5 ms·
Nice final result but I would have skipped the PWM detour. PWM sucks and has known bad aliasing issues. Sigma-Delta (AKA "1-bit DAC") is error diffusing, cos
by FullyFunctional 4y ago
Nice final result but I would have skipped the PWM detour. PWM sucks and has known bad aliasing issues. Sigma-Delta (AKA "1-bit DAC") is error diffusing, cost the same to implement, and should always be preferred IMO.
A lot of "tricks" from the past were accommodating the slow processing powers, but if you are driving this from, say, an FPGA, you there's no reason for not just doing the best thing.
One thing I didn't see mentioned: the reason this all works is because the liquid crystals don't turn very fast so effectively they are providing a filter that implements the gray-scale output from a binary input. What I'm curious about is if this is a linear process. Based on the PWM result it looks pretty linear.
- bee_rider 4y agoFWIW, as someone who doesn’t really know anything about LCDs but has messed around with circuits and LEDs, the digression into PWM bridged the gap nicely for me at least. It probably wasn’t necessary from a technical point of view but it helped tell the story.
- robinsonb5 4y agoPWM still has its place - it's not uncommon for high-end sigma deltas to have a multi-bit rather than one-bit output, which feeds into a PWM final output stage. It helps with numerical stability. I've used a similar technique to improve the audio output in FPGA projects where a simple 1st order SD feeds a 5-bit PWM. On the boards in question the output drivers seem to be somewhat asymmetric, making an SD quite noisy at higher clock frequencies. With the PWM final output stage the same effect manifests as a DC offset instead, since (when not saturated) the PWM has a fixed number of rising and falling edges in a given time period.