilt gds/ and lef/ files are the physical source for the submitted layout. src/project.v documents and syntax-checks the mixed-signal partition used by the layout; it is not synthesized by the submission action into a new layout. The public tt_um_odgrip_polywave module keeps the standard Tiny Tapeout analog port list, instantiates polywave_top_digital for the digital waveform engine, and instantiates polywave_top_analog_stub as the analog boundary that represents the custom GDS. The R-2R buses are internal signals between those two blocks, not top-level ports.

The submitted analog frame uses the GF180 pgvaa Tiny Tapeout interface, so VAPWR remains part of the project interface even though the current digital engine does not consume the analog supply internally.

Digital controls

Generated mode

Set ui_in[7] low to use the autonomous waveform generator.

Signal	Function
`ui_in[2:0]`	Extra live modulation bits and low-cost phase nudges
`ui_in[3]`	Fast internal tempo select
`ui_in[5:4]`	Scene selection for the waveform formulas
`ui_in[6]`	Freeze phase accumulator updates while held high
`uio_in[7:0]`	Live modulation/control bus used by the waveform engine

In this mode the four phase accumulators, cross-modulation paths, sequencer, noise source, saw/triangle/PWM/stepped waveforms and live controls generate the four DAC values.

Direct DAC mode

Set ui_in[7] high to stop generated DAC updates and write DAC codes directly.

Signal	Function
`ui_in[5:4]`	DAC channel select: 0 to 3
`ui_in[3]`	Byte select: 0 for low byte, 1 for high byte
`uio_in[7:0]`	Byte value to load
`ui_in[6]`	Rising-edge load strobe

To write a full 16-bit DAC code, load the low byte and high byte separately with two pulses on ui_in[6].

Outputs

Signal	Function
`ua[0]`	DAC A analog output
`ua[1]`	DAC B analog output
`ua[2]`	DAC C analog output
`ua[3]`	DAC D analog output
`uo_out[2:0]`	Mirror of `ui_in[2:0]` live modulation bits
`uo_out[6:3]`	Current 4-bit sequencer step
`uo_out[7]`	Tempo tick
`uio_out[7:0]`	Always zero
`uio_oe[7:0]`	Always zero, so the bidirectional pins are input-only controls

How to test

Apply power to the design.
Provide the system clock and release reset.
Hold ui_in[7] low for generated-waveform mode.
Observe ua[0] to ua[3] with an oscilloscope or data acquisition system.
Change ui_in[5:4], ui_in[3], ui_in[2:0] and uio_in[7:0] to exercise the live waveform controls.
Set ui_in[7] high and use direct DAC mode to write known 16-bit codes to each channel.
Check uo_out[7] and uo_out[6:3] for the tempo tick and sequencer state.

External hardware

Use a clock/reset source, digital control source for ui_in and uio_in, and an oscilloscope, logic analyzer or data acquisition system to observe the analog and status outputs.

IO

#	Input	Output	Bidirectional
0	MOD0	MOD0_MON	LIVE0
1	MOD1	MOD1_MON	LIVE1
2	MOD2	MOD2_MON	LIVE2
3	TEMPO_HI	SEQ0	LIVE3
4	SCENE0	SEQ1	LIVE4
5	SCENE1	SEQ2	LIVE5
6	FREEZE/LOAD	SEQ3	LIVE6
7	DIRECT	TEMPO_TICK	LIVE7

Analog pins

`ua`	PCB Pin	Internal index	Description
0	A4	4	DAC_A
1	A1	1	DAC_B
2	A3	3	DAC_C
3	A2	2	DAC_D