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Class 1 ceramic capacitors (such as C0G/NP0) are the stability choice: their capacitance and loss change relatively little with temperature, voltage, and time, but available values are usually lower. Class 2 ceramics (such as X7R and X5R) provide much more capacitance in a small package, while their effective capacitance can shift with temperature, applied DC voltage, and aging.
Choose by the capacitance your circuit will actually have in operation, not by the number printed on the component alone. A C0G part is normally the safer choice for timing, tuning, filters, and other functions that depend on a predictable value. An X7R or X5R part is usually more practical for bypass, smoothing, and decoupling when board space and capacitance density matter.
What “Class 1” and “Class 2” mean
The class describes the behavior of the ceramic dielectric inside the capacitor. It is not simply a quality ranking. Each class trades capacitance density against stability.
Class 1: temperature-compensating ceramics
Class 1 dielectrics use materials with a relatively low dielectric constant. That limits the maximum capacitance available in a given volume, but it also produces a highly stable component. C0G and NP0 are the most familiar Class 1 designations. Murata describes this category as having a small capacitance change with temperature and no listed DC-bias or aging characteristic for its temperature-compensating group (Murata’s ceramic-capacitor comparison). TDK likewise characterizes C0G/NP0 as highly stable over temperature (TDK’s Class I/Class II FAQ).
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Class 2: high-dielectric ceramics
Class 2 materials have a much higher relative dielectric constant. They can therefore deliver larger nominal capacitance in the same package size or voltage rating. X7R and X5R are common examples. The price of that density is a greater change in capacitance with temperature, an effective-capacitance loss under DC bias, and an aging characteristic. The size of each effect depends on the specific part, not just the family name.
Class 1 versus Class 2 at a glance
| Design factor | Class 1: C0G/NP0 examples | Class 2: X7R/X5R examples |
|---|---|---|
| Temperature stability | Small capacitance change; C0G/NP0 is described as highly stable over temperature by TDK. | Larger change than Class 1. The permitted behavior depends on the temperature code and the individual part. |
| DC-bias dependence | Murata reports no DC-bias characteristic for its temperature-compensating category. | Applied DC voltage changes effective capacitance. The amount must be read from the manufacturer’s bias-versus-capacitance data. |
| Aging | Murata reports no aging characteristic for its Class 1 category. | Murata reports an aging characteristic for its high-dielectric category. |
| Capacitance density | Lower relative dielectric constant means lower available capacitance for a given size. | Higher relative dielectric constant allows larger capacitance in a compact component. |
| Typical uses | Oscillation, tuning and filtering, coupling, and matching. | Bypass, smoothing, decoupling, and coupling. |
These are category-level tendencies, not guarantees for every catalog number. Tolerance, rated voltage, package geometry, temperature range, frequency, and construction can change the result. The exact part datasheet remains the authority.
Why the nominal value can be misleading
A capacitor marked with a particular capacitance is normally specified under defined test conditions. Your circuit may apply a DC voltage, operate at a different temperature, or use a package and geometry that produce a different effective value. This distinction is most important with Class 2 parts.
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Nominal capacitance
The nominal value is the value used to identify and order the component. It is useful for comparing parts and selecting an initial design value, but it does not describe every operating condition. A nominally identical capacitor from another case size, voltage rating, or internal construction can have a different in-circuit capacitance.
Effective capacitance
Effective capacitance is the value available at the voltage, temperature, and signal conditions your circuit applies. For an X7R or X5R component, read the manufacturer’s capacitance-versus-DC-bias curve at the expected bias voltage rather than assuming the marked value remains available. Analog Devices specifically warns that the X7R/X5R temperature code does not, by itself, state how much capacitance the part loses under DC bias (Analog Devices’ temperature and voltage variation article).
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Temperature behavior and code designations
Temperature is one of the clearest differences between the classes. Class 1 C0G/NP0 parts are designed for a small change as temperature moves through their specified range. Class 2 parts have a larger permitted change; the exact range and limits are associated with the code and the individual manufacturer’s specification.
Codes such as C0G, NP0, X7R, and X5R identify a dielectric family and its specified temperature behavior. They do not provide a complete performance guarantee. Two X7R capacitors can have noticeably different voltage-bias curves because of differences in capacitance value, package size, rated voltage, and construction. Treat the code as a starting filter for parts, then inspect the data for the exact ordering code.
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Use Class 1 when a change in capacitance would move an oscillator, alter a tuned filter, shift a matching network, or change a timing or sensing result beyond the circuit’s allowance. The low temperature dependence makes the design easier to predict across its operating environment.
When some temperature change is acceptable
Class 2 is often appropriate when the capacitor’s main job is to provide a charge reservoir, shunt high-frequency energy, or smooth a supply rail. In those roles, the design may have enough margin that a changing value is acceptable, while the higher capacitance density is valuable.
DC-bias effects in Class 2 capacitors
Applying a DC voltage across a Class 2 ceramic changes the dielectric’s behavior and can reduce its effective capacitance. The reduction is not represented by the X5R or X7R label alone. It varies with the part’s capacitance, rated voltage, package, dielectric formulation, and construction.
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How to use a bias curve
- Find the exact manufacturer datasheet for the proposed part number.
- Locate the graph or table labeled capacitance versus DC bias, voltage coefficient, or effective capacitance.
- Read the curve at the highest steady-state voltage the capacitor will see, including any DC offset in an AC-coupled circuit.
- Account for the operating temperature and tolerance specified for your design; use the worst credible combination rather than the room-temperature nominal point.
- Compare the resulting effective value with the minimum capacitance your circuit requires.
Do not substitute a universal derating percentage. Analog Devices notes that voltage-bias behavior must be checked for the individual component, and the available sources do not establish one factor that applies to every X5R or X7R part.
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Two parts with the same nominal capacitance can use different ceramic volumes and electrode structures. A higher voltage rating may use a different construction from a lower-voltage version, and a smaller case may have less dielectric volume. These differences can change the bias curve. Select the exact package and rating first, then evaluate its data.
Aging: the change that continues with time
Class 2 high-dielectric materials exhibit an aging characteristic: their capacitance changes gradually with elapsed time after processing and use. Murata identifies aging for its high-dielectric category, while it lists no aging characteristic for its temperature-compensating Class 1 category.
KEMET’s technical discussion similarly reports negligible DC-bias change and nearly no change over time for C0G and U2J technologies (KEMET’s ceramic-technologies article). If a long-term drift budget is important, use the manufacturer’s aging information for the exact dielectric and value, and include that drift in the tolerance analysis.
Where each class is commonly used
Class 1 applications
- Oscillation: A stable capacitor helps keep the intended resonant or timing condition from moving with temperature.
- Tuning and filtering: Filter corner frequencies and tuned networks remain more predictable when capacitance is stable.
- Matching: RF or signal-path matching can be sensitive to small value changes, making a stable dielectric useful.
- Coupling: Class 1 can be selected when the coupling network’s reactance must remain consistent. Murata includes coupling among its examples.
Class 2 applications
- Bypass and decoupling: A high-capacitance ceramic can shunt transient or high-frequency supply energy close to an integrated circuit.
- Smoothing: Larger capacitance in a small package is useful for reducing supply ripple, subject to the effective value available at the rail voltage.
- Coupling: Class 2 may be suitable when the circuit tolerates value variation and needs more capacitance per unit volume.
These examples are guidance, not prohibitions. A coupling network may use either class: choose Class 1 when its impedance must be stable, or Class 2 when density is more important and the bias, temperature, and aging shifts fit the circuit budget.
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How to choose a capacitor for a real design
Use this sequence instead of choosing a dielectric from the nominal capacitance alone.
- Define the electrical requirement. Write down the minimum and maximum capacitance that the circuit can accept, the signal frequency, the DC voltage, ripple or transient conditions, and the temperature range.
- Decide whether stability or density is dominant. If the value sets a frequency, time constant, tuned impedance, or measurement result, start with Class 1. If the part is primarily a supply bypass or smoothing reservoir and space is constrained, start with Class 2.
- Choose a candidate dielectric and value. Use C0G/NP0 for the stable Class 1 path, or X7R/X5R for the high-density Class 2 path. Treat the printed capacitance as nominal.
- Check effective capacitance under DC bias. For Class 2, read the exact part’s bias curve at the real operating voltage. If the resulting minimum value is too low, increase the nominal value, select another package or voltage rating, use multiple capacitors, or move to Class 1 if its available capacitance meets the requirement.
- Check temperature and aging. Verify the specified temperature range and account for the permitted temperature change. Include the stated aging behavior when the circuit must remain within limits over its service life.
- Verify tolerance and rated voltage. A nominally suitable value can still fail if its tolerance is too broad or if the voltage rating is inadequate. Use the manufacturer’s current datasheet for the exact ordering code.
- Confirm package and layout constraints. Case size, pad geometry, mechanical stress, and available board area can eliminate an otherwise suitable part. The package is part of the electrical choice because it can affect bias behavior and capacitance density.
- Recalculate the circuit with worst-case values. Use the lowest and highest credible effective capacitance, not just the nominal number, and verify the resulting frequency, impedance, ripple, or transient response.
Worked selection examples
Example: a timing or oscillator network
Suppose a capacitor participates directly in an oscillator’s frequency-setting network. Temperature movement or aging changes the oscillation frequency, and the circuit has little calibration margin. Start with a C0G/NP0 Class 1 part. Check its tolerance, temperature range, rated voltage, and the oscillator’s signal amplitude. An X7R may provide the required nominal value in a smaller case, but its temperature, bias, and aging changes would have to fit the frequency error budget; if they do not, density is the wrong tradeoff.
Example: an integrated-circuit supply bypass
For a local bypass capacitor, the design often benefits from the high capacitance density of X7R or X5R. The correct procedure is to check the capacitance remaining at the supply’s DC voltage and temperature, then verify that the minimum effective value still meets the transient or impedance target. If the curve shows a large loss, a physically larger part, a higher nominal value, or several capacitors may be needed. The X7R label alone is not sufficient evidence that the target capacitance is present.
Example: an AC-coupling path
Both classes can be candidates. If the coupling corner frequency must remain tightly controlled over temperature and voltage, Class 1 offers the more predictable value. If the corner frequency has generous margin and the design needs substantially more capacitance in a small area, Class 2 may be the practical choice. Evaluate the capacitor’s effective value at the circuit’s DC bias, not only the AC signal level.
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Mistake: treating the class as a pass/fail quality grade
Class 2 is not an inferior version of Class 1. It is a different optimization: more capacitance per volume in exchange for larger environmental and electrical variation. Fix the mistake by matching the dielectric to the circuit’s sensitivity.
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Mistake: reading X7R or X5R as a voltage-coefficient specification
The temperature code does not tell you the exact capacitance loss at your DC voltage. Fix it by retrieving the individual part’s bias-versus-capacitance curve and using the operating point that matters.
Mistake: comparing nominal values from different packages
Identical markings do not ensure identical effective capacitance when case size, voltage rating, or construction differs. Fix it by comparing complete part numbers and their datasheet curves.
Mistake: ignoring tolerance and lifetime drift
A design can pass at room temperature when new and fail after temperature excursions or elapsed time. Fix it by including initial tolerance, temperature change, DC-bias loss, and the stated aging characteristic in the worst-case calculation.
Mistake: applying one derating rule to every Class 2 part
There is no single factor supported for all X5R and X7R components. Fix it by using the manufacturer’s data for the exact capacitance, package, and voltage rating, as advised in Analog Devices’ component-selection guidance (Analog Devices’ regulator component-selection note).
What to record in a design review
For each ceramic capacitor that affects circuit performance, record the complete part number, dielectric class, nominal capacitance, tolerance, rated voltage, package, operating temperature range, and the effective-capacitance evidence used in the calculation. For Class 2 parts, attach the bias curve or datasheet page and identify the voltage and temperature points read from it. For Class 1 parts, record why the circuit requires stability and verify that the available capacitance and voltage rating are sufficient.
This record prevents a later substitution from silently changing the circuit. Replacing C0G with X7R, or changing an X7R package while keeping the same nominal value, can alter the actual capacitance enough to change timing, filtering, matching, or transient performance.
Bottom line for the design decision
Pick Class 1 C0G/NP0 when predictable capacitance, low loss, and low drift are worth giving up capacitance density. Pick Class 2 X7R/X5R when a compact, high-capacitance part is more important and the circuit can tolerate temperature, DC-bias, and aging changes. In either case, approve the exact part only after checking its tolerance, voltage rating, package, temperature range, and effective capacitance under the conditions your circuit will actually experience.
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