[volt-nuts] Low Frequency noise on LTZ1000A and tempco ofunheatedLTZ

Andreas Jahn Andreas_-_Jahn at t-online.de
Sat Mar 5 22:22:45 UTC 2011


> On my noise measurements I had around up to +/- 15uV which give around 
> 4-5ppm peak-peak
> But I did not have a 24h measurement.Only relative short times looking on 
> the oscilloscope.
>> Perhaps those glitches are caused by the MUX switch of the DVM (34401A or 
>> 3458A).
> In my case I do not believe that it has something to do with the ADC. I 
> have seen some pattern
> with repeating rate all 0,8 seconds or 2,8 seconds then switching off for 
> a time and coming back again.
> So for my side it looks like a pulse package heated device like a laser 
> printer or something like that
> causing trouble on the mains line. Perhaps comming in to my cirquit by the 
> oscilloscope.

The low frequency noise was not generated by the LTZ1000A in my case
but came from the measurement amplifier.

For the 0.1Hz lower edge Frequency I had a 20uF foil capacitor
+ a 150k pull down resistor. Together with the current noise of
the operational amplifier (LT1013) some kind of shot noise came up.

The fatal thing was that this low frequency noise was only generated
when the LTZ1000 was connected.
Never with other (more noisy) references,
and never when the input of the amplifier was shorted.

Now I'm using a much more low impedant design (3200uF + 1k) togeter
with a LT1037 low noise amplifier to avoid the current noise.

The measurement results are now close to the datasheet value of the LTZ.

best regards


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