[time-nuts] Odd-order multiplication of CMOS-output OCXO

[Gerhard Hoffmann]

Am 20.01.20 um 01:48 schrieb Magnus Danielson:
>
> Yes, the steep phase-slopes makes any shift cause great phase-shifts,
> which is another way of experiencing the group delay (= dphi/df), and
> the amplitude of that is proportional to the Q of a resonance. The phase
> is still 45 degrees at the -3 dB points, it's just that those is very close.

Not only proportional, that _is_ the operating Q. And in some oscillators

it is easy to measure with the Randall-Hock correction for the 
self-terminated

loop and an ordinary network analyzer. The RH-correction delivers the

exact loop gain of the cascade as if it was fed from its own output and

loaded by its own input, just from the s-parameters of the opened loop.

The oscillator works where phase(S21) goes through 0 and it helps 
tremendously

if you can see that your optimum Q happens 30 Hz lower thanks to the tank

circuit or a mistuned spurious trap.


> I would be very interested to do exactly that. I've actually had issues
> getting the Prologix do things exactly as I want, and I blame that on my
> inability to focus long enough to read the manual to understand it
> properly. The lack of being able to debug the GPIB properly helps with
> the confusion. I need to do more GPIB programming, and perferably in
> Linux as I feel right at home there in general. One of my 89410s have
> cross-correlator capabilities, and I have a bit of other goodies, so it
> is about bringing things together.

My 89410/41 has nearly all the options, including the RF box but one

thing I really miss is the ability to do logarithmic sweeps from mHz

to 1 MHz. It has the network option for BNC-Ethernet, and with a

BNC-RJ45 bridge from Amazon I could connect it to my LAN.

Then I could simply open port 5025 or so on 192.168.178.x and

feed it with SCPI strings. That actually worked quite good but

sometimes the 89441A would stop listening and nothing but a

power cycle would bring it back online.


The network access clearly missed things like "interface clear".

So my interface program got the option -488 and multiplexers

in open_89441(), close(), cmnd() and query_89441(). That was

the easy part. But for the state as of NOW I have just replaced

an unwilling tcp/ip socket with an unwilling Prologix dongle that

is even harder to bring into a known state.   :-(


My control program makes a FFT for each of the typically 7 decades

of interest, collects the data, adjusts for resolution BW and finally

calls gnuplot  to make nice .eps, .png and QT-terminal pictures.


I have also provided some access to cross correlation, but the results

are unreasonably good. My HP3325 does not have > 110 dB harmonics

suppression. But that is a minor problem once the interface is stable.


> The idea was just to measure 1/f noise on my AF and RF transistors
>
> in a circuit inspired by that in Art Of Electronics V3.
>
> Good book. Must have.
> That's not a bad starting-point if you only have that one book.

That's always a good book.

Like the Hobbits: They loved to have many books of things they understood...

>
> Now, which of the circuits did you get inspired from? I assume you where
> using one of the Chapter 8 circuits.
>
Fig. 8.92.

I added a TL431 for the ability to pull the base/gate voltage down to -1V

for measuring FETs. That requires a polarity reversal switch for the

160000 uF base shorting capacitors. The bias pot needs a protection

resistor in case you turn it to the GND side with the capacitor charged.

One might wipe out the wiper otherwise. The -1V mod takes care of that

as a byproduct.


The capacitance multiplier did not help much. Just connecting that thing

to a R&S NGT20 power supply introduced a lot of GND loop noise.

I operate it from NiMH or Li cells.

I also added a cascode for RF performance and 3 stages of ADA4898 as

a post amplifier.


The test signal injection for gain measurement  goes through the bottom

side of the huge base capacitor. That is not directly connected to GND but

only through some MilliOhms. A 49R9 resistor from the test-signal-in-BNC

completes that to a 60 dB attenuator. One Volt of input gives 1 mV at 
the base.

Just leave it open if not needed. I did not like the semi-floating BNC 
in the

original design.


In the DUT base connection is an optional 60 Ohm resistor that provides an

1nV/rtHz voltage noise reference. It needed to be switched in / shorted out

by an SMD relay. Wiring this connection to a switch on the wall of the box

picked up way too much noise.


Pic: left is the cap multiplier, then the bias/DUT section, right side 
5*33000 uF

base shorting cap. It is definitely needed that large if you want to 
examine the 1/f region.


Cheers, Gerhard




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