ADC charge bucket RC
ADC charge bucket RC with explicit circuit assumptions and worked equations.
Development preview. Check the assumptions below before relying on a result. Calculations run in your browser.
How it calculates
Full-step recovery: error = VFS exp[−tacq/((Rs + Rf)(Cf + Csh))]
Charge sharing: ΔVinitial = VFS Csh/(Cf + Csh)
Half-LSB time: tsettle = (Rs + Rf)(Cf + Csh)(N + 1) ln 2
Assumptions
- First-order lumped RC model. The charge-sharing case assumes Cf starts at the correct signal voltage and Csh starts one full-scale away. Full-step result assumes both capacitors see a new full-scale input. Switch resistance, amplifier dynamics, kickback spectrum and dielectric absorption are omitted; use OA-20 for an amplifier approximation.
Worked example
These are the calculator's default inputs. Change any input above to recalculate.
Inputs
- Filter resistance
- 100 Ω
- Source resistance
- 10 Ω
- Filter capacitor
- 2e-9 F
- Sample capacitor
- 2e-11 F
- ADC resolution
- 12 bits
- Acquisition time
- 0.000001 s
- Full-scale step
- 3.3 V
Results
- Charge sharing residual
- 0.450317 LSB
- Full-scale step residual
- 45.482 LSB
- Filter/sample capacitance ratio
- 100
- RC corner
- 716269 Hz
- Maximum total R for full-scale acquisition
- 54.9389 Ω
- Full-scale settling time
- 0.00000200222 s