Exploring ceramic resonators and filters

These devices provide stable oscillation and selective filtering across a wide range of applications. The post Exploring ceramic resonators and filters appeared first on EDN.

Electronics Dec 23, 2025 0 6 Add to Reading List

Exploring ceramic resonators and filters

Ceramic resonators and filters occupy a practical middle ground in frequency control and signal conditioning, offering designers cost-effective alternatives to quartz crystals and LC networks. Built on piezoelectric ceramics, these devices provide stable oscillation and selective filtering across a wide range of applications—from timing circuits in consumer electronics to noise suppression in RF designs.

Their appeal lies in balancing performance with simplicity: easy integration, modest accuracy, and reliable operation where ultimate precision is not required.

Getting started with ceramic resonators

Ceramic resonators offer an attractive alternative to quartz crystals for stabilizing oscillation frequencies in many applications. Compared with quartz devices, their ease of mass production, low cost, mechanical ruggedness, and compact size often outweigh the reduced precision in frequency control.

In addition, ceramic resonators are better suited to handle fluctuations in external circuitry or supply voltage. By relying on mechanical resonance, they deliver stable oscillation without adjustment. These characteristics also enable faster rise times and performance that remains independent of drive-level considerations.

Recall that ceramic resonators utilize the mechanical resonance of piezoelectric ceramics. Quartz crystals remain the most familiar resonating devices, while RC and LC circuits are widely used to produce electrical resonance in oscillating circuits. Unlike RC or LC networks, ceramic resonators rely on mechanical resonance, making them largely unaffected by external circuitry or supply-voltage fluctuations.

As a result, highly stable oscillation circuits can be achieved without adjustment. Figure below shows two types of commonly available ceramic resonators.

Figure 1 A mix of common 2-pin and 3-pin ceramic resonators demonstrates their typical package styles. Source: Author

Ceramic resonators are available in both 2-pin and 3-pin versions. The 2-pin type requires external load capacitors for proper oscillation, whereas the 3-pin type incorporates these capacitors internally, simplifying circuit design and reducing component count. Both versions provide stable frequency control, with the choice guided by board space, cost, and design convenience.

Figure 2 Here are the standard circuit symbols for 2-pin and 3-pin ceramic resonators. Source: Author

Getting into basic oscillating circuits, these can generally be grouped into three categories: positive feedback, negative resistance elements, and delay of transfer time or phase. For ceramic resonators, quartz crystal resonators and LC oscillators, positive feedback is the preferred circuit approach.

And the most common oscillator circuit for a ceramic resonator is the Colpitts configuration. Circuit design details vary with the application and the IC employed. Increasingly, oscillation circuits are implemented with digital ICs, often using an inverter gate. A typical practical example (455 kHz) with a CMOS inverter is shown below.

Figure 3 A practical oscillator circuit employing a CMOS inverter and ceramic resonator shows its typical configuration. Source: Author

In the above schematic, IC1A functions as an inverting amplifier for the oscillating circuit, while IC1B shapes the waveform and buffers the output. The feedback resistor R1 provides negative feedback around the inverter, ensuring oscillation starts when power is applied.

If R1 is too large and the input inverter’s insulation resistance is low, oscillation may stop due to loss of loop gain. Excessive R1 can also introduce noise from other circuits, while being too small a value reduces loop gain.

The load capacitors C1 and C2 provide a 180° phase lag. Their values must be chosen carefully based on application, integrated circuit, and frequency. Undervalued capacitors increase loop gain at high frequencies, raising the risk of spurious oscillation. Since oscillation frequency is influenced by loading capacitance, caution is required when tight frequency tolerance is needed.

Note that the damping resistor R2, sometimes omitted, loosens the coupling between the inverter and feedback circuit, reducing the load on the inverter output. It also stabilizes the feedback phase and limits high-frequency gain, helping prevent spurious oscillation.

Having introduced the basics of ceramic resonators (just another surface scratch), we now shift focus to ceramic filters. The deeper fundamentals of resonator operation can be addressed later or explored through further discussion; for now, the emphasis turns to filter applications.

Ceramic filters and their practical applications

A filter is an electrical component designed to pass or block specific frequencies. Filters are classified by their structures and the materials used. A ceramic filter employs piezoelectric ceramics as both an electromechanical transducer and a mechanical resonator, combining electrical and mechanical systems within a single device to achieve its characteristic response.

Like other filters, ceramic filters possess unique traits that distinguish them from alternatives and make them valuable for targeted applications. They are typically realized in bandpass configurations or as duplexers, but not as broadband low-pass or high-pass filters, since ceramic resonators are inherently narrowband.

In practice, ceramic filters are widely used in IF and RF bandpass applications for radio receivers and transmitters. These RF and IF ceramic filters are low-cost, easy to implement, and well-suited for many designs where the precision and performance of a crystal filter are unnecessary.

Figure 4 A mix of ceramic filters presents examples of their available packages. Source: Author

A quick theory talk: A 455-kHz ceramic filter is essentially a bandpass filter with a sharp frequency response centered at 455 kHz. In theory, attenuation at the center frequency is 0 dB, though in practice insertion loss is typically 2–6 dB. As the input frequency shifts away from 455 kHz, attenuation rises steeply.

Depending on the filter grade, the effective passband spans from about 455 kHz ± 2 kHz for narrow designs and up to ±15 kHz for wider types (in theory often cited as ±10 kHz). Signals outside this range are strongly suppressed, with stopband attenuation reaching 40 dB or more at ±100 kHz.

On a related note, ceramic discriminators function by converting frequency variations into voltage signals, which are then processed into audio detection method widely used in FM receivers. FM wave detection is achieved through circuits where the relationship between frequency and output voltage is linear. Common FM detection methods include ratio detection, Foster-Seeley detection, quadrature detection, and differential peak detection.

Now I recall the CDB450C24, a ceramic discriminator designed for FM detection at 450 kHz. Employing piezoelectric ceramics, it provides a stable center frequency and linear frequency-to-voltage conversion, making it well-suited for quadrature detection circuits such as those built with the nostalgic Toshiba TA31136F FM IF detector IC for cordless phones. Compact and cost‑effective, the CDB450C24 exemplifies the role of ceramic discriminators in reliable FM audio detection.

Figure 5 TA31136F IC application circuit shows the practical role of the CDB450C24. Source: Toshiba

As a loosely connected observation, the choice of 450 kHz for ceramic discriminators reflected receiver design practices of the time. AM radios had long standardized on 455 kHz as their intermediate frequency (IF), while FM receivers typically used 10.7 MHz for selectivity.

To achieve cost-effective FM detection, however, many designs employed a secondary IF stage around 450 kHz, where ceramic discriminators could provide stable, narrowband frequency-to-voltage conversion.

This dual-IF approach balanced the high-frequency selectivity of 10.7 MHz with the practical detection capabilities of 450 kHz, making ceramic discriminators like the CDB450C24 a natural fit for FM audio demodulation.

Thus, ceramic filters remain vital for compact, reliable frequency selection, valued for their stability and low cost. Multipole ceramic filters extend this role by combining multiple resonators to sharpen selectivity and steepen attenuation slopes, their real purpose being to separate closely spaced channels and suppress adjacent interference.

Together, they illustrate how ceramic technology continues to balance simplicity with performance across consumer and professional communication systems.

Closing thoughts

Time for a quick pause—but before you step away, consider how ceramic resonators and filters continue to anchor reliable frequency control and signal shaping across modern designs. Their balance of simplicity, cost-effectiveness, and performance makes them a quiet force behind countless applications.

Share your own experiences with these components and keep an eye out for more exploration into the fundamentals that drive today’s electronics.

T. K. Hareendran is a self-taught electronics enthusiast with a strong passion for innovative circuit design and hands-on technology. He develops both experimental and practical electronic projects, documenting and sharing his work to support fellow tinkerers and learners. Beyond the workbench, he dedicates time to technical writing and hardware evaluations to contribute meaningfully to the maker community.