[time-nuts] High rate, high precision/accuracy time interval counter methods

[Bruce Griffiths]

Hoi Attila
Yes, the only way to reduce emitter-emitter inductance is indeed to connect them on the die. Its even better if the current source transistor collector is also connected to the common emitter node of the long tailed pair on the die as this minimises the capacitance at this node. 

Alternatively one can add a small series resistance to reduce the associated emitter circuit time constant as Wavecrest do.

The Wavecrest patent is somewhat detailed and complete with reasonably detailed circuit diagrams and explanatory text.
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Bruce 

    On Tuesday, 10 May 2016 9:17 PM, Attila Kinali <attila at kinali.ch> wrote:
 

 Hoi Bruce,

On Mon, 9 May 2016 23:34:24 +0000 (UTC)
Bruce Griffiths <bruce.griffiths at xtra.co.nz> wrote:

> Its probably easier/cheaper to construct a suitable filter for a GSPS ADC
> than to construct a TAC that is fast enough to suit an ADC with a GHz clock.

Probably. 

> Minimising the emitter to emitter inductance of a longtailed pair or
> equivalent is key to achieving a fast enough switching time for a suitable
> TAC. 

How does one minimize this inductance? The only way I am aware of is
to use a package with a pair of transistors with common emiter pin.

> The somewhat heroic measures employed in the Wavecrest counters is
> perhaps the limit of discrete construction techniques.

Are these heroic measures documented somewhere?
So far I have not even seen a block diagram of a Wavecrest counter,
much less a schematic.

            Attila kinali

-- 
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use without that foundation.
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