A switched-capacitor (SC) filter replaces the resistors in a traditional active filter with capacitors that get rapidly switched between two nodes. The trick: a capacitor C shuttling charge between nodes at frequency f_clk behaves like a resistor with value R_eq = 1 / (f_clk · C). Change the clock, change the resistor, change the cutoff frequency — all without touching a single component.

Why bother? Three big wins:

• Tunability: A digital clock sets your cutoff. No potentiometers, no swapping resistors.
• IC-friendly: Capacitor ratios on silicon are accurate to 0.1%, while absolute resistor values vary 20%+. SC filters give you precision filtering on-chip.
• Self-clocking precision: Cutoff frequency tracks your crystal oscillator, not RC tolerance.

The classic part is the MF10 (or its modern cousin, the LTC1064). It's a universal SC filter where you pick lowpass, highpass, bandpass, or notch by connecting pins. The cutoff frequency is locked to the clock by a fixed ratio — typically f_clk/f₀ = 100 or 50. Want a 1 kHz lowpass? Feed it a 100 kHz clock. Want to sweep from 100 Hz to 10 kHz? Sweep the clock from 10 kHz to 1 MHz.

Real-world example: A spectrum analyzer front-end where you need a tracking bandpass filter. Use an MF10 in bandpass mode with Q=10, drive its clock from a DDS chip, and you've got a filter whose center frequency tracks your sweep without any analog tuning components.

Quick design rule: For an MF10 lowpass with f₀ = 2 kHz at the 100:1 ratio, set f_clk = 200 kHz. The Q is set by two external resistor ratios (not values!) — for a Butterworth response, R2/R3 ≈ 0.707.

The catch — and it's important: SC filters are sampled-data systems. They alias just like ADCs. You must precede them with a simple RC anti-aliasing filter (cutoff well below f_clk/2), and follow them with a reconstruction filter to smooth the staircase output. Clock feedthrough also injects spurs at f_clk and its harmonics into your signal — fine for audio if f_clk > 100 kHz, deadly for sensitive instrumentation without post-filtering.

Other limits: bandwidth caps around 100 kHz (silicon switch speed), dynamic range typically 80-90 dB (worse than continuous-time active filters), and noise that scales with kT/C.