Block:SC LPF
← All blocks · durable page
Switched-Capacitor Low-Pass Filter
A switched-capacitor low-pass filter follows the Gm-C integrator in the AFE to band-limit the neural/recording signal before digitisation by the SAR ADC.
Design equation
Corner frequency is set by the capacitor ratio and the switch clock: <math>f_c = \frac{1}{2\pi} \cdot \frac{C_2}{C_1} \cdot f_{clk}</math>
Budgeting procedure
- Choose <math>f_c</math> from the signal band of interest.
- Pick <math>C_1</math> for kTC-noise floor; <math>C_2</math> follows from the ratio.
- Verify switch on-resistance gives adequate settling within the clock phase.
- Run kTC noise budget (method) to confirm.
Known failure modes
- Clock feedthrough corrupting the passband.
- Incomplete settling (too-high switch <math>R_{on}</math>) causing gain error.
- kTC noise dominating the front-end floor if <math>C_1</math> is too small.