Crystal equivalent circuit - Page 1
Forum section: electronics / beginners

author: Richardcavell
author_rank: Contributor
timestamp: April 06, 2023, 05:54:02 pm
content: Hello. This is part of the Wikipedia article on crystal oscillators. I don’t understand the first sentence at all. Can someone please explain it?

author: ataradov
author_rank: Super Contributor
timestamp: April 06, 2023, 06:05:49 pm
content: It is pretty clear. It says that crystal electrical model looks like shown on the picture.Don't confuse the model with an actual thing, you can't solder together those components and get a working crystal out of it.But if you apply inputs to the real crystal, it would behave electrically just like that circuit.It is hard to provide a better explanation without knowing your background and the final goal. Usually you don't need to think about this if you just want to use a crustal in an oscillator.

author: ejeffrey
author_rank: Super Contributor
timestamp: April 06, 2023, 06:15:29 pm
content: Quote from: Richardcavell on April 06, 2023, 05:54:02 pmIt's describing the same thing as the circuit diagram. Can you be more specific about what you don't understand? Perhaps you want to read up about series and parallel resonances?The series LCR part is an electrical model of the crystal mechanics (it's mass, spring constant, and mechanical damping). It doesn't correspond to a real inductance, capacitor, or resistor and if you look at the model parameters they will not be realistic for regular electrical components. The crystal is piezoelectric and strain on the crystal causes an electric field, that allows coupling to an electronic circuit and is why we assign an electrical model to the crystal. In order to couple the crystal to our circuit we need to add electrodes to it. These electrodes have a capacitance -- this is a real electrical capacitance, and it shows up in parallel to the crystal LCR. So whole crystal effectively operates as if it were the electrical circuit shown in that diagram.

author: Richardcavell
author_rank: Contributor
timestamp: April 06, 2023, 06:27:20 pm
content: 1. Does the term “electrical network” mean “a bunch of electrical components that are electrically connected”, or “a part of a circuit”, or something like that?2. What are resonant points, and where are they on that schematic?

author: Bud
author_rank: Super Contributor
timestamp: April 06, 2023, 06:40:13 pm
content: 2. Refer to the last line of formulas in your screenshot. Ws is the series resonance frequency (2*pi*Fs), Wp is the parallel resonance frequency (2*pi*Fp).

author: RoGeorge
author_rank: Super Contributor
timestamp: April 06, 2023, 06:48:32 pm
content: Wikipedia is a lousy learning resource. It won't make much sense unless you already know the subject. Find some classes instead, or a good book to learn from.

author: ataradov
author_rank: Super Contributor
timestamp: April 06, 2023, 08:03:45 pm
content: Quote from: Richardcavell on April 06, 2023, 06:27:20 pmExactly. Just the connected components.Quote from: Richardcavell on April 06, 2023, 06:27:20 pmThose are not actual connection points. "resonant point" is a standard term, which basically means resonant frequency.

author: boB
author_rank: Frequent Contributor
timestamp: April 06, 2023, 08:07:17 pm
content: That sentence you are having trouble with is worded very poorly.The word "points" should probably be replaced with the word "frequencies"There are a lot of great Wikipedia articles. Not all of them and certainly not that first sentence I would agree.boB

author: Richardcavell
author_rank: Contributor
timestamp: April 07, 2023, 10:33:21 am
content: 3. I take it that the term “series” means “when a capacitor is connected in series”, and “parallel” means “when a capacitor is connected in parallel”?4. Then low-impedance means “slightly lower impedance”?5. Is the term “impedance” being used to refer mainly to reactance (the alternating current component of impedance), not resistance (the DC component)?

author: Bud
author_rank: Super Contributor
timestamp: April 07, 2023, 01:09:29 pm
content: It is not "slightly", it is a Lot lower (for series resonance) or a Lot higher (for parallel resonance) then out-of-resonance impedance. In case of a crystal resonator the difference is from thousands to tens of thousands times.The term impedance refers to complex impedance which is a combination of resistance and reactance. When the reactive component is zero, the impedance becomes purely resistive. When the resistive component is zero , the impedance becomes purely reactive.