R-2R ladder DAC
12 parts
A mod-8 counter drives the top three bits of an R-2R ladder while a digital-constant part holds the LSB at 1, so the scope shows a live staircase: eight plateaus from 0.31 V to 4.69 V in exact 0.625 V steps, one full ramp per millisecond. Just two resistor values make a perfect binary-weighted converter — each ladder node halves the weight of the bit before it. The counter and constant are behavioural logic macromodels whose outputs are ideal 0/5 V sources, which is precisely the source-impedance assumption R-2R arithmetic relies on; a real DAC has to engineer its switch resistance away.
- V1 5V·8kHz
- V2 0V step
- CTR41
- DIGC1
- R1 20kΩ
- R2 20kΩ
- R3 10kΩ
- R4 20kΩ
- R5 10kΩ
- R6 20kΩ
- R7 10kΩ
- R8 20kΩ
