ECL oscillator just won't oscillate

[capslock]

This is from D. Nührmann, Industrielle Schaltungstechnik (again gif disguised as zip). The output signal is AC-coupled via the 2.2 uF capacitor to the AA143 germanium diode. It will clamp the negative excursions, while the positive excursions charge the 220 uF + 12 nF capacitors through the 39 k resistor. The op amp will control the tail current in trying to balance its inputs. The amplitude is set by controlling the reference voltage on the non-inverting input.

Is the AA143 adequate for HF clamping? Is there a more suitable replacement, i.e. a HF Schottky diode? Is there a simpler AGC circuit?


Thanks,

Eric

[Jocko Homo]

Been watching this thread casually, and I am planning to work on a schematic for a low-noise oscillator that uses NPN transistors, so it will be easier to build.

Recommendations on program to use that will let me post a readable schematic? (I never use schematic capture........too old to care about learning something that new.) [joke]


Jocko

[ergo]

Jocko, I find MicroCap to be absolutely wonderful for drawing schematics. It a very powerful simulator etc. but also very suitable for schematic drawing. There is a demo version available, with no time limitation and 50 part simulation restriction, but there is no restriction in just schematic drawing.

I have tried many such programs and MicroCap is in my opinion by far the easiest and most intuitive to use as circuit drawing tool. There are also nice tutorial scripts that get you running in no time

http://www.spectrum-soft.com

Check the JLH amp thread for sample schematic made with MicroCap

JLH 10 Watt class A amplifier

UHH. Hope you forgive me for such preaching

Ergo

[Jocko Homo]

Preach on.

Let's see if I can upload this kludge schematic made a different way.

Nope too big. I have a .gif of it if anyone is interested. Email me.

Jocko

[Jocko Homo]

OK......now it is my turn to be the idiot..........

How do you save this in a format that will be accepted here?

Jocko

[Jocko Homo]

Let's try it again.......

This originally appeared in EDN in 5/73. I have seen it several places, including the ARRL Handbook.

The trick about this is that the crystal acts as both a low-pass, and sideband filter. This version is 11.2896 MHz. C4 should be about 680 pF, but I increased it to keep the harmonics down in Q3. Probably could have done the same by playing with R11, but I just grabbed the handiest values around. That way anyone should be able to build it.

I did not include the power supply decoupling capacitors. I leave that part up to your discretion.

[wildmonkeysects]

Hey all:

In wireless/telecom circles where I wear my golden handcuffs, the Colpitts topology is widely regarded as the most straightforward low phase noise osc: if you want clean, do a differential jfet colpitts and feed it to a high speed comparitor is the word I have been hearing. Having ignored a number of subtle hints, and finally listening to Elso, I heated up the slobbering iron, and dove in a built a couple. So far, wow. Night and day sonic improvement over stock CMOS and comparitor oscs replaced.

There are still issues, largely implementation. The comparitor does not swing high enough with a 5 volt supply, so it has a 6.25 volt supply to swing 5 volts. When driving even a single CMOS/TTL load, the comparitor "causes" sufficient ground bounce to create glitches in the Colpitts sine and sine bar outs, jfet sources. Mostly common moded out, but I still don't like them. Yes, even with rf scope probes. Version three will have a split ground plane. Maybe it will be ready for primetime.

Sorry for the fuzzy sch, had to squeeze it to fit. Source resistors are 475r, gate resistors are 10M, comp snubber resistors are 100r, top cap is 47p, bottom cap is 100p.
Not in sch are bypass caps galore. Jfet supply is an LT1021, comp supply is an LT1086. Built "3D" on a copper foil ground plane. XTAL is sorbothane mounted, as is whole assembly. Caps are silver-mica, jfets are 2n5457s for now, matched Idss of 4 mA, comp is MAX1116 for now. Jfets draw ~~2mA ea in circuit, source voltages ~~0.8v.

Enjoy...

WMS

[capslock]

Jocko,

could you elaborate on how your comment that the crystal works as both low pass as well as side band filter? I seem to have trouble understanding circuits that were divised in the 70s when engineers were still thinking in tubes...

Does Q1 act as a free-running oscillator?


Puzzled,

Eric

[Jocko Homo]

Problem with JFETs is that they don't have enough transconductance to really drive the crystal hard. Diff pair might get the drive a bit higher.

My telecom days are over. At least for now. Which also means I do not have access to MY H-P phase noise setup.

Ther signal is picked off from the 22 ohm resistor. It has to go through the crystal to get there. Neat idea. Wish I had thought it up.

Jocko

[capslock]

Anybody have a foolproof way to measure phase noise? I have a good number of high bandwidth real time sampling scopes around but I have the feeling I cannot trust their clocks and converter aperture jitter....


Eric