Datasheet

ManualsBrandsMURATA ManualsMicrocontrollers, Microprocessors & QuartzesResonator

1. Differences between a

C E R A LO C K

and a q u artz cry stal

reso nato r

Figure 1 shows the typical frequency

characteristics of phase and im pe-

d ance for CE R A LO CK

CE R A LO CK

is ind uctiv e in the fre-

quency range b etween the resonant

frequency (f

) of the m inim um im pe-

d ance v alue and the anti-resonant

frequency (f

) of the m ax im um

im ped ance v alue. O utsid e these

ranges it is capacitiv e.

W hen using CE R A LO CK

to construct

an oscillator circuit, the ind uctiv e

characteristics b etween f

and f

are

utiliz ed instead of L in the LC oscilla-

tor circuit.

Figure 2 shows the equiv alent circuit

of either CE R A LO CK

or quartz crys-

tal resonators. T he circuit is a series-

parallel resonator circuit that com -

prises the equiv alent resistance R

the equiv alent ind uctance L

, the

equiv alent capacitance C

and the

capacitance b etween the electrod es

. Tab le 1 shows typical v alues for

each circuit elem ent of b oth

CE R A LO CK

and quartz crystal re-

sonators.

Figure 3 shows the analogy b etween

the electrical equation of m otion and

the m echanical equation of m otion.

How to design an oscillator

circu it with C E R A L O C K

www.murata.com

T h e fo llo wing article d escribes h o w to d esig n a clo ck o scillato r circu it by

u sing C E R A L O C K

(reso nato rs), h o w to g et th e o p tim u m circu it co nstant o f

each co m p o nent, and also d iscu sses th e d ifferences between C E R A L O C K

and a q u artz cry stal reso nato r.

F ig u re 1 - F req u ency ch aracteristics

o f im p ed ance and p h ase o f C E R A L O C K

F ig u re 2 - E q u iv alent circu it o f C E R A L O C K

F ig u re 3 - M ech anical and electrical

eq u atio n o f m o tio n

Summary of content (4 pages)

PAGE 1
www.murata.com utiliz ed instead of L in the L C oscillator circuit. Figure 2 shows the equiv alent circuit of either CE R A L O CK ® or quartz crystal resonators.
PAGE 2
www.murata.com Figure 5 - Oscillation characteristics when feedback resistance Rf is changed (2) Load capacitance: CL (CL1 = CL2) (3) Damping resistance: Rd Figure 6a shows the change of oscillation voltage when load capacitance CL is varied. CL is an important parameter that affects the stability and frequency of oscillation. Load capacitance must be carefully selected to match the IC as, when CL gets too small, the wave form becomes distorted (Figure 6b) and oscillation becomes unstable.
PAGE 3
www.murata.com Table 1 - Typical electrical characteristics of CERALOCK® and a quartz crystal resonator CERALOCK® Q uartz crystal resonator Frequency 4 .0 0 MH z 4 .0 0 MH z L1 (µ H ) 887 3.08 x 105 C1 (pF) 1.8 8 5.13 x 10-3 C0 (pF) 15.7 1.8 3 x 103 R1 (Ω) 8 .04 8 .4 8 As shown in Table 1, CERALOCK® has a smaller value of L1 which is equivalent to mass M of the mechanical equation of motion, and a larger value of C1 which is equivalent to the reciprocal of the spring constant k.
PAGE 4
www.murata.com Figure 7 - Oscillation characteristics when damping resistance Rd is changed. range. Another role of Rd is to reduce the current consumption and noise radiation. 3.