Ceramic Resonators

Description: The feedback resistor sets the bias of the oscillation circuit. Typically, CMOS ICs utilize feedback resistances ranging from 100k ohms to 10M ohms (commonly 1M ohms), while TTL ICs employ feedback resistances from 1k ohms to 10k ohms (usually 4.7k ohms) due to their low I/O impedance. An excessively high feedback resistance can lead to reduced feedback, making the operating point unstable. Conversely, if the feedback resistance is too low, the gain may decrease or the current may increase (recently, many ICs integrate the feedback resistor). The damping resistor and loading capacitors act as low-pass filters, suppressing abnormal harmonic oscillation by lowering gain in the high-frequency range. Additionally, the IC gain can be limited, and with proper matching of CERALOCK®, unwanted ringing, overshoot, and undershoot can be mitigated. For damping resistance, several kilo-ohms are recommended in the kHz range, while in the MHz range, it should be between tens and hundreds of ohms. The damping resistor is optional but crucial for determining the stability of the oscillation circuit. If the load capacitance is too small, the oscillating waveform will distort, resulting in unstable oscillation, while excessive load capacitance may halt oscillation. When comparing the same IC, oscillation circuits designed for lower frequencies require larger capacitance. If the IC gain is excessively high or if a TTL or triple-stage buffered IC is employed, a bias resistor may be used to intentionally adjust the bias point to decrease the IC gain or suppress unstable oscillation. CMOS ICs typically use bias resistors between 1M ohms and 10M ohms, while TTL employs bias resistors from several kilo-ohms to 10 kilo-ohms. A ceramic capacitor with excellent frequency characteristics is ideal as a loading capacitor in an oscillation circuit, typically requiring load capacitance of approximately 3pF to 2200pF. Since the oscillation frequency of CERALOCK® varies with load capacitance, it is advisable to select a higher-precision type, temperature drift-compensating type (with high Q), and a temperature coefficient "0" type (tolerance "J," temperature characteristics "CH"). Generally, a capacitor with a total tolerance of +/-20% (including initial capacitance tolerance and fluctuations due to temperature changes from -20 °C to 80 °C) is acceptable. However, abnormal oscillation or oscillation stoppage may occur depending on the specific IC used, although such cases are rare. Based on Murata's evaluation results, if stable oscillation is achieved after adjusting the load capacitance by two steps from the recommended constant under the E6 system, there should be no issues. Furthermore, it is essential to verify that the system operates normally while the load capacitance changes, as the oscillation frequency is affected by load capacitance variations. To differentiate between two scenarios, replace the CERALOCK® with a capacitor (Cx) of the same capacitance. In the second scenario, the circuit can maintain normal oscillation even if CERALOCK® is substituted with Cx. CERALOCK® can generate various parasitic oscillations (spurious oscillations) alongside the intended main oscillation frequency. If the oscillation circuit operates with inappropriate circuit constants, parasitic oscillations may arise. Commonly observed spurious modes are documented. Should oscillation stoppage or failure occur, it is necessary to investigate potential causes, including malfunction of the CERALOCK®, mismatch between CERALOCK® and IC, or reset program errors. However, if the IC does not function as an amplifier, oscillation will be disabled regardless. Therefore, an initial check of IC operation is essential, which can be performed by simply connecting the IC.

The feedback resistor plays a critical role in determining the stability and performance of oscillation circuits in both CMOS and TTL technologies. The choice of feedback resistance directly influences the circuit's bias point, gain, and overall stability. In CMOS applications, feedback resistances of 1M ohm are common due to the higher input impedance, while TTL circuits require lower values to accommodate their lower I/O impedance characteristics. The damping resistor and loading capacitors are vital components that function to mitigate unwanted high-frequency oscillations, helping to stabilize the output waveform.

The selection of damping resistance values is crucial; in lower frequency applications (kHz), several kilo-ohms are typically employed, while higher frequency circuits (MHz) may require values in the tens to hundreds of ohms range. This careful selection of damping resistance aids in preventing potential oscillation instability and ensures reliable circuit performance.

The load capacitance is another key parameter that must be optimized for stable oscillation. An imbalance in load capacitance can lead to waveform distortion or complete cessation of oscillation. The design of oscillation circuits for lower frequencies necessitates larger capacitors to maintain stability. The use of ceramic capacitors is recommended due to their favorable frequency characteristics, and careful consideration should be given to the tolerance and temperature coefficients of these capacitors to ensure consistent performance across varying environmental conditions.

In conclusion, the proper configuration of feedback and bias resistors, along with the appropriate selection of damping resistors and load capacitance, is essential for the reliable operation of oscillation circuits. Regular evaluation and testing are recommended to confirm that the circuit maintains stable oscillation under varying conditions, ensuring optimal functionality and performance.The feedback resistor determines the bias of the oscillation circuit. Generally, C-MOS IC uses 100k ohms to 10M ohms (normally, 1M ohms) feedback resistance, while TTL IC uses 1k ohms to 10k ohms (normally, 4. 7k ohms) feedback resistance because of low I/O impedance. If the feedback resistance is too large, the amount of feedback will be reduced, making the operating point unstable. If the feedback resistance is too small, the gain will be reduced, or the current will be increased (Recently, most ICs intgrates the feedback resistor). Damping resistor and loading capacitors work as low-passfilter that can suppress abnormal harmonic oscillation by reducing the gain in the high frequency range.

Also, the IC gain can be limited and CERALOCK ® properly match IC, unwanted ringing, overshoot and undershoot can be suppressed. In the kHz band, the damping resistance should be several kilo-ohms, and in the MHz band, it should be between tens ohms and hundreds ohms.

The damping resistor is optional. This parameter is the most important for determining the stability of the oscillation circuit. If the load capacitance is too small, the oscillating waveform will be distorted, resulting in unstable oscillation. If it is too large, oscillation may stop. When compared with the same IC, the oscillation circuit providing lower frequency needs larger capacitance.

When the IC gain is too high, or when TTL or triple-stage buffered IC is used, the bias resistor can be used to change the bias point intentionally in order to reduce the IC gain or suppress unstable oscillation. C-MOS IC uses a bias resistor of 1M ohms to 10M ohms, while TTL uses a bias resistor of several kilo-ohms to 10 kilo-ohms.

A ceramic capacitor with excellent frequency characteristics is most suitable as a loading capacitor in an oscillation circuit, because normally the load capacitance of approx. 3pF to 2200pF is required for an oscillation circuit. Since the oscillation frequency of the CERALOCK ® varies depending on the value of the load capacitance, we recommend you select higher-precision type, temperature drift-compensating type (with high Q), and temperature coefficient "0" type (tolerance "J, " temperature characteristics "CH").

Generally, you will have no problem using a capacitor providing total tolerance of +/-20% (including the initial capacitance tolerance and fluctuations due to temperature change from -20 °C to 80 °C). However, you must remember that abnormal oscillation or oscillation stop may occur depending on the IC being used, although this is a rare case.

Judging from Murata`s evaluation results, if stable oscillation is provided after the load capacitance is increased/reduced by two steps from the recommended constant under the E6 system, it raises no problem. Furthermore, you must confirm that the set can operate normally while the load capacitance changes, because the oscillation frequency varies with the change in load capacitance.

In order to distinguish 1 from 2 above, replace the CERALOCK ® with a capacitor (Cx) with the same capacitance as the CERALOCK ®. In case of Type 2, the circuit can provide normal oscillation even if the CERALOCK ® is replaced by Cx.

The CERALOCK ® will develop many kinds of parasitic oscillations (spurious oscillations) in addition to the oscillation with the target frequency (main oscillation frequency). If the oscillation circuit is operated with improper circuit constants, parasitic oscillations may occur.

Commonly observed spurious modes are listed in Table 1. If oscillation stop occurs, or oscillation is disabled, you must examine the cause of the problem, such as malfunction of the CERALOCK ®, mismatching between CERALOCK ® and IC or reset program error. However, if the IC is not operating as an amplifier, oscillation is disabled by any means. Therefore, you must perform IC operation check first. The IC operation can be checked simply by connecting the IC