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

1. Choose <math>f_c</math> from the signal band of interest.
2. Pick <math>C_1</math> for kTC-noise floor; <math>C_2</math> follows from the ratio.
3. Verify switch on-resistance gives adequate settling within the clock phase.
4. 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.

Instances

• RC1.9 — implemented, post-PEX verified
• RC2.0 — TBD