203 Digital Filter
203 : Digital Filter
- Author: Gregor Flachs
- Description: A third order digital FIR filter with 8-bit architecture, configurable cut-off frequency and selectable low-pass or high-pass behaviour.
- GitHub repository
- Open in 3D viewer
- Clock: 0 Hz
TinyTapeout: Digital FIR Filter
Module: tt_um_df_top
A third order digital FIR filter for TinyTapeout. It has a configurable cut-off frequency and two selectable behaviours. The sampling frequency is equal to the clock frequency. Results are available after one clock-cycle. Data is unsigned and the output is bounded to fit 8 bits.
Features
- Four cut-off frequencies: 0.125, 0.375, 0.625 and 0.875
- Two filter behaviours: lowpass and highpass
- Single-cycle execution
- No overflows
Top-Level I/O (TinyTapeout)
| Signal | Dir | W | Description |
|---|---|---|---|
clk |
in | 1 | System clock |
rst_n |
in | 1 | Async reset (active-low) |
ena |
in | 1 | Always '1' on TinyTapeout |
ui_in[7:0] |
in | 8 | Unsigned input data |
uo_out[7:0] |
out | 8 | Unsigned output data |
uio_in[7:4] |
in | 4 | Unused - should be set to '0' |
uio_in[3] |
in | 1 | Config enable (active-high) - change current config |
uio_in[2] |
in | 1 | Config filter behaviour ('0' = lowpass, '1' = highpass) |
uio_in[1:0] |
in | 2 | Config cut-off frequency (wg = b0.xx1) |
uio_out[7:0] |
out | 8 | Unused - set to '0' |
uio_oe[7:0] |
out | 8 | Unused - set to '0' |
Reset defaults:
- Filter behaviour: lowpass
- Cut-off frequency: 0.125
Testing on hardware
- Connect DAC + oscilloscope to output.
- Connect ADC + signal generator to input.
- Reset filter.
- (Optional) Configure filter.
- Test filter with different input signals.
Notes
- Reset before changing config.
- Output signal may be slightly cut off.
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | data_in[0] | data_out[0] | config_wg[0] |
| 1 | data_in[1] | data_out[1] | config_wg[1] |
| 2 | data_in[2] | data_out[2] | config_hp |
| 3 | data_in[3] | data_out[3] | config_en |
| 4 | data_in[4] | data_out[4] | |
| 5 | data_in[5] | data_out[5] | |
| 6 | data_in[6] | data_out[6] | |
| 7 | data_in[7] | data_out[7] |