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Design Notes

Parameters That Shape Your Design

The numbers that decide whether your clock works.
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Five parameters worth a second look before you lock the BOM.

Frequency Stability.

How much your oscillator drifts over temperature. If your device sees -40°C to +85°C, a standard XO might shift enough to slip timing margins. TCXOs and OCXOs tighten that window. Sometimes the BOM delta is cheaper than a field recall.

Frequency Pullability.

How far you can tune the output frequency with a control voltage. Matters if your PLL, clock recovery, or synchronization design needs a VCXO or VCTCXO. Pull range and linearity determine your tuning margin.

Start-up Time.

The microseconds between power-on and stable oscillation. Long start-up means your MCU might boot before the clock is ready. This failure is subtle — it only shows up at low temperature or low voltage. Check your IC’s oscillator start-up spec against the crystal you’ve chosen.

Power Consumption.

For battery-powered designs, the oscillator’s current draw can dominate the always-on power budget. A 32.768 kHz crystal with CL = 6 pF draws roughly a quarter of the current of the same crystal with CL = 12.5 pF. Small parameter choices, multi-year battery life differences.

Phase Noise & Jitter.

The short-term frequency wobble that degrades signal integrity. In RF chains, phase noise limits channel selectivity. In high-speed digital links, jitter eats into the timing budget. The Low Phase Noise and Low Jitter series are built to tighter specification targets.

Getting the Circuit Right

Three numbers to check before you route.
Most crystal circuit issues trace back to one of these.

Load Capacitance.

The crystal datasheet says CL = 12.5 pF. But your PCB adds 3–5 pF of stray capacitance — from traces, pads, and the oscillator pin itself. If you don't subtract the stray from your external caps, the effective CL shifts and so does the frequency. Start with the formula in our Crystal Matching Guide, then verify on the bench.

Negative Resistance Margin.

The oscillator circuit needs enough gain to overcome the crystal's ESR, with margin. A common target: |R(neg)| ≥ 5× ESR at your highest operating temperature. Too little margin and the oscillator may fail to start at cold or low voltage.

Drive Level.

Too much drive ages the crystal. Too little and it won't start. Tuning-fork crystals (32.768 kHz) are especially sensitive — often rated for <1 µW. If your oscillator stage drives harder than expected, add a series resistor. Check the crystal's max drive spec against your IC's oscillator output.

Good circuit. Bad layout. Still fails.

Four board-level habits that keep your oscillator quiet.

01

Keep traces short.

The loop from oscillator output → crystal → oscillator input is your most sensitive net. Every millimeter adds stray capacitance and picks up noise. Route the crystal as close to the IC pins as your footprint allows.

02

Use a solid ground plane.

A continuous ground plane under the oscillator section gives you a low-impedance return path and shields against EMI. Do not split it. Do not run digital traces through it.

03

Guard the high-impedance node.

For 32.768 kHz tuning-fork crystals, the oscillator input pin is a high-impedance node. A guard ring tied to ground around the crystal pads prevents leakage currents from disturbing start-up. This matters especially in humid or condensing environments.

04

Decouple locally.

Place a 100 nF MLCC as close to the oscillator V(dd) pin as possible. If your oscillator feeds a PLL or clock tree downstream, add a ferrite bead between the oscillator supply and the noisy rail.

You've Checked the Parameters. Now Pick Your Path.

Self-serve resources for straightforward questions. Our engineers for the rest.

If you know what you need:

To browse by specification

— Filter by frequency, stability, package, and output type.

To compare oscillator types side by side

— XO, TCXO, OCXO, VCXO at a glance.

To match a crystal to your IC

— CL, ESR, and drive level calculations.

For full datasheets and specifications

If you know what you need:

Custom frequency. Non-standard package. Tighter stability window. Extended temperature range. Our engineering team works from your target specification to qualified samples — not from a catalog page.

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