[time-nuts] DAC resistors

AL1 alain2.bouchet at wanadoo.fr
Wed Oct 7 16:23:07 UTC 2009


Hi all,
you can try Caddock resistor networks (Caddock electronics)
They have precision networks, i don't know if they have R-2R anyway.
Alain
F4GBC

----- Original Message ----- 
From: "Bruce Griffiths" <bruce.griffiths at xtra.co.nz>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Wednesday, October 07, 2009 1:43 AM
Subject: Re: [time-nuts] DAC resistors


> Neville Michie wrote:
>> Hi,
>> I am constructing a phase meter to monitor the phase creep of clocks.
>> It consists of a BCD counter counting say microseconds that has its
>> count strobed into a latch by a pulse from the clock.
>> The Latch drives a DAC which drives a pen recorder and an analogue
>> data logger.
>> Now I am familiar with R - 2R networks, and that method is used on
>> each decade
>> but the resistors that combine the decades in a 10:1 ratio are the
>> problem.
>> I have an approximate value, and I will probably have to trim them to
>> eliminate
>> digital errors later.
>> But I can not find a reference anywhere to how to calculate the correct
>> resistors or even a working example except for an old Analog Devices
>> data sheet which seems to use a different structure, by reducing the
>> supply voltage of each decade.
>> Can anyone Help?
>>
>> Cheers, Neville Michie
>>
> Neville
>
> If there was an easier method it would probably have been used.
>
> It is probably simpler to use a different structure than the R-2R ladder.
>
> For example the R, 2R, 4R, 8R connected to a summing bus followed by a
> 4.8R interstage resistor connecting to the summing bus of the next
> decade etc works well.
> See attached partial circuit for details.
>
> Bruce
>


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