On Wednesday, November 14, 2012 10:58:16 AM UTC-5, o pere o wrote:> I have thought of two causes for this. The first one is feedback via the > > DC supply: the spikes generated by the gate switching get coupled back > > to the oscillator. The second one could be the change in input impedance > > seen by the oscillator -does this make sense?Reason # 3 : Logic gate input is clamping the signal to one or more rails.
Oscillator buffer
Started by ●November 14, 2012
Reply by ●November 15, 20122012-11-15
Reply by ●November 16, 20122012-11-16
On 11/15/2012 06:55 PM, Jim Thompson wrote:> On Thu, 15 Nov 2012 18:44:59 +0100, o pere o <me@somewhere.net> wrote: > > [snip] >> >> You mean something like the DS90C032? You mean sensing with the LVDS >> side and feeding back from the CMOS side to provide the gain? I guess >> that this would not work, as I need a wide linear part where the >> oscillator grows up more or less slowly... >> >> Thanks for your inputs. >> >> Pere >> > > Does your buffer need to replicate the oscillator amplitude ramp-up, > or can the buffer simply square it up? > > ...Jim Thompson >The end effect has to be just driving a digital input when the amplitude is sufficiently high. It does not need to replicate the transient. If it does, I guess that it will be better behaved in terms of constant loading, but it is not necessary. Pere
Reply by ●November 16, 20122012-11-16
On 11/16/2012 01:25 AM, George Herold wrote: <snip>> Nice thread, (wiki calls the tickler the Armstrong.) > The only RF oscillator I know is used to drive a Rb discharge lamp. > It's a Hartly basically copied from an efratom lamp circuit. > > To Opere, I don't quite get your problem. > To sense the circuit you're going to have to take a bit of energy > out. > This must change the Q and (thus) the resonant frequency. > If it's a changing Q when you switch in your circuit.. (?) > then you have to balance it out. > > George H.Current oscillator version is Vcc Vcc Vcc | | | C L R1 | | | | C-*--*-----C---*----Dig. Gate *-B C1 | | E-*-* R2 R | | | | Re C2 gnd ctrl | | gnd If the Gate impedance were constant for small and large signal, this would be ok (controlled loading). What I am seeing is that when the Gate sees enough signal to begin toggling the transient changes. Hope this sketch helps explaining: envelope: ************* * * ***** ***** | 0****** | --------------------------0 <smooth rising> | <saturated> | start toggling-> (very) fast rising As mentioned in my original post, I see 2 possible causes for this: 1. Coupling through the Vcc rail (although more ore less well bypassed) and 2. Different behavior of the gate for small and large signal. The cure for 2 is what I am looking for. Cure for 1 would be better bypassing. The other configuration I have used (at ~900MHz) is Ctrl- Rb C---Vcc --C-*---B | | E L C1 | | | | | *----* | C2 Re | | | gnd gnd gnd And a similar one, with a transmission line instead of L has been used at 2.4 GHz. A minicircuits gain block with a hairpin resonator has also worked ok at 2.4 GHz, although this was not low-power (tens of mA): �---Amp---� | | �-� �---� <-Phasing lines || || || || <--Resonator || || �-� (Maximum simplicity)
Reply by ●November 16, 20122012-11-16
On 11/15/2012 08:11 PM, John Larkin wrote:> On Thu, 15 Nov 2012 18:44:59 +0100, o pere o <me@somewhere.net> wrote: > >> On 11/15/2012 04:20 PM, John Larkin wrote: >>> On Thu, 15 Nov 2012 09:24:50 +0100, o pere o <me@somewhere.net> wrote: >>> >>>> On 11/14/2012 06:19 PM, John Larkin wrote: >>>>> On Wed, 14 Nov 2012 16:58:13 +0100, o pere o <me@somewhere.net> wrote: >>>>> >>>>>> The thread related to large signal PSpice models and an emitter follower >>>>>> comes from the following problem: >>>>>> >>>>>> I have an oscillator that should drive a digital part of the system. >>>>>> In short, what is the best way to achieve this? >>>>>> >>>>>> My first attempt has been a common base Colpitts oscillator that gives a >>>>>> signal riding on the +Vcc rail. This has been AC coupled to a 74AC gate >>>>>> biased to the point that gives square output signals. >>>>>> >>>>>> This works more ore less ok, but: the startup transient, which is >>>>>> important here, is different depending if the oscillator amplitude is >>>>>> sufficient to toggle the gate. This translates into an envelope that >>>>>> raises more ore less smoothly until the gate begins toggling, where the >>>>>> envelope raises more abruptly -and I guess that the instantaneous >>>>>> frequency changes. >>>>>> >>>>>> I have thought of two causes for this. The first one is feedback via the >>>>>> DC supply: the spikes generated by the gate switching get coupled back >>>>>> to the oscillator. The second one could be the change in input impedance >>>>>> seen by the oscillator -does this make sense? The cure for #1 could be >>>>>> better supply bypassing. The cure for #2 a buffer stage. >>>>>> >>>>>> So, what could be a good way to generate a digital signal from an >>>>>> oscillator without loading it? Ideally I would like to preserve the >>>>>> instantaneous frequency of the unloaded startup transient. And: power >>>>>> consumption should be low, say preferably (much) less than 1 mA. >>>>>> Operating frequency should be initially 27 MHz, but ideally scalable up >>>>>> to ~1 GHz. >>>>>> >>>>>> Pere >>>>> >>>>> Do you want an LC oscillator that starts instantly and coherently, >>>>> with a digital clock output? We do that, with LCs at low frequencies, >>>>> and coaxial ceramic resonators at 500 MHz or so. 1 GHz shouldn't be >>>>> horribly difficult, except for the milliwatt constraint. It's just a >>>>> matter of getting the initial conditions right. >>>>> >>>>> https://dl.dropbox.com/u/53724080/Circuits/Burst_Osc.jpg >>>> >>>> Are you building some kind of synchronous oscillator? >>> >>> We use gated oscillators in our digital delay generators. When we gat >>> a rrigger, we start a clock oscillator, and count ticks to get coarse >>> delay. An analog ramp thing gives fine delay to interpolate down to >>> picoseconds. Sometimes just the LC is good enough, for short delays. >>> The coaxial resonator things are great for medium accuracy and delay. >>> he best is to use a gated LC for the clock, but phase-lock it to a >>> crystal oscillator to get longterm precision. >> >> I have used ceramic coaxial resonators to build oscillators at ~433 MHz, >> and they are quite stable. >> I have also seen that you make stuff on FPGAs. IIRC there are >> interesting techniques to achieve high timing precision making use only >> of digital resources (keywords: time to digital FPGA)... > > That stuff is interesting, but we haven't done it inside an FPGA. We > don't see a big demand for TDCs these days, and a couple of people do > it really well. No point trying to compete with someone established in > a small market. > > We did do a new TDC lately, at a customer's request, but we used our > old analog technique, with the FPGA just doing clocked logic. > > >> >>> In our application >>>> an external signal influences the startup transient (think superreg. >>>> principle) and the information contained therein should be more or less >>>> preserved. >>> >>> OK, that's different. It's an externally quenched superregen, I guess. >>> >>> Why not use a grounded LC and a non-inverting gain element? Or you >>> could use a tiny toroidal transformer, with a secondary winding for >>> the base of a PNP transistor, to provide the gain. >> >> I have used several oscillator topologies. At 800 MHz the tapped-C // L >> resonator plus emitter follower works ok, i.e. it is a non-inverting >> topology. But the problem is more or less the same: how to tap the >> signal out. >> >>> One oscillator that I really like is an LVDS-CMOS converter chip that >>> is both the feedback gain and the comparator, with the LC grounded. >>> But that wouldn't work for your application, if I understand it. >> >> You mean something like the DS90C032? You mean sensing with the LVDS >> side and feeding back from the CMOS side to provide the gain? I guess >> that this would not work, as I need a wide linear part where the >> oscillator grows up more or less slowly... > > Yeah, if you want a clasic exponential oscillation buildup, you need a > linear gain element, a transistor or a fast opamp or a MMIC. Given > your power budget, a transistor might be best. > > How about a powdered-iron toroid with a feedback winding for the > transistor/fet drive? The LC could be grounded. A fet would be cool, > to keep the Q up. > > Or something like this.... > > https://dl.dropbox.com/u/53724080/Circuits/Oscillators/LC_quench.JPG > > > > >But how would this behave for a load that changes impedance depending on impedance level (if this is the cause for my observations)? Is there any advantage to be expected with respect to the circuits I have posted in response to GH? Pere
Reply by ●November 16, 20122012-11-16
On Nov 15, 2:58=A0am, o pere o <m...@somewhere.net> wrote:> The thread related to large signal PSpice models and an emitter follower > comes from the following problem: > > I have an oscillator that should drive a digital part of the system. > In short, what is the best way to achieve this? > > My first attempt has been a common base Colpitts oscillator that gives a > signal riding on the +Vcc rail. This has been AC coupled to a 74AC gate > biased to the point that gives square output signals. > > This works more ore less ok, but: the startup transient, which is > important here, is different depending if the oscillator amplitude is > sufficient to toggle the gate. This translates into an envelope that > raises more ore less smoothly until the gate begins toggling, where the > envelope raises more abruptly -and I guess that the instantaneous > frequency changes. > > I have thought of two causes for this. The first one is feedback via the > DC supply: the spikes generated by the gate switching get coupled back > to the oscillator. The second one could be the change in input impedance > seen by the oscillator -does this make sense? The cure for #1 could be > better supply bypassing. The cure for #2 a buffer stage. > > So, what could be a good way to generate a digital signal from an > oscillator without loading it? Ideally I would like to preserve the > instantaneous frequency of the unloaded startup transient. And: power > consumption should be low, say preferably (much) less than 1 mA. > Operating frequency should =A0be initially 27 MHz, but ideally scalable u=p> to ~1 GHz.One weird and expensive approach would be to use something like an AD834 as your gain stage; set it up with enough initial gain to get the oscillator to start up respectably fast, then drop the gain back to a level that sustains the oscillation when the digital logic detects an edge. If you can live with a little bit of clipping, the "sustain" gain wouldn't have to be too well defined. http://www.analog.com/static/imported-files/data_sheets/AD834.pdf The power consumption is rather higher than you want. Multipliers are designed to have the same gain over a respectable range of input amplitudes, so the start-up ought to be well-defined. -- Bill Sloman, Sydney
Reply by ●November 16, 20122012-11-16
On 11/16/2012 02:07 AM, bloggs.fredbloggs.fred@gmail.com wrote:> On Wednesday, November 14, 2012 10:58:16 AM UTC-5, o pere o wrote: > >> I have thought of two causes for this. The first one is feedback via the >> >> DC supply: the spikes generated by the gate switching get coupled back >> >> to the oscillator. The second one could be the change in input impedance >> >> seen by the oscillator -does this make sense? > > Reason # 3 : Logic gate input is clamping the signal to one or more rails.Well, that could be the reason if the oscillator amplitude became large enough. However, in practice -though not in theory- the oscillator amplitude however tends to saturate at levels that, even riding on 0.5 Vcc should not reach the rails (iirc less than 1 Vpp). But I will have to check that to be sure... Pere
Reply by ●November 16, 20122012-11-16
On 11/16/2012 12:16 PM, Bill Sloman wrote:> On Nov 15, 2:58 am, o pere o <m...@somewhere.net> wrote: >> The thread related to large signal PSpice models and an emitter follower >> comes from the following problem: >> >> I have an oscillator that should drive a digital part of the system. >> In short, what is the best way to achieve this? >> >> My first attempt has been a common base Colpitts oscillator that gives a >> signal riding on the +Vcc rail. This has been AC coupled to a 74AC gate >> biased to the point that gives square output signals. >> >> This works more ore less ok, but: the startup transient, which is >> important here, is different depending if the oscillator amplitude is >> sufficient to toggle the gate. This translates into an envelope that >> raises more ore less smoothly until the gate begins toggling, where the >> envelope raises more abruptly -and I guess that the instantaneous >> frequency changes. >> >> I have thought of two causes for this. The first one is feedback via the >> DC supply: the spikes generated by the gate switching get coupled back >> to the oscillator. The second one could be the change in input impedance >> seen by the oscillator -does this make sense? The cure for #1 could be >> better supply bypassing. The cure for #2 a buffer stage. >> >> So, what could be a good way to generate a digital signal from an >> oscillator without loading it? Ideally I would like to preserve the >> instantaneous frequency of the unloaded startup transient. And: power >> consumption should be low, say preferably (much) less than 1 mA. >> Operating frequency should be initially 27 MHz, but ideally scalable up >> to ~1 GHz. > > One weird and expensive approach would be to use something like an > AD834 as your gain stage; set it up with enough initial gain to get > the oscillator to start up respectably fast, then drop the gain back > to a level that sustains the oscillation when the digital logic > detects an edge. If you can live with a little bit of clipping, the > "sustain" gain wouldn't have to be too well defined. > > http://www.analog.com/static/imported-files/data_sheets/AD834.pdf > > The power consumption is rather higher than you want. > > Multipliers are designed to have the same gain over a respectable > range of input amplitudes, so the start-up ought to be well-defined. > > -- > Bill Sloman, SydneyA multiplier would offer a better control of gain, which could translate into a bigger linear range of operation. Of course, at the price of cost and power consumption but it could serve as an idealized prototype. However, when I played with analog multipliers in the past (at frequencies much much lower than the 500MHz of your suggestion), they did not perform as well as announced in the datasheets -it could have been my fault... Pere
Reply by ●November 16, 20122012-11-16
On Fri, 16 Nov 2012 12:04:00 +0100, o pere o <me@somewhere.net> wrote:>On 11/16/2012 01:25 AM, George Herold wrote: > ><snip> > >> Nice thread, (wiki calls the tickler the Armstrong.) >> The only RF oscillator I know is used to drive a Rb discharge lamp. >> It's a Hartly basically copied from an efratom lamp circuit. >> >> To Opere, I don't quite get your problem. >> To sense the circuit you're going to have to take a bit of energy >> out. >> This must change the Q and (thus) the resonant frequency. >> If it's a changing Q when you switch in your circuit.. (?) >> then you have to balance it out. >> >> George H. > > >Current oscillator version is > > Vcc Vcc Vcc > | | | > C L R1 > | | | > | C-*--*-----C---*----Dig. Gate > *-B C1 | > | E-*-* R2 > R | | | > | Re C2 gnd >ctrl | | > gnd > >If the Gate impedance were constant for small and large signal, this >would be ok (controlled loading). What I am seeing is that when the Gate >sees enough signal to begin toggling the transient changes. Hope this >sketch helps explaining: > >envelope: ************* > * > * > ***** > ***** | >0****** | --------------------------0 ><smooth rising> | <saturated> > | > start toggling-> (very) fast rising > >As mentioned in my original post, I see 2 possible causes for this: 1. >Coupling through the Vcc rail (although more ore less well bypassed) >and 2. Different behavior of the gate for small and large signal. > >The cure for 2 is what I am looking for. Cure for 1 would be better >bypassing. > >The other configuration I have used (at ~900MHz) is > >Ctrl- > Rb C---Vcc >--C-*---B >| | E >L C1 | >| | | >| *----* >| C2 Re >| | | >gnd gnd gnd > >And a similar one, with a transmission line instead of L has been used >at 2.4 GHz. > >A minicircuits gain block with a hairpin resonator has also worked ok at >2.4 GHz, although this was not low-power (tens of mA): > >�---Amp---� >| | >�-� �---� <-Phasing lines > || || > || || <--Resonator > || || > �-� > >(Maximum simplicity)Here's the LLarkin oscillator, which uses a MMIC and a couple of inductors in the gain path. This works well with coaxial resonators. Too much power for your app, unfortunately. Version 4 SHEET 1 880 680 WIRE 32 -64 -160 -64 WIRE 208 -64 112 -64 WIRE 304 -64 256 -64 WIRE 432 -64 304 -64 WIRE 208 -48 208 -64 WIRE 304 -48 304 -64 WIRE 256 -32 256 -64 WIRE -160 -16 -160 -64 WIRE 432 -16 432 -64 WIRE 256 32 256 16 WIRE 304 32 256 32 WIRE 208 48 208 32 WIRE 304 48 304 32 WIRE -160 96 -160 48 WIRE -112 96 -160 96 WIRE 32 96 -32 96 WIRE 128 96 32 96 WIRE 208 96 128 96 WIRE 320 96 208 96 WIRE 432 96 432 48 WIRE 432 96 400 96 WIRE 32 128 32 96 WIRE 128 144 128 96 WIRE 208 144 208 96 WIRE 32 256 32 208 WIRE 128 256 128 208 WIRE 128 256 32 256 WIRE 208 256 208 224 WIRE 208 256 128 256 WIRE 208 288 208 256 FLAG 208 288 0 FLAG 208 48 0 FLAG 304 48 0 SYMBOL ind 192 128 R0 SYMATTR InstName L1 SYMATTR Value 100n SYMBOL ind 304 112 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName L2 SYMATTR Value 5� SYMBOL ind -128 112 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName L3 SYMATTR Value 5� SYMBOL cap 112 144 R0 SYMATTR InstName C1 SYMATTR Value 20p SYMBOL e 208 -64 M0 SYMATTR InstName E1 SYMATTR Value -10 SYMBOL res 288 -64 R0 SYMATTR InstName R1 SYMATTR Value 50 SYMBOL res 128 -80 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 50 SYMBOL cap 416 -16 R0 SYMATTR InstName C2 SYMATTR Value 1� SYMBOL cap -176 -16 R0 SYMATTR InstName C3 SYMATTR Value 1� SYMBOL current 32 128 R0 WINDOW 3 -250 87 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName I1 SYMATTR Value PULSE(10u 0 10n) TEXT -184 160 Left 2 !.tran 1u TEXT 56 -160 Left 2 ;LLarlin Oscillator Nov 2012 TEXT 200 -104 Left 2 ;MMIC -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Reply by ●November 16, 20122012-11-16
John Larkin a �crit :> On Fri, 16 Nov 2012 12:04:00 +0100, o pere o <me@somewhere.net> wrote: > >> On 11/16/2012 01:25 AM, George Herold wrote: >> >> <snip> >> >>> Nice thread, (wiki calls the tickler the Armstrong.) >>> The only RF oscillator I know is used to drive a Rb discharge lamp. >>> It's a Hartly basically copied from an efratom lamp circuit. >>> >>> To Opere, I don't quite get your problem. >>> To sense the circuit you're going to have to take a bit of energy >>> out. >>> This must change the Q and (thus) the resonant frequency. >>> If it's a changing Q when you switch in your circuit.. (?) >>> then you have to balance it out. >>> >>> George H. >> >> Current oscillator version is >> >> Vcc Vcc Vcc >> | | | >> C L R1 >> | | | >> | C-*--*-----C---*----Dig. Gate >> *-B C1 | >> | E-*-* R2 >> R | | | >> | Re C2 gnd >> ctrl | | >> gnd >> >> If the Gate impedance were constant for small and large signal, this >> would be ok (controlled loading). What I am seeing is that when the Gate >> sees enough signal to begin toggling the transient changes. Hope this >> sketch helps explaining: >> >> envelope: ************* >> * >> * >> ***** >> ***** | >> 0****** | --------------------------0 >> <smooth rising> | <saturated> >> | >> start toggling-> (very) fast rising >> >> As mentioned in my original post, I see 2 possible causes for this: 1. >> Coupling through the Vcc rail (although more ore less well bypassed) >> and 2. Different behavior of the gate for small and large signal. >> >> The cure for 2 is what I am looking for. Cure for 1 would be better >> bypassing. >> >> The other configuration I have used (at ~900MHz) is >> >> Ctrl- >> Rb C---Vcc >> --C-*---B >> | | E >> L C1 | >> | | | >> | *----* >> | C2 Re >> | | | >> gnd gnd gnd >> >> And a similar one, with a transmission line instead of L has been used >> at 2.4 GHz. >> >> A minicircuits gain block with a hairpin resonator has also worked ok at >> 2.4 GHz, although this was not low-power (tens of mA): >> >> �---Amp---� >> | | >> �-� �---� <-Phasing lines >> || || >> || || <--Resonator >> || || >> �-� >> >> (Maximum simplicity) > > > Here's the LLarkin oscillator, which uses a MMIC and a couple of > inductors in the gain path.Oh, I thought LO stood for Local Oscillator... -- Thanks, Fred.
Reply by ●November 16, 20122012-11-16
On Nov 17, 12:39=A0am, o pere o <m...@somewhere.net> wrote:> On 11/16/2012 12:16 PM,BillSlomanwrote: > > > > > > > > > > > On Nov 15, 2:58 am, o pere o <m...@somewhere.net> wrote: > >> The thread related to large signal PSpice models and an emitter follow=er> >> comes from the following problem: > > >> I have an oscillator that should drive a digital part of the system. > >> In short, what is the best way to achieve this? > > >> My first attempt has been a common base Colpitts oscillator that gives=a> >> signal riding on the +Vcc rail. This has been AC coupled to a 74AC gat=e> >> biased to the point that gives square output signals. > > >> This works more ore less ok, but: the startup transient, which is > >> important here, is different depending if the oscillator amplitude is > >> sufficient to toggle the gate. This translates into an envelope that > >> raises more ore less smoothly until the gate begins toggling, where th=e> >> envelope raises more abruptly -and I guess that the instantaneous > >> frequency changes. > > >> I have thought of two causes for this. The first one is feedback via t=he> >> DC supply: the spikes generated by the gate switching get coupled back > >> to the oscillator. The second one could be the change in input impedan=ce> >> seen by the oscillator -does this make sense? The cure for #1 could be > >> better supply bypassing. The cure for #2 a buffer stage. > > >> So, what could be a good way to generate a digital signal from an > >> oscillator without loading it? Ideally I would like to preserve the > >> instantaneous frequency of the unloaded startup transient. And: power > >> consumption should be low, say preferably (much) less than 1 mA. > >> Operating frequency should =A0be initially 27 MHz, but ideally scalabl=e up> >> to ~1 GHz. > > > One weird and expensive approach would be to use something like an > > AD834 as your gain stage; set it up with enough initial gain to get > > the oscillator to start up respectably fast, then drop the gain back > > to a level that sustains the oscillation when the digital logic > > detects an edge. If you can live with a little bit of clipping, the > > "sustain" gain wouldn't have to be too well defined. > > >http://www.analog.com/static/imported-files/data_sheets/AD834.pdf > > > The power consumption is rather higher than you want. > > > Multipliers are designed to have the same gain over a respectable > > range of input amplitudes, so the start-up ought to be well-defined. > > A multiplier would offer a better control of gain, which could translate > into a bigger linear range of operation. Of course, at the price of cost > and power consumption but it could serve as an idealized prototype. > However, when I played with analog multipliers in the past (at > frequencies much much lower than the 500MHz of your suggestion), they > did not perform as well as announced in the datasheets -it could have > been my fault...The Analog Devices multipliers all have added extra Barry Gilbert. He invented the concept and has run with it for a long time now. There are a variety of copies available, all much cheaper, but not as good. -- Bill Sloman, Sydney
