Talk:Pierce oscillator

Function
Currently, the function of C1, C2, and the crystal is misleading. The internal resistance of the inverter (R0, which is not depicted) and C2 create an RC network, giving something like 70 degrees of phase at resonance. Then, the crystal/C1 network gives another 110 degrees or so at resonance, giving the required 360 degrees of phase. Would someone please change the description and figure? Please see pages 48 and 52. Rocketman768 (talk) 19:13, 23 September 2011 (UTC)

Load capacitance
The average capacitance (C1+C2)/2 is called the "load capacitance". (this article)
 * "In the popular Pierce oscillator circuit, which has a capacitor to ground on either side of the crystal, the load capacitance is equal to the series combination of the two capacitors plus Cstray."(James B. Northcutt)
 * "So what load is your Pierce-gate oscillator presenting to the crystal? A simple calculation illustrated with Figure 2 will tell you: Cload = {[Cin+C1][C2+Cout]/[Cin+C1+C2+Cout]} + pcb strays (2~3pF)" (Ramon Cerda)
 * "to implement a Pierce oscillator ... The load capacitance is given by: CL = ((C1 x C2) / (C1 + C2)) + Stray"(D. Ibarra)
 * Load capacitance is calculated as follows: Pierce circuit CL = (C1 x C2) / (C1 + C2) + Cstray(Abracon)
 * The CX crystal calibration tolerance is influenced by the effective circuit capacitances, specified as the load capacitance (CL.) CL is approximately equal to: CL = (C1 x C2) / (C1 + C2) + CS(Euroquartz)
 * CA and CB are chosen such that their series combination capacitance equals the load capacitance specified by the manufacturer, ie 20 pF or 32 pF as mentioned.(fairchild)
 * It should be noted that the actual loading capacitance to the crystal equals CL1 || CL2 plus the parasitic capacitance of board and the terminals of the inverters.(Maxim)

What is it really, for our purposes? Provide a reference. — Omegatron 19:36, 18 May 2007 (UTC)


 * Oh wait. I just realized that "series combination" means the same thing as (C1 x C2) / (C1 + C2), which makes these all agree with each other, more or less, and the article is the only thing that disagrees.  So the stray capacitance is in parallel and therefore summed with a normal addition sign? — Omegatron 19:50, 29 May 2007 (UTC)

Yes, you are right. "series combination" means the same thing as all those other formulas (except the incorrect formula I originally posted).

The incorrect formula came from a hasty mis-reading of this text:
 * "The total value of capacitance at the crystal's terminals is (Ca+Cp)/2, where Ca is the actual value of capacitor, per pin, that you place at the OSC1 and OSC2 pins, and Cp is the per pin parasitic capacitance. Cp is usually about 8pF or so. So, if your crystal wants to see a 20pF load, you will need to put 32pF capacitors at both OSC1 and OSC2: (32+8)/2 = 20pF." -- http://techref.massmind.org/techref/clocks.htm

Sorry about that. --76.209.28.72 05:28, 13 June 2007 (UTC)

I'm pretty sure there are 2 "stray capacitances". One stray capacitance from one pin of the crystal to GND (including the gate input capacitance), in parallel with C1. And another stray capacitance from the other crystal pin to GND (including the gate output capacitance). So we have


 * $$C_L = (C_1 + C_{s1}) \| (C_2 + C_{s2}) = {1 \over {1 \over C_1 + C_{s1} } + {1 \over C_2 + C_{s2} } }$$

For the very common case where (approximately) C1 &asymp; C2 and C_s1 &asymp; C_s2, we have
 * $$C_L \approx (C_1 + C_{s1})/2 = {C_1 \over 2} + {C_{s1} \over 2} = {C_1 \over 2} + C_{stray}$$

Since both C_s1 and C_s2 (and their series combination, C_stray) are so small that they are difficult to measure -- and since the crystal will still oscillate very close to the nominal frequency even if your estimate of that capacitance is off by an order of magnitude -- then the slightly simplified rule-of-thumb equations are more than adequate. --76.209.28.72 05:28, 13 June 2007 (UTC)

Move
Someone left a comment in the text:

perhaps move some of this text to Crystal_oscillator ?

— Omegatron 14:56, 4 June 2007 (UTC)

Incomprehensible to non-experts
Sentences such as "The total capacitance seen from the crystal looking into the rest of the circuit is called the "load capacitance". When a manufacturer makes a "parallel" crystal, a technician uses a Pierce oscillator with a particular load capacitance (often 18 or 20 pF) while trimming the crystal to oscillate at exactly the frequency written on its package." are assumingly inscrutable for readers who do not happen to be technicians. 213.196.212.227 (talk) 00:39, 1 February 2011 (UTC)

Too long link?
Link reference n. 2 is too long and create an orizzontal scrollbar and a very large page. — Preceding unsigned comment added by 151.60.125.226 (talk) 15:11, 9 July 2011 (UTC)

Misleading figure
It is quite obvious that if you actually build the circuit in the figure nothing will happen. It is just a bunch of passive components (two capacitors, a transistor and a crystal) connected to the ground. Anybody trying to understand why this thing may be oscillating will just be puzzled, loose time and feel disgusted by electronics.

Could the local Wikipedia-ayatollah who feels in charge of this page make the changes to correct it?

Sorry for not spending the time to investigate the question and do it myself. I got a PhD in physics and nuclear engineering 15 years ago, working in computational biology since then. I was one of the earliest writer and promoter of Wikipedia, but I have spent too much time editing pages in my true domain of expertise seeing my contribution reverted by narrow-minded Wikipedia purists to actually make much more efforts for this community. (This edit may well be my last contribution ever to Wikipedia.) — Preceding unsigned comment added by 84.75.57.200 (talk) 18:52, 31 May 2013 (UTC)

I removed the circuit diagram at the right, as you suggested. Without any place for power to go into the circuit, how can it possibly work? --DavidCary (talk) 00:02, 29 July 2013 (UTC)


 * It is a simplified schematic. The biasing details have been omitted to show just the basic circuit topology. I have seen such figures in texts. Glrx (talk) 04:52, 29 July 2013 (UTC)


 * It has been simplified beyond legibility. The PhD above, and me with a BS, are unable to stare at the diagram and suss it out. You expect the average wikipedia reader to do better? Deleting again. Add power, polarity, and ground.


 * Many text books have similar figures to show basic principle. Anyone familiar with transistor know that NPN transistors have positive terminal of power supply at its collector, as evident by arrowhead. And for high frequency, power is supplied through a 'choke' coil. شہاب (talk) 18:46, 14 August 2018 (UTC)


 * Get rid of that diagram. The top one is simpler to understand. This diagram omits a crucial resistor/choke which makes the diagram confusing. If other text books have the diagram, let their readers be confused. 206.125.145.230 (talk) 18:30, 20 June 2021 (UTC)