Talk:Colpitts oscillator

message: This is a real electrical circuit design and should exist. I am not best qualified to provide the content Rjstott 05:10, 9 Aug 2004 (UTC)
thread_title: Early comment

message: Is this your original analysis, or does it come from a published source?
: This particular derivation is my own work, but similar analyses exist in various engineering texts. The results can be verified in a Spice simulation as well. Madhu 21:40, 16 October 2006 (UTC)
replies: text: I think it is. Perhaps it should be a bit more concise, but I think it's good to show exactly why the circuit oscillates. Yes, many more considerations should be added, but as with all other articles, this is still a work in progress. Feel free to add any more details you think seem fit. -Roger (talk) 06:23, 11 December 2008 (UTC)
replies: text: Having looked at other pages (transformer), I see that the idea is to have a short, concise introduction, and then - in a structured manner - add as much detail as one is able to write :-). Thanks, Roger. -- Rainglasz (talk) 09:33, 11 December 2008 (UTC)
thread_title:  Stability analysis 

message: Basic intention was to clarify that in the circuit used in Fig. 2, the common point of the two capacitors is not output, but input of the LC tank. This required a larger rewrite and induced other changes, e.g. in the first paragraph. -- Rainglasz (talk) 22:14, 10 December 2008 (UTC)
thread_title:  Introduction rewrite 

message: Hi guys.
I'm new to electronics and oscillators are confusing to me. Would it be possible for someone to include a section describing qualitatively how the oscillator works, in reference to one of the circuit diagrams already included in the article? There's a good description of how an astable mulitvibrator works here: http://en.wikipedia.org/wiki/Astable_multivibrator#Operation which I found quite useful in understanding its operation. Something like that would be quite helpful. It seems wherever I look on the net to find an explanation, most results only offer minimal, vague descriptions which I am sure is sufficient for those in the know but its hard to understand for a newcomer, particularly where it seems like there are million different ways to design or incorporate any particular type of oscillator into a circuit. Hopefully something more than 'this part is the tank circuit, this part feeds back into it to sustain oscillations'. That may (or may not) be an apt description of its operation but it requires you to just accept a lot of it on faith, if you know what I mean. Like, there is a bit of a gap going from understanding how an oscillating circuit with only a charged capacitor and an inductor works to trying to understand 
something more complex like this.
That's just my opinion of a novice reading the article however...
Cheers. 
Gunnergrady (talk) 05:35, 18 July 2011 (UTC)
thread_title:  How does it work? 

message: Hi again guys,
Sorry to be a nuisance. I am still trying to get my head around how LC oscillators in general work. 
The query I have is regarding Figures 1 and 2. The symbol with the designation Ic (the circle with the arrow in it) I am assuming indicates a DC current, is this correct? This is the closest symbol definition I could come up with. In any case, if there is a connection between the two capacitors straight to ground as seems to be what is indicated in the figures, the second capacitor is grounded on either side, so what role can it play in the circuit? I fully admit that I may have misinterpreted the diagram but I would like to confirm that they are actually correct. 
Furthermore, wouldn't it be useful on the figures to indicate from which point in the circuit the output is taken?
Cheers,
Gunnergrady (talk) 07:17, 5 August 2011 (UTC)
replies: text: The figure with an arrow is a DC current source. There is no connection straight to ground. A current source has an infinite impedance (unlike a voltage source that has a zero impedance). Glrx (talk) 18:41, 5 August 2011 (UTC)
replies: text: Fair enough. You guys obviously know what you are talking about, even though it's over my head. Gunnergrady (talk) 04:28, 6 August 2011 (UTC)
thread_title:  Figures 1 and 2 

message: I've just answered a Colpitts question over on Stack Exchange, referring them here. Figures 1 and 2, the C1 and C2 component designators get swapped between the common base and common collector versions. That's not a noob-friendly thing to do to somebody struggling with the concepts of 'ground's just another node', and 'neglecting bias components' that we experienced EEs do all the time. Does anybody feel ownership of these diagrams and be motivated to change it? Should I just change it myself once I've figured out how to do it? I'll read through the text to make sure that any references it makes are consistent with both diagrams of course, maybe even add the common emitter diagram for completeness Apostrostomper (talk) 04:00, 5 May 2020 (UTC)
thread_title: More on Figures 1 and 2

message: The original text placed too much emphasis on the requirement of a capacitive feedback voltage divider. This is very misleading as the Colpitts oscillator does not require such a connection. Indeed, such a required connection was clearly contradicted by Fig 2, and the original patent drawing version.  
Kevin aylward (talk) 16:24, 26 December 2012 (UTC)
replies: text: The Colpitts is distinguished in that feedback is taken from a capacitive voltage divider across the inductor.  The Clapp oscillator has a capacitive voltage divider, but it is not across the inductor; there is an extra capacitor in there.  Fig. 2 of the Colpitts patent clearly shows a capacitor voltage divider connected to the tube's cathode.   I changed the introductory text back. If you have doubts check the 4 citations at the end of the sentence. --ChetvornoTALK 19:48, 28 December 2012 (UTC)

text: Patent figure 2 clearly has the two capacitors (labeled 16 and 13). Figure 3 of the patent does not have capacitor 13, but the text of the patent explains that the capacity of antenna 28 is used in place of 13. Patent figure 1 shows a topological Clapp, but the text explains that capacitor 21 is a blocking capacitor (DC stopping) rather than a tuning capacitor. Glrx (talk) 18:04, 29 December 2012 (UTC)
replies: text: And it's not important what a Colpitts oscillator was back then.  For WP what counts is the current usage in technical literature (WP:RS), such as the citations given. --ChetvornoTALK 14:12, 7 February 2013 (UTC)
thread_title:  Basic Theory Description

message: I have re-added in the information that the Colpitts oscillator uses only one active component. This was an absolutely crucial reason for the invention and patent of this particular oscillator. Many oscillators at the time had several tubes and consequently, were very expensive. A single tube was the key distinguishing feature of the Colpitts oscillator, and this should be noted, more so than the simple presence of two capacitors, and a single inductor.  — Preceding unsigned comment added by Kevin aylward (talk • contribs) 11:44, 28 December 2012 (UTC)
replies: text: Do you have a source for a single tube being a distinguishing feature? My understanding is that early oscillators were all one tube affairs. The 1913 tickler oscillator was one tube. The single tube did not distinguish the 1918 Colpitts from the 1915 Hartley according to you. There was a significant effort to put many functions into a single tube (e.g., oscillator and a mixer). Glrx (talk) 17:36, 29 December 2012 (UTC)
thread_title: Single Active Device

message: The practical circuit will need decoupling between 0v and the + side of the inductor else the power supply will form part of the tank circuit.
In fact, it needs to be a low inductance, low resistance high capacitance (much higher than c1 and c2 in order not to load the tank circuit.Nick Hill (talk) 12:35, 9 August 2015 (UTC)
replies: text: It's not a "practical schematic"; power supplies are typically viewed as a perfect short. Glrx (talk) 03:02, 15 August 2015 (UTC)
replies: text:  Agreed. But since it is described as practical, and since a modification makes the design realisable using practical components (I have built this design with real components) it would be only fair to demonstrate the supply as decoupled. This could have an added benefit of making the tank circuit structure more obvious to those with less EE experience. Nick Hill (talk) 22:21, 19 August 2015 (UTC)
replies: text: The practical example has now a capacitor between power supply and ground - as every RF engineer includes automatically. Simulation with LTSpice gives easy oscillation and breadboarding of circuit was immediate success, too. AndreAdrian (talk) 14:32, 20 February 2024 (UTC)
thread_title: Practical circuit example

message: 1. It would be nice to replace figures 1 and 2 with circuits that show the bias.
2. "If the two capacitors are replaced by inductors and magnetic coupling is ignored, the circuit becomes a Hartley oscillator. In that case, the input impedance is the sum of the two inductors and a negative resistance given by: R_{in} = -g_m \omega ^ 2 L_1 L_2.
In the Hartley circuit, oscillation is more likely for larger values of transconductance and larger values of inductance.
Interestingly, the above analysis also describes the behavior of the Pierce oscillator. The Pierce oscillator, with two capacitors and one inductor, is equivalent to the Colpitts oscillator. Equivalence can be shown by choosing the junction of the two capacitors as the ground point. An electrical dual of the standard Pierce oscillator using two inductors and one capacitor is equivalent to the Hartley oscillator."
All of the above information should not be in this article. It should be in the Hartley and Pierce oscillators articles.
3. For the equation V_C = 2 I_C R_L \frac{C_2}{C_1 + C_2}, what is RL if there is an inductor at the collector?
ICE77 (talk) 08:53, 11 August 2015 (UTC)
thread_title:  Comments and question 

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thread_title:  External links modified 

message: The circuit has the inductor connected to the positive rail which has no RF decoupling at all.  The positive rail should have a capacitor (0.01 uF) connected between it and common negative.  This allows the current that is circulating between inductor and the two capacitors to do so without having to go through the power supply.  In the real world, this can make the difference between the circuit oscillating and not oscillating.
This is also the reason why it should not be a practical circuit - it is incomplete.  — Preceding unsigned comment added by 2600:1700:CD40:C510:5CFC:C486:54E6:F04C (talk) 05:56, 30 January 2022 (UTC)
replies: text: Added capacitor parallel to battery, added load resistor, removed "dubious" flag. AndreAdrian (talk) 12:55, 17 February 2024 (UTC)
thread_title: Practicality of circuit in diagram

message: It seems odd that right after saying it was invented in 1918, we start giving examples of transistor circuits.  Wouldn't it make more sense to start with a tube circuit and then segue into the more modern implementations? RoySmith (talk) 19:19, 30 January 2024 (UTC)
thread_title:  Why no tubes?