Temperature Coefficient
Understanding Temperature Coefficient
Temperature coefficient determines the frequency stability of filters, oscillators, and resonant circuits. Even small TC values can cause significant frequency drift over the operating temperature range.
TC by Component Type
| Component | TC (ppm/C) | Application |
|---|---|---|
| NPO/C0G capacitor | 0 +/- 30 | Tuned circuits, filters |
| X7R capacitor | +/- 15% | Bypass only (not tuning!) |
| Wire-wound inductor | +50 to +200 | Low-frequency filters |
| Alumina substrate (er) | +140 | Microstrip circuits |
| AT-cut quartz | +/- 0.5 (parabolic) | Oscillators |
Frequently Asked Questions
What is temperature coefficient?
TC measures how a component value changes with temperature (ppm/C). NPO caps: ~0 ppm/C. X7R caps: +/- 15%. Critical for filters and oscillators where small value changes cause frequency drift.
Why do filters drift with temperature?
Filter center frequency depends on component values. If capacitors change +100 ppm/C, a 10 GHz filter shifts 1 MHz per degree. Over 50C range: 50 MHz drift. Use NPO/C0G capacitors in tuned circuits to minimize this.
What TC is acceptable for RF?
Tuned circuits: Only NPO/C0G capacitors (TC < 30 ppm/C). Bypass/decoupling: X7R or X5R acceptable. Oscillators: AT-cut quartz (< 1 ppm/C) or TCXO (< 0.5 ppm/C). The application determines the required TC.