Abusuabɔ a Ɛda Abɔnten So Adesoa Capacitors ne Crystal Adesoa Ntam

Wɔ ɛlɛtrɔnik akwansin mu no, ahwehwɛ a ɛwosow yɛ dɔn no fibea a wɔtaa de di dwuma no mu biako. Sɛnea ɛbɛyɛ a wobɛhwɛ sɛ crystal oscillator no fi ase yiye na ɛyɛ adwuma yiye no, ɛsɛ sɛ wɔyɛ abɔnten so adesoa capacitors a ɛwɔ ɔmansin no mu no yiye sɛnea ne adesoa capacitance (CL) te. Capacitor a ɛnsɛ sɛ ɛne ne ho hyia no betumi ama ayɛ den wɔ oscillation mu, frequency deviation a ɛkɔ soro, na mpo system no ntumi nnyina.

Saa asɛm yi bɛma nhwehwɛmu a ɛkɔ akyiri a ɛfa nea crystal oscillator load capacitance kyerɛ, ɔkwan a wɔfa so bu akontaa ma abɔnten capacitors, ne nsusuwii a mfaso wɔ so wɔ circuit nhyehyɛe mu.

Ⅰ. Dɛn ne adesoa capacitance (CL) a ɛwɔ crystal oscillator mu?

Crystal manufacturers taa kyerɛ nominal load capacitance value (CL) wɔ datasheet no mu, te sɛ 18pF, 20pF, 12pF, ne nea ɛkeka ho Eyi gyina hɔ ma capacitive adesoa a ɛwɔ ase calibrated crystal no sɛnea ɛbɛyɛ a wobenya ne nominal oscillation frequency.

Ɔkwan foforo so no, crystal oscillator no betumi de frequency a ɛyɛ pɛpɛɛpɛ adi bere a adesoa capacitance a ɛyɛ pɛ no yɛ pɛ CL nkutoo.

Ⅱ. Ɔkwan Bɛn so na Abɔnten So Adesoa Capacitors Ka Adesoa Capacitors?

Crystal oscillator circuit a wɔtaa yɛ no fa ɔkwan a edidi so yi so:

C1 ne C2 yɛ abɔnten capacitors abien a ɛka asase ho (mpɛn pii no SMD capacitors);

XTAL no ntwamutam abien no bata crystal oscillator no pin abien no ho;

Wɔ nneyɛe mu no, adesoa capacitance CL a ɛyɛ pɛ a ɛwɔ crystal no mu no, C1 ne C2 a ɛtoatoa so na ɛkyerɛ, a wɔde parasitic capacitance Cp a PCB ne package no de bae no ka ho.

Ⅲ. Nkontaabu Fomula: Ɔkwan Bɛn so na Wogyina CL So Hu Abɔnten Capacitor Bo?

Fomula a wɔde yɛ adesoa a ɛyɛ pɛ (CL) no te sɛ nea edidi so yi:

Ɛhe:

C1, C2: Abɔnten capacitors a wɔde abɔ asase ho;

Cp: ​​Parasitic capacitance a PCB traces, packaging, ne nea ɛkeka ho de ba (mpɛn pii no 2pF kosi 5pF, wobetumi asusuw ho denam simulation anaa osuahu so);

CL: Nominal adesoa capacitance a wɔakyerɛ wɔ crystal oscillator datasheet no mu.

【Nhwɛso a Wɔde Kyerɛkyerɛ】

Fa no sɛ ahwehwɛ nkyerɛkyerɛmu no yɛ CL=18pF, na PCB parasitic capacitance Cp ≈ 5pF. Sɛ wobɛbu nsusuiɛ a ɛfata ama C1 ne C2 a:

Nea edi kan no, fa gyinapɛn ahorow no si fomula no ananmu:

Sɛ yɛfa no sɛ C1=C2=C a, fomula no yɛ mmerɛw sɛ:

Nea afi mu aba ne sɛ:

✅ Enti, abɔnten capacitors a wɔkamfo kyerɛ ne: C1=C2=.27pF na ɛwɔ hɔ (Gyinapɛn Botae).

Ⅳ. Dɛn Nti na Abɔnten so Capacitors a Ɛnhyia no De Ɔhaw Ba?

Frequency deviation: Sɛ abɔnten capacitors no sua dodo anaasɛ ɛsõ dodo a, crystal no bɛtwe ne ho afi ne frequency a wɔfrɛ no no ho, na ɛde system clock mfomso bɛba.

Start-up difficulty anaa instability: Adesoa a ɛboro so ma mfasoɔ so tew, a ɛbɛtumi ama crystal no rentumi mfi aseɛ anaasɛ ɛnte frequency jitter.

Tumi a wɔde di dwuma a ɛkɔ soro: Nneɛma a wɔde gu mu a ɛnsɛ no ma ahoɔden a wɔde di dwuma kɛse wɔ crystal oscillator circuit no mu.

EMI a ɛkɔ soro: Oscillations a entumi nnyina no betumi ama spurious frequency ahorow aba, na aka system electromagnetic compatibility (EMC).

5. Design Recommendations ne Engineering Nneyɛe

Hwɛ crystal oscillator datasheet no mu yiye

Kyerɛ CL bo a ɛsom.

Te ɔmansin topology a wɔkamfo kyerɛ no ase.

Hwɛ sɛ wɔkamfo abɔnten capacitor botae ahorow bi kyerɛ anaa.

2. Susuw board tebea ankasa ho

Fa PCB simulation anaa osuahu di dwuma de bu Cp ho akontaa.

Wɔ dɔn a ɛwɔ ahoɔhare kɛse anaa nea ɛyɛ pɛpɛɛpɛ (sɛ nhwɛso no, nkitahodi nhyehyɛe, MCU frequency titiriw > 100MHz) ho no, wɔkamfo akontaabu anaa sɔhwɛ a ɛyɛ pɛpɛɛpɛ kyerɛ.

3. Fa capacitors a ɛyɛ symmetrical di dwuma

Wɔtaa kamfo kyerɛ sɛ C1=C2 mfa frequency no mfinimfini na ɛkari pɛ dede.

Wobetumi nso de asymmetrical design adi dwuma ama ahwehwɛde soronko a ɛne ne ho hyia.

4. Fa SMD capacitor array di dwuma ma debugging

Sɔ SMD capacitors (sɛ nhwɛso no, 10pF, 15pF, 22pF, 27pF, ne nea ɛkeka ho) hwɛ na woahu nea ɛfata;

Hwɛ output stability ne frequency pɛpɛɛpɛ denam spectrum analyzer anaa oscilloscope so.

6,Daa daaFAQ

Awie

Nsusuwii a wɔde yɛ abɔnten adesoa capacitors ma crystal oscillator yɛ ade ketewaa bi nanso ɛho hia a ɛka dɔn nhyehyɛe no gyinabea ne pɛpɛɛpɛyɛ tẽẽ. Nteaseɛ a ɛfa akontabuo abusuabɔ a ɛda CL ne C1/C2 ntam, ne nsakraeɛ a ɛfa parameters a egyina PCB parasitic capacitance ankasa so no yɛ ade titire a ɛbɛma yɛanya oscillation a wotumi de ho to so ne frequency a ɛyɛ pɛpɛɛpɛ.

Wɔ digyital nhyehyɛe a ɛyɛ ahoɔhare kɛse, nkitahodi mfiri, anaa nhyehyɛe a ɛwɔ dɔn ahwehwɛde a ɛyɛ den yiye mu no, paw a ɛfata na ɛne crystal oscillator no adesoa ahoɔden hyia no yɛ mfiridwuma adwuma a ɛsɛ sɛ wobu no aniberesɛm.

HCI na ɛyɛ adwumawɔ aduruyɛdan a ɛyɛ adwumayɛfo de ne mfiridwumayɛfo kuw bi a wɔde bɛboro mfe 20 ayɛ adwuma, a wɔde adwumayɛfo a wɔde wɔn ho hyɛ mu ne sɔhwɛ adwuma a wontua hwee ma adetɔfo. Sɛ wowɔ ahiade biara wɔ eyi ho a, yɛsrɛ wo ntwentwɛn wo nan ase sɛ wobɛka yɛn adetɔn anaa mfiridwuma adwumayɛfo no ho nkɔmmɔ.