B2 · Diodes

Clipping and Clamping: Shaping Waveforms with a Diode

Reshape a signal with a single one-way valve. Adjust clipping, which slices off the peaks, then follow the same diode into clamping, which shifts the baseline.

Lower the threshold and slice the peaks

The faint curve is the input and the bold curve is the output. Lower the diode threshold and the part above it is sliced away, flattening the peaks.

Clipping threshold VclipVclip = 0.95

Output peak

Vout = Vin

The threshold sits above the peaks. The diode never turns on, so the output equals the input.

Nothing clipped

A parallel diode pins the peaks

Place a diode in parallel with the signal and tie its far end to a reference voltage. Once the input exceeds that reference plus the diode threshold, the diode turns on, passes a large current, and pins the output at that value. Above it, no matter how high the input climbs, the output cannot follow and is sliced off. This is clipping.

Add a series capacitor and it clamps

This time put the diode in series with the signal and pair it with a capacitor. On the first peak the diode turns on and the capacitor charges up to that peak; once the diode shuts off it traps that charge and adds a steady DC voltage to the signal. So the shape of the waveform stays the same, but the whole thing shifts up or down as one. Shifting the baseline without cutting anything is clamping.

The faint curve is the input, the bold curve the clamped output. Same shape, only the baseline has risen.

One valve, two uses

Both clipping and clamping are, in the end, the same act of a diode pinning a voltage at its threshold. Placed in parallel with the signal it caps what rises above, setting a limit; paired with a series capacitor it adds the once-pinned voltage as DC, shifting the baseline. What gets cut or shifted is set by the reference voltage and the direction of the diode.

ObserveVout = min(Vin, Vclip)

An ideal clipper cuts the output at the threshold.

ChooseVclip = Vref + ?

The real threshold is the reference plus the diode drop.

Fill inVout = Vin + ?

Clamping adds a steady DC to the input.

On your ownVdc ≈ ?

The added DC is the peak the capacitor charged to.

Back to the first screen

The lower you set the threshold, the more the peaks were sliced and the flatter the top of the output became. That flat line is the trace of the diode turning on and pinning the output at one value. Add a series capacitor and the same pinning lifts the whole waveform instead of cutting it. In the end, clipping and clamping are two faces of one fact: a diode fixes a voltage at its threshold. The one-way valve of B1 thus becomes a tool that shapes signals.

Clipping uses a diode in parallel with the signal to slice off the part above a threshold, setting a limit (Vout = min(Vin, Vclip)). Clamping uses a diode with a series capacitor to add a steady DC and shift the baseline while keeping the shape (Vout = Vin + Vdc). Both are two uses of one principle: a one-way valve fixing a voltage at its threshold.

What comes next

So far the diode worked in forward. The next unit pushes it deliberately deep into reverse, to meet the Zener diode, which at a certain voltage suddenly breaks down, passes current, and holds that voltage firmly. Where clamping shifted the baseline, the Zener fixes the output voltage itself: a tool for voltage regulation.