TBC!
Continuing my previous VGA DAC experiments (tt06-grab-bag, tt08-vga-fun, and ttihp0p3-antonalog), this implements three current-switching DACs, intended for generating analog VGA display signals, using a 16x16 matrix of unit current sources, converting 8-bit digital inputs to inverted analog current sink "outputs" in the range of 3.3V down to 1.3V (depending on external pull-up resistance).
NOTE: At the time of writing, the display controller digital block is not yet implemented, but is expected to be done before tapeout and will be based on my previous projects listed above.
TBC!
Use a pull-up resistor on each of the red, green, and blue analog output pins -- pull up to 3.3V using (say) a 500-ohm or 1k resistor, then shift this to 0-0.7V using an inverting opamp configuration. Alternatively, use a TIA (Transimpedance Amplifier) externally.
Set Vbias internally using digital inputs (through 8 possible levels).
TBC!
# | Input | Output | Bidirectional |
---|---|---|---|
0 | mode[0] / dac_in[0] | r7 | vblank_out |
1 | mode[1] / dac_in[1] | g7 | hblank_out |
2 | mode[2] / dac_in[2] | b7 | bias1_in |
3 | mode[3] / dac_in[3] | vsync | bias2_in |
4 | mode[4] / dac_in[4] | r6 | bias3_in |
5 | mode[5] / dac_in[5] | g6 | |
6 | mode[6] / dac_in[6] | b6 | |
7 | mode[7] / dac_in[7] | hsync |
ua | PCB Pin | Internal index | Description |
---|---|---|---|
0 | B0 | 6 | ra |
1 | B1 | 7 | ga |
2 | B3 | 9 | ba |
3 | B2 | 8 | atest |