[time-nuts] Divider circuit for Rubidium Standard

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Jan 9 21:36:35 UTC 2016

Splitting the resistor in 2 and ac coupling the emitters together reduces the effects of Vbe and/or base biasing mismatch allowing a more symmetric output and/or operation at lower input signal levels.The inductor reduces the high frequency variations in the total emitter current. It also reduces the tail current noise at high frequencies.

    On Sunday, 10 January 2016 10:05 AM, Attila Kinali <attila at kinali.ch> wrote:

 Moin John,

Yes, I know I am comming back to an "old" discussion, but I have questions
that need to be answered! :-)

On Wed, 06 May 2015 08:56:10 -0400
John Ackermann N8UR <jra at febo.com> wrote:

> Wenzel has published the schematic of an excellent squaring circuit.  I 
> don't have the URL for their version handy, but I used it (with a couple 
> of mods) in the TADD-2 and TADD-2 Mini designs.  You can see the 
> schematic in the T2-Mini users guide at
> http://www.tapr.org/~n8ur/T2_Mini_Manual.pdf.

The manual says:
The purpose of the input circuit is to convert the RF input signal
into a low-jitter square wave that can drive the PIC clock input.
The circuit is closely based on the one published by Wenzel at 
http://www.wenzel.com/documents/waveform.html, with modifications
suggested by Bruce Griffiths and Ulrich Bangert. The revised circuit
works with inputs as low as -20dBm.

The modification I can see is that the "current source" part of the
differential pair changed from being a single, shared resistor of 100R to
an inductor of 100uH, then splits up into two resistors of 220R,
which are bridged by a 100nF capacitor. The inductor results in a
reactance between 62R (100kHz) and 12k (20MHz) for the input range.

Can you shed a bit of light on why you did those modifications 
and what the intended effect is?

            Attila Kinali

It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                -- Miss Matheson, The Diamond Age, Neil Stephenson
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