Electronics > Metrology

Lowest drift, lowest noise voltage reference (ADR1000AHZ)

<< < (39/48) > >>

Andreas:
Hello,

its not 1K for the upper resistor but 1K8. (I wanted to stay below 5 mA)

with best regards

Andreas

Andreas:
Hello,

pre-test for burn in cirquit with a temperature sweep from 60 to 130 deg C.
Above ~80 deg C the base emitter voltage of T2 decreases by the shunted current of the FET.
So the cirquit works.

But obviously the zener current decreases from initially 4.1 mA (410mV) to around 3 mA (300 mV) at 130 deg C.
So the cirquit is not ideal but should be ok for burn in.

Another effect is due to the massive heat sink capacity of the aluminium bar where the ADR is connected to.
The self heating seems to be only around 2-3 deg C.
(but this is measured with around 8 NPLC of my ADC#25 since my DMMs are occupied by ADR#1)

with best regards

Andreas

dietert1:
While the p-channel mosfet works similar to the usual opamp, there is another variant with a p-channel depletion JFET shunt parallel to R1, i.e. S = U1pin4, G= U1pin5 and D=Gnd. That variant does not shunt zener current at high temperatures. The J175 datasheet says it can be used up to 150 °C.

Regards, DIeter

Kleinstein:
In the normal operation with the closed loop the zener current is not constant, but going down. So the change in current is normal. The unusual part is more the constant current at lower temperature.

A problem with the circuit is that the noise and drift may well be more effected by the FET and not so much the reference itself. So one would not get a good real time measurement of the aging / burn in.

dietert1:
From previous discussion it was clear that the loop amplifier in this application isn't critical. If one uses the output of the on-chip transistor, it becomes the input stage and determines noise and temperature dependent offset.

Regards, Dieter

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version