Why ceramic resonators? Ceramic resonators stand between quartz crystal oscillators and LC/RC oscillators in regard to accuracy. They are considerably smaller, require no adjustments, with improved start-up time and low in cost.
Package: Ceramic resonators come with standard, single-in-line package (ZTA, ZTB and ZTT), or 3-leads with built-in capacitors (ZTTS, ZTTCV).
Properties: The oscillation of ceramic resonators is dependent upon mechanical resonance associated with their piezoelectric crystal structure. These materials (usually barium titanate or lead-zirconium titanate) have large dipole movement which causes the distortion or growth of the crystal by an applied electric field.
Frequency Range: The available frequency range varies from 190 kHz to 50 MHz.
Frequency Stability: The maximum allowable frequency deviation compared to the measured frequency at 25o C over the temperature window, i.e., -20oC to +80oC. The typical stability is ± 0.3% (±3000ppm).
Frequency Tolerance: The allowable deviation from the nominal frequency at room temperature. Frequency tolerance is expressed in percentage, typical ±0.5% or in parts per millions (ppm), ±5000ppm.
Resonant Impedance: The value of impedance the crystal exhibits in the operating resonant circuit.
Aging: The relative frequency change over a certain period of time. This rate of change of frequency is normally exponential in character. Typically, aging is ±0.5% over 10 years.
Load Capacitance: Load capacitance (CL) is the amount of capacitance that the oscillator exhibits when looking into the circuit through the two resonator terminals. Load capacitance is expressed in a pair of Cl and C2 with the default values given in table.
Equivalent Circuit: Its equivalent circuit is similar to the quartz crystal equivalent circuit, i.e., consists of a series Ll, Cl, Rl circuit shunting with a parallel CO capacitance. A standard ZTAS-MG-4.00MHz has its typical parameters as follows: L – 330uH, Cl – 5pF, C0 – 40pF, and Q ~ 900.
TEST CIRCUITS FOR CERAMIC RESONATORS
Ceramic resonators: with built-in capacitors: It consists of a CMOS inverter with a feedback resistor Rf (figure 2). The feedback resistor allows oscillation to start when power is initially applied. Its value is generally 1 MΩ. The values of Cl and C2 are given in the table or specified by customer.
Ceramic resonators are used mainly as a source of clock signals for many microprocessors, where tight frequency stability is not a primary concern. Ceramic resonators are low in cost and are built-in with capacitance for space savings. Ceramic resonators are mainly used in consumer electronics applications (TV, VCR, games, radios) and household appliances.