Block:SC LPF: Difference between revisions
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=== Design equation === | === Design equation === | ||
Corner frequency is set by the capacitor ratio and the switch clock: | Corner frequency is set by the capacitor ratio and the switch clock: | ||
''f_c = \frac{1}{2\pi} \cdot \frac{C_2}{C_1} \cdot f_{clk}'' | |||
=== Budgeting procedure === | === Budgeting procedure === | ||
# Choose | # Choose ''f_c'' from the signal band of interest. | ||
# Pick | # Pick ''C_1'' for kTC-noise floor; ''C_2'' follows from the ratio. | ||
# Verify switch on-resistance gives adequate settling within the clock phase. | # Verify switch on-resistance gives adequate settling within the clock phase. | ||
# Run kTC noise budget ([[Method:kTC noise budget|method]]) to confirm. | # Run kTC noise budget ([[Method:kTC noise budget|method]]) to confirm. | ||
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=== Known failure modes === | === Known failure modes === | ||
* Clock feedthrough corrupting the passband. | * Clock feedthrough corrupting the passband. | ||
* Incomplete settling (too-high switch | * Incomplete settling (too-high switch ''R_{on}'') causing gain error. | ||
* kTC noise dominating the front-end floor if | * kTC noise dominating the front-end floor if ''C_1'' is too small. | ||
=== Instances === | === Instances === | ||
* [[Block:SC LPF RC1.9|RC1.9]] — implemented, post-PEX verified | * [[Block:SC LPF RC1.9|RC1.9]] — implemented, post-PEX verified | ||
* [[Block:SC LPF RC2.0|RC2.0]] — ''TBD'' | * [[Block:SC LPF RC2.0|RC2.0]] — ''TBD'' | ||
Latest revision as of 09:19, 4 September 2026
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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: f_c = \frac{1}{2\pi} \cdot \frac{C_2}{C_1} \cdot f_{clk}
Budgeting procedure
- Choose f_c from the signal band of interest.
- Pick C_1 for kTC-noise floor; C_2 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 R_{on}) causing gain error.
- kTC noise dominating the front-end floor if C_1 is too small.