Oscillator buffer

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

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 | | 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---· | | ·-· ·---·

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

p

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.

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

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

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...

Pere

On Fri, 16 Nov 2012 12:04:00 +0100, o pere o wrote:

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 5µ SYMBOL ind -128 112 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName L3 SYMATTR Value 5µ 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 1µ SYMBOL cap -176 -16 R0 SYMATTR InstName C3 SYMATTR Value 1µ 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

Oh, I thought LO stood for Local Oscillator...

--
Thanks, 
Fred.

er

a e e

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e up

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

Maybe buy the MC12148 equivalent of my mid-60's design...

Which has a buffered PECL output, which can be easily capacitor-coupled to CMOS. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     | 
| Analog Innovations, Inc.                         |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

I had used the 1648 in the past! A simple and nice VCO indeed. Now it seems the only successor is the MC100EL1648 from OnSemi, but I may have overlooked something.

I remember having tried to use that chip to make a quenchable oscillator but with modest success. Perhaps you could suggest a clever way to tweak the gain to allow for this? Power consumption would still not be within the desired range, but I might learn something from it.

Pere

Why don't you use small C's instead of L2 and L3? That should give similar impedance transformation at less expense...

For mmic and coaxial resonator I have used a tapped C at the input and output:

--C--*----*-----C--*---- | | | C res C | | |

-----*----*--------*-----

Pere

The mmic has something over 180 degrees of phase lag, and the two Ls can be sized to make up the rest of 360. If the gain element's net phase shift is zero, the thing will oscillate at the unloaded resonant peak frequency of the resonator, which should give high Q. I think. Anyhow, it works. It seems to do gated/burst oscillators pretty well with ceramic coaxial resonators.

--

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

Do you need to quench the oscillator itself, or just the buffered output? The output is simple PECL. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     | 
| Analog Innovations, Inc.                         |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

It is the oscillator that has to be quenched. I recall fiddling around with ramping up the Vcc of the oscillator part (with the last original

1648's that I had left) and perhaps I even tried something else -it is quite a long time ago. Do you see a possibility via the AGC pin, for instance?

Pere

Ok. But to take profit from the resonator Q you have to be careful with the loading. And you will have trouble finding inductors that achieve the required high reactance (for instance, in your example, 5 uH at 100 MHz is not easy). With capacitors you don't have this problem.

And, at higher frequencies, you can just add some transmission line length to tweak the phase.

Pere

I just threw together that LT Spice thing to show the concept... the frequency just accidentally came out to 100 MHz. We use a 600 MHz coaxial resonator on one product, and that's about the lowest frequency resonator that you can buy. The inductors are reasonable at

600 MHz.

I TDRd some coaxial ceramic resonators, and they really do look like shorted transmission lines, in the 10-15 ohm range. So a good simulation would not treat them as an LC tank, but as a real transmission line.

We also do a lot of gated/burst LC oscillators, generally in the 50 MHz sort of range. I usually use a tiny LVDS-to-CMOS converter chip, as the comparator and gain element all at once. Done right, the first output clock rips through a few ns after the gate comes up, and successive edges are right on schedule +- not too many picoseconds.

--

John Larkin         Highland Technology, Inc 

jlarkin at highlandtechnology dot com 
http://www.highlandtechnology.com 

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom laser drivers and controllers 
Photonics and fiberoptic TTL data links 
VME thermocouple, LVDT, synchro   acquisition and simulation

Pulling AGC pin low will "quench" the oscillator... anything below ~1.4V stops it.

Maybe use an open-drain or open-collector device. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     | 
| Analog Innovations, Inc.                         |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.